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  • Electronic Resource  (25,313)
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  • 1990-1994  (25,313)
  • Polymer and Materials Science  (21,194)
  • Biochemistry and Biotechnology  (4,119)
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  • Electronic Resource  (25,313)
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Year
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  • 101
    Electronic Resource
    Electronic Resource
    Acyclic diene metathesis (ADMET) depolymerization of functionalized furan-based polymers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2469-2477 
    Details
    ISSN: 0887-624X
    Keywords: acyclic dience metathesis ; ADMET ; depolymerization ; aqueous ring-opening metathesis polymerization ; ROMP ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acyclic dience metathesis (ADMET) depolymerization of functionalized furan-based polymers prepared via aqueous ring-opening polymerization of 7-oxanobornenes has been investigated. Results indicate that while very high molecular weight poly [exo-N-methyl-7-oxabicyclo [2.2.1] hept-2,5-diene-2,3-dicarboximide] can be depolymerized to oligomers with ease, poly [2,3-dicarbomethoxy-7-oxabicyclo [2.2.1] hept-2,5-diene] is more resistant to depolymerization under similar conditions. This difference may be due to differential interaction of the carbonyls in the side chains with the metal atom of the catalyst in the proposed metallacyclobutane intermediate. ADMET depolymerization of poly [2,3-bis (trifluoromethyl)-7-oxabicyclo [2.2.1] hept-2,5-diene] was feasible, however, the extent of depolymerization was decreased due to the use of a coordinating solvent (THF) used during the depolymerization process. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321308
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  • 102
    Electronic Resource
    Electronic Resource
    Thermoreversible reaction of diels - alder polymer composed of difurufuryladipate with bismaleimidodiphenylmethane (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2501-2504 
    Details
    ISSN: 0887-624X
    Keywords: thermoreversible polymer ; Diels-Alder polymerization ; retro-Diels-Alder degradation ; difurufuryladipate ; bismaleimidodiphenylmethane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermoreversible reaction of Diels-Alder polymer composed of difurufuryladipate with bismaleimidodiphenylmethane was studied in dimethylformamide solution. The retro-Diels-Alder degradation occurred gradually at 90°C and Diels-Alder polymerization proceeded quickly at 60°C. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321312
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  • 103
    Electronic Resource
    Electronic Resource
    Annealing effects on the thermal properties of liquid crystalline polyurethanes (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2559-2563 
    Details
    ISSN: 0887-624X
    Keywords: main-chain liquid crystalline polymers ; thermotropic polyurethane ; annealing effect ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work is a continuation of our earlier investigations of liquid crystalline polyurethanes prepared from 4,4′-bis(2-hydroxyethoxy) biphenyl (BHBP), 2,4-tolylene diisocyanate (TDI), and poly (oxytetramethylene) diols (PTMO). The annealing effects on the thermal properties of the investigation polyurethanes are presented for three samples with the same BHBP content, different flexible spacer length, and different molecular weight of the polyurethanes. The annealed polyurethanes were investigated by means of DSC, and polarizing microscopy. The results of the thermal analysis show that the temperatures of phase transitions depend on the annealing temperature and time. These dependences are different for different molecular weights. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321319
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  • 104
    Electronic Resource
    Electronic Resource
    Synthesis and dielectric analysis of aliphatic poly(carbonate-sulfone)s based on 1,4-bis(3-hydroxypropylsulfonyl) butane (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2809-2816 
    Details
    ISSN: 0887-624X
    Keywords: 1,4-bis((3-hydroxypropylsulfonyl)butane ; polycarbonate ; poly(carbonatesulfone) ; liquid crystalline ; dipole-dipole interaction ; dielectric constant ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High molecular weight aliphatic poly(carbonate-sulfone) homopolymer (PC-343) and random copolymer (PC-343-10) were synthesized from 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343) and a 1/1 molar mixture of Diol-343 and 1,10-decanediol, respectively. As a comparison, an aliphatic polycarbonate homopolymer (PC-10) was prepared from 1,10-decanediol. While PC-10 exhibited a single melting peak during its DSC heating scan, both PC-343 and PC-343-10 exhibited multiple reproducible first-order transitions during DSC heating scans. Both PC-343 and PC-343-10 showed broad reflections in their WAXD diagrams; the crystalline order of PC-343 is higher than that of PC-343-10. Based on the DSC and WAXD results and our discovery on the liquid crystalline behavior of aliphatic poly(carbonate-sulfone)s from 1,3-bis(hydroxypropylsulfonyl)propane, we suggest PC-343 and PC-343-10 are liquid crystalline and the liquid crystalline phase formation is directed by the dipole-dipole interactions between sulfone groups. Films were obtained from these polymers by compression molding and dielectric analyses were conducted on them. One glass transition related dielectric relaxation was observed in PC-343-10. One glass transition related dielectric relaxation and one sub-glass transition related dielectric relaxation were observed in PC-343. The glass transition temperature increases with the increase of sulfone content in the polymers. A dramatic rise in dielectric constant with temperature was observed in PC-343 and PC-343-10 at low frequencies, which is probably due to the sulfone dipole interaction with the electrical field. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321502
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  • 105
    Electronic Resource
    Electronic Resource
    New results of the free radical ring-opening polymerization (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2867-2871 
    Details
    ISSN: 0887-624X
    Keywords: radical ring-opening polymerization ; keten-O, N-acetal ; cyclic esteramide ; benzoyl peroxide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 5-ring ketene-O, N-acetals with peroxides was investigated. It was shown that benzoyl peroxide adds to monomers 5a and 5b by ring opening, giving the corresponding linear diester amides 6a and 6b, respectively. The ketene-O,N-acetal 5c adds benzoyl peroxide, without ring opening, by addition to the exomethylene group, giving the cyclic-O,N-acetal diester 6c. With phthaloyl peroxide cyclic esteramides 7 and oligomeric products are formed. The chemical structures of the addition products were confirmed by NMR spectra and elemental analysis. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321508
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  • 106
    Electronic Resource
    Electronic Resource
    Synthesis, characterization, and polymerization of propenyl ether analogues (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2895-2909 
    Details
    ISSN: 0887-624X
    Keywords: propenyl ether analogues ; cationic photopolymerization ; monomer synthesis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of aromatic monomers bearing cationically polymerizable propenyl groups were prepared and characterized using the readily available starting materials: isoeugenol and o-allyl phenol. Monomers with both propenyl and vinyl ether functional groups were also synthesized by the reaction of these starting materials with chloroethyl vinyl ether. The reactivity of the resulting monomers in photoinitiated cationic polymerization was studied using differential scanning photocalorimetry and photogel point measurements. Their thermal properties were determined using thermogravimetric analysis. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321511
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  • 107
    Electronic Resource
    Electronic Resource
    A facile synthesis of aliphatic polybenzoxazoles from a bis(o-aminophenol) or its hydrochloride and aliphatic dinitriles (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2947-2951 
    Details
    ISSN: 0887-624X
    Keywords: aliphatic polybenzoxazoles ; melt polycondensation ; dinitrile monomers ; crystalline polybenzoxazoles ; thermal behavior ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A facile one-step method for the synthesis of aliphatic polybenzoxazoles has been developed. Thus, a series of aliphatic polybenzoxazoles having inherent viscosities of 0.2-0.7 dL/g in concentrated sulfuric acid were successfully synthesized by the melt polycondensation of alipatic dinitriles with 4,4′-diamino-3,3′-dihydroxybiphenyl (AHB) or its hydrochloride (AHB-HCl) with the elimination of ammonia or ammonium chloride, respectively. Monomer AHB-HCl was more reactive than the parent AHB, thereby affording higher molecular weight polybenzoxazoles in a shorter reaction time. The aliphatic polybenzoxazoles having 6-10 methylene units were highly crystalline with melting temperatures in the range of 187-308°C, which were stable up to 400°C in a melt state in nitrogen. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321516
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  • 108
    Electronic Resource
    Electronic Resource
    Copolymerization of ethylene and 1-butene with highly active Ticl4/THF/Mgcl2, Ticl4/THF/Mgcl2/SiO2, and TiCl3.1/3AlCl3 catalysts (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2979-2987 
    Details
    ISSN: 0887-624X
    Keywords: ethylene/1-butene copolymerization ; Mg/Ti bimetallic catalyst ; copolymer sequence distribution ; solvent fractionation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Highly active catalysts for copolymerization have been prepared by the precipitation of MgCl2/ToCl4 complex with or without high surface area silica. Copolymerization of ethylene and 1-butene has been tested by using the prepared catalysts at various concentrations of 1-butene. The catalytic activities are 20-80 kg/g Ti h. The rate of copolymerization is strongly affected by the addition of 1-butene. The decay rate of copolymerization is first order with respect to time. Analyses of copolymers with solvent extraction, DSC, IR, XRD, and NMR were performed. Ethylene reactivity ratio (k11) for TiCl4/MgCl2/THF catalyst is calculated to be about 26 by NMR spectrum. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321521
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  • 109
    Electronic Resource
    Electronic Resource
    Structural study of methyl methacrylate-α-trifluoromethacrylic acid copolymer by 1H-NMR (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2803-2807 
    Details
    ISSN: 0887-624X
    Keywords: copolymer sequence ; NMR ; methyl methacrylate ; styrene ; α-trifluorome-thacrylic acid ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [no Abstrat]
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321501
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  • 110
    Electronic Resource
    Electronic Resource
    A comparison of thermoreactive water-soluble poly-N,N-diethylacrylamide prepared by anionic and by group transfer polymerization (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3019-3030 
    Details
    ISSN: 0887-624X
    Keywords: LCST ; thermoprecipitation ; poly-N,N-diethylacrylamide ; group transfer polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several batches of poly-N,N-diethylacrylamide were synthesized by anionic and by group transfer polymerization (GTP). A radical poly-N,N-diethylacrylamide prepared from the same monomer was also included in the comparison. According to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) both types of living polymerization resulted in narrow molecular weight distributions with Mw/Mn values below 1.5. Average molecular weights (Mn) between 888 and 4678 g/mol were calculated in these cases. The radical polymer had an average molecular weight (Mn) of approximately 130,000 g/mol. The dry anionic and GTP polymers were investigated by differential scanning calorimetry (DSC) and x-ray diffraction spectrometry. Evidence for partial crystallinity in the solid state was found. The conformation of all polymers was examined by high resolution (600 MHz) NMR. According to these measurements, 75% of the —CHR— groups of the anionic poly-N,N-diethylacrylamide were located in an isotactic triade. The remaining 25% had heterotactic structure, while no indication for the presence of syndiotactic protons was found. Poly-N,N-diethylacrylamide prepared by GTP, on the other hand, had mainly syndiotactic structure. The aqueous solutions of the polymers showed phase separation upon heating. Whereas the lower critical solution temperature (LCST) was approximately 30°C in the case of the poly-N,N-diethylacrylamide prepared by GTP and by radical polymerization, uncommonly high LCSTs of more than 40°C were observed for the anionic poly-N,N-diethylacrylamide. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321603
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  • 111
    Electronic Resource
    Electronic Resource
    Palladium- and platinum-catalyzed coupling reactions of allyloxy aromatics with hydridosilanes and hydridosiloxanes: Novel liquid crystalline/organosilane materials (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3069-3089 
    Details
    ISSN: 0887-624X
    Keywords: hydrosilylation ; silsesquioxane ; oxysilylation ; allyloxyaromatic ; hydridosilane ; hydridosiloxane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pt-and Pd-catalyzed reactions of a set of allyloxyaromatic mono-and diesters with selected silanes were examined to develop simple, mild methods of forming liquid crystal (LC)/ siloxane and LC/silsesquioxane polymers. Pt complexes catalyze hydrosilylation to give primarily (≤ 80% selectivity at 100% conversion) terminal silylation of the allyloxys. The catalyst, platinum-1,3-divinyltetramethyldisiloxane [Pt (dvs), gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydrosilylation of 4-allyloxy methylbenzoate gave relative reactivities (HSiO1.5)8 ≫ Et3SiH 〉 HMe2Si—O—SiMe2H 〉 Ph2SiH2. The cubic silsesquioxane, (HSiO1.5)8, is so reactive hydrosilylation is over in 1-3 h at 0°C. All other reactions required 〉 40°C and longer reaction times. Initial efforts to form high polymers by Pt-catalyzed reactions of bis-allyloxy aromatics with Ph2SiH2 provide polymers with bimodal MW distributions (polystyrene), Mws ≈ 30 kDa, and PDIs ≈ 5. Pd catalysis gives quite different products resulting from loss of propene with coincident formation of Si—O bonds, “oxysilylation.” The same products appear (10-15%) in some Pt catalyzed reactions. Palladium dibenzylideneacetone/ Ph3P[Pd(dba)2/Ph3P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph2SiH2 〉 HMe2SiOSiMe2H 〉 Et3SiH. Polymerization with Pd catalysts provides polymers with Mws ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO1.5)8 with 4 equiv. of 4-(4-allyloxy-benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [Mn ≈ 1860 Da, PDI ≈ 1.09 (styrene equiv.) vs. 1746 Da caled.] A detailed analysis of the products formed, the catalytic reactivity patterns of the his (allyloxy) aromatic diesters and their LC transitions is presented. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321608
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  • 112
    Electronic Resource
    Electronic Resource
    Solution polymerization of vinyl monomers in the presence of poly(N-acetyliminoethylene) macroazoinitiators (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3123-3132 
    Details
    ISSN: 0887-624X
    Keywords: vinyl monomers ; solution polymerization ; poly(N-acetyliminoethylene) ; macroazoinitiator ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New block copolymers with poly(N-acetyliminoethylene) and vinyl sequences were obtained by a two-step synthetic approach. In the first stage macroinitiators of poly(N-acetyliminoethylene) type, with azo groups inserted in the main chain, were prepared. They were latter used in the radical polymerization of some vinyl monomers [styrene, methacrylic acid, methyl methacrylate, butyl methacrylate, β-(N-carbazolyl)ethyl acrylate, β-(methacryloyfoxy)ethyl 3,5-dinitrobenzoate]. The resulting block copolymers were characterized by spectral methods, elemental analysis, gel permeation chromatography, and electron microscopy. The kinetic study of the thermal and photochemical decomposition of the synthesized macroazoinitiators, as well as the polymerization data, suggest a dependence of their initiating efficiency on the length of the poly(N-acetyliminoethylene) segments. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321612
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  • 113
    Electronic Resource
    Electronic Resource
    Amphiphilic networks. VII. Synthesis and characterization of pH-sensitive poly(sulfoethyl methacrylate)-1-polyisobutylene networksFor Part VI of this series, see REFERENCE 22. (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3153-3160 
    Details
    ISSN: 0887-624X
    Keywords: polyisobutylene ; 2-sulfoethyl methacrylate ; copolymer ; network ; synthesis ; characterization ; swelling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of environmentally sensitive amphiphilic networks consisting of 2-sulfoethyl methacrylate (SEMA) chains linked by methacrylate-ditelechelic polyisobutylene (MA-PIB-MA) chains have been prepared and characterized. Network composition was determined after sequential solvent extraction by elemental analysis. These networks are two-phase microheterogeneous systems containing hydrophobic rubbery PIB domains (Tg ∼ -60°C) and hydrophilic poly(2-sulfoethyl methacrylate) domains (Tg ∼ -15°C). They exhibit large contact-angle hysteresis in water which is due to surface segmental mobility and microheterogeneity. By increasing the SEMA content of the networks the contact-angle hysteresis increases. This phenomenon is due to an increase in the advancing contact angle most likely caused by the migration of the nonpolar PIB domains toward the surface and concomitant decrease of the receding contact angle. These amphiphilic networks exhibit non-Fickian swelling in n-heptane, as well as in water, and show pH-sensitive swelling in aqueous media. They rapidly and reversibly swell and deswell in response to increasing or decreasing the pH of the media (cycling between pH = 2 and 12). © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321616
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  • 114
    Electronic Resource
    Electronic Resource
    Synthesis of polyallylamine derivatives with N-carbamoylguanidine groups (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3189-3191 
    Details
    ISSN: 0887-624X
    Keywords: polycationic polymer ; poly(allyl-N-carbamoylguanidino-co-allylamine) ; poly(allylguanidino-co-allylamine) ; potentiometric titration ; thermogravimetric analysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321620
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  • 115
    Electronic Resource
    Electronic Resource
    Thermotropic liquid crystalline main-chain viologen polymers: Homopolymer-of 4,4′-bipyridyl with ditosylate of trans-1,4-cyclohexanedimethanol and its copolymers with ditosylate of 1,8-octanediol (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 3205-3209 
    Details
    ISSN: 0887-624X
    Keywords: viologen polymer ; thermotropic ; smectic ; synthesis ; characterization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321624
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  • 116
    Electronic Resource
    Electronic Resource
    Crystallization and preliminary crystallographic studies of the precursor and mature forms of a neutral lipase from the fungus Rhizopus delemar (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 301-306 
    Details
    ISSN: 0887-3585
    Keywords: triglyceride lipase ; proenzyme ; molecular replacement ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A neutral lipase from the filamentous fungus Rhizopus delemar has been crystallized in both its proenzyme and mature forms. Although the latter crystallizes readily and produces a variety of crystal forms, only one was found to be suitable for X-ray studies. It is monoclinic (C2, a = 92.8 Å, b = 128.9 Å, c = 78.3 Å, β = 135.8) with two molecules in the asymmetric unit related by a noncrystallographic diad. The prolipase crystals are orthorhombic (P212121, with a = 79.8 Å, b = 115.2 Å, c = 73.0 Å) and also contain a pair of molecules in the asymmetric unit. Initial results of molecular replacement calculations using the refined coordinates of the related lipase from Rhizomucor miehei identified the correct orientations and positions of the protein molecules in the unit cells of crystals of both proenzyme and the mature form. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180311
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  • 117
    Electronic Resource
    Electronic Resource
    Correlated mutations and residue contacts in proteins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 309-317 
    Details
    ISSN: 0887-3585
    Keywords: protein structure prediction ; predicted contact maps ; correlated mutations ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The maintenance of protein function and structure constrains the evolution of amino acid sequences. This fact can be exploited to interpret correlated mutations observed in a sequence family as an indication of probable physical contact in three dimensions. Here we present a simple and general method to analyze correlations in mutational behavior between different positions in a multiple sequence alignment. We then use these correlations to predict contact maps for each of 11 protein families and compare the result with the contacts determined by crystallography. For the most strongly correlated residue pairs predicted to be in contact, the prediction accuracy ranges from 37 to 68% and the improvement ratio relative to a random prediction from 1.4 to 5.1. Predicted contact maps can be used as input for the calculation of protein tertiary structure, either from sequence information alone or in combination with experimental information. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180402
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  • 118
    Electronic Resource
    Electronic Resource
    Expression, purification, and crystallization of restriction endonuclease PvuII with DNA containing its recognition site (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 77-79 
    Details
    ISSN: 0887-3585
    Keywords: endonuclease overexpression ; crystallization ; X-ray diffraction ; protein-DNA complex ; Type II restriction enzyme ; vapor diffusion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have overexpressed the type II restriction endonuclease PvuII (R.PvuII) in E. coli, prepared large amounts of the homogeneous enzyme, and crystallized it with an oligonucleotide carrying a PvuII recognition site. The cocrystals are orthorhombic space group P212121 with cell constants a = 95.8 Å, b = 86.3 Å, c = 48.5 Å, and diffract X-rays to at least 2.7 Å. There is a complex of two protein subunits and one oligonucleotide duplex in the asymmetric unit. © 1994 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340190110
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  • 119
    Electronic Resource
    Electronic Resource
    Investigation of the functional interplay between the primary site and the subsite of RNase T1: Kinetic analysis of single and multiple mutants for modified substrates (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 318-323 
    Details
    ISSN: 0887-3585
    Keywords: ribonuclease T1 ; functional cooperativity ; double mutant cycle ; subsite ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We report on the functional cooperativity of the primary site and the sub-site of ribonuclease T1 (RNase T1; EC 3.1.27.3). The kinetic properties of the single Tyr-38-Phe and Asn-98-Ala mutants have been compared with those of the corresponding double mutant. The Tyr-38-Phe mutation has been used to probe enzyme-substrate interactions at the primary site; the Asn-98-Ala mutation monitors subsite interactions.1 In addition to the dinucleoside phosphate substrate GpC, we measured the kinetics for GpMe, a synthetic substrate in which the leaving nucleoside cytosine has been replaced by methanol. All data were combined in a triple mutant box to analyze the interplay between Tyr-38, Asn-98, and the leaving group. The free energy barriers to kcat, introduced by the single Tyr-38-Phe and Asn-98-Ala mutations are not additive in the corresponding double mutant. The energetic coupling between both mutations is independent of the binding of the leaving cytosine at the subsite. We conclude that the coupling of the Tyr-38-Phe and Asn-98-Ala mutations arises through distortion or reorientation of the 3′-guanylic acid moiety bound at the primary site. The experimental data indicate that the enzyme-substrate interactions beyond the scissile phosphodiester bond contribute to catalysis through the formation of new or improved contacts in going from ground state to transition state, which are functionally independent of primary site interactions. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180403
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    1.56 Å structure of mature truncated human fibroblast collagenase (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 98-109 
    Details
    ISSN: 0887-3585
    Keywords: crystallography ; hydroxamate ; high resolution ; metalloproteinase ; zinc ; X-ray ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 Å resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded β-sheet and three α-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase. © 1994 Wiley-Liss, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190203
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    Kinetic study on myoglobin refolding monitored by five optical probe stopped-flow methods (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 110-119 
    Details
    ISSN: 0887-3585
    Keywords: folding intermediate ; urea denaturation ; stopped-flow circular dichroism ; molten globule ; hemindicyanide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The refolding kinetics of horse cyanometmyoglobin induced by concentration jump of urea was investigated by five optical probe stopped-flow methods: absorption at 422 nm, tryptophyl fluorescence at around 340 nm, circular dichroism (CD) at 222 nm, CD at 260 nm, and CD at 422 nm. In the refolding process, we detected three phases with rate constants of 〉 1 × 102 s-1, (4.5-9.3) S-1, and (2-5) × 10-3 s-1. In the fastest phase, a substantial amount of secondary structure (40%) is formed within the dead time of the CD stopped-flow apparatus (10.7 ms). The kinetic intermediate populated in the fastest phase is shown to capture a hemindicyanide, suggesting that a “heme pocket precursor” recognized by hemindicyanide must be constructed within the dead time. In the middle phase, most of secondary and tertiary structures, especially around the captured hemindicyanide, have been constructed. In the slowest phase, we detected a minor structural rearrangement accompanying the ligand-exchange reaction in the fifth coordination of ferric iron. We present a possible model for the refolding process of myoglobin in the presence of the heme group. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190204
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    Decoupling of melting domains in immobilized ribonuclease A (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 120-131 
    Details
    ISSN: 0887-3585
    Keywords: enzymes ; protein immobilization ; microcalorimetry ; protein melting domains ; protein DSC ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Ribonuclease A has been immobilized on silica beads through glutaraldeyde-mediated chemical coupling in order to improve the stability of the protein against thermal denaturation. The thermodynamic and binding properties of the immobilized enzyme have been studied and compared with those of the free enzyme. The parameters describing the binding of the inhibitor 3′ -CMP (Ka and ΔH) as monitored by spectrophotometry and calorimetry were not significantly affected after immobilization. Conversely both the stability and unfolding mechanism drastically changed. Thermodynamic analysis of the DSC data suggests that uncoupling of protein domains has occurred as a consequence of the immobilization. The two state approximation of the protein unfolding process is not longer valid for the immobilized RNase. Protein stability strongly depends on the hydrophobicity properties of the support surface as well as on the presence of the inhibitor and pH. For example, after immobilization on a highly hydrophobic surface, the enzyme is partially in the unfolded state. The binding of a ligand is able to reorganize the protein structure into a native-like conformation. The refolding rates are different for the two protein domains and vary as a function of pH and presence of the inhibitor 3′-CMP. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190205
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    Recognition of distantly related proteins through energy calculations (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 132-140 
    Details
    ISSN: 0887-3585
    Keywords: distant protein folds ; sequence homology ; database searching ; profile analysis ; protein structure comparison ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A new method to detect remote relationships between protein sequences and known three-dimensional structures based on direct energy calculations and without reliance on statistics has been developed. The likelihood of a residue to occupy a given position on the structural template was represented by an estimate of the stabilization free energy made after explicit prediction of the substituted side chain conformation. The profile matrix derived from these energy values and modified by increasing the residue self-exchange values successfully predicted compatibility of heatshock protein and globin sequences with the three-dimensional structures of actin and phycocyanin, respectively, from a full protein sequence databank search. The high sensitivity of the method makes it a unique tool for predicting the three-dimensional fold for the rapidly growing number of protein sequences. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340190206
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    Characterization of two crystal forms of Clostridium thermocellum endoglucanase CelC (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 158-160 
    Details
    ISSN: 0887-3585
    Keywords: crystallization ; cellulases ; X-ray crystallography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Endoglucanase CelC from Clostridium thermocellum expressed in Escherichia coli has been crystallized in two different crystal forms by the hanging drop method. Crystals of form I were grown with polyethylene glycol as a precipitant. They are orthorhombic, space group P212121, with cell dimensions a =51.4 Å, b =84.3 Å, and c =87.5 Å. Crystals of form II, obtained in ammonium sulfate solutions, belong to the tetragonal space group P41212 (or P43212) with cell dimensions of a = b = 130.7 Å and c = 69.6 Å. Diffraction data to 2.8 Å resolution were observed for both crystal forms with a rotating anode generator. Preliminary oscillation images of the orthorhombic form I crystals using a synchrotron radiation source show diffraction to 2.2 Å resolution, indicating that these crystals are suitable for high resolution crystallographic analysis. © 1994 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190209
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340190301
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    The closed conformation of a highly flexible protein: The structure of E. coli adenylate kinase with bound AMP and AMPPNPThe structure is listed as 1ANK in the Brookhaven Protein Data Bank. (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 183-198 
    Details
    ISSN: 0887-3585
    Keywords: X-ray crystallography ; Rfree ; ATP and AMP binding sites ; Mg2+ coordination ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure of E. coli adenylate kinase with bound AMP and AMPPNP at 2.0 Å resolution is presented. The protein crystallizes in space group C2 with two molecules in the asymmetric unit, and has been refined to an R factor of 20.1% and an Rfree of 31.6%. In the present structure, the protein is in the closed (globular) form with the large flexible lid domain covering the AMPPNP molecule. Within the protein, AMP and AMPPNP, an ATP analog, occupy the AMP and ATP sites respectively, which had been suggested by the most recent crystal structure of E. coli adenylate kinase with AP5A bound (Müller and Schulz, 1992, ref. 1) and prior fluorescence studies (Liang et al., 1991, ref. 2). The binding of substrates and the positions of the active site residues are compared between the present structure and the E. coli adenylate kinase/Ap5A structure. We failed to detect a peak in the density map corresponding to the Mg2+ ion which is required for catalysis, and its absence has been attributed to the use of ammonium sulfate in the crystallization solution. Finally, a comparison is made between the present structure and the structure of the heavy chain of muscle myosin. © 1994 Wiley-Liss, Inc.
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    Conformational analysis of hemopexin by fourier-transform infrared and circular dichroism spectroscopy (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 185-190 
    Details
    ISSN: 0887-3585
    Keywords: heme ; secondary structure ; conformation ; hemopexin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Hemopexin is a serum glyco-protein that binds heme with the highest known affinity of any characterized heme-binding protein and plays an important role in receptormediated cellular heme uptake. Complete understanding of the function of hemopexin will require the elucidation of its molecular structure. Previous analysis of the secondary structure of hemopexin by far-UV circular dichroism (CD) failed due to the unusual positive ellipticity of this protein at 233 nm. In this paper, we present an examination of the structure of hemopexin by both Fourier-transform infrared (FTIR) and circular dichroism spectroscopy. Our studies show that hemopexin contains about 55% β-structure, 15% α-helix, and 20% turns. The two isolated structural domains of hemopexin each have secondary structures similar to hemopexin. Although there are significant tertiary conformational changes indicated by the CD spectra, the overall secondary structure of hemopexin is not affected by binding heme. However, moderate changes in secondary structure do occur when the heme-binding domain of hemopexin associates with heme. In spite of the exceptionally tight binding at neutral pH, heme is released from the bis-histidyl heme-hemopexin complex at pH 5.0. Under this acidic condition, hemopexin maintains the same overall secondary structure as the native protein and is able to resume the heme-binding function and the native structure of the hemeprotein (as indicated by the CD spectra) when returned to neutral pH. We propose that the state of hemopexin identified in vitro at pH 5.0 resembles that of this protein in the acidic environment of the endosomes in vivo when hemopexin releases heme during receptor-mediated endocytosis. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340200208
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    Crystallization of a scRIP - gelonin isolated from plant seeds Gelonium multiforum (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 340-342 
    Details
    ISSN: 0887-3585
    Keywords: protein ; ribosome ; inactivation ; toxin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Single crystals of the protein gelonin isolated from the seeds of Gelonium multiforum have been grown at room temperature by vapor diffusion method. The crystals are monclinic with a = 49.4 Å, b = 44.9 Å, c = 137.4 Å, and β = 98.3°. The space group is P21, with two molecules in the asymmetric unit which are related by a noncrystallographic 2-fold axis along ψ =13° and φ =88°. The crystals diffract X-rays to high resolution, making it possible to obtain an accurate structure of this single chain ribosome inactivating protein. © 1994 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190409
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    Homologous modeling of the lysosomal protective protein/carboxypeptidase L: Structural and functional implications of mutations identified in galactosialidosis patients (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 81-93 
    Details
    ISSN: 0887-3585
    Keywords: serine carboxypeptidase ; protein modeling ; mutation analysis ; comparative modeling ; cathepsin A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The deficiency of the lysosomal protective protein/carboxypeptidase L (CARB L) causes the lysosomal storage disorder, galactosialidosis, characterized by neuraminidase and β-galactosidase deficiencies in patients' cells. The three enzymes form a complex inside the lysosome, and the neuraminidase and β-galactosidase deficiencies are secondary to CARB L deficiency. Sequence similarity and common enzymological properties suggest that the protomeric tertiary structure of CARB L is conserved within a family of serine carboxypeptidases which includes the yeast carboxypeptidase Y, killer expression I gene product and several plant carboxypeptidases. We used this homology to build a model of the CARB L structure based on the recently published X-ray atomic coordinates of the wheat carboxypeptidase II (CPDW-II) which shares 32% primary structure identity with CARB L. Small insertions and deletions were accommodated into the model structure by energy minimization using the DREIDING II force field. The Cα atomic-coordinates of the final CARB L model have a RMS shift of 1.01 Å compared to the corresponding conserved residues in the CPDW-II template structure. The correct orientation of the homologous catalytic triad residues Ser150, His429 and Asp392, the potential energy calculations and the distribution of hydrophobic and hydrophillic residues in the structure all support the validity of the CARB L model. Most missense mutations identified in galactosialidosis patients were located in secondary structural elements except for the Tyr211→Asn mutation which is in a loop. The other mutant residues have their side chains deeply buried in the central β-sheet of the model structure except for the Phe412→Val mutation which is located in the dimer interface. The predicted effects of specific mutations on CARB L structural stability correlates well with recently published transient expression studies of mutant CARB L (Shimmoto, M. et al., J. Clin. Invest., 91:2393-2399, 1993). © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180110
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    Molecular dynamics simulations of trp apo-and holorepressors: Domain structure and ligand-protein interaction (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 248-258 
    Details
    ISSN: 0887-3585
    Keywords: molecular dynamics ; trp-repressor ; ligand ; domain ; dynamic cross-correlation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Molecular dynamics simulations of the apo- and holo-forms of thetrp-repressor protein were performed under extensively solvated conditions in order to elucidate their dynamic structures and ligand-protein interactions. The root mean square fluctuations calculated from the trajectories agreed with those calculated from X-ray temperature factors. Distance, distance fluctuation, and dynamic cross-correlation maps were drawn to provide information on the dynamic structures and communications among the domains. A three-domain format has been proposed for the crystal structure (Zhang et at., Nature 327:591-597, 1987) namely, helices A-C and F of both subunits make up a central core, and D and E of each subunit forms a DNA binding head. The results of the simulations were mostly consistent with the three-domain format. However, helix F was more flexible and freer than other parts of the central core. The turn DE, the helix-turn-helix DNA binding motif, was free from interactions and correlations with other domains in both forms of the repressor. A comparison of the simulations of the aporepressor and holorepressor showed that tryptophan binding made the DNA-binding helix D more flexible but helix F less flexible. Several amino acid residues in contact with the bound tryptophan were identified as making concerted motions with it. Interaction energies between the corepressor and the amino acid residues of the protein were analyzed; the results were mostly consistent with the mutational experiments. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340200305
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    Protein simulations using techniques suitable for very large systems: The cell multipole method for nonbond interactions and the Newton-Euler inverse mass operator method for internal coordinate dynamics (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 227-247 
    Details
    ISSN: 0887-3585
    Keywords: cell multipole method ; Newton-Euler inverse mass operator ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Two new methods developed for molecular dynamics simulations of very large proteins are applied to a series of proteins ranging up to the protein capsid of tomato bushy stunt virus (TBSV).For molecular dynamics of very large proteins and polymers, it is useful to carry out the dynamics using internal coordinates (say, torsions only) rather than Cartesian coordinates. This allows larger time steps, eliminates problems with the classical description of high energy modes, and focuses on the important degrees of freedom. The resulting equation of motion has the form where for T is the vector of generalized forces, M(θ) is the moments of inertia tensor, is the vector of torsions, and C is a vector containing Coriolis forces and nonbond forces. The problem is that to calculate the acceleration vector from M, C, and Trequires inverting. M(θ), an order N3calculation. Since the number of degrees of freedom might be 300,000 for a million atom system, solving these equations every time step is impractical, restricting internal coordinate methods to small systems. The new method, Newton-Euler Inverse Mass Operator (NEIMO) dynamics, constructs the torsional accelerations vector directly by an order N process, allowing internal-coordinate dynamics to be solved for super larger (million atom) systems, The first use of the NEIMO method for molecular dynamics of proteins is presented here.A second serious difficulty for large proteins is calculation of the nonbond forces. We report here the first application to proteins of the new Cell Multipole Method (CMM) to evaluate the Coulomb and van der Waals interactions. The cost of CMM scales linearly with the number of particles while retaining an accuracy significantly better than standard non bond methods (involving cutoffs).Results for NEIMO and CMM are given for simulations of a wide range of peptide and protein systems, including the protein capsid of TBSV with 488,000 atoms. The computational times for NEIMO and CMM are demonstrated to scale linearly with size. With NEIMO the dynamics time steps can be as large as 20 fs (for small peptides), much larger than possible with standard Cartesian coordinate dynamics.For TBSV we considered both the normal form and the high pH form, in which the Ca2+ ions are removed. These calculations lead to a contraction of the protein for both forms (probably because of ignoring the RNA core not observed in the X-ray). © 1994 Wiley-Liss, Inc.
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    A surface mutant (G82R) of a human α-glutathione S-transferase shows decreased thermal stability and a new mode of molecular association in the crystal (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 259-263 
    Details
    ISSN: 0887-3585
    Keywords: glutathione S. transferase ; temperature-sensitive protein ; chimeric protein ; mutant protein ; X-ray analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A chimeric enzyme (GST121) of the human α-glutathione S-transferases GST1-1 and GST2-2, which has improved catalytic efficiency and thermostability from its wild-type parent proteins, has been crystallized in a space group that is isomorphous with that reported for crystals of GST1-1. However, a single-site (G82R) mutant of GST121, which exhibits a significant reduction both in vitro and in vivo in protein thermostability, forms crystals that are not isomorphous with GST1-1. The mutant protein crystallizes in space group P212121, with cell dimensions a = 49.5, b = 92.9, c = 115.9 Å, and one dimer per asymmetric unit. Preliminary crystallographic results show that a mutation of the surface residue Gly 82 from a neutral to a charged residue causes new salt bridges to be formed among the GST dimers, suggesting that the G82R mutant might aggregate more readily than does GST121 in solution resulting in a change of its solution properties. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340200306
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    Polar and nonpolar atomic environments in the protein core: Implications for folding and binding (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 20 (1994), S. 264-278 
    Details
    ISSN: 0887-3585
    Keywords: hydrophobic interactions ; protein stability ; hydrophobicity scale ; protein mutant stability ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Hydrophobic interactions are believed to play an important role in protein folding and stability. Semi-empirical attempts to estimate these interactions are usually based on a model of solvation, whose contribution to the stability of proteins is assumed to be proportional to the surface area buried upon folding. Here we propose an extension of this idea by defining an environment free energy that characterizes the environment of each atom of the protein, including solvent, polar or nonpolar atoms of the same protein or of another molecule that interacts with the protein. In our model, the difference of this environment free energy between the folded state and the unfolded (extended) state of a protein is shown to be proportional to the area buried by nonpolar atoms upon folding. General properties of this environment free energy are derived from statistical studies on a database of 82 well-refined protein structures. This free energy is shown to be able to discriminate misfolded from correct structural models, to provide an estimate of the stabilization due to oligomerization, and to predict the stability of mutants in which hydrophobic residues have been substituted by site-directed mutagenesis, provided that no large structural modifications occur. © 1994 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340200307
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    An evaluation of implicit and explicit solvent model systems for the molecular dynamics simulation of bacteriophage T4 lysozyme (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 19-33 
    Details
    ISSN: 0887-3585
    Keywords: Discover program ; protein dynamics ; computer simulation ; protein motions ; counterions ; dielectric ; protein electrostatics ; aqueous simulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this report we examine several solvent models for use in molecular dynamics simulations of protein molecules with the Discover program from Biosym Technologies. Our goal was to find a solvent system which strikes a reasonable balance among theoretical rigor, computational efficiency, and experimental reality. We chose phage T4 lysozyme as our model protein and analyzed 14 simulations using different solvent models. We tested both implicit and explicit solvent models using either a linear distance-dependent dielectric or a constant dielectric. Use of a linear distance-dependent dielectric with implicit solvent significantly diminished atomic fluctuations in the protein and kept the protein close to the starting crystal structure. In systems using a constant dielectric and explicit solvent, atomic fluctuations were much greater and the protein was able to sample a larger portion of conformational space. A series of nonbonded cutoff distances (9.0, 11.5, 15.0, 20.0 Å) using both abrupt and smooth truncation of the nonbonded cutoff distances were tested. The method of dual cutoffs was also tested. We found that a minimum nonbonded cutoff distance of 15.0 Å was needed in order to properly couple solvent and solute. Distances shorter than 15.0 Å resulted in a significant temperature gradient between the solvent and solute. In all trajectories using the proprietary Discover switching function, we found significant denaturation in the protein backbone; we were able to run successful trajectories only in those simulations that used no switching function. We were able to significantly reduce the computational burden by using dual cutoffs and still calculate a quality trajectory. In this method, we found that an outer cutoff distance of 15.0 Å and an inner cutoff distance of 11.5 worked well. While a 10 Å shell of explicit water yielded the best results, a 6 A shell of water yielded satisfactory results with nearly a 40% reduction in computational cost. © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340180105
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    Collective motions in proteins investigated by X-ray diffuse scattering (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 34-48 
    Details
    ISSN: 0887-3585
    Keywords: normal mode refinement ; correlation function ; intra- and intermolecular correlation ; higher order scattering ; human lysozyme ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have developed theoretical models for analysis of X-ray diffuse scattering from protein crystals. A series of models are proposed to be used for experimental data with different degrees of precision. First, we propose the normal mode model, where conformational dynamics of a protein is assumed to occur mostly in a limited conformational subspace spanned by a small number of low-frequency normal modes in the protein. When high precision data are available, variances and covariances of the normal mode variables can be determined from experimental data using this model. For experimental data with lower degrees of precision, we introduce a series of simpler models. These models express the covariance matrix using relatively simple empirical correlation functions by assuming the correlation between a pair of atoms to be isotropic. As an application of these simpler models, we calculate diffuse-scattering patterns from a human lysozyme crystal to examine how each adjustable parameter in the models affects general features of the resulting patterns. The results of the calculation are summarized as follows. (1) The higher order scattering makes a significant contribution at high resolutions. (2) The resulting simulated patterns are sensitive to changes in correlation lengths of about 1 Å, as well as to changes of the functional form of the correlation function. (3) But only the “average” value of the intra- and intermolecular correlation lengths seems to determine the gross features of the pattern. (4) The effect of the atom-dependent amplitude of fluctuations is difficult to observe. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340180106
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    X-ray structures of fragments from binding and nonbinding versions of a humanized anti-CD18 antibody: Structural indications of the key role of VH residues 59 to 65 (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 49-62 
    Details
    ISSN: 0887-3585
    Keywords: protein ; mutation ; Fab ; Fv ; complementarity determining region ; hypervariability ; integrin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: X-ray crystal structures of fragments from two different humanized antiCD18 antibodies are reported. The Fv fragment of the nonbinding version has been refined in space group C2 with a=64.2 Å, b=61.3 Å, c=51.8 Å, and β=99° to an R-value of 18.0% at 1.9 Å, and the Fab fragment of the tight-binding version has been refined in space group P3 with a=101. Å and c=45.5 Å to an R-value of 17.8% at 3.0 Å resolution. The very large difference in their binding affinity (〉1000-fold) is attributed to large and local structural differences in the C-terminal part of CDR-H2, and from this we conclude there is direct contact between this region and antigen when they combine. X-ray structures of antibody-antigen complexes available in the literature have yet to show this part of CDR-H2 in contact with antigen, despite its hypervariable sequence. Implications of this result for antibody humanization are discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340180107
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    Entropy in biological binding processes: Estimation of translational entropy loss (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 63-67 
    Details
    ISSN: 0887-3585
    Keywords: entropy ; thermodynamics ; binding energetics ; translational entropy ; macromolecular interactions ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The loss of translational degrees of freedom makes an important, unfavorable contribution to the free energy of binding. Examination of experimental values suggest that calculation of this entropy using the Sackur-Tetrode equation produces largely overestimated values. Better agreement is obtained using the cratic entropy. Theoretical considerations suggest that the volumes available for the movement of a ligand in solution and in a complex are rather similar, suggesting also that the cratic entropy provides the best estimate of the loss of translational entropy. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180108
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    Masthead (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994) 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180201
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    Molecular surface representations by sparse critical points (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 94-101 
    Details
    ISSN: 0887-3585
    Keywords: surface representation ; molecular recognition ; protein docking ; surface triangulation ; molecular graphics ; molecular visualization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have defined a molecular surface representation that describes precisely and concisely the complete molecular surface. The representation consists of a limited number of critical points disposed at key locations over the surface. These points adequately represent the shape and the important characteristics of the surface, despite the fact that they are modest in number. We expect the representation to be useful in areas such as molecular recognition and visualization. In particular, using this representation, we are able to achieve accurate and efficient protein-protein and protein-small molecule docking. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340180111
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    Introducing “Future Directions” (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. i 
    Details
    ISSN: 0887-3585
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340180202
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  • 141
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    Crystallization and characterization of colicin E1 channel-forming polypeptides (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 150-157 
    Details
    ISSN: 0887-3585
    Keywords: X-ray crystallography ; membrane protein ; ion channels ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystals of the channel-forming domain of colicin E1 from E. coli were grown by vapor diffusion at pH 6.4 and higher pH values. Cleavage of the colicin molecule with trypsin or thermolysin produced two of the pore-forming polypeptides used in these experiments. The third polypeptide was purified from a constructed plasmid that overexpresses only the C-terminal domain of colicin E1. Polypeptide crystals are tetragonal with space group I4, have one monomer in the asymmetric unit, and diffract to 2.2-2.4 Å. Unit cell parameters for the tryptic and thermolytic polypeptides are a = 102.9 Å and c = 35.6 Å. Crystals of the overexpressed polypeptide have unit cell parameters of a =87.2 Å and c =59.1 Å. The crystals were characterized by precession photography, and native data sets of each channel-forming fragment were collected on a Siemens-Nicolet area detector. The crystallization and characterization of these polypeptides are the first steps in the structure determination of the channel-forming domain of colicin E1. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190208
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  • 142
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    Accuracy of protein flexibility predictions (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 141-149 
    Details
    ISSN: 0887-3585
    Keywords: dynamics ; flexibility index ; protein stability ; antigenic regions ; epitopes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Protein structural flexibility is important for catalysis, binding, and allostery. Flexibility has been predicted from amino acid sequence with a sliding window averaging technique and applied primarily to epitope search. New prediction parameters were derived from 92 refined protein structures in an unbiased selection of the Protein Data Bank by developing further the method of Karplus and Schulz (Naturwissenschaften 72:212-213, 1985). The accuracy of four flexibility prediction techniques was studied by comparing atomic temperature factors of known three-dimensional protein structures to predictions by using correlation coefficients. The size of the prediction window was optimized for each method. Predictions made with our new parameters, using an optimized window size of 9 residues in the prediction window, were giving the best results. The difference from another previously used technique was small, whereas two other methods were much poorer. Applicability of the predictions was also tested by searching for known epitopes from amino acid sequences. The best techniques predicted correctly 20 of 31 continuous epitopes in seven proteins. Flexibility parameters have previously been used for calculating protein average flexibility indices which are inversely correlated to protein stability. Indices with the new parameters showed better correlation to protein stability than those used previously; furthermore they had relationship even when the old parameters failed. © 1994 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190207
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  • 143
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    Crystallization of an enzyme-inhibitor complex: Proteinase K with its protein inhibitor, PK13 (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 161-162 
    Details
    ISSN: 0887-3585
    Keywords: Proteinase K ; naturally occurring inhibitor ; enzyme-inhibitor complex ; microdialysis ; crystal ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Crystals of a complex of proteinase K (molecular mass, 28,790 Da) with its naturally occurring protein inhibitor PK13 (19,641 Da), have been prepared by a microdialysis technique and modified by hanging drop vapor diffusion against 25% ammonium sulfate in 50 mM Tris-HCl, pH 7.8. The crystals are long prisms with diamond-shaped cross sections of 0.2 × 0.4 × 1.5 mm3 and they diffract X-rays to a resolution of 2.5 Å. They belong to the orthorhombic space group P212121 with cell dimensions a = 64.1 Å, b = 66.8 Å, and c = 133.8 Å. Assuming one whole complex in the asymmetric unit, one obtains VM = 2.95 Å3/Da and the solvent content, Vsolv = 58.3%. © 1994 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190210
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  • 144
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    Molecular dynamics simulation of the docking of substrates to proteins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 174-182 
    Details
    ISSN: 0887-3585
    Keywords: molecular dynamics ; docking ; computer simulation ; substrate docking ; immunoglobulin ; rational drug design ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A simple method is described to perform docking of subtrates to proteins or probes to receptor molecules by a modification of molecular dynamics simulations. The method consists of a separation of the center-of-mass motion of the substrate from its internal and rotational motions, and a separate coupling to different thermal baths for both types of motion of the substrate and for the motion of the receptor. Thus the temperatures and the time constants of coupling to the baths can be arbitrarily varied for these three types of motion, allowing either a frozen or a flexible receptor and allowing control of search rate without disturbance of internal structure. In addition, an extra repulsive term between substrate and protein was applied to smooth the interaction. The method was applied to a model substrate docking onto a model surface, and to the docking of phosphocholine onto immunoglobulin McPC603, in both cases with a frozen receptor. Using transrational temperatures of the substrate in the range of 1300-1700 K and room temperature for the internal degrees of freedom of the substrate, an efficient nontrapping exploratory search (“helicopter view”) is obtained, which visits the correct binding sites. Low energy conformations can then be further investigated by separate search or by dynamic simulated annealing. In both cases the correct minima were identified. The possibility to work with flexible receptors is discussed. © 1994 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190303
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  • 145
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    Spatial optimization of electrostatic interactions between the ionized groups in globular proteins (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 222-229 
    Details
    ISSN: 0887-3585
    Keywords: protein electrostatics ; energy calculations ; ion pairs ; Monte-Carlo simulations ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A model approach is suggested to estimate the degree of spatial optimization of the electrostatic interactions in protein molecules. The method is tested on a set of 44 globular proteins, representative of the available crystallographic data. The theoretical model is based on macroscopic computation of the contribution of charge-charge interactions to the electrostatic term of the free energy for the native proteins and for a big number of virtual structures with randomly distributed on protein surface charge consetellations (generated by a Monte-Carlo technique). The statistical probability of occurrence of random structures with electrostatic energies lower than the energy of the native protein is suggested as a criterion for spatial optimization of the electrostatic interactions. The results support the hypothesis that the folding process optimizes the stabilizing effect of electrostatic interactions, but to very different degree for different proteins. A parallel analysis of ion pairs shows that the optimization of the electrostatic term in globular proteins has increasingly gone in the direction of rejecting the repulsive short contacts between charges of equal sign than of creating of more salt bridges (in comparison with the statistically expected number of shortrange ion pairs in the simulated random structures). It is observed that the decrease in the spatial optimization of the electrostatic interactions is usually compensated for by an appearance of disulfide bridges in the covalent structure of the examined proteins. © 1994 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190306
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  • 146
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    Energy minimization method using automata network for sequence and side-chain conformation prediction from given backbone geometry (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 244-255 
    Details
    ISSN: 0887-3585
    Keywords: energy minimization ; rotamers ; automaton ; de novo design ; sequence prediction ; side-chain conformation prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Globular proteins have high packing densities as a result of residue side chains in the core achieving a tight, complementary packing. The internal packing is considered the main determinant of native protein structure. From that point of view, we present here a method of energy minimization using an automata network to predict a set of amino acid sequences and their side-chain conformations from a desired backbone geometry for de novo design of proteins. Using discrete side-chain conformations, that is, rotamers, the sequence generation problem from a given backbone geometry becomes one of combinatorial problems. We focused on the residues composing the interior core region and predicted a set of amino acid Sequences and their side-chain conformations only from a given backbone geometry. The kinds of residues were restricted to six hydrophobic amino acids (Ala, Ile, Met, Leu, Phe, and Val) because the core regions are almost always composed of hydrophobic residues. The obtained sequences were well packed as was the native sequence. The method can be used for automated sequence generation in the de novo design of proteins. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190308
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  • 147
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    Parser for protein folding units (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 256-268 
    Details
    ISSN: 0887-3585
    Keywords: unfolding ; solvation ; contact maps ; protein design ; structural domains ; normal modes ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: General patterns of protein structural organization have emerged from studies of hundreds of structures elucidated by X-ray crystallography and nuclear magnetic resonance. Structural units are commonly identified by visual inspection of molecular models using qualitative criteria. Here, we propose an algorithm for identification of structural units by objective, quantitative criteria based on atomic interactions. The underlying physical concept is maximal interactions within each unit and minimal interaction between units (domains). In a simple harmonic approximation, interdomain dynamics is determined by the strength of the interface and the distribution of masses. The most likely domain decomposition involves units with the most correlated motion, or largest interdomain fluctuation time. The decomposition of a convoluted 3-D structure is complicated by the possibility that the chain can cross over several times between units. Grouping the residues by solving an eigenvalue problem for the contact matrix reduces the problem to a one-dimensional search for all reasonable trial bisections. Recursive bisection yields a tree of putative folding units. Simple physical criteria are used to identify units that could exist by themselves. The units so defined closely correspond to crystallographers' notion of structural domains. The results are useful for the analysis of folding principles, for modular protein design and for protein engineering. © 1994 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190309
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  • 148
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    Multiple copy sampling: Rigid versus flexible protein (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 324-329 
    Details
    ISSN: 0887-3585
    Keywords: multiple copy conformational sampling ; protein flexibility ; sampling convergence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Effects of protein flexibility on multiple copy conformational sampling were systematically evaluated by studying the side-chain placement of Phe-14 in protein Zif268. The multiple copy sampling is shown to be significantly more efficient when a flexible but harmonically constrained protein is used instead of a rigid protein. A range of constraint force from 1 to 25 kcal/mol. Å per atom is determined to be sufficient to prevent the protein from distortion while allowing the protein to fluctuate for enhanced sampling. The protein fluctuations are essential in smoothing the effective energy surface as shown by the opening-closing of a protein hydrophobic pocket during a multiple copy energy minimization, a phenomenon that has been previously observed only in molecular dynamics. These results provide a practical guidance for applying the multiple copy techniques to molecular modeling and computer-aided drug design. © 1994 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340190407
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  • 149
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    Crystallization and preliminary X-ray diffraction studies of mandelonitrile lyase from almonds (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 343-347 
    Details
    ISSN: 0887-3585
    Keywords: hydroxynitrile lyase ; flavoenzyme ; X-ray crystallography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Single crystals of three different isoenzymes of (R)-(+) mandelonitrile lyase (hydroxynitrile lyase) from almonds (Prunus amygdalus) have been obtained by hanging drop vapor diffusion using polyethylene glycol 4000 and isopropanol as co-precipitants. The crystals belong to the monoclinic space group P2l with unit cell parameters a = 69.9, b = 95.1, c = 95.6 Å, and β = 118.5°. A complete set of diffraction data has been collected to 2.6 Å resolution on native crystals of isoenzyme III. © 1994 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190410
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  • 150
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    X-ray crystal structure and molecular dynamics simulation of bovine pancreas phospholipase A2-n-dodecylphosphorylcholine complex (1994)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 19 (1994), S. 330-339 
    Details
    ISSN: 0887-3585
    Keywords: phospholipase A2 ; n-dodecylphosphorylcholine ; complex ; inhibitor ; X-ray crystal analysis ; molecular dynamics simulation ; interaction ; calcium-binding ; catalytic network ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The crystal structure of n-dodecylphosphorylcholine (n-C12PC)-bovine pancreas phospholipase A2 (PLA2) complex provided the following structural.characteristics: (1) the dodecyl chain of n-C12PC was located at the PLA2 N -terminal helical region by hydrophobic interactions, which corresponds to the binding pocket of 2-acyl fatty acid chain (β-chain) of the substrate phospholipid, (2) the region from Lys-53 to Lys-56 creates a cholinereceiving pocket of n-C12PC and (3) the N-termillal group of Ala-1 shifts significantly toward the Tyr-52 OH group by the binding of the n-C12PC inhibitor. Since the accuracy of the X-ray analysis (R = 0.275 at 2.3 Å resolution) was insufficient to establish these important X-ray insights, the complex structure was further investigated through the molecular dynamics (M D) simulation, assuming a system in aqueous solution at 310K. The M D simulation covering 176 ps showed that the structural characteristics observed by X-ray analysis are intrinsic and also stable in the dynamic state. Furthermore, the M D simulation made clear that the PLA2 binding pocket is large enough to permit the conformational fluctuation of the n-C12PC hydrocarbon chain. © 1994 Wiley-Liss, Inc. © 1994 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340190408
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  • 151
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    On the formation and properties of a high-temperature resin from a bisphthalonitrile (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1-8 
    Details
    ISSN: 0887-624X
    Keywords: bisphthalonitrile ; cure catalysis ; polymerization mechanism ; polymer properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When 4,4'-bis (3,4-dicyanophenoxy) biphenyl is heated with small amounts of aromatic amine or amidine salts, a highly crosslinked polytriazine is obtained. This polymer has been shown to be the same as that reported when bisphthalonitriles are heated with amines. Salts promote this reaction more readily and the glass transition temperature of the polymer after post-cure at 315°C is generally 30°C higher than when free bases are used. The fracture properties and elasticity of the salt-cured polymer have been measured at temperatures up to 250°C. As a model system, the self reaction of phthalonitrile promoted by amines and their salts has been studied. In both cases, poly[4-(2-cyanophenyl)-1,3,5-triazine-2,6-diyl-1,2-phenylene] is produced, and more efficiently using the salts. A reaction mechanism for this polymerization has been proposed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320101
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  • 152
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    The synthesis and characterization of amine-terminated poly(aryl ether ketone)s as a function of side group and molecular weight (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 73-87 
    Details
    ISSN: 0887-624X
    Keywords: reactive thermoplastic oligomers ; amine-terminated poly(aryl ether ketone)s ; side group interactions ; controlled molecular weight ; characterization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that amine-terminated poly(aryl ether ketone)s based on the reaction of 4,4'-difluorobenzophenone, and a substituted hydroquinone [either methylhydroquinone (MePK), t-butylhydroquinone (tBPK), or phenylhydroquinone (PhPK)] of controlled molecular weight and high amine-termination efficiency can be synthesized by a two-step reaction technique. Attempts to synthesize analogous materials by a one-step method were shown to be unsuccessful. The side groups are shown to have a large influence on the aromatic proton chemical shifts and this effect is characterized. The side groups and molecular weight are also shown to influence the thermal transitions of the respective polymers. The tBPK polymer possessed the highest glass transition temperature, while the MePK polymer was found to be the only semi-crystalline polymer; a unit cell is proposed. The side groups and molecular weight effects are also characterized as a function of thermal stability and mechanical properties. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320109
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  • 153
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    The effect of supporting electrolyte on the electrochemical synthesis, morphology, and conductivity of polyaniline (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 105-111 
    Details
    ISSN: 0887-624X
    Keywords: polyaniline ; conducting polymers ; morphology ; conductivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrochemical synthesis of polyaniline (PANI) was carried out under cyclovoltammetric conditions using H2SO4, HCl, HNO3, and HClO4 as supporting electrolytes. The observed different rate of PANI deposit growth depending on the acid in the solution has been explained on the grounds of a different degree of specific adsorption for particular anion. It has been found that morphology of the deposit depends greatly upon the anion present in the solution. Thus, PANI synthesized from the solution of oxyacids results in a dense sponge-like structure while PANI from the hydrochloric acid solution results in a spaghetti-like structure. The structure of the deposit influences the conductivity, being higher for a dense deposit from oxyacid solutions and three orders of magnitude lower in case of a deposit from hydrochloric acid solution. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320112
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  • 154
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    NMR study of PMR-15 prepolymerization steps (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 203-217 
    Details
    ISSN: 0887-624X
    Keywords: PMR-15 ; polyimides ; PMR-15 NMR-analyses ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variations in PMR-15 composites properties could be due to differences in their chemical compositions occurring during the curing cycle. Variations in the composition of the PMR-15 resin were studied for four different curing cycles, to determine the influences of parameters such as the heating rate or the presence of a temperature stage. The resin mixture was sampled at the same four different temperature points in each cycle and analyzed mainly by 1H- and 13C-NMR. Quantitative analysis of the different chemical species were realized by deconvolution of NMR spectra. At a given temperature, the resin contains the same molecules but in proportions which depend on the curing conditions and which reflect differences in the chemical reactivity of the monomeric species. We have precisely defined the temperature ranges at which each of the key reactions (amidization, imidization, exoendo isomerization) occurs. An imine condensation product of NE and MDA has been identified and shown to be present in the resin mixture even at low temperature. As a result of this study, two possible causes of resin alteration during ageing can be put forward: the presence of nonimidized BTDE moieties and the endo-exo isomerization reaction which will result in deformation and, possibly, microcracking, if reticulation of the end-capped nadimides is not total. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320201
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    Template polymerization of multiacrylate (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 295-300 
    Details
    ISSN: 0887-624X
    Keywords: multiacrylate ; template polymerization ; ladder polymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By reacting poly (2-hydroxyethyl methacrylate) with acryloyl chloride, multiacrylate connected through a covalent bond with polymethacrylate chain (template) has been obtained. The free-radical polymerization of multiacrylate in dilute dioxane solutions at 75°C and 85°C was examined by IR spectrophotometry and the distribution of molecular weights of the resultant products was evaluated by gel permeation chromatography. The findings show that under selected conditions the polymerization proceeds along ordered acrylic double bonds on the template and results in a ladder-type polymer. At a temperature of 85°C, in addition to the intramolecular cyclopolymerization, intermolecular reactions proceed to a minor extent. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320210
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  • 156
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    Quantification of end groups in polystyrenes by pyrolysis-gas chromatography (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 383-388 
    Details
    ISSN: 0887-624X
    Keywords: polystyrene ; pyrolysis-gas chromatography ; end groups ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The determination of end groups in polystyrenes (PSts) polymerized anionically with n-butyllithium as the initiator was carried out by pyrolysis-gas chromatography (Py-GC). The relative proportions of the end groups decrease with increasing molecular weight (MW). Consequently, the peaks which reflect the structure of the end groups can be distinguished by comparing pyrograms of samples with different MW. By comparing the intensities of these peaks relative to total intensities of all the peaks in the pyrogram, the numberaverage molecular weight (Mn) of the polymer can be estimated. The observed Mn values of PSts estimated by this method are compared with those determined by size exclusion chromatography (SEC). By this method it was possible to make direct determination of Mn values of PSts with MWs between 1000 and ca. 1 million. Furthermore, the calibration curve produced by the relative intensity of one of the most characteristic peaks (2-phenyl-1-heptene; C4H9—CH2C (Ph) = CH2) for the end group to total intensity of all the peaks in the pyrogram, gave rapid and highly reproducible Mn values. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320220
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  • 157
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    Preparation and properties of aromatic polyamides and polyimides derived from 3,3-bis [4-(4-aminophenoxy) phenyl] phthalide (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 423-433 
    Details
    ISSN: 0887-624X
    Keywords: 3,3-bis[4-(4-aminophenoxy)phenyl]phthalide ; aromatic polyamides ; soluble aromatic polyimides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,3-Bis[4-(4-aminophenoxy)phenyl]phthalide (II) was used as a monomer with various aromatic dicarboxylic acids and dianhydrides to synthesize polyamides and polyimides, respectively. The diamine II was derived by a nucleophilic substitution of phenolphthalein with p-chloronitrobenzene in the presence of K2CO3. Polyamides IVa-g having inherent viscosities of 0.77-2.46 dL/g were prepared by the direct polycondensation of diamine II with diacids IIIa-g using triphenyl phosphite and pyridine as condensing agents. The polyamides were readily soluble in a variety of solvents such as N, N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP) and afforded transparent and flexible films from the polymer solutions. These polymers had glass transition temperatures (Tgs) in the 227-307°C range and 10% weight loss temperatures occurred up to 450°C. Polyimides VIa-e based on diamine II and various aromatic dianhydrides Va-e were synthesized by the two-stage procedure that included ring-opening, followed by thermal or chemical conversion to polyimides. Most of the polyimides obtained by chemical cyclodehydration procedure were found to soluble in DMF, NMP, o-chlorophenol, and m-cresol. The Tgs of these polyimides were in the 260-328°C range and showed almost no weight loss up to 500°C under air and nitrogen atmosphere. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320303
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    New poly(amide-imide)s syntheses. VIII. Preparation and properties of poly (amide-imide)s derived from 2,3-bis(4-aminophenoxy)naphthalene, trimellitic anhydride, and various aromatic diamines (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 435-444 
    Details
    ISSN: 0887-624X
    Keywords: poly(amide-imide)s ; direct polycondensation ; 2,3-bis (4-aminophenoxy) naphthalene ; 2,3-bis (4-trimellitimidophenoxy) naphthalene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new polymer-forming diimide-diacid, 2,3-bis(4-trimellitimidophenoxy) naphthalene (I), was readily obtained by the condensation reaction of 2,3-bis (4-aminophenoxy) naphthalene with trimellitic anhydride. A series of novel aromatic poly (amide-imide)s were prepared by the direct polycondensation of diimide-diacid I with various aromatic diamines using triphenyl phosphite in N-methyl-2-pyrrolidone (NMP)/pyridine solution containing dissolved calcium chloride. The resultant polymers have inherent viscosities in the range of 0.65-1.02 dL/g at 30°C in N, N-dimethylacetamide. These polymers were readily soluble in various organic solvents and could be cast into transparent, tough, and flexible films. Their casting films showed tensile strength at break up to 86 MPa, elongation to break of 5-9%, and initial moduli up to 2.35 GPa. The wide-angle X-ray diffraction revealed that those polymers containing p-phenylene or p-oxyphenylene group are partially crystalline, and the other polymers are evidenced as amorphous patterns. These polymers show a glass transition in the range of 213-290°C in their differential scanning calorimetry (DSC) traces. The thermal stability of the polymers was evaluated by thermogravimetry analysis, which showed the 10% weight-loss temperatures in the range of 508-565°C in nitrogen and 480-529°C in air atmosphere. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320304
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    Novel preparation of electrically conducting poly (vinyl chloride) by photo-dehydrochlorination from poly (vinyl chloride)/polypyrrole composite film (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 33-38 
    Details
    ISSN: 0887-624X
    Keywords: electrical conductivity ; poly (vinyl chloride) ; photo-dehydrochlorination ; composite film ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polypyrrole (PPy) was deposited electrochemically on a platinum plate from a nitric acid solution of pyrrole. The PVC/PPy composite film was finally obtained by casting poly(vinyl chloride) (PVC) onto the PPy electrode from a tetrahydrofuran solution of PVC. The prepared composite film was irradiated at 90°C with a low-pressure mercury lamp in the stream of hydrogen gas saturated with steam, and the PVC film was dehydrochlorinated, leading to the formation of conjugated polyene. The electrical conductivity (σ) of the PVC film in the irradiated composite film was reveled: σ=2.51 × 10-5S cm-1. By iodine doping, σ was further enhanced up to 5.04 X 10-3 S cm-1. The tensile strength of the irradiated composite film became larger than that of the original PVC film; i.e., the stress at break was: 461 (composite film); 401 kg cm-2 (PVC). These results were brought about by the doping of radical species to the conjugated polyene. The anion, NO-3, doped during the electrodeposition of PPy was photodecomposed to generate radical NO2 and this species was doped to the polyene, resulting in the formation of electrically conductive PVC and mechanically improved composite film. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320104
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    Chemical preparation of conductive elastomeric blends: Polypyrrole/EPDM. I. Oxidant particle-size effect (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1001-1008 
    Details
    ISSN: 0887-624X
    Keywords: conductive rubber ; polypyrrole/EPDM blend ; chemical preparation ; electrical conductivity ; mechanical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work describes the preparation of polypyrrole and EPDM rubber blends, PPy/EPDM, by the sorption of pyrrole (vapor phase) in an EPDM matrix containing CuCl2. We investigated the effect of the oxidant particle-size on the sorption and polymerization equilibrium, electrical conductivity, and mechanical properties of the blends. Independently of the CuCl2 concentration and polymerization time, the polypyrrole weight fraction in the blend, Xppy, increases when the oxidant particle-size in changed from 150-250 μm to smaller than 106 μm. For blends containing 50 phr of CuCl2, obtained following 72 h of exposure to pyrrole, an increase in the Young's Modulus (from 2.2 ± 0.2 to 3.9 ± 0.6 MPa) and an increase in the electrical conductivity (from 10-9 to 10-7 S cm-1) was observed when the oxidant particle-size was decreased. Infrared spectroscopy, thermogravimetric analysis, scanning differential calorimetry, and scanning electron microscopy were used in sample characterization. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320601
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    Preparation of polyalkylviologen-polyanion complexes and their applications to the debromination of diphenyl bromomethane under heterophase condition (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1043-1048 
    Details
    ISSN: 0887-624X
    Keywords: polyalkylviologen - polyanion complex ; electron-transfer catalysis (ETC) ; diphenyl bromomethane (Ph2CHBr) ; debromination ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several polyelectrolyte complexes were prepared by the reaction of polyalkylviologens [polyethylviologen (PEV2+), polypropylviologen (PPrV2+), and polybutylviologen (PBV2+)] with polyanions [sodium alginic (ALG), sodium polyacrylate (PAA), or sodium polystyrenesulfonate (PSS)]. These complexes were used as electron-transfer catalysts (ETC) on the debromination of diphenyl bromomethane (Ph2CHBr) under heterophase condition [reductant: Na2S2O4, in H2O (liquid)-polyelectrolyte complex(S) - Ph2CHBr in CH2Cl2]. The work showed that these complexes could induce the debromination of Ph2CHBr to afford tetraphenyl ethane, and different polyanions in the complexes also affected the mediating abilities. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320605
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    Synthesis and characterization of new fluorescent poly(arylene ether)s (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1071-1076 
    Details
    ISSN: 0887-624X
    Keywords: functional aromatic polyethers ; fluorescent polymers ; aromatic nucleophillic substitution polymerization ; thermal behavior ; electron spin resonance ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The poly(arylene ether)s were prepared by the nucleophillic aromatic substitution polymerization of phenolphthalin and its derivatives with activated aromatic difluorides. The polymers had glass transition temperatures ranging from 210 to 240°C. Though the monomers have no fluorescence, the resulting polymers fluoresced a light green color in solid and solution states. The maximum excitation and emission wavelengths are 420 nm and 470 nm, respectively. In the polymer solutions, the fluorescence intensity decreased gradually, but the intensity was recovered by heating the polymer at 220°C for a few minutes. The fluorescent polymer had a stable radical. A model compound having the same repeating unit of the polymer was also prepared. The fluorescence properties of this model were almost the same as those of the polymers. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320609
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    1H-NMR and UV studies of Rh complexes as a stereoregular polymerization catalysts for phenylacetylenes: Effects of ligands and solvents on its catalyst activity (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1113-1120 
    Details
    ISSN: 0887-624X
    Keywords: phenylacetylene ; stereoregular polymerization ; Rh complex catalyst ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenylacetylene and its homologues bearing methoxy or chloro groups in the para position of the phenyl ring were stereoregularly polymerized by Rh complex catalysts, e.g., [Rh (norbornadiene) Cl]2, in the presence of various solvents. The 1H-NMR and UV study of the Rh complex showed that the activity of the Rh catalysts greatly depends upon not only the ligand in the Rh catalyst but also on the solvent used, e.g., polyphenylacetylene with a highly cis-transoidal content was quantitatively obtained when norbornadiene was coordinated as the ligand, and triethylamine (TEA) was used as solvent, whereas tetrahydrofuran (THF) and benzene reduced the cis content. It was also found that the Rh catalyst as a dimer complex dissociates into the monomeric species not only when TEA was used but also when alcohol, benzene, and THF were used. The resulting monomeric species was considered as the important propagation species in this polymerization. The sharp line width observed in the 1H-NMR spectrum of polyphenylacetylene and its homologues which were prepared in ethanol or TEA was interpreted by the narrow chemical shift distribution arising from the high cis content. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320613
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    Comparative characterization of MgCl2/ethyl benzoate/TiCl4 and MgCl2/2,2,6,6 tetramethylpiperidine/TiCl4 Ziegler-Natta precatalysts (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1137-1147 
    Details
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalysts ; propylene polymerization ; catalysts characterization ; supported catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article we present the results of the preparation and characterization of two Ziegler-Natta precatalysts: MgCl2/Ethyl benzoate (EB)/TiCl4 and MgCl2/2,2,6,6 tetramethylpiperidine (TMPiP)/TiCl4 by means of FTIR, X-ray diffraction, SEM, BET surface area measurements, and other techniques applied at different steps of their preparation procedures.The precatalysts were prepared by impregnating with TiCl4 a given amount of MgCl2, which was previously ball-milled with the electron donor chosen.Prior to impregnation, the ball-milled material presented different surface compounds depending on the electron donor used: [(MgCl2)2] · 2EB, MgCl2 · EB, or a salt of the amine. The solid milled with EB is more homogeneous than the one milled with the TMPiP.Titanium is better retained in the solid milled with EB. This precatalyst has better morphological properties and larger BET surface area. By means of FTIR, we found evidences that an adequate surface structure for the formation of stereospecific sites in MgCl2/TMPiP/TiCl4 was formed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320616
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    A comparison of models for hydrogen bonding in polymer blends (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1189-1193 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320622
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    Swelling kinetics and release characteristic of crosslinked chitosan: Polyether polymer network (semi-IPN) hydrogels (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1213-1223 
    Details
    ISSN: 0887-624X
    Keywords: chitosan ; semi-IPN hydrogel ; swelling kinetics ; pH-sensitivity ; controlled release ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aqueous swelling kinetics of a series of crosslinked chitosan (cr-CS) with glutaraldehyde (GA) interpenetrating polyether hydrogels have been studied as functions of pH, the N-deacetylation degree of chitosan, the amount of crosslinking agent, the electrolyte composition in solution, temperature, and gel composition. Based on these results, the swelling mechanism of the hydrogels was discussed. The release profiles of chlorhexidini acetas from the semi-IPN were also investigated. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320702
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    Fully aromatic thermotropic liquid crystalline homopolyesters of 3,4′-benzophenone dicarboxylic acid (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 333-342 
    Details
    ISSN: 0887-624X
    Keywords: liquid crystalline polymer ; thermotropic homopolyester ; nematic ; X-ray diffraction ; synthesis ; characterization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of fully aromatic, thermotropic homopolyesters, derived from 3,4′-benzophenone dicarboxylic acid and various aromatic diols, was prepared by the melt polycondensation method and examined for thermotropic behavior by a variety of experimental techniques. The aromatic diols used in the study were hydroquinone, 2,6-, 1,4-, 1,5-, 2,3-, and 2,7-naphthalenediol isomers. All of the homopolyesters of 3,4′-benzophenone dicarboxylic acid with aromatic diols (except that with 2,7-naphthalenediol) formed a nematic LC phase in the melt. They had the glass transition temperatures (Tg) in the range of 133-164°C, the melting transitions (Tm) in the range 305-360°C and the high thermal stabilities (Td) in the range of 410-483°C. The 2,6-naphthalenediol based homopolymer had the highest Tm (360°C) and the 2,3-naphthalenediol based homopolymer had the lowest Tm (305°C) among all of the homopolymers of naphthalenediol isomers. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320215
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    Synthesis and characterization of poly (2-vinylpridine)-b-poly (t-butyl methacrylate) (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 363-368 
    Details
    ISSN: 0887-624X
    Keywords: 2-vinylpyridine ; t-butyl methacrylate ; anionic polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of well defined and monodisperse (Mw/Mn ≤ 1.2) narrow molecular weight distribution poly (2-vinylpyridine)-poly (t-butyl methacrylate) (P2VP-PTBMA) AB block copolymers is carried out by initiation of 2-vinylpyridine polymerization by 1,1-diphenylhexyllithium in THF at-78°C, followed by addition of TBMA and termination at -78°C using MeOH. The formation of the BAB block copolymer is carried out in a similar fashion except that 1,4-dilithio-1,1,4,4-tetraphenylbutane is used as initiator. The corresponding synthesis of P2VP-PMMA block copolymers is carried in a similar manner, except that 1-2 equivalents of TBMA is used to end-functionalize the living P2VP before the addition of MMA. Without the addition of TBMA, trimodal molecular weight distributions in P2VP-b-PMMA are obtained. All the block copolymers are characterized by Size Exclusion Chromatography (SEC), Nuclear Magnetic Resonance (NMR), and Differential Scanning Calorimetry (DSC). © 1994 John Wiley & Sons, Inc.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320218
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  • 169
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    Molecular composites from sulfonated poly(p-phenylene terephthalamide) (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 397-400 
    Details
    ISSN: 0887-624X
    Keywords: molecular composites ; rigid polymers ; sulfonated poly(p-phenylene terephthalamide) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320223
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    Polymerization of surface-active monomers. VIII. Tacticity of polymers prepared by radical polymerization of quaternary salts of dimethylaminoethyl methacrylate in micellar and isotropic media (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 445-449 
    Details
    ISSN: 0887-624X
    Keywords: radical polymerization ; surface-active monomer ; quaternary salt ; dimethylaminoethyl methacrylate ; stereochemistry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of monomer micellization on the polymerization was studied from the standpoint of stereochemistry in the polymerization. Quaternary salts (CnBr) of dimethylaminoethyl methacrylate with n-alkyl bromide having N (=4, 8 and 12) carbon atoms were polymerized with radical initiators in isotropic and anisotropic media and the resulting polymers were converted to poly (methyl methacrylate) (PMMA) to determine their tacticity. Tacticities of poly (C12Br)s were little affected by initiators and solvents used for their preparations. There was little dependence of the tacticities on alkyl chain length (N) for poly (CnBr)s prepared in water and dimethylformamide (DMF). Most of polymers produced here conformed to Bernoullian propagation statistics and a definite difference was not found in the tacticities between the polymers prepared in isotropic and anisotropic media. From the results obtained here it was deduced that the micellar aggregation has little influence upon the stereochemistry in the polymerization of the quaternary monomers. © 1994 John Wiley & Sons, Inc.
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    Synthesis and characterization of poly(ester-sulfone)s (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1351-1360 
    Details
    ISSN: 0887-624X
    Keywords: 1,3-bis(3-hydroxypropylsulfonyl)propane ; 1,4-bis(3-hydroxysulfonyl)butane ; polyesters ; poly(ester-sulfone) ; liquid crystalline ; glass transition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aliphatic and aromatic-aliphatic poly(ester-sulfone)s were synthesized by the transesterifications of diphenyl adipate and diphenyl phthalates (ortho, meta, para) with two sulfonecontaining diols, 1,3-bis (3-hydroxypropylsulfonyl) propane (Diol-333) and 1,4-bis(3-hydroxypropylsulfonyl) butane (Diol-343). Based on DSC and WAXD studies, the aliphatic homopoly(ester-sulfone)s are semicrystalline at room temperature and liquid crystalline at elevated temperature, while their copolymers with alkanediols are liquid crystalline. The liquid crystalline phase formation in aliphatic poly(ester-sulfone)s is attributed to the strong dipole-dipole interactions between sulfone groups. The aromatic-aliphatic poly(estersulfone)s from diphenyl phthalate (ortho) and isophthalate (meta) are amorphous. They are soluble in trifluoroacetic acid and m-cresol at room temperature, and DMF, DMAC, and DMSO at elevated temperature. The aromatic-aliphatic poly(ester-sulfone)s from diphenyl terephthalate are semicrystalline and are soluble only in trifluoroacetic acid. For a given diol, the glass transition temperatures of aromatic-aliphatic poly(ester-sulfone)s increase from phthalate to isophthalate to terephthalate. This is because the flexibility of the benzene ring in the polymer backbone decreases from ortho to meta to para substitution. As a comparison, polyesters without sulfone groups were synthesized from two alkanediols, 1,9-nonanediol and 1,10-decanediol, and the diphenyl esters. The poly(ester-sulfone)s have glass transition temperatures 60-80°C higher than the corresponding polyesters without sulfone groups, due to the strong dipolar interactions between sulfone groups. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320716
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    Facile synthesis of a semicrystalline aromatic fluoroaliphatic poly (ether sulfone) (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 389-392 
    Details
    ISSN: 0887-624X
    Keywords: fluorinated poly (ether sulfone) ; semicrystalline polymer ; aromatic nucleophilic substitution ; trimethylsilyl ether ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320221
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    Synthesis of crosslinked poly(styrene-co-sodium styrenesulfonate) latexes (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1431-1435 
    Details
    ISSN: 0887-624X
    Keywords: polystyrene ; latex ; sodium styrenesulfonate ; crosslinked ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Latexes of 100 nm diameter were synthesized by emulsifier-free copolymerization of styrene, sodium styrenesulfonate, and 1-5 wt% divinylbenzene using persulfate initiator at 91°C. A shot growth method was used to incorporate a high density of sulfonate groups. Coefficients of variation of particle size were 0.04-0.08 without resort to seed growth polymerization. Redox initiation at 40-50°C produced larger, more polydisperse, and less colloidally stable crosslinked latexes. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320804
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    Role of N,N-dimethyl-para-toluidine and saccharin in the radical polymerization of methyl methacrylate initiated by a redox system. I. Cumene hydroperoxide/copper saccharinate (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1459-1469 
    Details
    ISSN: 0887-624X
    Keywords: methyl methacrylate ; redox polymerization ; kinetics ; mechanism ; additives ; copper saccharinate ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetics of methyl methacrylate polymerization initiated by a redox system [cumene hydroperoxide (CHP)/copper saccharinate] were studied in bulk at 20°C in the presence of accelerators such as N,N-dimethyl-p-toluidine (DMPT) and o-benzoic sulphimide (saccharin). Assuming a steady-state concentration of propagating radicals, the polymerization rate depends on the square root of the initiation rate and the kinetic orders with respect to each compound in the initiation step may be deduced. Initiation is first-order in CHP, copper saccharinate, and saccharin and second-order in DMPT. A reaction scheme consistent with these orders is proposed. The main features are the following: (1) CHP reduces rapidly Cu(II) to Cu(I); (2) a small fraction of Cu(I) is complexed with DMPT; (3) the complexed ions (Cu+, DMPT2) are strong reductants with respect to CHP whereas uncomplexed Cu+ are almost inactive; (4) the decomposition of CHP is strongly catalyzed by saccharin (protonated CHP is 13000 times more reactive than free CHP). Thus both accelerators are necessary to get high polymerization rates. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320807
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    Self-Crosslinkable poly(arylene ether)s containing pendent phenylenetriazene groups (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1507-1521 
    Details
    ISSN: 0887-624X
    Keywords: crosslinkable ; poly(arylene ether) ; triazene ; gel content ; dielectric constant ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Self-crosslinkable poly(arylene ether)s 6, and 8, containing pendent triazene groups were prepared by nucleophilic substitution reaction of poly(arylene ether)s 5, and 7, respectively, with 1-[4-(4-hydroxyphenoxy)phenylene]triazenes, 4, in the presence of potassium carbonate in N,N-dimethylacetamide. A series of triazenes 4 containing various substituents have been synthesized. Self-crosslinkable polymer 6e containing phenyl-substituted triazene pendants can be crosslinked at 215°C, which is about 40°C lower than the glass transition temperature of the virgin base polymer 5. The degree of crosslinking can be tailored by varying the concentration of the pendent phenylenetriazene groups in the polymer. After curing, the flexible polymer films (ca. 10 μm thick) exhibit high gel contents, increased glass transition temperatures, improved resistance to organic solvents, and little change in dielectric constant and thermal stability. These self-crosslinkable poly(arylene ether)s are potential candidates for electronic applications. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320811
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    Synthesis and characterization of poly(urethane-sulfone)s (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1531-1537 
    Details
    ISSN: 0887-624X
    Keywords: 1,3-bis(3 hydroxy propyl sulfonyl)propane ; 1,4-bis(3-hydroxypropyl sulfonyl)butane ; 1,3-propane dithiol ; 1,4-butane dithiol ; poly(urethane) ; poly sulfone ; methylene diphenyl diisocyanate (MDI) ; toluene diisocyanate (TDI) ; hexamethylene diisocyanate (HMDI) ; melt temperature ; glass transition temperature ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eight poly(urethane-sulfone)s were synthesized from two sulfone-containing diols, 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333) and 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343), and three diisocyanates, 1,6-hexamethylene diisocyanate (HMDI), 4,4′-diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI, 2,4- 80%; 2,6-20%). As a comparison, eight polyurethanes were also synthesized from two alkanediols, 1,9-nonanediol and 1,10-decanediol, and three diisocyanates. Diol-333 and Diol-343 were prepared by the addition of 1,3-propanedithiol or 1,4-butanedithiol to allyl alcohol and subsequent oxidation of the resulting sulfide-containing diols. The homopoly(urethanesulfone)s from HMDI and MDI are semicrystalline, and are soluble in m-cresol and hot DMF, DMAC, and DMSO. The copoly(urethane-sulfone)s from a 1/1 molar ratio mixture of Diol-333 and Diol-343 with HMDI or MDI have lower crystallinity and better solubility than the corresponding homopoly(urethane-sulfone)s. The poly(urethane-sulfone)s from TDI are amorphous, and are readily soluble in m-cresol, DMF, DMAC, and DMSO at room temperature. Differential scanning calorimetry data showed that poly(urethane-sulfone)s have higher glass transition temperatures and melting points than the corresponding polyurethanes without sulfone groups. The rise in glass transition temperature is 20-25°C while the rise in melting temperature is 46-71°C. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320813
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    Pyrazoles - A novel class of blocking agents for isocyanates (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 753-765 
    Details
    ISSN: 0887-624X
    Keywords: pyrazole blocked isocyanate ; pyrazole masked isocyanate ; blocking group ; blocking agent ; synthesis ; deblocking reaction ; reactivity ; gelation time ; latency ; stability ; adhesion ; primer ; polymer ; bis (pyrazole) ; EPIC-systems ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrazoles were found as a novel class of blocking groups for isocyanates. Adhesive mixtures of pyrazole blocked isocyanates and amine terminated prepolymers like Jeffamines® (Texaco Chem. Co.) combine excellent reactivities (gelation times within minutes at 100-120°C), good latencies (more than 170 days at 40°C), and good adhesion properties on many substrates. The reactivity of pyrazole blocked isocyanates toward nucleophiles increases with the number of electron donor substituents on the pyrazole nucleus and, thus, can be fine tuned by the appropriate substitution pattern. This behavior contrasts sharply with that of phenolic blocked isocyanates, where reactivities with the same nucleophiles decrease with more and stronger electron donor substituents on the phenol nucleus. Therefore, different deblocking reaction mechanisms were proposed for pyrazole vs. phenol blocked isocyanates. The excellent latency of pyrazole blocked isocyanate/Jeffamine® mixtures is due to the insolubility of the two components at ambient temperature and the slow endothermic dissolution process at higher temperature. The good adhesion of formulations with pyrazole blocked isocyanates as reactive components on most plastic and metal substrates is ascribed to the primer action of the released blocking group. © 1994 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320414
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    Biodegradable and pH-sensitive hydrogels: Synthesis by crosslinking of N,N-dimethylacrylamide copolymer precursors (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1627-1637 
    Details
    ISSN: 0887-624X
    Keywords: degradable hydrogels ; crosslinking of polymeric precursors ; colon-specific polymer ; pH-dependent swelling ; azoaromatic crosslinks ; N,N-dimethylacrylamide copolymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel pH-sensitive hydrogels containing azoaromatic crosslinks were synthesized by the crosslinking of polymeric precursors. First, a reactive polymeric precursor was synthesized by copolymerization of N,N-dimethylacrylamide, N-tert-butylacrylamide, acrylic acid, and N-methacryloylglycylglycine p-nitrophenyl ester. The hydrogel was prepared in the second step by the reaction of the polymeric precursor with N,N′-(ω-aminocaproyl)-4,4′-diaminoazobenzene. The hydrogels were characterized by the network structure, (that is, content of crosslinks, unreacted pendent groups, and cycles), the equilibrium swelling ratio as a function of pH, modulus of elasticity in compression, and the degradability in vitro. The results obtained indicated that the hydrogel network structure strongly depends on the reaction conditions such as polymer concentration, and the ratio of the reactive groups during the crosslinking reaction. The swelling and mechanical properties of hydrogels can be controlled by the modification of polymer backbone structure and/or the crosslinking density. The rates of hydrogel degradation depended on their degree of swelling. The higher the degree of swelling, the higher the degradability. The properties of the hydrogels suggest that they have a potential as carriers for colon-specific drug delivery. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320904
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    Synthesis and characterization of bismaleimides derived from polyurethanes (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1665-1672 
    Details
    ISSN: 0887-624X
    Keywords: polyurethane ; bismaleimide ; crosslinking reaction ; mechanical property ; thermal property ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of novel bismaleimides (BMIs) were prepared from maleic anhydride and polyurethane prepolymers based on MDI (4,4′-diphenylmethane diisocyanate) and polyether and polyester diols with various chain lengths. All the BMIs were characterized by IR, 1H-NMR, and elemental analysis. DSC studies indicated that the thermal polymerization of the BMIs could be carried out in the temperature range of 102-245°C, and that curing behavior was significantly affected by the molecular weight of the BMIs. The crosslinked BMI elastomers showed good mechanical properties and much better thermal stability than that of the traditional polyurethane elastomers. The glass transition temperatures, mechanical, and dynamic mechanical properties were dependent on the types of polyols used and the resultant crosslink densities due to various chain lengths of the BMIs. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320908
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    Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1703-1710 
    Details
    ISSN: 0887-624X
    Keywords: cationic polymerization ; 10-methylphenothiazine ; cation radical ; electron transfer ; initiation mechanism ; vinyl ethers ; electrochemical oxidation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A small quantity of 10-methylphenothiazine cation radical (MPT.+), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. 1H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D2O indicated that electron transfer from the monomer to MPT.+ was involved in the initiation step. 1H- and 13C-NMR and MO calculation implied that monomers with higher electron densities on the vinyl groups and with lower ionization potentials were more susceptible to the initiation of MPT.+. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320912
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    Acyloin condensation in aqueous system by durable polymer-supported thiazolium salt catalysts (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1711-1717 
    Details
    ISSN: 0887-624X
    Keywords: durable catalyst ; thiazolium salt ; aqueous system ; acyloin condensation ; enzyme model ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We characterized three low-molecular-weight thiazolium salt analogues: N-methyl-5-(2′-benzyloxyethyl)-4-methylthiazolium iodide (MBMTI), N-methyl-4-phenylthiazolium iodide (MPTI), and N-methylbenzothiazolium iodide (MBTI). MBMTI, having high-electron density on the thiezolium ring, was found to be a durable thiazolium salt in buffer solution. Then, the polymer-supported thiazolium salt catalyst having MBMTI structure as a catalytic site for acyloin condensation was prepared by the polymerization of the corresponding thiazole monomer and the following quaternization. The polymer catalyst had excellent catalytic activity even in buffer solution, while the corresponding low molecular weight catalyst did not show any activity in aqueous system. Furthermore, the durable polymer catalyst could be reused under the aqueous condition. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320913
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    Living cationic polymerization of isobutyl vinyl ether by EtAlCl2 in the presence of ether additives: Cyclic ethers, cyclic formals, and acyclic ethers with oxyethylene units (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1719-1728 
    Details
    ISSN: 0887-624X
    Keywords: living cationic polymerization ; isobutyl vinyl ether ; cyclic ether additives ; cyclic formal additives ; acyclic ether additives with oxyethylene units ; EtAlCl2 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The living cationic polymerization of isobutyl vinyl ether (IBVE) was investigated in the presence of various cyclic and acyclic ethers with 1-(isobutoxy)ethyl acetate [CH3CH(OiBu)OCOCH3, 1]/EtAlCl2 initiating system in hexane at 0°C. In particular, the effect of the basicity and steric hindrance of the ethers on the living nature and the polymerization rate was studied. The polymerization in the presence of a wide variety of cyclic ethers [tetrahydrofuran (THF), tetrahydropyran (THP), oxepane, 1,4-dioxane] and cyclic formals (1,3-dioxolane, 1,3-dioxane) gave living polymers with a very narrow molecular weight distribution (MWD) (M̄ω/M̄n ≤ 1.1). On the other hand, propylene oxide and oxetane additives resulted in no polymerization, whereas 1,3,5-trioxane gave the nonliving polymer with a broader MWD. The polymerization rates were dependent on the number of oxygen and ring sizes, which were related to the basicity and the steric hindrance. The order of the apparent polymerization rates in the presence of cyclic ether and formal additives was as follows: nonadditive ∼ 1,3,5-trioxane ≫ 1,3-dioxane 〉 1,3-dioxolane ≫ 1,4-dioxane ≫ THP 〉 oxepane ≫ THF ≫ oxetane, propylene oxide ≫ 0. The polymerization in the presence of the cyclic formals was much faster than that of the cyclic ethers: for example, the apparent propagation rate constant k in the presence of 1,3-dioxolane was 103 times larger than that in the presence of THF. Another series of experiments showed that acyclic ethers with oxyethylene units were effective as additives for the living polymerization with 1/EtAlCl2 initiating system in hexane at 0°C. The polymers obtained in the presence of ethylene glycol diethyl ether and diethylene glycol diethyle ether had very narrow molecular weight distribution (M̄ω/M̄n ≤ 1.1), and the M̄n was directly proportional to the monomer conversion. The polymerization behavior was quite different in the polymerization rates and the MWD of the obtained polymers from that in the presence of diethyl ether. These results suggested the polydentate-type interaction or the alternate interaction of two or three ether oxygens in oxyethylene units with the propagating carbocation, to permit the living polymerization of IBVE. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320914
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    Preparation and properties of polyborosiloxanes as precursors for borosilicate formation of SiO2-B2O3 gel fibers and oxides by the sol-gel method using tetraacetoxysilane and boron tri-n-butoxide (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1049-1056 
    Details
    ISSN: 0887-624X
    Keywords: tetraacetoxysilane ; boron tri-n-butoxide ; sol-gel method ; condensation ; SiO2 - B2O3 gel fibers ; borosilicates ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formation of SiO2-B2O3 gel fibers and oxides was investigated by the sol-gel method using tetraacetoxysilane (TAS) and boron tri-n-butoxide (BTB). Low molecular weight borosiloxanes (BS) were formed by the reaction of TAS with BTB in THF. Partial alkoxylation and hydrolysis of BS followed by further condensation of the resulting polymer (PBS) solutions led to the formation of highly polymerized polyborosiloxanes (HPBS) with good spinnability. Gel fibers were obtained by dry spinning of HPBS. The compositions of PBS and gels were not consistent with that in feed. Heat treatment of the gels, however, provided SiO2-B2O3 oxides with compositions almost compatible with those of the gels. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320606
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    Synthesis and thermal behavior of side-chain liquid crystalline polymethacrylates containing tolane-based mesogenic side groups (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1077-1085 
    Details
    ISSN: 0887-624X
    Keywords: liquid crystal polymer ; polymethacrylate ; tolane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterization of nine polymethacrylates containing 4-alkoxy-4′-trifluoromethyltolane, 4-alkoxy-4′-cyanotolane, and 4-alkoxy-4′-nitrotolane side groups were described in this study. The phase behavior of the prepared monomers and polymers was characterized by differential scanning calorimetry, optical polarizing microscopy, and x-ray diffraction. All of the obtained monomers exhibit no mesophase, while most of the synthesized polymers reveal enantiotropic mesomorphism. The polymethacrylate containing 4-propanyloxy-4′-nitrotolane side groups was the only one which shows no mesomorphic behavior. Both the spacer length and the nature of terminal groups have profound influence on the phase transition temperatures and thermal stability of the mesophase. The polymers with longer spacers tend to form a more ordered mesophase with a wider temperature range. Among three polymers with the same spacer length, the polymer with a trifluoromethyl terminal end group is inclined to form a more ordered mesophase than the other two polymers. No side chain crystallization occurred for all obtained polymers. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320610
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    Anionic polymerization of propylene oxide: Isomerization of allyl ether to propenyl ether end groups (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1131-1135 
    Details
    ISSN: 0887-624X
    Keywords: poly(propylene oxide) ; allyl, propenyl ; isomerization ; 1H NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomerization of allyl ether to propenyl ether end group in anionically-polymerized poly (propylene oxide) was monitored by 1H NMR spectroscopy. It was confirmed that the reaction followed a simple second-order rate law: -d[allyl]dt = k2[allyl] [O-]. Values of k2 determined over the 90-130°C temperature range, indicated an activation energy of 116 kJ mol-1. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320615
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    Dimethyltitanocene-induced surface chemical degradation of synthetic biodegradable polyesters (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 949-960 
    Details
    ISSN: 0887-624X
    Keywords: dimethyltitanocene ; biodegradable polymers ; poly(glycolic acid) ; surface degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of this research was to selectively alter the rate of surface degradation of linear aliphatic polyesters without adversely affecting their bulk properties by way of functional group transformation, where the surface ester linkages would be converted to vinyl ether functionalities with dimethyltitanocene. It has been observed that dimethyl titanocene causes surface degradation of poly (glycolic acid) without adversely affecting its bulk properties, such as Mv, bursting strength, and thermal properties The vinvl ether resulting from the conversion of the PGA ester groups was unstable under ambient conditions, and further reacted by polymer chain scissioning, as was observed from measurements of molecular weight. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080320516
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    Laser-Induced generation of thin silicone layers with high chemical and spectral purity (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1893-1898 
    Details
    ISSN: 0887-624X
    Keywords: excimer laser ; organosilicon compounds ; additive-free polymers ; high chemical and spectral purity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Excimer lasers (ArF, λ = 193 nm, and KrF, λ = 248 nm) were used to generate polymers free of additives such as catalysts, initiators, or sensitizers. The layers obtained are of potential interest for medical applications and future molecular electronics. Dimethylpolysiloxanes and dimethylsiloxane copolymers that contain phenyl-, n-hexyl- or 3.3.3-trifluoropropyl groups or silicon-bound hydrogen atoms were crosslinked in the liquid phase, whereby layer thicknesses in the range from 1-300 μm were obtained. Disiloxanes and alkoxysilanes were deposited from the gas phase (LCVD, laser chemical vapor deposition) resulting in layer thicknesses below 1 μm. In almost all cases, organic layers with a smooth surface, transparency, and good adhesion were obtained on silicon as well as quartz substrates. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080321010
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    Phase-Transfer catalyzed free-radical polymerization of acrylonitrile (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1909-1914 
    Details
    ISSN: 0887-624X
    Keywords: phase transfer catalyst ; free-radical polymerization ; kinetics of polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of phase-transfer catalyzed free-radical polymerization of acrylonitrile (AN) was carried out with water-soluble initiator peroxomonosulphate (PMS) with phase-transfer catalysts (tetrabutylammonium chloride and benzyltributylammonium chloride (TBAC and BTBAC) in tolune/water two-phase systems in the temperature range of 45-55°C at fixed pH (4) and ionic strength. The rates of polymerization (Rp) were evaluated at various values of [PMS], [PTC], and [AN]. It has been observed that the rates of polymerization increase with an increase of [AN], [PMS], and [PTC]. A kinetic scheme has been proposed to account for the experimental observations. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1994.080321013
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    Study on chain transfer to acetic anhydride of THF polymerization (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1939-1947 
    Details
    ISSN: 0887-624X
    Keywords: polytetrahydrofuran ; acetylhexachloro-antimonate ; chain transfer ; THF ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of acetic anhydride, the catalyst containing protons makes the polymerization complex.1,2 Thus, whether the living center, during the polymerization process of THF, transfers to the acetic anhydride is a difficult problem to answer. In this article, CH3COSbCl6 is used as the catalyst to avoid the interference of the protons. It is found that acetic anhydride is an effective chain transfer agent, by the experiment at different temperatures for two systems in the presence or absence of acetic anhydride, and by the comparison of kinetic behavior. In the system without acetic anhydride at the temperature of 7, 15, and 22°C, the propagation rate constants of THF, kp are 7.90, 14.23, and 23.35 10-3L/Mol.S, respectively. In the presence of acetic anhydride, kp are 1.51, 2.85, and 4.98 10-3L/Mol.S; and ktr are 2.04, 3.59, and 6.49 10-4L/Mol.S, respectively. © 1994 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321017
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  • 190
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    Styrene polymerization with some new macro or macromonomeric azoinitiators having peg units (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1739-1746 
    Details
    ISSN: 0887-624X
    Keywords: macromerinitiator (macroinimer) ; crosslinked block copolymer ; macroinitiator ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new macroinitiators and macromerinitiators (macroinimers) were synthesized and evaluated for the bulk polymerization of sytrene at 60°C. Macroinitiators were prepared from the reaction of 4,4′-dicyano-4,4′ azovaleryl chloride (1) with poly(ethylene glycol) (PEG) with a Mω of 400 and with either benzoyl chloride, acetyl chloride, phenyl isocyanate, or poly(ethylene glycol) oleyl ether. Macromer initiators were also prepared from the reaction of 1 with PEG having Mω values of 200, 400, 600, 1000, or 1500 and with 4-vinylbenzyl chloride. The bulk polymerization of styrene by macroinimers gave crosslinked styrene-PEG block copolymers, while the polymerization by macroinitiators gave soluble copolymers. The molecular weights of the styrene-PEG block copolymers obtained with macroinitiators having either oleyl, benzoyl, or phenyl urethane end groups were 22000-29000 g/mol. DSC measurements showed that the crosslinked block copolymers had crystalline PEG units with melting transitions ranging from 11-37°C. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320916
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  • 191
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    Studies on the formation of PEN. II. Polymerization of bis(hydroxyethyl) naphthalate by various metallic catalysts (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1305-1315 
    Details
    ISSN: 0887-624X
    Keywords: polyethylenenaphthalate ; bis(hydroxyethyl)naphthalate ; molecular weight ; polycondensation kinetics ; intrinsic viscosity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(hydroxyethyl) naphthalate (BHEN) was polymerized to polyethylenenaphthalate (PEN) in the presence of various metallic catalysts. The influence of the nature and concentration of these catalysts on the rate of polymerization has been investigated. The order of decreasing catalytic influence of various metal ions on the polymerization of BHEN was found to be: Ti 〉 Sb 〉 Zn 〉 Co 〉 Pb 〉 Ni(Mg). The effect of the reaction temperature has also been studied. The optimal concentration of these catalyst and reaction temperature were found to be 30 × 10-5 (mol/mol BHEN) and 285-293°C, respectively. Because of its insolubility in ordinary solvent, the molecular weight of PEN was measured using the light scattering method. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320711
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  • 192
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    Primary thermal degradation processes occurring in poly(phenylenesulfide) investigated by direct pyrolysis-mass spectrometry (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1807-1815 
    Details
    ISSN: 0887-624X
    Keywords: poly(phenylenesulfide) ; thermal degradation ; direct pyrolysis-mass spectrometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal degradation Processes which occur in poly(phenylenesulfide) (PPS) have been studied by direct pyrolysis-mass spectrometry (DPMS). The structure of the compounds evolved in the overall temperature range of PPS decomposition (400-700°C) suggests the occurrence of several thermal decomposition steps. At the onset of the thermal degradation (430-450°C) this polymer decomposes with the formation of cyclic oligomers, generated by a simple cylization mechanism either initiated at the - SH end groups or by the exchange between the inner sulfur atoms along the polymer chain. At higher temperature (〉 500°C) another decomposition reaction takes over with the formation of aromatic linear thiols. The formation of thiodibenzofuran units by a subsequent dehydrogenation reaction occurs in the temperature range of 550-650°C; in fact, pyrolysis products with a quasi-ladder structure have also been detected. Ultimately, above 600°C, extrusion of sulfur from the pyrolysis residue occurs with the maximum evolution at the end of decomposition (about 700°C). It appears, therefore, that the residue obtained at high temperature tends to have a crosslinked graphite-like structure from which the bonded sulfur is extruded. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321002
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  • 193
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    Effects of chain end group composition and concentration on the properties of bisphenol A-tetrabromobisphenol A copolycarbonates (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1885-1891 
    Details
    ISSN: 0887-624X
    Keywords: copolycarbonate ; bisphenol A ; tetrabromobisphenol A ; end group ; analysis ; properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The types and concentrations of end groups present in bisphenol A-tetrabromobisphenol A copolycarbonates (BA-TBBA coPCs) have major effects on the copolymer solution washability and thermal stability. Six types of coPC end groups are possible: two by monophenol capping of each comonomer, two phenolics (BA-OH and TBBA-OH), and two carbamates (one from each comonomer). BA-TBBA coPCs were prepared by typical solution and interfacial methods and their phenolic and carbamate end group concentrations were correlated with their solution washability and thermal discoloration. Both phenolic and carbamate end groups proved deleterious to these two copolymer properties. An improved interfacial process that employs 4-N,N-dimethylaminopyridine as the coupling catalyst provides coPCs having low concentrations of phenolic and carbamate end groups and that, therefore, wash without emulsification and are thermally stable. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321009
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  • 194
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    Synthesis and thermal stability of the resins prepared from the reactions of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines and electrical conductivity of the resulting materials following pyrolysis (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1915-1921 
    Details
    ISSN: 0887-624X
    Keywords: 1,4-bis(2,2-dicyanovinyl)benzene ; thermally stable polymers ; thermosetting resins ; conductive polymers ; electrical resistivity ; cyano-substituted polymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New thermosetting resins were prepared from the reaction of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines in varying molar ratios. The thermal stability of these resins was correlated with their composition and the curing conditions. They were stable in N2 up to 370-448°C and afforded anaerobic char yields of 73-84% at 800°C after curing at 300°C for 20-60 h. The temperature dependence of the electrical resistivity of all resins pyrolyzed at 700°C for 15 h was studied in the temperature range from -173-327°C (100-600 K). The results showed that at room temperature the unpyrolyzed polymers have insulating properties, whereas a dramatic decrease in the electrical resistivity is observed following pyrolysis. The temperature dependence of the electrical resistivity suggests that all of the materials studied have semiconducting properties. The observed electrical conductivity is thermally activated with activation energies ranging from 0.03-0.06 eV. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321014
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  • 195
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    Synthesis of poly(γ-methoxypropylmethylsilylene) and poly(γ-methoxypropylmethylsilylene-co-di-n-hexylsilylene) (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1949-1956 
    Details
    ISSN: 0887-624X
    Keywords: polysilanes ; polysilylenes ; copolysilane ; alkoxy-substituted polysilane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of γ;-methoxypropylmethyldichlorosilane, and its subsequent polymerization and copolymerization with di;-n;-hexyldichlorosilane through the reductive coupling with sodium has been accomplished. The resulting polymers contain methyl ether side groups that allow further synthetic transformations on the polysilane backbone. For poly (γ;-methoxypropylmethylsilylene) these groups impart solubility characteristics different than typical alkyl and aryl substituted polysilanes. These new polymers and copolymers have been characterized by GPC and 1H-, 13C-, and 29Si-NMR. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321018
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  • 196
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    Basic structure-property behavior of polyurethane cationomers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1983-1989 
    Details
    ISSN: 0887-624X
    Keywords: polyurethane cationomer ; PTAd ; IPDI ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyurethane (PU) cationomers were synthesized from polytetramethylene adipate glycol (PTAd), isophorone diisocyanate (IPDI), and N-methyl diethanolamine (MDEA) according to a prepolymer mixing process. Basic structure-property behavior of the emulsion (obtained by adding water to the ionomer solution) and emulsion cast film was studied with regard to the molecular weight (Mn) of PTAd, MDEA content, degree of neutralization, and extender functionality. Particle size decreased asymptotically with increasing Mn of PTAd due to the increased chain flexibility, and with the degree of neutralization due to the increased hydrophilicity of the PU. Emulsion viscosity generally showed the opposite tendency with particle size dependence. The major transition temperature, corresponding to the glass transition (Tg) of phase mixed PU or hard segment-rich phase of the PU monotonically increased with MDEA content, degree of neutralization, and with increasing extender functionality. However, with increasing Mn of PTAd, Tg first decreased (Mn = 1000) and then increased (Mn = 1500, 2000), due respectively to the increased hard fraction of phase mixed PU, and soft segment crystallization. Tensile strength increased and elongation at break decreased with MDEA content, degree of neutralization, and extender functionality. © 1994 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321022
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  • 197
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    Analysis of 1H-NMR spectra of various end-functionalized polyisobutylenes (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2011-2021 
    Details
    ISSN: 0887-624X
    Keywords: polyisobutylene ; living carbocationic polymerization ; proton NMR analysis ; hydroxyl-ended, chlorine-ended, olefin-ended, phenyl-ended polyisobutylenes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-NMR spectra of various telechelic (i.e., ∼ CH2C(CH3)2Cl, ∼ CH2C(CH3)=CH2, ∼ CH=C(CH3)2, and ∼ CH2CH(CH3)CH2OH capped) polyisobutylenes (PIB) have been analyzed. The products were prepared by living carbocationic polymerization followed by end-group functionalization. Shielding and deshielding effects strongly influence the 1H-NMR spectra of these products. Inductive effects (chlorine-ended PIBs), magnetically anisotropic end-groups (olefin groups and phenyl rings), allylic coupling (olefin end-groups), chirality (hydroxyl end-groups), and the interaction of these effects on the 1H-NMR spectra are discussed. Numerous heretofore unidentified resonances have been assigned and better insight into the detailed structure of end-functionalized PIBs has been obtained. © 1994 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321102
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  • 198
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    Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2049-2056 
    Details
    ISSN: 0887-624X
    Keywords: metallocenes ; olefin polymerizations ; Ziegler-Natta catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propylene was polymerized with rac-ethylene-bis (1-η5-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; 13C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321106
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  • 199
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    Radical polymerization of N-substituted itaconamic esters and itaconamides (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2085-2091 
    Details
    ISSN: 0887-624X
    Keywords: radical polymerization ; 1,1-disubstituted ethylene itaconamate ; itaconamide ; thermal property ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two kinds of itaconamic esters, α-substituted acrylate derivatives (IAE-I) and α-substituted acrylamide derivatives (IAE-II), as well as itaconamides (IAm) were prepared and polymerized with a radical initiator. It has been revealed that N,N-disubstituted IAE-I as an acrylate is more reactive in polymerization than N,N-disubstituted IAE-II as an acrylamide and that N,N′-dialkyl substituted IAm homopolymerizes but N,N,N′,N′;-tetraalkyl substituted one does not. In radical copolymerization with styrene, IAE-I showed a higher polymerization reactivity than IAE-II. The effects of the N-substituents on the polymerization reactivity were discussed on the basis of conformation of the monomers. The polymers obtained were also characterized. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321110
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    Polymer-supported Ziegler-Natta catalysts. I. A preliminary study of catalyst synthesis (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2127-2134 
    Details
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalyst ; polymer support ; ethylene ; polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymer-supported Ziegler-Natta catalysts based on various polymer carriers were synthesized by different methods, including (1) loading TiCl4 directly onto the polymer supports; (2) loading TiCl4 onto the polymer supports modified by magnesium chloride (MgCl2); (3) loading TiCl4 onto the polymer supports modified by Grignard reagent (RMgCl); and (4) loading TiCl4 onto the polymer supports modified by magnesium alkyls (MgR2). The activity and kinetic features of the catalysts for ethylene polymerization were examined. Among the combinations tested, the best was found to be TiCl4/n-Bu2Mg.Et3Al/poly(ethylene-co-acrylic acid) (92:8), which produced a catalyst of very high activity for ethylene polymerization. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321115
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