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  • 2010-2014
  • 1990-1994  (10,382)
  • 1992  (10,382)
  • Chemistry  (10,382)
  • 101
    Electronic Resource
    Electronic Resource
    Compartmentalization of chromophores in a molecular composite consisting of amphiphilic polyelectrolyte-surfactant ion complexes (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2099-2108 
    Details
    ISSN: 0887-624X
    Keywords: amphiphilic polyelectrolyte ; compartmentalization ; photoinduced electron transfer ; molecular composite ; polymer-bound chromophore ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular composite of an amphiphilic polyanion and cationic surfactants was prepared by treating a terpolymer [consisting of sodium 2-acrylamido-2-methylpropanesulfonate, N-(1-adamantyl)methacrylamide, and a small mole fraction of N-(1-pyrenylmethyl)methacrylamide] with didodocyldimethylammonium bromide in aqueous solution. The molecular composite was soluble in organic solvents with a wide range of polarities. Fluorescence spectra indicated that the pyrenyl (Py) residues in the molecular composite experienced polar microenvironments even though the composite was dissolved in nonpolar solvents. Exciplex formation of the Py residue with 4,4′-dicyanobenzene was strongly suppressed due to the polar microenvironments and steric “protection” of the chromophore. Photoinduced electron transfer (ET) from the Py residue to pyromellitic dianhydride (PMDA) in acetonitrile showed characteristics of long-range ET between fixed donor and acceptor sites and yielded long-lived transient Py cation radicals and PMDA anion radicals which persisted for tens of milliseconds. These findings imply that the micellelike structure of the parent amphiphilic polyelectrolyte formed in aqueous solution is retained, to some degree, in the molecular composite dissolved in organic solvents. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301003
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  • 102
    Electronic Resource
    Electronic Resource
    Characterization of the changes in the initial morphology for MgCl2-supported Ziegler-Natta polymerization catalysts (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2131-2141 
    Details
    ISSN: 0887-624X
    Keywords: polypropylene, catalyst dynamics for ; Ziegler-Natta ; heterogeneous catalysis of; catalysis ; polyolefins, fragmentation of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently considerable detail has become available on the initial morphology and the morphological changes that occur for silica based Cr catalysts for ethylene polymerization. These catalysts are produced as a dry powder and may be employed either in gas phase or in slurry processes. MgCl2-supported Ziegler-Natta polymerization catalysts are often prepared and employed as slurries. They usually are never dried and thus few studies have employed the spectra of physical techniques common to the characterization of pore structure. In the current study, we have carefully removed the solvent for both ball-milled and precipitated MgCl2-supported catalysts. These catalysts are characterized by physical sorption, mercury porosimetry, and electron microscopy both as prepared and during the initial stages of polymerization (to ∼ 100 g of polymer/g of catalyst). We find that the initial catalyst may be represented by a complex agglomerate of small crystallites as contrasted with the branched pore network found in Cr/silica catalysts. As a result, it is concluded that the initial fragmentation of the MgCl2 based systems is more uniform as contrasted with the progressive fragmentation of the silica-based system. This fragmentation mechanism facilitates the retention of greater polymer/catalyst surface during the initial stages of the polymerization. © 1992 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301006
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  • 103
    Electronic Resource
    Electronic Resource
    The crosslinking of chitosan fibers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2187-2193 
    Details
    ISSN: 0887-624X
    Keywords: chitin ; chitosan ; fibers ; crosslinking ; epichlorohydrin ; film ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A need exists for the development of totally biodegradable packaging materials. Chitosan is an under-utilized polymer which possesses many of the desired characteristics for this application. This article describes the crosslinking of chitosan fibers. Epichlorohydrin (ECH) was selected as a convenient base catalyzed crosslinking agent. The strength of chitosan fibers, especially wet tenacity, is improved by crosslinking. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301013
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  • 104
    Electronic Resource
    Electronic Resource
    Organoborazines. III. Homo- and copolymerization of p-vinylphenylcyclotriborazinesFor Part II, see Reference 1. (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 577-581 
    Details
    ISSN: 0887-624X
    Keywords: organoborazine homopolymers ; organoborazine copolymers ; radical polymerization ; thermal behavior ; monomer reactivity ratios ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The polymerization and copolymerization with styrene of a series of unsymmetrically B-p-vinylphenyl-N-methyl and N-phenyl borazines [R3(R2)2B3N3(R1)3; R1 = methyl, phenyl, R2 = methyl phenyl, R3 = p-vinylphenyl] has been studied. The polymerization of these monomers yielded both tractable and crosslinked materials. The polymers obtained were characterized by 1H- and 13C-NMR spectroscopy, elemental analysis, gel permeation chromatography, and thermogravimeteric analysis. The reactivity ratios for the copolymerization reaction were calculated by the Mortimer-Tidwell method.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300408
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  • 105
    Electronic Resource
    Electronic Resource
    Laser-Initiated copolymerization of N-vinylpyrrolidone with maleic anhydride and maleimide (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 589-595 
    Details
    ISSN: 0887-624X
    Keywords: laser copolymerization ; charge transfer complexes ; N-vinylpyrrolidone ; maleic anhydride ; maleimide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the laser-initiated copolymerization of N-vinylpyrrolidone with maleic anhydride and maleimide via charge transfer complexes. The dependence of copolymer yield on the molar ratios of the monomers in the feed and on the irradiation time is described. Based on the ultraviolet and infrared spectroscopy, and chemical analysis results, a tentative mechanism of polymerization is suggested. The rates of polymerization of several monomer systems are compared. The N-vinylpyrrolidone and maleimide system shows the highest rate of polymerization.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300410
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  • 106
    Electronic Resource
    Electronic Resource
    Thermal redistribution reactions in crosslinked polysiloxanes (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 613-623 
    Details
    ISSN: 0887-624X
    Keywords: thermolysis of crosslinked polysiloxanes ; redistribution reactions ; Si—C/Si—O and Si—H/Si—O bonds exchange ; thermogravimetric analysis/mass spectroscopy ; solid-state 29Si-NMR ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermolysis under argon of various polysiloxane resins containing D, T, DH, or TH units was investigated using thermogravimetric analysis combined with mass spectroscopy (TG/MS analysis) and solid-state 29Si-NMR. Redistribution reactions involving the exchange of Si—C/Si—O bonds or Si—H/Si—O bonds were evidenced in addition to the exchange of Si—O/Si—O bonds reported to date. These reactions significantly modify the initial siloxane units and lead to an escape of volatile silanes or siloxanes. The exchange of Si—H/Si—O bonds takes place at lower temperatures (300°C) than the exchange of Si—C/Si—O bonds (500°C).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300413
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  • 107
    Electronic Resource
    Electronic Resource
    Catalytic aminolysis of acrylic copolymers in solution and in the melt. I. Mechanism and kinetics (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 625-634 
    Details
    ISSN: 0887-624X
    Keywords: catalysis ; mechanism ; kinetics ; aminolysis ; tautomer ; molten state ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aminolysis of poly(styrene-co-methyl acrylate) (SMA) by octadecylamine was studied in solution and in the melt at temperatures around 200°C. This reaction is rather slow, so several types of catalysts were tested to accelerate it. The most efficient is 2-pyridone, a compound in tautomeric equilibrium with 2-hydroxypyridine. A mechanism of the catalytic reaction is proposed whereby the tautomeric nature of the catalyst plays a key role in a very important step of the reaction, namely the proton transfer. This mechanism is confirmed by the kinetic data determined in a 1,2,4-trichlorobenzene solution and in the melt. In addition, it was found that the kinetic data obtained in both media are very close, indicating no significant difference of local polarity in the two reaction media. Data also show only a minor effect due to difference in viscosity. Finally, the question of the homogeneity of the molten medium is discussed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300414
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  • 108
    Electronic Resource
    Electronic Resource
    Polymerization of vinylcyclohexane with ziegler-natta catalyst (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 679-683 
    Details
    ISSN: 0887-624X
    Keywords: coordination polymerization ; vinylcyclohexane ; Ziegler-Natta catalyst ; isomerization ; monomer-isomerization copolymerization ; 2-butene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymerization of vinylcyclohexane (VCHA) with TiCl3-aluminum alkyl catalysts was investigated. The polymerization rate of VCHA was low due to the branch at the position adjacent to the reacting double bond. The effects of aluminum alkyl on the polymerization and monomer-isomerization were observed; the polymer yield decreased in the following order: (CH3)3Al 〉 (i-C4H9)3Al 〉 (C2H5)3Al. Isomerization of VCHA was observed with the TiCl3-(i-C4H9)3Al and the TiCl3-(C2H5)3Al catalysts during the polymerization, while with the TiCl3-(CH3)3Al catalyst such isomerization was not observed. Monomer-isomerization copolymerization of VCHA and trans-2-butene took place to give copolymers consisting of VCHA and 1-butene units.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300420
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  • 109
    Electronic Resource
    Electronic Resource
    Synthesis and radical ring-opening polymerization of 2,2-diphenyl-4-methylene-5-methyl-1,3-dioxolane, alternating copolymer of propylene, and carbon monoxide (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 689-690 
    Details
    ISSN: 0887-624X
    Keywords: radical polymerization ; ring-opening polymerization ; 4-methylene-1,3-dioxolanes ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300422
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  • 110
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of bismaleimides from epoxy resins (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 723-729 
    Details
    ISSN: 0887-624X
    Keywords: bismaleimides ; structure effect ; crosslinking reaction ; heat resistance ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel bismaleimides (BMIs) were prepared from functional monomaleimides and diglycidyl ether of bisphenol A (DGEBA) and some of them were shown to have good processibility and improved water resistance while retaining characteristic thermal stability of polyimide. Functional monomaleimides were synthesized via the condensation reaction of maleic anhydride with either aminobenzoic acid or aminophenol. Crosslinking reaction of thus obtained BMIs was carried out with or without catalyst at the temperature range of 100-250°C. The type of the functional group species and their position in monomaleimides significantly affected the crosslinking behavior of the resulting BMIs and the thermal property of their crosslinked products. BMIs with meta linkage, obtained from meta monomaleimides, exhibited much faster thermal crosslinking behavior than corresponding para BMIs. When the molecular weight of BMI was larger, the crosslinking density became smaller and Tg was lower as expected, while the viscosity started to increase at a higher temperature. Glass transition temperatures of the crosslinked resins were in the range of 160-250°C and these resins showed excellent thermal stability up to 370°C.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300504
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  • 111
    Electronic Resource
    Electronic Resource
    Template polymerization of N-vinylimidazole along poly(methacrylic acid) in water. VI. Crosslinked PMAA as template (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 787-796 
    Details
    ISSN: 0887-624X
    Keywords: template polymerization ; crosslinked PMAA ; calorimetry ; morphology ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of crosslinked poly(methacrylic acid) (c-PMAA) on the polymerization of N-vinylimidazole in aqueous solution was studied using UV, calorimetry, SEM, and TEM. It was established that synthetic lightly crosslinked PMAA samples behaved intermediate between rigid crosslinked PMAA particles functioning as microreactors, and linear conventional PMAA, where template and conventional polymerization in the surrounding solution are integrated. A modified calorimetric technique was used to measure monomer conversion, and to correct for the rapid adsorption process. Rate enhancements up to a factor of 4 were obtained for the c-PMAA's, which were lower than those obtained for linear conventional PMAA, and which slightly decreased with increasing crosslink density of the samples. Template complexes possessed a platelet-like morphology similar to template complexes obtained for linear PMAA.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300508
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  • 112
    Electronic Resource
    Electronic Resource
    Imide-aryl ether ketone block copolymers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2085-2097 
    Details
    ISSN: 0887-624X
    Keywords: imide-aryl ether ketone block copolymers ; multiphase morphologies ; mechanical and thermal properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Imide-aryl ether ketone block copolymers were prepared and their morphology and thermal and mechanical properties investigated. Two aryl ether ketone blocks were incorporated; the first was an amorphous block derived from bisphenol-A and the second block was a semi-crystalline poly(aryl ether ether ketone) prepared from a soluble and amorphous ketimine precursor. Bis(amino) aryl ether ketone and aryl ether ketimine oligomers were prepared via a nucleophilic aromaic substitution reaction with molecular weights ranging from 6,000 to 12,000 g/mol. The oligomers were co-reacted with 4,4′-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in N-methyl-2-pyrrolidone (NMP) in the presence of N-methylmorpholine. The copolymer compositions, determined by H-NMR, of the resulting amic ester based copolymers ranged from 8 to 50 wt % aryl ether ketone or ketimine content. Prior to imide formation, the ketimine moiety of the aryl ether ketimine block was hydrolyzed (p-toluene sulfonic acid) to the ketone form producing the aryl ether ether ketone block. Compositions of this block were maintained low to retain solubility. Solutions of the copolymers were cast and cured to effect imidization, producing clear films with high moduli (ca. 2200 MPa) and elongations (33-100%). The copolymers displayed good thermal stability with decomposition temperatures in excess of 450°C. Multiphase morphologies were observed irrespective of the co-block type, block length or composition. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301002
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  • 113
    Electronic Resource
    Electronic Resource
    Synthesis, characterization, and curing of well-defined allyl ether-maleate functional ester oligomers: Linear versus nonlinear structures (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2203-2210 
    Details
    ISSN: 0887-624X
    Keywords: allyl ether ; star polymers ; rheology ; curing kinetics ; molecular architecture ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of allyl ether-maleate functional star-shaped esters with from one to four arms has been synthesized. The structures that have been made are an analogous series with increasing molecular weight and functionality where the increase in molecular weight has been made nonlinear, i.e., star-shaped. The resins are monodisperse in the sense that each arm has a well-defined structure and that, within a certain sample, only one type of molecule exists. The viscosity and rheological behavior of the resins have been studied. The curing kinetics of the star-shaped (branched) resins and the properties of the films formed have also been studied. These properties have been related to differences in functionality and to differences in the molecular architecture of the resins. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301015
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  • 114
    Electronic Resource
    Electronic Resource
    Formose reaction by polymer-supported thiazolium salts (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2247-2250 
    Details
    ISSN: 0887-624X
    Keywords: polymer catalyst ; formose reaction ; thiazolium salt ; hydrocarbons ; dihydroxy acetone ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thiazolium salt polymers synthesized by quaternization of 4-(4′-vinylphenyl)thiazole (VPT) polymers with methyl iodide had a highly catalytic activity for “the formose reaction.” Their catalytic activities were comparable to that of a low molecular weight analog, 3-methyl-4-phenylthiazolium iodide (MPTI). In the reaction catalyzed by the polymer catalyst, a main product, dihydroxyacetone (DHA), was detected by gas-liquid chromatography. The polymer catalysts were easily recovered from the reaction mixture and reused with a sustained catalytic activity. © 1992 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301021
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  • 115
    Electronic Resource
    Electronic Resource
    Para-Xylylenes and analogues by base-induced elimination from 1,4-bis-(dialkylsulfoniomethyl)arene salts in poly(1,4-arylene vinylene) synthesis by the wessling soluble precursor method (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2233-2240 
    Details
    ISSN: 0887-624X
    Keywords: para-xylylenes ; 1,4-benzoquinodimethanes ; conducting polymers ; poly(arylene vinylene)s ; poly(phenylene vinylene)s ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: para-Xylylenes are generated by treatment of various 1,4-bis(dialkylsulfoniomethyl)arene dihalides with base in water, methanol, and aqueous acetonitrile, as shown by UV-Vis spectroscopy. This procedure allows the monitoring of the transient xylylene monomers that yield polyelectrolyte precursor polymers for poly(arylene vinylene)s, formed by variations of the chemistry developed originally by Wessling and co-workers. Alkoxy, alkyl, and halogen ring substituents on the sulfonium salt precursors do not greatly affect the ability to generate and observe the growth and decay of steady-state concentrations of the para-xylylene intermediates. Use of strong resonance-acceptor substituents - such as cyano or nitro - on the ring reduces production of a strong para-xylylene absorption, possibly due to reluctance of the ylides initially formed from the bis-sulfonium salts to eliminate to the xylylenes. By variation of UV-Vis conditions, it was found that use of 20% aqueous acetonitrile rather than water allowed formation of low to modest molecular weight polyelectrolytes in cyano-substituted cases (Mw = 8000-37,000). Use of UV-Vis test experiments should be useful for screening of bis sulfonium salt precursors that may be expected to give high molecular weight polyelectrolytes - in cases where para-xylylene formation is easy - as well as for finding reaction conditions that will optimize polymer formation. © 1992 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301019
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  • 116
    Electronic Resource
    Electronic Resource
    Effect of light intensity on the photooxidation kinetics of high-density polyethylene (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2277-2280 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; photooxidation kinetics ; light intensity ; oxygen uptake ; 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.1992.080301025
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  • 117
    Electronic Resource
    Electronic Resource
    Polyimides derived from diels-alder polymerization of furfuryl-substituted maleamic acids or from the reaction of bismaleamic with bisfurfurylpyromellitamic acids (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2559-2567 
    Details
    ISSN: 0887-624X
    Keywords: Diels-Alder polymerization ; polyimides ; bismaleimide ; bismaleamic acid ; bisfurfurylpyromellitimide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Certain AB or AA and BB Diels-Alder polymer precursors bearing maleimide and furan segments were synthesized, characterized, and polymerized. Particularly, the monomaleamic acid derived from 4,4'-diaminodiphenylmethane, reacted with the monofurfurylpyromellitamic acid to yield a triamic acid which was cyclodehydrated to the corresponding triimide. A polyimide was obtained upon heat-curing of triimide or the intermediate triamic acid. In addition, equimolar amounts of N,N'-bismaleimido-4,4'-diphenylmethane (BMDM) and bisfurfurylpyromellitimide or their intermediate diamic acids were cured to afford a polyimide. The polymer precursors were characterized by IR and 1H-NMR spectroscopy and their curing behavior was investigated by DTA. It was shown that the Diels-Alder polymerization of monomers took place at lower temperature than that required for crosslinking of BMDM. The thermal stabilities of polymers were ascertained by TGA and isothermal gravimetric analysis (IGA). The synthesized Diels-Alder polymers were remarkably more heat-resistant than the crosslinked polymer obtained from BMDM or its intermediate bismaleamic acid. They were stable up to about 360°C in N2 or air and afforded anaerobic char yield of 58% at 800°C. © 1992 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301210
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  • 118
    Electronic Resource
    Electronic Resource
    Kinetics and steric limitation of quaternization of poly(4-vinylpyridine) with mesogenic ω-(4′-methoxy-4-biphenylyloxy)alkyl bromides (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2587-2594 
    Details
    ISSN: 0887-624X
    Keywords: kinetics of quaternization ; poly(4-vinyl pyridine) ; steric hindrance ; liquidcrystalline copolymers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics and characteristics of the quaternization of poly(4-vinylpyridine) with very large alkylating agents are studied with the main aim to demonstrate the occurrence of a limitation of the reaction due to steric effect. Kinetics are carried out in sulfolane at different temperatures with two ω-(4'-methoxy-4-biphenylyloxy)alkyl bromides. An important limitation of the reaction is demonstrated: 30% of the pyridine groups are inaccessible at 333 K, 23% at 355.5 K, and 4% at 363 K. Post-quaternization experiments with butyl bromide of already partially quaternized P4VP also demonstrate this limitation. The occurrence of global steric hindrance and hydrophobic effects affecting the conformation of the chain in solution is proposed to explain the limited accessibility of the pyridine groups. The results question the classical neighboring group model generally used to describe the slowing down of the quaternization reaction with increasing quaternization ratio. The thermal stability of the quaternized polymers and the colors of the reaction medium are also discussed. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301213
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  • 119
    Electronic Resource
    Electronic Resource
    Emulsion polymerization of vinyl acetate using a polymerizable surfactant. I. Kinetic studies (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2619-2629 
    Details
    ISSN: 0887-624X
    Keywords: emulsion polymerization, vinyl acetate ; emulsion polymerization, polymerizable surfactant ; emulsion polymerization, kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A polymerizable surfactant, sodium dodecyl allyl sulfosuccinate (TREM LF-40; Henkel) and its nonpolymerizable counterpart were used in comparative studies of the emulsion polymerization of vinyl acetate. The conversion-time behavior differed for the two surfactants; the TREM LF-40 showed a decrease in the polymerization rate with increasing concentration while its hydrogenated derivative showed the opposite behavior, the rate increasing with increasing surfactant. Particle size analysis revealed a decreasing particle size with increasing surfactant concentration for both series of reactions. An explanation for the seemingly ambiguous results obtained for the polymerizable surfactant was sought by examining the reactivity of its vinyl group in copolymerization with vinyl acetate and its allylic group in a chain transfer reaction. The results suggest that both the copolymerization and chain transfer reactions can lead to the observed reduction in polymerization rate with increasing TREM LF-40 concentration. © 1992 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301216
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    Errata (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2663-2663 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301221
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    Photooxidation of polystyrene by O2 and N2O (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2677-2681 
    Details
    ISSN: 0887-624X
    Keywords: polystyrene ; photooxidation ; oxygen ; nitrous oxide ; ultraviolet ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Strips of polystyrene held in a flowing O2 or N2O atmosphere have been exposed to 240-600 nm radiation. The extent of photooxidation has been followed by x-ray photoelectron spectroscopy (XPS). Although N2O is a more reactive gas than O2, it produces a less oxidized polymer surface. This surprising observation can be correlated to the photochemistry occurring at the gas/polystyrene interface. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301302
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    Thermal oxidation of blends of poly(ethylene oxide) and poly(methyl methacrylate) (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2693-2698 
    Details
    ISSN: 0887-624X
    Keywords: thermal oxidation ; polymer blends, poly(ethylene oxide) ; poly(methyl methacrylate) ; miscibility ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal oxidation of poly(ethylene oxide) (PEO) and its blends with poly(methyl methacrylate) (PMMA) were studied using oxygen uptake measurements. The rates of oxidation and maximum oxygen uptake contents were reduced as the content of PMMA was increased in the blends. The results were indicative of a stabilizing effect by PMMA on the oxidation of PEO. The oxidation reaction at 140°C was stopped at various stages and PMMA was separated from PEO and its molecular weights were measured by gel permeation chromatography (GPC). The decrease in the number-average molecular weight of PMMA was larger as the content of PEO increased in the blends. The visual appearance of the films suggested that phase separation did not occur after thermal oxidation. The activation energy for the rates of oxidation in the blends was slightly increased compared to pure PEO. © 1992 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301304
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    Thermal degradation of poly((E,E)-[6.2]paracyclophane-1,5-diene) (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2781-2790 
    Details
    ISSN: 0887-624X
    Keywords: poly((E,E)-[6.2]paracyclophane-1,5-diene ; thermal analysis ; thermal degradation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal degradation of poly((E,E)-[6.2]paracyclophane-1,5-diene) is studied in inert and oxidative environments by using thermogravimetric analysis, pyrolysis GC/MS, pyrolysis GC/FT-IR, and variable temperature-diffuse reflectance infrared spectroscopy (VT-DRIFTS). Thermal degradation in helium begins by depolymerization yielding a volatile product capable of abstracting hydrogens from the polymer residue. Multiple hydrogen abstractions result in a variety of volatile species containing benzyl-benzyl bonds. In the presence of oxygen, polymer decomposition is dictated by reactions of peroxy and hydroperoxy radicals. At low temperatures, oxygenated species are the primary products. At higher temperatures, increased unsaturation is detected in the polymer residue. In both inert and oxidative environments, the strain associated with alignment of paracyclophane aromatic rings is lost during the initial stages of thermal degradation. © 1992 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301314
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    Carbonation of polymeric organolithium compounds: Effects of chain end structure (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2349-2355 
    Details
    ISSN: 0887-624X
    Keywords: carbonation ; functionalization ; polystyrene ; polyisoprene ; polybutadiene ; poly(styryl)lithium ; poly(butadienyl)lithium ; anionic polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The carbonation of the adduct of poly(styryl)lithium with 1,1-diphenylethylene with gaseous carbon dioxide in benzene proceeds in high yield (〉99%) compared to the inefficient functionalizations for poly(styryl)lithium (66%), poly(isoprenyl)lithium (59%), and polybutadienyl)lithium (27%). The quantitative carboxylation of poly(isoprenyl)lithium and poly(butadienyl)lithium requires the presence of larger amounts of Lewis bases such as THF ([THF]/[Li] = 300) or TMEDA ([TMEDA]/[Li] = 46) compared to poly(styryl)lithium in which a ratio of [TMEDA]/[Li] = 12 is effective. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301108
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    Photocrosslinking of copolymers of vinyloxyethyl methacrylate-styrene initiated by sulfonium salts. I. Transient species formed on photolysis of sulfonium salt (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2365-2369 
    Details
    ISSN: 0887-624X
    Keywords: photolysis ; transient species ; sulfonium salt ; benzyl cation ; time-resolved measurements ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Benzyl cation was detected by transient absorption spectroscopy with a spectroscopic multichannel analyzer on pulse excitation (fourth harmonic of Nd:YAG laser, 266 nm; 10 ns fwhm) of benzyl(4-hydroxyphenyl) methylsulfonium hexafluoroantimonate(BSS) in 1,2-dichloroethane (EDC). The benzyl cation was long-lived (lifetime, 59 ms) at room temperature and quenched by a vinyl ether compound. The formation of the benzyl cation as active species on photolysis of BSS is in contrast to the formation of Brønsted acids in other sulfonium salts so far reported. © 1992 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301110
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    Synthesis of thermally-induced phase separating polymer with well-defined polymer structure by living cationic polymerization. I. Synthesis of poly(vinyl ether)s with oxyethylene units in the pendant and its phase separation behavior in aqueous solution (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2407-2413 
    Details
    ISSN: 0887-624X
    Keywords: living cationic polymerization ; alkoxyethyl vinyl ether ; pendant oxyethylene unit ; water-soluble polymer ; phase separation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Living cationic polymerization of alkoxyethyl vinyl ether [CH2=CHOCH2CH2OR; R: CH3 (MOVE), C2H5 (EOVE)] and related vinyl ethers with oxyethylene units in the pendant was achieved by 1-(isobutoxy)ethyl acetate (1)/Et1.5AlCl1.5 initiating system in the presence of an added base (ethyl acetate or THF) in toluene at 0°C. The polymers had a very narrow molecular weight distribution (M̄w/M̄n = 1.1-1.2) and the M̄n proportionally increased with the progress of the polymerization reaction. On the other hand, the polymerization by 1/EtAlCl2 initiating system in the presence of ethyl acetate, which produces living polymer of isobutyl vinyl ether, yielded the nonliving polymer. When an aqueous solution of the polymers thus obtained was heated, the phase separation phenomenon was clearly observed in each polymer at a definite critical temperature (Tps). For example, Tps was 70°C for poly(MOVE), and 20°C for poly(EOVE) (1 wt % aqueous solution, M̄n ∼ 2 × 104). The phase separation for each case was quite sensitive (ΔTps = 0.3-0.5°C) and reversible on heating and cooling. The Tps or ΔTps was clearly dependent not only on the structure of polymer side chains (oxyethylene chain length and ω-alkyl group), but also on the molecular weight (M̄n = 5 × 103-7 × 104) and its distribution. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301115
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    Metallocene catalysts for olefin polymerizations. XXIV. Stereoblock propylene polymerization catalyzed by rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl)(1-η5-indenyl)dimethyltitanium: A two-state propagationSee Reference 1. (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2601-2617 
    Details
    ISSN: 0887-624X
    Keywords: Ziegler-Natta catalysts ; ansa-metallocene catalyst ; thermoplastic elastomeric poly(propylene) ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic-anti-[ethylidene(1-η5-tetramethylcyclopentadienyl) (1-η5-indenyl)dimethyltitanium (6) has been synthesized and its molecular structure determined by x-ray diffraction methods. The two Ti=Me(1) and Ti=Me(2) units have bond distances differing by 0.08 Å and their proton NMR resonances are separated by over 1 ppm. Using this compound and methylaluminoxane (MAO) as the activator, at 25°C the 6/MAO catalyst produced polypropylene having crystalline domain with physical crosslinks. The polymers obtained at lower polymerization temperatures are rheologically liquids. The behaviors of this catalyst system resembles closely the previously reported rac-[anti-ethylidene(1-η5-tetramethylcyclopentadienyl) (1-η5-indenyl)dichlorotitanium (4)/MAO system. The structure of 6 determined here furnishes tangible support for the proposed two-state (isomeric)-switching propagation mechanism. Addition of MAO to 6 causes broadening of the Me(1) resonance in the 1H-NMR spectra, and 6 is decomposed by Ph3C+B(C6F5)-4. © 1992 John Wiley & Sons, Inc.
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301215
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    Melt-processable oligoamides having internal acetylene groups in the backbone, and thermally stable polyamides therefrom (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2645-2652 
    Details
    ISSN: 0887-624X
    Keywords: Soluble oligoamide ; internal acetylene ; crosslinking ; melt-processing ; high-temperature polymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aromatic oligoamides of DP = 5 and 11 that have all meta-phenylene linkages were prepared by controlling the ratio of isophthaloyl chloride and diamines [m-phenylenediamine and bis(3-aminophenyl)acetylene], and then end-capped with aniline or 2-aminobiphenylene. Aromatic oligoamides having para-phenylene linkages were also prepared similarly using terephthaloyl chloride as a monomer. The oligoamides that have all m-phenylene linkages were soluble in organic solvents such as N-methyl-2-pyrrolidone and N,N-dimethylacetamide, though the oligoamides having p-phenylene linkages were much less soluble. The oligoamides having acetylene units in the backbone showed exotherm due to crosslinking. The onset of the exotherm appeared at 310-340°C for the oligoamides having all m-phenylene linkages, and 330-370°C for the oligoamides having p-phenylene linkages. They were melt-processed at 350 or 380°C for 1 h, giving tough and insoluble films from oligoamides having all m-phenylene linkages and brittle films from oligoamides having p-phenylene linkages. The films showed excellent thermal properties. For example, viscoelastic analyses showed little decrease of mechanical property up to 370°C, and Tg was not observed below the temperature. Thermogravimetric analyses also showed that thermal stability of the melt-processed films were excellent. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301218
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    Polymerization of propargylamine and 1,1-diethylpropargylamine by transition metal catalysts (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2657-2662 
    Details
    ISSN: 0887-624X
    Keywords: poly(propargylamine) ; poly(1,1-diethylpropargylamine) ; polyacetylene derivatives ; transition metal catalysts ; organoaluminum cocatalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some polyacetylene derivatives containing an amine functional group were prepared by the polymerization of propargylamine (PA) and 1,1-diethylpropargylamine (DEPA) with various transition metal catalysts. In the polymerization of PA, Mo-based catalysts were more effective than that of W-based catalysts, and organoaluminum compounds, especially EtAlCl2, were found to be very effective cocatalysts. In the polymerization of DEPA, Mo-and W-based catalyst systems showed a similar catalytic activity. The polymerization easily proceeded in polar solvents such as nitrobenzene and DMF as well as nonpolar aromatic solvents such as chlorobenzene, toluene, etc. The resulting poly(PA) and poly(DEPA) were insoluble in organic solvents regardless of polymerization catalysts but the polymers were found to be stable to air oxidation. Thermogravimetric analyses and thermal transitions of poly(PA) and poly(DEPA) were also studied. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301220
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    Molecular weight distribution of emulsion-polymerized polyethylene (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2709-2713 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; emulsion polymerization ; molecular weight distribution ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Emulsion polymerizations of ethylene were run using potassium persulfate as the initiator and either an anionic or a cationic surfactant, usually at five times the critical micellar concentration. The molecular weight distributions had at least two major peaks. The broadly distributed lower molecular weight component is formed in the early stages of polymerization. The higher molecular weight component has a narrow distribution characteristic of termination by the combination of chain radicals. The weight-average molecular weight of this component was about 400,000 when the surfactant was sodium laurate and 33,600,000 when the surfactant was dodecyl amine hydrochloride. © 1992 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301306
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    Synthesis of poly(arylene ethyne)s via palladium-catalyzed cross-coupling reactions with Cu and Sn reagents (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2503-2510 
    Details
    ISSN: 0887-624X
    Keywords: Poly(arylene ethyne) ; palladium ; cross-coupling reaction ; copper acetylide ; tin alkynyl reagent ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comparative studies have been carried out of the effectiveness of two organometallic coupling reagents for the synthesis of poly(alkynylarene)s via palladium catalyzed cross-coupling reactions of dialkynes with organic dibromides. In comparison to copper reagents, monomeric difunctional trialkyltin acetylides show increased thermal stability which allows reactions to be performed at higher temperatures; they give oligomeric and polymeric materials of improved molecular weight. By contrast, the inferior solubility of copper acetylides limits chain growth, and above 140°C the Pd/Cul system is prone to homopolymerization of the dialkyne. The coupling reactions are solvent-dependent but not strongly influenced by the nature of the palladium precursor complex or the phosphine ligand. © 1992 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301204
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    New liquid crystal polyethers and polyesters based on diphenylbutadiene mesogens (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2541-2547 
    Details
    ISSN: 0887-624X
    Keywords: nonlinear optics ; liquid crystal ; polymers ; photocrosslinking ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New liquid-crystalline (LC) polymers and small molecules have been synthesized based on the 1,4-diphenylbutadiene mesogen, a chromophore with χ(3) nonlinear optical properties. Polyethers were formed by phase-transfer reaction, and polyesters were prepared by Schotten-Bauman polymerization from these 4,4'-bisphenolic mesogenic structures. Liquid crystallinity was examined using differential scanning calorimetry (DSC) and optical microscopy. Most of the model compounds were found to be nematic. All mesomorphic polymers were nematic and displayed LC ranges of up to 50°C as well as a wide diversity of melting points. The melting points varied with the flexible (methylene) spacer length and were strongly dependent upon the presence of substituents in the mesogenic core. Crosslinking and cis-trans isomerization were observed under the influence of heat and ultraviolet radiation. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301208
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    The synthesis and characterization of a poly(maleimide-ether) containing pendent thiophene rings (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2773-2780 
    Details
    ISSN: 0887-624X
    Keywords: poly(maleimide-ether) ; thiophene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of a poly(maleimide-ether) containing pendent thiophene rings via the reaction of 2-(3-thienylmethyl)-1,3-N,N'-bis(3,4-dichloromaleimido) propane with 1,4-dihydroxybenzene is described. The novel 2-substituted-1,3-N,N'-bis(3,4-dichloromaleimido) propanes were obtained by allowing their corresponding diamine hydrochlorides to react with 3,4-dichloromaleic anhydride in acetic acid in the presence of sodium methoxide. The diamine hydrochlorides were prepared by the reduction of their respective diamides. The poly(maleimide-ether)s were fully characterized and 13C-NMR spectroscopy was used to confirm the microstructure of the materials. The properties of the thiophene substituted polymer are compared with model poly(maleimide-ether)s. Electrochemical studies indicated that the thiophene rings in the thiophene-substituted poly(maleimide-ether) were not electroactive. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301313
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    Metalloporphyrins catalyze polyene-polymers to polyepoxides (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2791-2795 
    Details
    ISSN: 0887-624X
    Keywords: polyene polymers ; polyepoxide ; epoxidation reaction ; catalysis ; metalloporphyrins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyene polymers [natural rubber (cis-polyisoprene), trans-polyisoprene, and cis-polybutadiene] were transformed to the corresponding polyepoxides which are a polyalcohol and soap precursor. The catalysts used were chloro- or acetato-manganese(III) tetraphenylporphyrin [MnIII(TPP)Cl or MnIII(TPP)OAc] in association with two different oxygen donors, sodium hypochloride and iodosylbenzene (Por, unspecified porphyrinato ligand; TPP, 5,10,15,20-tetraphenylporphyrinato ligand). This transformation in either biphasic system, H2O(aqua)-CH2Cl2 or PhIO(solid)-CH2Cl2, was monitored by 1H-NMR and IR spectroscopy. In both cases the transformation to the polyepoxide was completed within a few hours. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080301315
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    Chemometrics: Applications of mathematics and statistics to laboratory systems, R. G. Brereton, Ellis Horwood, Chichester, ISBN-0-13-131350-9, 307 pp., £54.50, (1990) (1992)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 228-228 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180060408
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    Diary (1992)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. i 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180060502
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    On the integration of kinetic models using a high-order taylor series method (1992)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 231-246 
    Details
    ISSN: 0886-9383
    Keywords: Integration methods ; Taylor series method ; Optimization methods ; Kinetic mechanisms ; Kinetic determinations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general equation to derive kinetic models up to any order is given. This equation greatly facilitates the application of the Taylor series method to the integration of kinetic models up to very high orders. When dealing with non-stiff models, computing time is always reduced by increasing the integration order, at least up to the 20th order. When the model is stiff, the integration order should be optimized; however, a twelfth order is recommended to integrate weakly stiff models. The use of an algorithm which permits the immediate calculation of the integration step size required to maintain a given accuracy leads to further reductions in computing time. When implemented as recommended here, a high-order Taylor series method is more rapid and accurate than Runge-Kutta and predictor-corrector methods and can be advantageously used in combination with optimization methods to perform mechanism studies and in multicomponent kinetic determinations.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/cem.1180060503
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    Three-dimensional chemical structure handling, Peter Willett, Research Studies Press, Taunton, Somerset, UK, 1991, ISBN 00 86380 121 8 (Wiley Inc. 0 471 93108 X), 241 pp (1992)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 283-284 
    Details
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180060507
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    A review of three-dimensional chemical structure retrieval systems (1992)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 6 (1992), S. 289-305 
    Details
    ISSN: 0886-9383
    Keywords: Chemical structure database ; Conformational searching ; Similarity searching ; Substructure searching ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents a review of the rapid developments that have taken place over the last few years for the searching of databases of three-dimensional (3D) molecules. The geometric arrangement of the atoms in a 3D molecule is described by an interatomic distance matrix. This is a form of labelled graph that can thus be searched using the subgraph-isomorphism algorithms that are widely used for searching databases of two-dimensional (2D) molecules. Several in-house and commercial systems have been developed for 3D database searching that are based on such techniques. These systems are reviewed and their effectiveness demonstrated by examples of their use in the discovery of novel, biologically active molecules. Current systems represent a molecule by one or a small number of low-energy conformations and there is hence much interest in the development of representational techniques and searching algorithms that account for the full set of geometric arrangements that can be adopted by a flexible molecule.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/cem.1180060602
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    Masthead (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992) 
    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.340120101
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    Metal ion stabilization of the conformation of a recombinant 19-kDa catalytic fragment of human fibroblast collagenase (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 42-48 
    Details
    ISSN: 0887-3585
    Keywords: calcium ; zinc ; tryptophan fluorescence ; denaturation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A recombinant 19-kDa human fibroblast collagenase catalytic fragment modeled on a naturally occurring proteolytic product was purified from E. coli inclusion bodies. Following renaturation in the presence of zinc and calcium, the fragment demonstrated catalytic activity with the same primary sequence specificity against small synthetic substrates as the full-length collagenase. Unlike the parent enzyme, it rapidly cleaved casein and gelatin but not native type I collagen. Intrinsic fluorescence of the three tryptophan residues was used to monitor the conformational state of the enzyme, which underwent a 24-nm red shift in emission upon denaturation accompanied by quenching of the fluorescence and loss of catalytic activity. Low concentrations of denaturant unfolded the fragment while the full-length enzyme displayed a shallow extended denaturation curve. Calcium remarkably stabilized the 19-kDa fragment, zinc less so, while together they were synergistically stabilizing. Among divalent cations, calcium was the most effective stabilizer, EC50 ∼60 μM, and similar amounts were required for substrate hydrolysis. Catalytic activity was more sensitive to denaturation than was tryptophan fluorescence. Least sensitive was the polypeptide backbone secondary structure assessed by CD. These observations suggest that the folding of the 19-kDa collagenase fragment is a multistep process stabilized by calcium.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120106
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    Addendum (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 100-100 
    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.340120112
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    Conformational analysis of a 12-residue analogue of mastoparan and of mastoparan X (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 111-116 
    Details
    ISSN: 0887-3585
    Keywords: protein folding ; multiple minima problem ; peptide conformation ; energy calculation ; helices ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have investigated the conformational properties of a truncated analogue of mastoparan and of mastoparan X, both peptides from wasp venom. The electrostatically driven Monte Carlo method was used to explore the conformational space of these short peptides. The initial conformations used in this study, mainly random ones, led to α-helical conformations. The α-helical conformations thus found exhibit an amphipathic character. These results are in accord with experimental data from NMR and CD spectroscopy.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120204
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    Masthead (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992) 
    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.340120401
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    Helix packing of leucine-rich peptides: A parallel leucine ladder in the structure of Boc-Aib-Leu-Aib-Aib-Leu-Leu-Leu-Aib-Leu-Aib-OMe (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 324-330 
    Details
    ISSN: 0887-3585
    Keywords: X-ray diffraction analysis ; hydrogen bonds ; peptide conformation ; 310/α-helix transition ; antiparallel helix packing ; leucyl-leucyl interaction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The packing of peptide helices in crystals of the leucine-rich decapeptide Boc-Aib-Leu-Aib-Aib-Leu-Leu-Leu-Aib-Leu-Aib-OMe provides an example of ladder-like leucylleucyl interactions between neighboring molecules. The peptide molecule forms a helix with five 5→1 hydrogen bonds and two 4→1 hydrogen bonds near the C terminus. Three head-to-tail NH ċ O = C hydrogen bonds between helices form continuous columns of helices in the crystal. The helicial columns associate in an antiparallel fashion, except for the association of Leu ċ Leu side chains, which occurs along the diagonal of the cell where the peptide helices are parallel. The peptide, with formula C56H102N10O13, crystallizes in space group P212121 with Z = 4 and cell parameters a = 16.774(3) Å, b = 20.032(3) Å and c = 20.117(3) Å; overall agreement factor R = 10.7% for 2014 data with |Fobs| 〈 3σ(F); resolution 1.0 Å.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120404
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    Folding of RNase T1 is decelerated by a specific tertiary contact in a folding intermediate (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 171-179 
    Details
    ISSN: 0887-3585
    Keywords: folding mutant ; proline isomerization ; folding kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The replacement of tryptophan 59 of ribonuclease T1 by a tyrosine residue does not change the stability of the protein. However, it leads to a strong acceleration of a major, proline-limited reaction that is unusually slow in the refolding of the wild-type protein. The distribution of fast- and slow-folding species and the kinetic mechanism of slow folding are not changed by the mutation. Trp-59 is in close contact to Pro-39 in native RNase T1 and probably also in an intermediate that forms rapidly during folding. We suggest that this specific interaction interferes with the trans→cis reisomerization of the Tyr-38-Pro-39 bond at the stage of a native-like folding intermediate. The steric hindrance is abolished either by changing Trp-59 to a less bulky residue, such as tyrosine, or, by a destabilization of folding intermediates at increased concentrations of denaturant. Under such conditions folding of the wild-type protein and of the W59Y variant no longer differ. These results provide strong support for the proposal that trans→cis isomerization of Pro-39 is responsible for the major, very slow refolding reaction of RNase T1. They also indicate that specific tertiary interactions in folding intermediates do exist, but do not necessarily facilitate folding. They can have adverse effects and decelerate ratelimiting steps by trapping partially folded structures.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120210
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  • 147
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    Masthead (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992) 
    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.340120301
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    A method for determining the positions of polar hydrogens added to a protein structure that maximizes protein hydrogen bonding (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 266-277 
    Details
    ISSN: 0887-3585
    Keywords: computer program ; hydrogen bonds ; molecular dynamics ; computer modeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: An automated method for the optimal placement of polar hydrogens in a protein structure is described. This method treats the polar, side chain hydrogens of lysine, serine, threonine, and tyrosine and the amino terminus of a protein. The program, called NETWORK, divides the potential hydrogen-bonding pairs of a protein into groups of interacting donors and acceptors. A search is conducted on each of the local groups to find an arrangement which forms the most hydrogen bonds. If two or more arrangements have the same number of hydrogen bonds, the arrangement with the shortest set of hydrogen bonds is selected. The polar hydrogens of the histidyl side chain are specifically treated, and the ionization state of this residue is allowed to change, if this change results in additional hydrogen bonds for the local group. The program will accept Protein Data Bank as well as Biosym-format coordinate files. Input and output routines can be easily modified to accept other coordinate file formats. The predictions from this method are compared to known hydrogen positions for bovine pancreatic trypsin inhibitor, insulin, RNase-A, and trypsin for which the neutron diffraction structures have been determined. The usefulness of this program is further demonstrated by a comparison of molecular dynamics simulations for the enzyme cytochrome P-450cam with and without using NETWORK.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120305
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    Analysis of solvent structure in proteins using neutron D2O—H2O solvent maps: Pattern of primary and secondary hydration of trypsin (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 223-236 
    Details
    ISSN: 0887-3585
    Keywords: neutron D2O—H2O solvent difference maps ; neutron diffraction ; trypsin water structure ; density modification ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A method of determining the water structure in protein crystals is described using neutron solvent difference maps. These maps are obtained by comparing the changes in diffracted intensities between two data sets, one in which H2O is the major solvent constituent, and a second in which D2O is the solvent medium. To a good first approximation, the protein atom contributions to the scattering intensities in both data sets are equal and cancel, but since H2O and D2O have very different neutron-scattering properties, their differences are accentuated to reveal an accurate representation of the solvent structure. The method also employs a series of density modification steps that impose known physical constraints on the density distribution function in the unit cell by making real space modifications directly to the density maps. Important attributes of the method are that (1) it is less subjective in the assignment of water positions than X-ray analysis; (2) there is threefold improvement in the signal-to-noise ratio for the solvent density; and (3) the iterative density modification produces a low-biased representation of the solvent density. Tests showed that water molecules with as low as 10% occupancy could be confidently assigned.About 300 water sites were assigned for trypsin from the refined solvent density; 140 of these sites were defined in the maps as discrete peaks, while the remaining were found within less-ordered channels of density. There is a very good correspondence between the sites in the primary hydration layer and waters found in the X-ray structure. Most water sites are clustered into H-bonding networks, many of which are found along intermolecular contact zones. The bound water is equally distributed between contacting apolar and polar atoms at the protein interface. A common occurence at hydrophobic surfaces is that apolar atoms are circumvented by one or more waters that are part of a larger water network. When the effects on surface accessibility by neighboring molecules in the crystal lattice are taken into consideration, only about 29% of the surface does not interface ordered water. About 25% of the ordered water is found in the second hydration sphere. In many instances these waters bridge larger clusters of primary layer waters. It is apparent that, in certain regions of the crystal, the organization of ordered water reflects the characteristics of the crystal environment more than those of trypsin's surface alone.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120303
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    Recurrent αβ loop structures in TIM barrel motifs show a distinct pattern of conserved structural features (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 299-313 
    Details
    ISSN: 0887-3585
    Keywords: α/β-barrels ; protein structure ; loops ; molecular modeling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A systematic survey of seven parallel α/β barrel protein domains, based on exhaustive structural comparisons, reveals that a sizable proportion of the αβ loops in these proteins - 20 out of a total of 49 - belong to either one of two loop types previously described by Thornton and co-workers. Six loops are of the αβ1 type, with one residue between the α-helix and β-strand, and 13 are of the αβ3 type, with three residues between the helix and the strand. Protein fragments embedding the identified loops, and termed αβ connections since they contain parts of the flanking helix and strand, have been analyzed in detail revealing that each type of connection has a distinct set of conserved structural features. The orientation of the β-strand relative to the helix and loop portions is different owing to a very localized difference in backbone conformation. In αβ1 connections, the chain enters the β-strand via a residue adopting an extended conformation, while in αβ3 it does so via a residue in a near α-helical conformation. Other conserved structural features include distinct patterns of side chain orientation relative to the β-sheet surface and of main chain H-bonds in the loop and the β-strand moieties. Significant differences also occur in packing interactions of conserved hydrophobic residues situated in the last turn of the helix. Yet the α-helix surface of both types of connections adopts similar orientations relative to the barrel sheet surface. Our results suggest furthermore that conserved hydrophobic residues along the sequence of the connections, may be correlated more with specific patterns of interactions made with neighboring helices and sheet strands than with helix/strand packing within the connection itself. A number of intriguing observations are also made on the distribution of the identified αβ1 and αβ3 loops within the α/β-barrel motifs. They often occur adjacent to each other; αβ3 loops invariably involve even numbered β-strands, while αβ1 loops involve preferentially odd β-strands; all the analyzed proteins contain at least one αβ3 loop in the first half of the eightfold α/β barrel. Possible origins of all these observations, and their relevance to the stability and folding of parallel α/β barrel. Possible origins of all these observations, and their relevance to the stability and folding of parallel α/β barrel motifs are discussed.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120402
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    Primary mutations in calmodulin prevent activation of the Ca+ +-dependent Na+ channel in Paramecium (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 365-371 
    Details
    ISSN: 0887-3585
    Keywords: Amino acid sequence/methylated lysines/protein conformation/Ca+ +-dependent K+ channel/cam behavioral mutants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Paramecium tetraurelia behavioral mutant cam12 displays a “fast-2” behavioral phenotype: it fails to respond to Na+ stimuli. Electrophysiologically, it lacks a Ca+ +-dependent Na+ current. Genetics and DNA sequencing showed the primary defect of cam12 to be in the calmodulin gene (Kink et al., 1990). To correlate calmodulin structure and function in Paramecium, we elucidated the primary structure of cam12 calmodulin. Peptide sequencing confirmed the two point mutations predicted by the DNA sequence: a glycine-to-glutamate substitution at position 40 and an aspartate-to-asparagine substitution at position 50. Our results further showed that lysine 13 and lysine 115 were methylated normally in cam12. It is likely that the electrophysiological abnormalities of cam12 are a direct reflection of the amino-acid substitutions, as opposed to improper posttranslational modification.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120408
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    The molecular structure of UDP-galactose 4-epimerase from Escherichia coli determined at 2.5 Å resolution (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 372-381 
    Details
    ISSN: 0887-3585
    Keywords: protein structure ; X-ray crystallography ; NAD binding domain ; galactose metabolism ; nonstereospecific hydride transfer ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: UDP-galactose 4-epimerase catalyzes the conversion of UDP-galactose to UDP-glucose during normal galactose metabolism. The molecular structure of UDP-galactose 4-epimerase from Escherichia coli has now been solved to a nominal resolution of 2.5 Å. As isolated from E. coli, the molecule is a dimer of chemically identical subunits with a total molecular weight of 79,000. Crystals of the enzyme used for this investigation were grown as a complex with the substrate analogue, UDP-benzene, and belonged to the space group P212121 with unit cell dimensions of a = 76.3 Å, b = 83.1 Å, c = 132.1 Å, and one dimer per asymmetric unit. An interpretable electron density map calculated to 2.5 Å resolution was obtained by a combination of multiple isomorphous replacement with six heavy atom derivatives, molecular averaging, and solvent flattening.Each subunit of epimerase is divided into two domains. The larger N-terminal domain, composed of amino acid residues 1-180, shows a classic NAD+ binding motif with seven strands of parallel β-pleated sheet flanked on either side of α-helices. The seventh strand of the β-pleated sheet is contributed by amino acid residues from the smaller domain. In addition, this smaller C-terminal domain, consisting of amino acid residues 181-338, contains three strands of β-pleated sheet, two major α-helices and one helical turn. The substrate analogue, UDP-benzene, binds in the cleft located between the two domains with its phenyl ring in close proximity to the nicotinamide ring of NAD+. Contrary to the extensive biochemical literature suggesting that epimerase binds only one NAD+ per functional dimer, the map clearly shows electron density for two nicotinamide cofactors binding in symmetry-related positions in the dimer. Likewise, each subunit in the dimer also binds one substrate analogue.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120409
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    Functional significance of conserved amino acid residues (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 13 (1992), S. 38-40 
    Details
    ISSN: 0887-3585
    Keywords: bacteriophage lysozyme ; mutation ; protein evolution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A systematic study of single amino acid substitutions in bacteriophage T4 lysozyme permitted a test of the concept that conserved amino acid residues are more functionally important than nonconserved residues. Substitutions of amino acid residues that are conserved among five bacteriophage-encoded lysozymes were found to lead more frequently to loss of function than substitutions of nonconserved residues. Of 163 residues tested, only 74 (45%) are sensitive to at least one substitution; however, all 14 residues that are fully conserved are sensitive to substitutions. © 1992 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340130104
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    Modeling of substrate and inhibitor binding to phospholipase A2 (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 45-64 
    Details
    ISSN: 0887-3585
    Keywords: proteins ; active site ; computer simulations ; molecular mechanics ; molecular graphics ; structure ; binding energies ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Molecular graphics and molecular mechanics techniques have been used to study the mode of ligand binding and mechanism of action of the enzyme phospholipase A2. A substrate-enzyme complex was constructed based on the crystal structure of the apoenzyme. The complex was minimized to relieve initial strain, and the structural and energetic features of the resultant complex analyzed in detail, at the molecular and residue level. The minimized complex was then used as a basis for examining the action of the enzyme on modified substrates, binding of inhibitors to the enzyme, and possible reaction intermedite complexes. The model is compatible with the suggested mechanism of hydrolysis and with experimental data about stereoselectivity, efficiency of hydrolysis of modified substrates, and inhibitor potency. In conclusion, the model can be used as a tool in evaluating new ligands as possible substrates and in the rational design of inhibitors, for the therapeutic treatment of diseases such as rheumatoid arthritis, atherosclerosis, and asthma. © 1992 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340140107
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    Variability of conformations at crystal contacts in BPTI represent true low-energy structures: Correspondence among lattice packing and molecular dynamics structures (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 65-74 
    Details
    ISSN: 0887-3585
    Keywords: lattice packing effects ; multiple low energy atructures ; basic pancreatic trypsin inhibitor ; comparison of X-ray structures ; molecular dynamics comparisons ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The structure of five basic pancreatic trypsin inhibitor (BPTI) molecules are compared to establish the extent and nature of the conformational variability resulting from crystal packing effects. BPTI is an ideal system to evaluate such factors because of the availability of high resolution X-ray models of five different BPTI structures, each in a different crystal packing environment. Differences observed among the structures are found to be distributed throughout the olecules, although the regions that display most variability are associated with the loop structures (residues 14-17 and 24-29). The regions of structure that show the largest rms deviations from the mean of the five packing motifs correlate well with the presence of intermolecular contacts in the crystal lattice. For most of the molecules there is also a correspondence between a larger number of intermolecular contacts and systematically higher B-factors, although it is not appearent whether this is induced by the crystal contact or results from the fact that the contacts are made predominantly through surface loops. The conformational differences seen among the X-ray models constitute more than local shifts at the lattice contact surfaces, and in fact involve in some cases the making and breaking of intramolecular H-bonds. The magnitudes of the differences among packing models are significantly larger than those usually associated with changes induced by mutagenesis; for instance, the structural differences at the site of mutation observed on removing an internal disulfide from the molecule are significantly less than those associated with lattice contact effects. The crystal packing conformations are compared to representative structures of BPTI generated during a 96-psec molecular dynamics (MD) simulation. This comparison shows a high level of correspondence between the protein flexibility indicated by the X-ray and MD analyses, and specifically between those regions that are most variable. This suggests that the regions that show most variability among the crystal packing models are not artifacts of crystallization, but rather represent true low-energy conformers that have been preferentially selected by crystallization factors. © 1992 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140108
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    Erratum (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 13 (1992), S. 272-272 
    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.340130309
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  • 157
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    Detection of native-like models for amino acid sequences of unknown three-dimensional structure in a data base of known protein conformations (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 13 (1992), S. 258-271 
    Details
    ISSN: 0887-3585
    Keywords: protein folding ; protein modeling ; knowledge-based prediction ; molecular force field ; statistical mechanics ; globins ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We present an approach which can be used to identify native-like folds in a data base of protein conformations in the absence of any sequence homology to proteins in the data base. The method is based on a knowledge-based force field derived from a set of known protein conformations. A given sequence is mounted on all conformations in the data base andthe associated energies are calculated. Using several conformations and sequences from the globin family we show that the native conformation is identified correctly. In fact the resolution of the force field is high enough to discriminate between a native fold and several closely related conformations. We then apply the procedure to several globins of known sequence but unknown three dimensional structure. The homology of these sequences to globins of known structures in the data base ranges from 49 to 17%. Withone exception we find that for all globin sequences one of the known globinfolds is identified as the most favorable conformation. These results are obtained using a force field derived from a data base devoid of globins of known structure. We briefly discuss useful applications in protein structurlresearch and future development of our approach. © 1992 Wiley-Liss, Inc.
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    URL: http://dx.doi.org/10.1002/prot.340130308
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    Masthead (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992) 
    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.340140101
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    Probing β-lactamase structure and function using random replacement mutagenesis (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 29-44 
    Details
    ISSN: 0887-3585
    Keywords: in vitro mutagenesis ; antibiotic resistance ; protein structure-function ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A new analytical mutagenesis technique is described that involves randomining the DNA sequence of a short stretch of a gene (3-6 codons) and determining the percentage of all possible random sequences that produce a functional protein. A low percentage of functional random sequences in a complete library of random substitutions indicates that the region mutagenized is important for the structure and/or function of the protein. Repeating the mutagenesis over many regions throughout a protein gives a global perspective of which amino acid sequences in a protein are critical. We applied this method to 66 codons of the gene encoding TEM-1 β-lactamase in 19 separate experiments. We found that TEM-1 β-lactamase is extremely tolerant of amino acid substitutions: on average, 44% of all mutants with random substitutions function and 20% of the substitutions are expressed, secreted, and fold well enough to function at levels similar to those for the wild-type enzyme. We also found a few exceptional regions where only a few random sequences function. Examination of the X-ray structures of homologous β-lactamases indicates that the regions most sensitive to substitution are in the vicinity of the active site pocket or buried in the hydrophobic core of the protein. DNA sequence analysis of functional random sequences has been used to obtain more detailed information about the amino acid sequence requirements for several regions and this information has been compared to sequence conservation among several related β-lactamases. © 1992 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140106
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    Structural effects induced by mutagenesis affected by crystal packing factors: The structure of a 30-51 disulfide mutant of basic pancreatic trypsin inhibitor (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 75-87 
    Details
    ISSN: 0887-3585
    Keywords: basic pancreatic trypsin inhibitor ; disulfide mutant ; X-ray structure ; crystal packing effects ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The X-ray structure of the C30V/C51A disulfide mutant of basic pancreatic trypsin inhibitor (BPTI) has been analyzed at 1.6 Å resolution. The mutant crystallizes in a cell having two molecules in the asymmetric unit. The packing environments of these two molecules are quite different, allowing for an assessment of which among the observed structural changes result from the mutation and which are produced by lattice packing considerations. The removal of the 30-51 disulfide bridge has little apparent affect on the B-factors of segments of adjacent polypeptide chain, although there are distinct differences in the structure compared to wild-type BPTI crystal structures. Both of the two C30V/C51A molecules show differences at the mutation site when compared to another 30-51 disulfide mutant, C30A/C51A, presumably due to the larger steric bulk of a valine versus an alanine at residue 30. A comparison of the two independent C30V/C51A molecules indicates that there are significant differences between them even at the site of mutation. The description of the specific structural differences of each molecule differs in detail and suggests different conclusions about the nature of structural perturbation near 30-51. In addition, when these two molecules are compared to two different wild-type structures, which had been determined from different space groups, a somewhat different pattern of changes is observed. These findings indicate that crystal packing can influence the observed perturbations in mutant structures. © 1992 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140109
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    Monte carlo minimization with thermalization for global optimization of polypeptide conformations in cartesian coordinate space (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 102-109 
    Details
    ISSN: 0887-3585
    Keywords: force field ; Metropolis criterion ; methionine enkephalin ; polypeptide folding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A new minimization procedure for the global optimization is cartesian coordinate space of the conformational energy of a polypeptide chain is presented. The Metropolis Monte Carlo minimization is thereby supplemented by a thermalization process, which is initiated whenever a structure becomes trapped in an area containing closely located local minima in the conformational space. The method has been applied to the endogenous opioid pentapeptide methionine enkephalin. Five among 13 different starting conformations led to the same apparent global minimum of an in-house developed energy function, a type II′ reverse turn, the central residues of which are Gly-3-Phe-4. A comparison between the ECEPP/2 global minimum conformation of methionine enkephalin and the apparent one achieved by the present method shows that minimum-energy conformations having a certain similarity can be generated by relatively different force fields. © 1992 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140111
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    Masthead (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992) 
    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.340140201
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  • 163
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    Empirical solvation models in the context of conformational energy searches: Application to bovine pancreatic trypsin inhibitor (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 110-119 
    Details
    ISSN: 0887-3585
    Keywords: solvation ; Monte Carlo ; minimization ; protein folding ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Continuum solvation models that estimate free energies of solvation as a function of solvent accessible surface area are computationally simple enough to be useful for predicting protein conformation. The behaviour of three such solvation models has been examined by applying them to the minimization of the conformational energy of bovine pancreatic trypsin inhibitor.The model differ only with regard to how the constants of proportionality between free energy and surface area were derived. Each model was derived by fitting to experimentally measured equilibrium solution properties. For two models, the solution property was free energy of hydration. For the thrid, the property was NMR coupling constants. The purpose of this study is to determine the effect of applying these solvation models to the nonequilibrium conformations of a protein arising in the course of global searches for conformational energy minima. Two approaches were used: (1) local energy minimization of an ensemble of conformations similar to the equilibrium conformation and (2) global search trajectories using Monte Carlo plus minimization starting from a single conformation similar to the equilibrium conformation.For the two models derived from free energy measurements, it was found that both the global searches and local minimizations yielded conformations more similar to the X-ray crystallographic structures than did searches or local minimizations carried out in the absence of a solvation component of the conformational energy. The model derived from NMR coupling constants behaved similarly to the other models in the context of a global search trajectory. For one of the models derived from measured free energies of hydration, it was found that minimization of an ensemble of near-equilibrium conformations yielded a new ensemble in which the conformation most similar to the X-ray determined structure PTI4 had the lowest total free energy.Despite the simplicity of the continuum slvation models, the final conformation generated in the trajectories for each of the models exhibited some of the characteristics that have been reported for conformations obtained from molecular dynamics simulations in the presence of a bath of explicit water molecules. They have smaller root mean square (rms) deviations from the experimentally determined conformation, fewer incorrect hydrogen bonds, and slightly larger radii of gyration than do conformations derived from search trajectories carried out in the absence of sovlent. © 1992 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140112
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  • 164
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    Generation of a substructure library for the description and classification of protein secondary structure. II. Application to spectra-structure correlations in fourier transform infrared spectroscopy (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 440-450 
    Details
    ISSN: 0887-3585
    Keywords: protein ; conformation ; infrared ; spectroscopy ; amide I ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Fourier transform infrared spectroscopy has become well known as a sensitive and informative tool for studying secondary structure in proteins. Present analysis of the conformation-sensitive amide I region in protein infrared spectra, when combined with band narrowing techniques, provides more information concerning protein secondary structure than can be meaningfully interpreted. This is due in part to limited models for secondary structure. Using the algorithm described in the previous paper of this series, we have generated a library of substructures for several trypsin-like serine proteases. This library was used as a basis for spectra-structure correlations with infrared spectra in the amide I′ region, for five homologous proteins for which spectra were collected. Use of the substructure library has allowed correlations not previously possible with template-based methods of protein conformational analysis. © 1992 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140405
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    Generation of a substructure library for the description and classification of protein secondary structure. I. Overview of the methods and results (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 430-439 
    Details
    ISSN: 0887-3585
    Keywords: protein ; conformation ; secondary ; substructure ; template ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Protein secondary structure has been typically classified into four major classes - α-helices, extended strands, reverse turns, and loops. Available methods for secondary structure analysis utilize predefined structure templates to search for structural matches among proteins. By this approach a significant portion of a proteins backbone conformation is assigned to one of a limited number of conformations or, if unassigned, to random coil. To expand our ability to describe protein secondary structure, we have developed an algorithm that operates independently of a predefined structure template. The procedure uses two geometric descriptors, the linear distance and the backbone dihedral angle, to represent the conformation form the α-carbon coordinates. The algorithm functions by searching for conformationally equivalent, contiguous fragments without regard to secondary structural classification and is thus independent of the complexity of the backbone fold. The result is a library of conformationally equivalent structure fragments that exhibit some novel characteristics. The library contains features that reproduce the major secondary structure classes as well as defining conformations previously described only as random or undefined conformations. Additionally, the library defines several subclassifications of β-strands. We present here a validation of this method and a presentation and discussion of the most significant results. In a second study, we report the results of application of this method to spectra-structure correlations in Fourier transform infrared spectroscopy. © 1992 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140404
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    Application of a directed conformational search for generating 3-D coordinates for protein structures from α-carbon coordinates (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 465-474 
    Details
    ISSN: 0887-3585
    Keywords: conformational search ; directed searches ; α-carbon coordinates ; modeling ; structure prediction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A directed conformational search algorithm using the program CONGEN (ref. 3), which samples backbone conformers, is described. The search technique uses information from the partially built structures to direct the search process and is tested on the problem of generating a full set of backbone Cartesian coordinates given only α-carbon coordinates. The method has been tested on six proteins of known structure, varying in size and classification, and was able to generate the original backbone coordinates with RMSs ranging from 0.30-0.87Å for the α-carbons and 0.5-0.99Å RMSs for the backbone atoms. Cis peptide linkages were also correctly identified. The procedure was also applied to two proteins available with only α-carbon coordinates in the Brookhaven Protein Data Bank; thioredoxin (SRX) and triacyiglycerol acylhydrolase (TGL). All-atom models are proposed for the backbone of both these proteins. In addition, the technique was applied to randomized coordinates of flavodoxin to assess the effects of irregularities in the data on the final RMS. This study represents the first time a deterministic conformational search was used on such a large scale. © 1992 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140407
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    MD simulation of subtilisin BPN′ in a crystal environment (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 451-464 
    Details
    ISSN: 0887-3585
    Keywords: protein force field ; protein crystal ; protein hydration ; Ca2+ binding site ; molecular dynamics ; subtilisin ; computer simulation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this paper we present a molecular dynamics (MD) simulation of subtilisin BPN′ in a crystalline environment containing four protein molecules and solvent. Con-formational and dynamic properties of the molecules are compared with each other and with respect to the X-ray structure to test the validity of the force field. The agreement between simulated and experimental structure using the GROMOS force field is better than that obtained in the literature using other force fields for protein crystals. The overall shape of the molecule is well preserved, as is the conformation of α-helices and β-strands. Structural differences are mainly found in loop regions. Solvent networks found in the X-ray structure were reproduced by the simulation, which was unbiased with respect to the crystalline hydration structure. These networks seem to play an important role in the stability of the protein; evidence of this is found in the structure of the active site. The weak ion binding site in the X-ray structure of subtilisin BPN′ is occupied by a monovalent ion. When a calcium ion is placed in the initial structure, three peptide ligands are replaced by 5 water ligands, whereas a potassium ion retains (in part) its original ligands. Existing force fields yield a reliable method to probe local structure and short-time dynamics of proteins, providing an accuracy of about 0.1 nm. © 1992 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140406
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    Modeling the anti-CEA antibody combining site by homology and conformational search (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 483-498 
    Details
    ISSN: 0887-3585
    Keywords: CEA ; antibody ; CDR ; homology modeling ; canonical structures ; rotamers ; tweak ; conformational search ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A model for an antibody specific for the carcinoembryonic antigen (CEA) has been constructed using a method which combines the concept of canonical structure with conformational search. A conformational search technique is introduced which couples random generation of backbone loop conformations to a simulated annealing method for assigning side chain conformations. This technique was used both to verify conformations selected from the set of known canonical structures and to explore conformations available at the H3 loop in CEA ab initio. Canonical structures are not available for H3 due to its variability in length, sequence, and observed conformation in known antibody structures Analysis of the results of conformational search resulted in three equally probable conformations for H3 loop in CEA. Force field energies, solvation free energies, exposure of charged residues and burial of hydrophobic residues, and packing of hydrophobic residues at the base of the loop were used as selection criteria. The existence of three equally plausible structures may reflect the high degree of flexibility expected for an exposed loop of this length. The nature of the combining site and features which could be important to interaction with antigen are discussed. © 1992 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140409
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    Investigation of the function of mutated cellulose-binding domains of Trichoderma reesei cellobiohydrolase I (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 475-482 
    Details
    ISSN: 0887-3585
    Keywords: cellobiohydrolase ; cellulose degradation ; substrate binding ; cellulose-binding domain ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The function of the cellulosebinding domain (CBD) of the cellobiohydrolase I of Trichoderma reesei was studied by site-directed mutagenesis of two amino acid residues identified by analyzing the 3D structure of this domain. The mutant enzymes were produced in yeast and tested for binding and activity on crystalline cellulose. Mutagenesis of the tyrosine residue (Y492) located at the tip of the wedge-shaped domain to alanine or aspartate reduced the binding and activity on crystalline cellulose to the level of the core protein lacking the CBD. However, there was no effect on the activity toward small oligosaccharide (4-methylumbellifery1 β-D-lactoside). The mutation tyrosine to histidine (Y492H) lowered but did not destroy the cellulose binding, suggesting that the interaction of the pyranose ring of the substrate with an aromatic side chain is important. However, the catalytic activity of this mutant on crystalline cellulose was identical to the other two mutants. The mutation P477R on the edge of the other face of the domain reduces both binding and activity of CBHI. These results support the hypothesis that both surfaces of the CBD are involved in the interaction of the binding domain with crystalline cellulose. © 1992 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140408
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  • 170
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    Crystallization, sequence, and preliminary crystallographic data for an antipeptide Fab 50.1 and peptide complexes with the principal neutralizing determinant of HIV-1 gpl20 (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 14 (1992), S. 499-508 
    Details
    ISSN: 0887-3585
    Keywords: X-ray crystallography ; HIV-1 ; principal neutralizing determinant ; protein crystallization ; antipeptide antibody ; Fab sequence ; PEG crystallization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: X-ray quality crystals of an Fab fragment from an antipeptide monoclonal antibody (R/V3-50.1) that recognizes the principal neutralizing determinant (PND) of the gpl20 glycoprotein of human immunodeficiency virus type 1 (HIV-1) (MN isolate) were grown as uncomplexed and peptide complexed forms. Crystals of the free Fab grew from high salt in orthorhombic space groups P212121 and I222 and from polyethylene glycol in space groups P1 and P21. Seeds from either the P1 and P21 native (uncomplexed) Fab crystals induced nucleation of crystals of the Fab complexed to a 16-residue synthetic peptide corresponding to the PND when streak seeded into preequilibrated solutions of this complex. Data were collected from these complex crystals and from each of the four native Fab forms to at least 2.8Å resolution. The genes for the variable domain of the Fab were cloned and sequenced and the primary amino acid sequence was deduced from this information. Knowledge of the three-dimensional structure of this Fab-pep-tide complex will be important in the understanding of the PND of HIV-1 and its recognition by neutralizing monoclonal antibodies. © 1992 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340140410
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    CLIX: A search algorithm for finding novel ligands capable of binding proteins of known three-dimensional structure (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 31-41 
    Details
    ISSN: 0887-3585
    Keywords: computer-aided drug design ; database search ; molecular docking ; protein structure ; protein-ligand interactions ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A computer algorithm, CLIX, capable of searching a crystallographic database of small molecules for candidates which have both steric and chemical likelihood of binding a protein of known three-dimensional structure is presented. The algorithm is a significant advance over previous strategies which consider solely steric or chemical requirements for binding. The algorithm is shown to be capable of predicting the correct binding geometry of sialic acid to a mutant influenzavirus hemagglutinin and of proposing a number of potential new ligands to this protein.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/prot.340120105
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  • 172
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    Effects of eglin-c binding to thermitase: Three-dimensional structure comparison of native thermitase and thermitase eglin-c complexes (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 12 (1992), S. 63-74 
    Details
    ISSN: 0887-3585
    Keywords: subtilisin ; serine proteinase ; serine proteinase inhibitor ; induced-fit mechanism ; protein crystallography ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Thermitase is a thermostable member of the subtilisin family of serine proteases. Four independently determined crystal structures of the enzyme are compared in this study: a high resolution native one and three medium resolution complexes of thermitase with eglin-c, grown from three different calcium concentrations. It appeared that the B-factors of the thermitase eglin complex obtained at 100 mM CaCl2 and elucidated at 2.0 Å resolution are remarkably similar to those of the 1.4 Å native structure: the main chain atoms have an rms difference of only 2.3 Å2; for all atoms this difference is 4.6 Å2. The rms positional differences between these two structures of thermitase are 0.31 Å for the main chain atoms and 0.58 Å for all atoms. There results show that not only atomic positions but also temperature factors can agree well in X-ray structures determined entirely independently by procedures which differ in virtually every possible technical aspect.A detailed comparison focussed on the effects of eglin binding on the structure of thermitase. Thermitase can be considered as consisting of (1) a central core of 94 residues, plus (2) four segments of 72 residues in total which shift as rigid bodies with respect to the core, plus (3) the remaining 113 residues which show small changes but, however, cannot be described as rigid bodies. The central cores of native thermitase and the 100 mM CaCl2 thermitase:eglin complex have an rms deviation of 0.13 Å for 376 main chain atoms. One of the segments, formed by loops of the strong calcium binding site, shows differences up to 1.0 Å in Cα positions. These are probably due to crystal packing effects.The three other segments, comprising 51 residues, are affected conformational changes upon eglin binding so that the P1 to P3 binding pockets of thermitase broaden by 0.4 to 0.7 Å. The residues involved in these changes correspond with residues which change position upon inhibitor binding in other subtilisins. This suggests that an induced fit mechanism is operational during substrate recognition by subtilisins.
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    URL: http://dx.doi.org/10.1002/prot.340120108
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    Synthesis and characterization of poly(4-vinylpyridine) substituted with a novel betaine salt derived from 4,5-dicyanoimidazole (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 203-210 
    Details
    ISSN: 0887-624X
    Keywords: poly(4-vinylpyridine) ; 4,5-dicyanoimidazole ; betaine salt ; nucleophillic aromatic substitution ; polyelectrolyte ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel betaine internal salt (3) has been synthesized by the reaction of pyridine with 1-methyl-2-bromo-4,5-dicyanoimidazole (1). The reaction of pyridine with 1 serves as a model for the reaction of poly(4-vinylpyridine) with 1. The reaction of poly(4-vinylpyridine) with 1 gives betaine salt substituted polymers which were characterized by IR, NMR, UV-visible spectroscopy, and viscometry. The substituted polymers were compared to the model compound (3) and to unsubstituted poly(4-vinylpyridine) in order to determine polymer structure and the degree of substitution. One of the substituted polymers shows polyelectrolyte behavior. Thermal characterization of the substituted polymers shows two exothermic transitions at 260 and 340°C attributed to chemical reactions of the pendant groups.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080300204
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    An improved method for the diimide hydrogenation of butadiene and isoprene containing polymers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 397-408 
    Details
    ISSN: 0887-624X
    Keywords: hydrogenation ; diimide ; p-toluenesulfonylhydrazide ; polybutadiene ; polyisoprene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrogenation of unsaturated polymers with diimide generated in-situ by thermolysis of p-toluenesulfonyl hydrazide (TSH) is a commonly used method for preparing laboratory scale quantities of saturated diene based polymers. The by-products from TSH, particularly p-toluenesulfinic acid, can attack at olefinic sites, adding p-tolylsulfone functionality and degrading polymer molecular weight. The addition of tri-n-propyl amine has been found to eliminate these side reactions in butadiene containing polymers and copolymers, enabling the preparation of polymers devoid of backbone unsaturation. No detectable sulfur-containing impurities were indicated by IR, NMR, or elemental analysis, and no chain degradation was observed via GPC analysis of the hydrogenated polymers. cis-Polybutadiene and butadiene containing random and block copolymers with styrene were hydrogenated cleanly using this technique. A ratio of 2 mol TSH and 2 mol amine/mol of olefin was necessary to assure 〉 99% hydrogenation, and a w/v ratio of 2 parts butadiene/100 parts o-xylene gave the most efficient hydrogenation. Polymers prepared from isoprene were only partially hydrogenated when treated with TSH in the presence of tri-n-propyl amine, and gave evidence of slight degradation of the polymer structure.
    Additional Material: 15 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080300307
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    Preparation of large, uniform size temperature-sensitive hydrogel beads (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 505-507 
    Details
    ISSN: 0887-624X
    Keywords: hydrogel ; beads ; poly(N-isopropylacrylamide) ; LCST ; Ca-alginate ; 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.1992.080300318
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    Fast atom bombardment mass spectrometric analysis of the partial ozonolysis products of poly(isoprene) and poly(chloroprene) (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 525-532 
    Details
    ISSN: 0887-624X
    Keywords: ozonolysis ; poly(chloroprene) ; FAB-MS ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low molecular weight compounds formed by partial ozonolysis of poly(isoprene) and poly(chloroprene) were analyzed by fast atom bombardment mass spectrometry (FABMS). In the poly(chloroprene) case, the ozonized mixtures were treated with piperidine before the MS analysis to transform in amide end groups the reactive acyl chlorides formed by the cleavage of double bonds along the main chain. Only one family of compounds having carboxyl and ketone or carboxyl and amide end groups were obtained from the ozonolysis of poly(isoprene) and poly(chloroprene), respectively. The assigned structures were confirmed by FAB-MS analysis of the GPC separation fractions [poly(chloroprene)] or by FAB-MS of the KOH-doped ozonolysis mixtures [poly(isoprene)]. It has been also ascertained, by GPC experiments, that poly(chloroprene) decomposes more rapidly than poly(isoprene) and poly(butadiene).
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080300402
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    Inhibition of acrylic acid polymerization by phenothiazine and p-methoxyphenol. II. Catalytic inhibition by phenothiazine (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 569-576 
    Details
    ISSN: 0887-624X
    Keywords: acrylic acid ; phenothiazine ; p-methoxyphenol ; inhibition, mechanism of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Inhibition of acrylic acid by p-methoxyphenol fits a conventional stoichiometric mechanism but phenothiazine inhibits acrylic acid via a completely different, catalytic cycle which does not depend on the presence of oxygen. We propose that this mechanism may involve a pair of single electron transfer reactions between free radicals, phenothiazine N-radicalcation, and phenothiazine itself, the latter being cyclically regenerated. Arrhenius equations were derived for the rates of disappearance of inhibitor and oxygen in acrylic acid stabilized with phenothiazine and with p-methoxyphenol and also with phenothiazine in the absence of oxygen. The practical implication of high oxygen to p-methoxyphenol consumption ratios is quite important: if commercial acrylic acid (usually stabilized with p-methoxyphenol) is inadvertently heated during storage, the limiting substance determining the onset of polymerization will be the dissolved oxygen and not p-methoxyphenol unless oxygen (air) is being supplied to and dissolved in the liquid at a rate sufficient to overcome the rate of its consumption.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300407
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  • 178
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    Catalytic aminolysis of acrylic copolymers in solution and in the melt. II. Comparison between styrenic and ethylenic copolymers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 635-641 
    Details
    ISSN: 0887-624X
    Keywords: aminolysis ; catalysis ; mechanism ; kinetics ; tautomeric compound ; melt ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aminolysis of poly(styrene-co-methyl acrylate) (SMA) by octadecylamine in solution and in the melt has been reported in Part I. We now have studied the aminolysis of poly(ethylene-co-methyl acrylate) (EMA) with the same amine in the melt and compared the two sets of data in this paper. With EMA, the data confirmed and precised the catalytic mechanism proposed in Part I. The best tautomeric catalysts are the ones which form an eight-atom ring structure with the ester and amine groups. With EMA aminolysis is faster than with SMA because of the steric hindrance of phenyl groups in SMA. But EMA aminolysis remains a rather slow reaction. In a corotating twin-screw extruder the conversion was only around 4% at 220°C with a mean residence time of 150 s. It was also shown that the EMA/octadecylamine/catalyst system, like the SMA system, is homogeneous in the molten state at temperatures around 200°C.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300415
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  • 179
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    Poly(N-acylethylenimine) copolymers containing pendant pentamethyldisiloxanyl groups. II. Thermal behavior and x-ray diffraction study (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 659-669 
    Details
    ISSN: 0887-624X
    Keywords: oxazolines ; copolymers ; siloxane ; DSC ; WAXD ; poly(N-acylethyleneimines) ; heat of fusion ; intercalation ; siloxane ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two series of random copolymers of 10-(pentamethyl disiloxanyl) decyl oxazoline (Si) with undecyl (U) (four copolymer compositions) and nonyl (N) (eight copolymer compositions) oxazolines over the whole composition range, with a total degree of polymerization of about 100, were studied by DSC and wide angle X-ray diffraction. All the polymers are crystalline. For the N/Si copolymers, the melting points, normalized ΔH and ΔS of fusion are almost constant in a broad range of copolymer composition from 10 to 65 mol % of Si. The rationale for this behavior is that the copolymers crystallize two dimensionally, with the crystalline polymethylene plates separated by the bulky flexible pentamethyl disiloxanyl (P) groups. In this range, increasing Si only increases the distance between the plates. With more than 65 mol % Si, the bulky P groups interfere with the packing of the alkyl chains and change the crystallization behavior; the polymers show disordered packing as demonstrated by their X-ray patterns and extremely low ΔH. In the U/Si copolymers, since the undecyl side chain has one more carbon than the decyl group to which the P group is attached, the P groups interfere much more strongly with the packing of the side chains than in the N/Si polymers. The copolymer melting points uniformly decrease as the concentration of Si increases. The plateau on the plot of normalized ΔH versus polymer composition is only from 10 to 50 mol % of Si. The average long spacings of the annealed polymers increase linearly from 24 Å (N/Si polymers) or 28 Å (U/Si polymers) to 34.1 Å with the increase of Si up to 50%. With more than 50% Si, the polymers have an identical lamellar thicknesses of 34 Å, within the experimental error. Copolymers with less than 75 mol % of Si can crystallize from hexadecane solutions forming gels down to polymer concentrations of 2-3 wt %. The long spacings of the gels are almost identical with those of the pure crystalline polymers and independent of the polymer/solvent ratios. When hexamethyl disiloxane is added to the solutions, it can intercalate and the resulting crystalline gels have long spacings larger than those found in the absence of siloxane.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300418
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    Particle nucleation and monomer partitioning in styrene O/W microemulsion polymerization (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 691-702 
    Details
    ISSN: 0887-624X
    Keywords: microemulsion, styrene ; microemulsion, partitioning behavior (thermodynamics) ; microemulsion, polymerization ; microemulsion, nucleation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Particle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The low n̄ (less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300501
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    Molecular weight distribution in emulsion polymerization. I. The homopolymer case (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 731-750 
    Details
    ISSN: 0887-624X
    Keywords: emulsion homopolymerization ; molecular weight modeling ; molecular weight distribution ; Markov chains ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for evaluating the instantaneous degree of polymerization distribution of homopolymers produced in emulsion, based on the mathematics of the Markov chains, is developed. The model accounts for any number of active chains per particle, as well as for the two fundamental mechanisms of chain termination: mono- and bi-molecular, both by combination and by disproportionation. The core of the model is the so called subprocessmain process treatment, which allows us to correctly evaluate the degree of polymerization of the chains growing in the polymer particles, by distinguishing between the events experienced by the polymer chain which imply a change of its degree of polymerization (subject transitions) and those which imply only a change in the particle state (environment transitions). This is obtained by properly defining the one-step transition probability matrix of the relevant Markov process. Once this is done, the evaluation of the distribution of the degrees of polymerization reduces to a few simple operations among matrices. Explicit expressions for the instantaneous probability density functions and the relative cumulative distributions are obtained. The application of such relationships is facilitated by the numerical procedures reported in the Appendices. The results of the model developed in this work are in agreement with those of earlier models in the range of parameter values of practical interest. In the limit of very low molecular weights, only the model developed in this work provides the correct answer. Moreover, a much more significant result is its applicability to the case of emulsion copolymerization, as it is shown in Part II.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080300505
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    Photocrosslinking of polymers containing cationically polymerizable groups in the side-chain by sulfonium salts (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 933-936 
    Details
    ISSN: 0887-624X
    Keywords: photocrosslinking ; vinylether ; sulfonium salt ; cationic polymerization ; swelling ; 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.1992.080300525
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    Polymer science and technology of plastics and rubbers, by Premamoy Ghosh, Tata McGraw-Hill, New Delhi, India, 1990, 424 pp. (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 955-956 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300531
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  • 184
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    Effect of the reaction state on the polymerization of p-xylenesulfonium salts (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 977-982 
    Details
    ISSN: 0887-624X
    Keywords: p-xylenesulfonium salts ; polymerization of poly(phenylene vinylene) ; preparation of precursor polymer for poly(phenylene vinylene) ; anionic polymerization of p-xylenesulfonium salts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,4-Phenylenebis(methylene) sulfonium salts were polymerized under different conditions to yield p-xylylene sulfonium salt polyelectrolytes in a broad range of molecular weights. The aqueous reaction mixture formed a reversible gel at initial monomer concentrations higher than 1.0M, but at lower concentrations it remained as an emulsion until reaction completion. The effect of reaction time on intrinsic viscosities and polymer yields for both the emulsion and the gel state is discussed. The higher yields obtained when the reaction was carried out in the presence of a water-immiscible organic solvent were apparently due to the effect of this solvent on increasing the concentration of the reactive intermediate that led to the polyelectrolyte. Both the addition of an organic solvent and the variation of the initial monomer concentrations allowed some control over the molecular weight of the polyelectrolyte formed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300603
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    Polymerization behavior of 2,2,6,6-tetramethylpiperidinyl methacrylate: A monomer carrying a hindered amine group (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 983-988 
    Details
    ISSN: 0887-624X
    Keywords: copolymerization ; 2,2,6,6-tetramethylpiperidinyl methacrylate ; HALS ; copolymer structure ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Copolymers of 2,2,6,6-tetramethylpiperidinyl methacrylate (TPMA) with styrene (S) and with methyl methacrylate (MMA) were synthesized using AIBN as initiator. S-TPMA copolymers from feed ranging from 0.10-0.80 mole fractions TPMA and MMA-TPMA copolymers from feed of 0.04-0.85 mole fractions TPMA were used in the determination of monomer reactivity ratios r1, r2. Four different methods were employed in the calculations of r1 and r2 and all calculated results were in good agreement with each other. The structure of S-TPMA copolymers was inferred to be of an alternating nature while that of MMA-TPMA copolymers was random. Both copolymers are potential hindered amine light stabilizers (HALS) and are expected to be less extractable from, and more compatible with, polystyrene and poly(methyl methacrylate) base polymers.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300604
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    Liquid crystalline polyethers based on conformational isomerism. XIX.For Part XVIII, see Reference 26. Synthesis and characterization of flexible polyethers based on 1-(4-hydroxyphenyl)-2-(2-r-4-hydroxyphenyl) ethane with H, F, CH3, Br, Cl, and CF3 as R groups (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 997-1016 
    Details
    ISSN: 0887-624X
    Keywords: 1-(4-hydroxyphenyl)-2-(2-R-4-hydroxyphenyl)ethane (RBPE), with H, F, CH3, Cl, Br, CF3 as R groups, polyethers ; phase transitions ; molecular breadth ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 1-(4-hydroxyphenyl)-2-(2-fluoro-4-hydroxyphenyl)ethane (FBPE), 1-(4-hydroxyphenyl)-2-(2-chloro-4-hydroxyphenyl)ethane (CIBPE), 1-(4-hydroxyphenyl)-2-(2-bromo-4-hydroxyphenyl)ethane (BrBPE), and 1-(4-hydroxyphenyl)-2-(2-trifluoromethyl-4-hydroxyphenyl)ethane (CF3BPE), of the corresponding polymers based on 1,5-dibromopentane (RBPE-5), 1,8-dibromooctane (RBPE-8), and of the copolymers based on various ratios of 1,5-dibromopentane and 1,8-dibromooctane [RBPE-5/8(A/B)] is described. The phase transition temperatures and thermodynamic parameters of RBPE-5 and RBPE-8 polymers were compared to those of the corresponding polyethers based on 1,2-bis(4-hydroxyphenyl)ethane (BPE) and 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane (MBPE) which were reported previously. Both isotropic-nematic transition temperatures and corresponding thermodynamic parameters (i.e., enthalpy and entropy changes) decrease in the following order of the substituent R: H 〉 F 〉 CH3 〉 Cl 〉 Br 〉 CF3. This order corresponds to the increase of the breadth of the RBPE molecules, and agrees with the similar trends observed in low molar mass liquid crystals.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300606
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    Soluble polyarylenes containing alternating binaphthylene and biphenylene structural units (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1037-1049 
    Details
    ISSN: 0887-624X
    Keywords: soluble polyarylenes ; cation-radical polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the synthesis of a novel series of soluble polyarylenes containing alternating binapthylene and biphenylene structural units. They were obtained by the cation-radical polymerization of bis(1-naphthyl) biphenyls. The following monomers were synthesized and polymerized : 4,4′-bis(1-naphthyl) biphenyl (9), 3,3′-bis(1-naphthyl) biphenyl (10), 2,2′-bis(1-naphthyl)biphenyl (11), and 2,5-bis(1-naphthyl)biphenyl (14). All polymerizations were performed in nitrobenzene using FeCl3 as oxidant. Polymers with number average molecular weights of up to 4000 g/mol were obtained.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300609
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  • 188
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    Polyacrylamide gels formed with Cr+3 ion and Cr(acetate)3: Thermodynamically and kinetically controlled crosslinking reactions (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1071-1075 
    Details
    ISSN: 0887-624X
    Keywords: polymer gels ; polyacrylamide ; metal ion crosslinking ; enhanced petroleum recovery ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gelation of buffered aqueous Cr+3/polyacrylamide (PAAm) solutions has been studied over the pH range 2-11. With Cr+3 supplied as Cr(NO3)3 and a 7.5% hydrolyzed PAAm the upper limit for gelation was about pH 7, but Cr(acetate)3/PAAm solutions gelled as high as pH 9. Evidence is presented that the formation of unreactive colloidal Cr(OH)3(H2O)3, rather than polymer crosslinking, is favored thermodynamically for Cr+3/PAAm solutions at pH 〉 7. The crosslinks formed in Cr(acetate)3/PAAm solutions at pH 7-9 are deduced to be kinetically controlled products. Independent evidence for the kinetic stability of Cr+3/PAAm gels above pH 7 has also been obtained. Other observations relevant to the mechanism of crosslinking of PAAm with Cr(acetate)3 are described.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300612
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    Synthesis and phase-transfer catalytic activity of crown ethers bound to microporous polystyrene resins by oxyethylene spacers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1089-1097 
    Details
    ISSN: 0887-624X
    Keywords: polymer-supported monoazacrown ethers ; phase-transfer catalysis ; spacer ; cooperative coordination ; complexation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crown ethers bound to microporous polystyrene resins by oxyethylene spacers were prepared by the reaction of monoazacrown ethers with 2-tosyloxyethoxymethylated or 2-(2-tosyloxyethoxy)ethoxymethylated polystyrene resins crosslinked with 2 mol % of divinylbenzene. The activity of the immobilized lariat crowns for halogen exchange reactions under triphase conditions has been studied as a function of catalyst structure, loading, substrate structure, reagent structure, and solvent. The lariat catalysts with extra oxygen donors in the spacer chain exhibited higher activity than the corresponding immobilized catalysts without the donors in the spacer. The increased activity of the catalyst containing 15-crown-5 unit and two extra donors for the reaction of 1-bromooctane with KI was concluded to result from the enhanced complexation with the K+ ion, induced by the cooperative coordination of the crown unit donors and the donors in the spacer chain. The recovered catalysts could be re-used without decrease in activity.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/pola.1992.080300615
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    Improvements in compressive properties of high modulus fibers by crosslinking (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1111-1122 
    Details
    ISSN: 0887-624X
    Keywords: polymer fibers ; crosslinking ; compressive properties ; aramids ; polybenzobisthiazoles ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A facile method was developed for crosslinking stiff chain polymer fibers such as Kevlar® and polybenzobisthiazoles (PBZT). The method is based on thermolysis of active aryl halides contained in the polymer unit and coupling of the free radicals formed. The method worked well for the PBZT polymers and improvements in fiber single filament recoil stress and shear modulus were demonstrated. In the case of the polyamides chain cleavage apparently accompanied the crosslinking, limiting improvement in the recoil stress test. The mode of degradation appeared to be rearrangement of the amide linkage to isocyanate.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300618
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    Polymer drying. V. Intramolecular-rotor fluorescence studies of evaporation from liquid-saturated poly(styrene-co-divinylbenzene) (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1129-1143 
    Details
    ISSN: 0887-624X
    Keywords: adsorption ; desorption ; association ; roto-fluorescence ; probe ; polystyrene ; glass-transition ; polymer transitions ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fluorescence intensity and residual weight of poly(styrene-co-divinylbenzene) saturated with a 〈 0.003M solution of a intramolecular-rotor-fluorescent probe-molecule in a volatile liquid were monitored simultaneously as the system evaporated at 23°C to virtual dryness. The “breakpoints” in the pattern for fluorescence increase coincided with the “breakpoints” in the kinetics of desorption with respect to the number, αt of residual sorbed volatile molecules per phenyl group in the polymer, showing that both time-studies reflect the same physical changes in the system that occur reproducibly as αt decreases monotonically through α′s and α′g the compositions that signal respectively incipient elimination of volatile molecules immobilized by adsorption to polymer, and incipient transition of the system from the rubbery state to the glassy state. The fluorescence intensity attained its asymptotic limit before αt became equal to αg the composition identified earlier to be that which marks completion of the transition to the glassy state.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300620
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    Preparation of hindered piperidine and its copolymerization with propylene over a supported high activity ziegler-natta catalyst (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1163-1170 
    Details
    ISSN: 0887-624X
    Keywords: Ziegler-Natta ; propylene ; copolymerization ; covalently bound antioxidant ; hindered piperidine ; UV-stabilizer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new polymerizable stabilizer 4-(hex-5-enyl)-2,2,6,6-tetramethylpiperidine is prepared. This sterically hindered piperidine was copolymerized with propylene over a fourth generation TiCl4/MgCl2 Ziegler-Natta catalyst, using Al(C2H5)3 as cocatalyst and diphenyldimethoxysilane, DMS, as external electron donor. The copolymer exhibited high thermo-oxidative stability even after exhaustive extraction with n-heptane.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300623
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    Radical copolymerization of an electron-accepting monomer, methyl cis-β-cyanoacrylate, with styrene or acrylonitrile (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1187-1192 
    Details
    ISSN: 0887-624X
    Keywords: radical copolymerization ; electron-accepting monomer ; methyl cis-β-cyanoacrylate ; penultimate unit effect ; terpolymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron-accepting property and the radical copolymerizability of methyl cis-β-cyanoacrylate (MCA) were studied. The monomer was found to form a contact charge-transfer complex with styrene (ST) in chloroform at 25°C and behaved as a weak electron acceptor. The copolymerization parameters were determined in dioxane at 50°C for systems involving ST or acrylonitrile (AN) as comonomer. The reactivity ratio of ST or AN was estimated by the Kelen-Tudös method considering both the penultimate unit effect and no homopropagation of MCA. The penultimate effect for the system ST-MCA was large compared with that for the system ST-dimethyl maleate (DMM), indicating that a polar effect is mainly responsible for the penultimate effect. The terpolymerization of ST, MCA, and maleic anhydride (MA) was also studied to compare the reactivity of MCA with that of MA.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300626
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    Preparation and properties of fluorine-containing aromatic polyamides from trimethylsilyl-substituted tetrafluoro-m-phenylenediamine and aromatic dicarboxylic acid chlorides (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1203-1207 
    Details
    ISSN: 0887-624X
    Keywords: high temperature soluble polymers ; fluorinecontaining aramids ; thermal behavior ; tetrafluoro-m-phenylenediamine ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300629
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    Photodegradation of polyimides. III. The effect of chemical composition, radiation source, atmosphere, and processing (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1233-1245 
    Details
    ISSN: 0887-624X
    Keywords: polyimides ; photolysis ; fluorinated polymers ; ablation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymide films made from diarylanhydrides with oxygen, carbonyl, and hexafluoroisopropylidene 6F bridging groups are photolabile when irradiated with unfiltered light from a medium-pressure mercury lamp. The presence of oxygen is necessary to the photolytic degradation process, which results in the ultimate oxidative ablation of thin polyimide films. Films based on the 6F dianhydride containing a hexafluoroisopropylidene hinge group are the most unstable. However, photolysis of 6F dianhydride based polyimides in an inert atmosphere with either the unfiltered medium pressure mercury lamp or an electron beam results in no detectable changes even after long exposure times.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300702
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  • 196
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    Accessible new acrylic monomers and polymers as highly transparent organic materials (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1279-1286 
    Details
    ISSN: 0887-624X
    Keywords: fluorinated acrylic monomers ; optical fiber polymers ; materials for optoelectronics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical studies of intrinsic absorption phenomena in organic compounds in a range of wavelengths from visible to near-infrared (NIR), led us to synthesize acrylic monomers with variable molar number of CH per cubic centimeter, NCH. Thus, halogenoalkyl or aryl α-chloroacrylates, α-fluoroacrylates, and methacrylates are prepared. The corresponding homo- and copolymers exhibit good thermal (Tg from 120 to 160°C) and optical properties.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300705
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  • 197
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    Oxidations of alkenes catalyzed by a Mn(III) porphyrin and cationic polymer latexes (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1305-1313 
    Details
    ISSN: 0887-624X
    Keywords: latex ; emulsion ; polymerization ; catalysis ; oxidation ; epoxidation ; porphyrin ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three types of cationic polymer latexes were prepared by emulsion copolymerization of vinylbenzyl chloride, divinylbenzene and a third monomer, vinyl octadecyl ether, styrene, or n-decyl methacrylate, followed by quaternization with trimethylamine. The latexes had 44-71 nm diam and polydispersity indices of 1.06-1.10. Vinyl octadecyl ether did not copolymerize but hydrolyzed under the polymerization conditions to produce 1-octadecanol, which as a coemulsifier gave highly viscous latexes. The tetraanion 5,10,15,20-tetrakis-(2,6-dichloro-3-sulfonatophenyl) porphinatomanganese (III) chloride bound irreversibly to the cationic latexes and was an active catalyst for oxidations of alkenes by sodium hypochlorite and potassium peroxymonosulfate in the absence of added organic solvent. The porphyrin catalyst in the latexes was more active than in solution. Porphyrin catalysis gave epoxides concurrently with competing uncatalyzed hypochlorous acid oxidations to complex mixtures of allylic chlorides, allylic alcohols, α,β-unsaturated ketones, and chlorohydrins.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300708
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  • 198
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    Electrochemically initiated chain polymerization of pyrrole in aqueous media (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1315-1325 
    Details
    ISSN: 0887-624X
    Keywords: electrochemical polymerization ; polypyrrole ; conducting polymers ; electroactive polymers ; quartz crystal microbalance ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical quartz crystal microbalance has been employed to investigate the electropolymerization of pyrrole in a variety of aqueous electrolytes. In contrast to the generally accepted cation-radical coupling process for the electropolymerization of pyrrole, an electrochemically initiated chain polymerization, featuring a high polymerization rate and involving little charge transport, was found under specific conditions in the presence of ClO-4, BF-4, and PF-6 electrolytes. The more typical cation-radical coupling mechanism, characterized by a constant polymerization charge to mass deposited ratio, is observed in the presence of Cl-, NO-3, dodecyl sulfate, copper phthalocyanine tetrasulfonate, β-cyclodextrin tetradecasulfate, and poly(styrene sulfonate). Electrochemical characterizations of polypyrrole films prepared in aqueous ClO-4 electrolytes reveal that the polymer formed via chain polymerization exhibits the ability to transport both cations and anions during electrochemical switching between redox states, while the polymer synthesized through cation-radical coupling is only capable of transporting a single ionic species.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300709
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  • 199
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    Synthesis and properties of aromatic polyureas from N,N′-bis(trimethylsilyl)-substituted aromatic diamines and aromatic diisocyanates (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1363-1368 
    Details
    ISSN: 0887-624X
    Keywords: silylated aromatic polyureas ; aromatic polyureas ; N-silylated aromatic diamines ; aromatic diisocyanates ; solubility ; thermal behavior ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Silylated aromatic polyureas were synthesized by the polyaddition of N,N′-bis(trimethylsilyl)-substituted aromatic diamines to aromatic diisocyanates in various organic solvents at a temperature ranging from 30 to 100°C. Colorless and transparent films of the silylated polyureas were obtained by casting directly from these solutions in a dry nitrogen atmosphere. The silylated polyureas thermally decomposed at around 200°C and were easily desilylated with alcohol to convert to almost amorphous aromatic polyureas having inherent viscosities of 0.4-1.0 dL/g. The polyureas exhibited better solubility in organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide and had somewhat lower thermal decomposition temperatures (around 300°C) than the polyureas prepared by a conventional method from the parent aromatic diamines and diisocyanates.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300714
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  • 200
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    Synthesis and characterization of 1,3,4-thiadiazole-containing polyazomethines and copolyazomethines (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1375-1381 
    Details
    ISSN: 0887-624X
    Keywords: 1,3,4-thiadiazole ; polyazomethine ; conjugated polymer ; thermally stable polymer ; semiconductive polymer ; polycondensation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel 1,3,4-thiadiazole-containing polyazomethines and copolyazomethines were synthesized by the solution polycondensation, in m-cresol at 25°C, of aromatic dialdehydes, isophthalaldehyde and terephthalaldehyde, with 2,5-bis (m-aminophenyl)-1,3,4-thiadiazole (BMAT) and with BMAT and aromatic diamines, bis (4-aminophenyl) ether and 1,5-diaminonaphthalene, respectively. These polymers were tan yellow to yellow in color and had reduced viscosities up to 0.32 dL/g in concentrated sulfuric acid and electric conductivity as high as 10-9-10-11 S cm-1 at 25°C. All the polymers were insoluble in common organic solvents but dissolved completely in concentrated sulfuric acid and formic acid. However, they were readily hydrolyzed in concentrated sulfuric acid. X-ray diffraction diagrams showed that the crystallinity of polyazomethines were low, but copolyazomethines were highly crystalline. These azomethine polymers are highly thermally and thermooxidativelly stable and exhibited no appreciable decomposition up to 400°C in both air and nitrogen atmospheres. Doping with iodine dramatically raised the conductivity and produced the dark brown- to completely black-colored semiconductive polymers with a maximum conductivity of the order of 10-5 S cm-1. Electronic spectra of the undoped polymers indicated a large bathochromic shift of the π-π* absorption band (310 nm) due to C=N bonds of BMAT. This result suggests that π-electrons of the polymers are extensively delocalized along the main chain.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300716
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