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  • 11
    Electronic Resource
    Electronic Resource
    Magnesium chloride supported high mileage catalysts for olefin polymerization. XX. Solid state NMR (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 2321-2333 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Magic-angle spinning cross polarization solid state NMR spectra and relaxation data have been obtained for the MgCl2/ethyl benzoate (EB)/p-cresol (PC)/AlEt3 (TEA)/TiCl4 catalyst (CW) system following each stage of preparation. The change of chemical shifts of certain carbons in EB and their extremely short TH1 suggest strong complexation of EB with MgCl2 and that the EB is in a rigid physical state. The broad linewidths indicate dispersity in binding sites giving a range of chemical shifts. PC also forms a rigid complex with MgCl2 and has the effect of rendering the bound EB less rigid. Reaction between PC and TEA produces EtnAl (OC6H4Me)3-n species. The ethyl carbons cannot be observed by cross polarization or by a simple π/2 carbon polarization. Treatment with TiCl4 removes most but not all of the PC moieties by extraction and conversion of the aluminum compounds to AlCl3. The 13C-NMR of EB in the catalyst have chemical shifts like in MgCl2/EB.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280908
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  • 12
    Electronic Resource
    Electronic Resource
    Magnesium chloride supported high mileage catalysts for olefin polymerization. XXI. Isospecific and regiospecific vanadium catalyst for propylene polymerization (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 2609-2632 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several CW-V catalysts were prepared by supporting VCl4 on Mg Cl2 with ethyl benzoate and CH-V catalysts prepared by reacting MgCl2.ROH, phthalic anhydride, and VCl4. These vanadium catalysts, activated with TEA (triethyl aluminum)/MPT (methyl-p-toluate) produce mainly (88-96%) refluxing n-heptane insoluble isotactic PP. The active site has \documentclass{article}\pagestyle{empty}\begin{document}$ k_{p,i} = 1580 \left( M {\rm s} \right)^{ - 1}, k_{tr,i}^{\rm A} = 2 \times 10^{ - 3} {\rm s}^{ - 1} , k_{tr}^{\rm H} = 3.8 \times 10^{ - 2} \left( {\rm torr} \right)^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{ - 1}$\end{document} for the isospecific ones and \documentclass{article}\pagestyle{empty}\begin{document}$ k_{p,a} = 58 \left( M {\rm s} \right)^{ - 1} ,k_{tr,a}^{\rm A} = 3 \times 10^{ - 3} {\rm s}^{ -1}$\end{document} for the nonspecific sites. Catalyst of VCl3 supported on MgCl2 has comparable productivity as the VCl4/MgCl2 catalyst but catalyst of VCl2 supported on MgCl2 exhibit only one-ninth of the productivity. Extensive comparison has been made between the CW-V and the CW-Ti systems which revealed striking similarities between their polymerization behaviors. MgCl2 exerts profound influence on the stereochemical control of the vanadium ion on its activity for monomer coordination and insertion.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080281003
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  • 13
    Electronic Resource
    Electronic Resource
    Olefin copolymerization with metallocene catalysts. II. Kinetics, cocatalyst, and additivesFor Part I, see References 1. (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1595-1601 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of ethylene/propylene copolymerization catalyzed by (ethylene bis (indeyl)-ZrCI2/methylaluminoxane) has been investigated. Radiolabeling found about 80% of the Zr to be catalytically active. The estimates for rate constants at 50°C are k11 = 1104 (Ms)-1, k12 = 430 (Ms)-1, k22 = 396 (Ms)-1,k21 = 1020 (Ms)-1, and kAtr,1 + kAtr.2 = 1.9 × 10-3 s-1. Substitution of trimethylaluminum for methylaluminoxane resulted in proportionate decrease in polymerization rate. The molecular weight of the copolymer is slightly increased by loweing the [Al]/[Zr] ratio, or addition of Lewis base modifier but at the expense of lowered catalytic activity and increase in ethylene content in the copolymer. Lowering of the polymerization temperature to 0°C resulted in a doubling of molecular weight but suffered 10-fold reduction in polymerization activity and increase of ethylene in copolymer.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291108
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  • 14
    Electronic Resource
    Electronic Resource
    Olefin copolymerization with metallocene catalysts. I. Comparison of catalysts (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1585-1593 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of metallocene/methylaluminoxane (MAO) catalysts have been compared for ethylene/propylene copolymerizations to find relationship between the polymerization activities, copolymer structures, and copolymerization reactivity ratio with the catalyst structures. Stereorigid racemic ethylene bis (indenyl) zirconium dichloride and the tetrahydro derivative exhibit very high activity of 10 7 g (mol Zr h bar)-1, giving copolymers having comonomer compositions about the same as the feed compositions, molecular weights increasing with the increase of ethylene in the feed, random incorporation of comonomers, and narrow molecular weight distribution indicative of a single catalytic species. Nonbridged bis (indenyl) zirconium behaved differently, favoring the incorporation of ethylene over propylene, producing copolymers whose molecular weight decreases with the increase of ethylene in the feed, broad molecular weight distribution, and a methanol soluble fraction. This catalyst system contains two or more active species. Simple methallocene catalysts have much lower polymerization activities. CpTiCl2/MAO produced copolymers with tendency toward alternation, whereas Cp2HfCl2/MAO gave copolymer containing short blocks of monomers.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291107
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  • 15
    Electronic Resource
    Electronic Resource
    Ethylene-hexene copolymerization by heterogeneous and homogeneous Ziegler-Natta catalysts and the “comonomer” effect (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 227-237 
    Details
    ISSN: 0887-624X
    Keywords: olefin copolymerization ; Ziegler-Natta catalyst ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homopolymerization of ethylene and 1-hexene and their copolymerizations were compared to investigate the influence of α-olefin on the enhancement of ethylene polymerization rate (Rp), which is often referred to as the “comonomer” effect. With the two homogeneous Ziegler-Natta catalysts, Et[Ind]2ZrCl2/MAO and (π-C5H5)2ZrCl2/MAO (MAO = methylaluminoxane), hexene causes reduction of Rp - in other words a negative “comonomer” effect. In the case of the high activity MgCl2 supported TiCl3 catalysts there is a slight positive “comonomer” effect; the Rp increases by 25 to 70% with the addition of 15 mol % of hexene. The “comonomer” effects in there catalyst systems are much smaller than that observed for the classical TiCl3 catalyst. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310127
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  • 16
    Electronic Resource
    Electronic Resource
    Hexene-1 polymerization by homogeneous zirconocene and heterogeneous-supported TiCl3 catalysts (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 1747-1754 
    Details
    ISSN: 0887-624X
    Keywords: zirconocene ; supported TiCl3 ; Ziegler-Natta catalysts ; hexene polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MgCl2-supported TiCl3 catalysts, with and/or without electron donor modifier (internal Bi or external Be), were compared with rac-ethylenebis(indenyl)zirconium dichloride (1) activated with either MAO or the cation forming agent, triphenyl carbenium tetrakis(pentafluorophenyl)borate (2), with triethylalumium (TEA). The activities of the heterogeneous catalysts depend on the presence or absence of the Lewis base, were relatively insensitive to the temperature of polymerization, and produce poly(hexene) with molecular weights up to 106. The 1/MAO catalyst has about five times higher activity at 50°C but is almost inactive at -30°C; the overall activation energy is 12.4 kcal mol-1. In contrast, the activity for hexene polymerization by the 1/2/TEA catalyst is actually slightly greater at lower temperature. The MW's of poly(hexene) obtained with the zirconocenium catalysts are only in the tens of thousands because of rapid β-hydride elimination by the electrophilic cationic Zr center. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310713
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  • 17
    Electronic Resource
    Electronic Resource
    Michaelis complexes of porcine pancreatic elastase with 7-[(alkylcarbamoyl)amino]-4-chloro-3-ethoxyisocoumarins: Translational sampling of inhibitor position and kinetic measurements (1992)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 13 (1992), S. 141-151 
    Details
    ISSN: 0887-3585
    Keywords: serine protease ; MNDO Hamiltonian ; SCF charges ; energy minimization ; dissociation constant ; inhibitor design ; catalytic mechanism ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A step leading to the formation of the covalent complexes between porcine pancreatic elastase (PPE) and 7-[(alkylcarbamoyl)amino]-4-chloro-3-ethoxyisocoumarins (alkylHNCO-EICs) is the formation of the non-covalent Michaelis complex. No average structures are available for the Michaelis complexes of PPE with alkylHNCO-EICs. We present the results of an initial step in obtaining these structures and have determined kinetic constants as well. The kinetic results indicate that formation of the Michaelis complex is what differentiates the effectiveness of these inhibitors in inactivating PPE. The structural and kinetic results together suggest that the structure of the Michaelis complex is necessary for the design of potent alkylHNCO-EIC inhibitors of PPE. Two novel alkylHNCO-EICs are predicted to be the best inhibitors of this series. An alternate mechanism for serine protease inhibition is also proposed. Evidence for, and studies that may add support to, the hypothesized mechanism are discussed. © 1992 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prot.340130207
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  • 18
    Electronic Resource
    Electronic Resource
    Metallocene-methyl aluminoxane catalysts for olefin polymerization. VIII. Infrared spectra of anisotactic polypropyleneFor Part VII, see Ref. 1. (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 2907-2915 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polypropylenes obtained with the homogeneous racemic ethylene bis(indenyl) zirconium dichloride/methyl-aluminoxane catalyst were fractionated by solvent extraction. The IR absorbance ratios, A998/A973 and A841/A973, were found to vary linearly with the homosteric sequence population, [m m m m] and [m m]. These results are compared with the results of a similar study by Burfield and Loi on commercial and laboratory polypropylenes of the conventional types.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080281102
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  • 19
    Electronic Resource
    Electronic Resource
    Polymer precursor synthesis of alumina fibers (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 495-503 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High strength alumina fibers were fabricated with a polymer precursor process which was monitored with 13C-NMR, elemental analysis, gas evolution, SEM, and X-ray diffraction. Methylaluminoxane was chain extended by reaction with H2O, the unreacted methyl groups were converted to propanoyloxyl and i-propanoyl groups in molar ratios of 0.2 : 0.8 to 0.4 : 0.6 to afford spinning dope of adequate fluidity which can be spun into filaments with suitable stability. These precursor fibers were hydrolyzed in two stages at ambient temperatures and at 320-350°C, and then calcined at 950°C. The resulting alumina fibers have average tensile strengths up to 1.1 GPa and modulus of greater than 140 GPa.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290406
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  • 20
    Electronic Resource
    Electronic Resource
    Olefin copolymerization with metallocene catalysts. III. Supported metallocene/methylaluminoxane catalyst for olefin copolymerizationFor Parts I and II, see References 1. (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1603-1607 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Supported catalyst for fluidized bed polymerization processes has been prepared by reacting macroporous SiO2 first with MAO (methylaluminoxane) and then with Et [Ind]2ZrCl2. It contains 0.60 wt % of Zr and an [Al]/[Zr] ratio of 50. This catalyst produces homogeneous E/P (ethylene/propylene) copolymers with truly random copolymerization behaviors and required to achieve the same copolymerization activity for the Et[Ind]2ZrCl2/MAO would be required a total [Al]/[Zr] of only 670. Several time larger amount of MAO would be required to achieve the same copolymerization activity for the Et [Ind]2ZrCl2/MAO catalyst in solution. This random copolymerization is independent of catalyst concentration and composition. Activation of the supported catalyst with i-butylaluminoxane, tri-i-butylaluminum, or trimethylaluminum resulted in lower activity and copolymers having high ethylene content and crystallinity.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291109
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