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  • Polymer and Materials Science  (184)
  • Life and Medical Sciences  (76)
  • Chemical Engineering  (52)
  • 1
    Electronic Resource
    Electronic Resource
    Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2049-2056 
    Details
    ISSN: 0887-624X
    Keywords: metallocenes ; olefin polymerizations ; Ziegler-Natta catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propylene was polymerized with rac-ethylene-bis (1-η5-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; 13C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321106
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  • 2
    Electronic Resource
    Electronic Resource
    Superactive and stereospecific catalysts. IV. Influence of structure of esters on MgCl2 supported olefin polymerization catalystsPart III of this series: J. C. W. Chien and Y. Hu, J. Polym. Sci. Polym. Chem. Ed., in press. (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 273-284 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CH-type catalysts were prepared by reacting MgCl2 · ROH, where ROH is 2-ethyl hexanol (EH), (R)-2-octanol (R-20), and (S)-2-octanol (S-20), with TiCl4 in the presence of di-i-butyl phthalate (BP), di-i-butyl terephthalate (BT), (-)-dimenthyl phthalate (MP), or (-)-dimenthyl terephthalate (MT). The MT catalysts were found to incorporate 8.9 to 13% Ti whereas the BP catalysts contain only 1.9 to 2.6% Ti. Comparison of the CH(EH, BP) and CH(EH, MT) catalysts showed that they have about equal number of isospecific active sites per gram of catalyst and the same rate constants of propagation for their nonspecific sites, however, the isospecific sites in the latter are less active by comparison. Consequently, the CH(EH, BP) catalysts is five times more active than the CH(EH, MT) catalysts and produces polypropylene which is 97% isotactic (reflux n-heptane insoluble) as compared to 84.7% for the latter. The catalysts derived from 2-octanols are much less active than the corresponding catalysts prepared with 2-ethyl hexanol due to lack of reactivity with phthalic anhydride which permits excessive incorporation of TiCl4 to form nonstereospecific catalytic sites as well as inactive Ti species.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080280204
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  • 3
    Electronic Resource
    Electronic Resource
    Solid-State NMR characterization of a superactive supported ziegler-natta catalystThis is Part XXXI of the series on MgCl2-supported Ziegler-Natta catalyst. Part XXX was: J. Vizzini, F. Ciardelli, and J. C. W. Chien, “Stereoselective Polymerization of α-Olefins by Heterogeneous Chiral Ziegler-Natta Catalysts,” Macromolecules, 25, 3199 (1992). (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 2173-2179 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The formation of CH-type catalysts has been investigated by high-resolution and solid-state NMR. These catalysts are prepared from a soluble MgCl2 and 2-ethyl-1-hexanol adduct (MgCl2·3EH) by reaction with phthalic anhydride (PA) to form dioctylphthalate (DOP) and then with TiCl4 in the presence of di-i-butylphthalate (BP). In the model systems MgCl2·3EH/PA, MgCl2/BP, and MgCl2/TiCl4/BP, the ester is complexed with MgCl2 and /or TiCl4 in two or more states. Only single-ester C=O and OCH2 resonances are seen in TiCl4/BP, probably due to exchange of ester coordinations. CH-catalysts prepared by three different procedures exhibit a single mode of bonding for the ester. The chemical shift values are consistent for ester complexed with MgCl2. The most active and stereoselective catalyst has the most shielded chemical shift values for the C=O and  - OCH2 -  carbons, shortest TH1 and TH1p, and longest TCH relaxation times. These parameters change monotonically with the decrease of activity and stereoselectivity of the catalyst preparation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070481211
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  • 4
    Electronic Resource
    Electronic Resource
    Difference in stereoselective polymerization of 4-methyl-1-hexene by homogeneous and heterogeneous Ziegler-Natta catalysts (1992)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 13 (1992), S. 479-484 
    Details
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1992.030131101
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  • 5
    Electronic Resource
    Electronic Resource
    Magnesium chloride-supported high-mileage catalysts for olefin polymerization XI. Determinations of poly(decene-1) molecular weight chain dimension and thermal transitions (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 24 (1986), S. 2217-2230 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Decene-1 was polymerized with the CW catalyst and fractionated by precipitation technique. Light-scattering and viscometric measurements on these fractions established the relationship [η] = 5.19 × 10-3 Mw0.77. The unperturbed mean square end-to-end distance is (〈Ro2〉/M)1/2 = (6.17 ± 0.34) × 10-9. Light-scattering data is consistent with a relatively stiff molecule with length of L = 1.75 × 10-5 cm for poly(decene-1) with MW = 397,000. Its mean square radius of gyration 〈Rg2〉 is 2.79 × 10-11 cm.2 The ratio of L2/〈Rg2〉 = 11 is close to the theoretical ratio of 12 for this kind of macromolecule.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1986.080240916
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  • 6
    Electronic Resource
    Electronic Resource
    A mechanistic study of polyimide formation from diester-diacids (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 2175-2183 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous work by a number of researchers has noted the presence of anhydride during the imidization step of polyimide polymer processing from diester-diacids and diamines. This has been often, and incorrectly, dismissed as being due to the reversion of the intermediate amide-acid. Comparison of the relative rates of reactions among model compounds demonstrates the intermediacy of anhydride in the imidization reaction. When creation of the anhydride is blocked, the production of amide-acid is greatly slowed. Infrared and NMR observations of mixtures of monomers confirm the production of anhydride as a necessary intermediate in the imidization reaction occuring during the production of polyimide polymers from diester diacids.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250814
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  • 7
    Electronic Resource
    Electronic Resource
    Magnesium chloride supported high-mileage catalysts for olefin polymerization. XVII. Effect of lewis base on propylene polymerization (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 2847-2870 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic study has been made on the functions of external Lewis base (Be, methyl-p-toluate, MPT) and internal Lewis base (Bi, ethyl benzoate, EB) for the CW-catalyst system MgCI2/EB/PC/AlEt3/TiCl4-AlEt3/MPT (PC, p-cresol). Bi is a nonstereoselective modifier. It increases the active site concentrations and rate constants of propagation, kp, of both the isospecific and nonspecific sites, and thus the productivities of the stereoregular and irregular polypropylenes by five- to tenfold. It seems that Bi complexes with the MgCl2 support to lower the electronegativity of the surface Mg atoms. It also acts to lower the rate constant of chain transfer to aluminum alkyl, kAtr, by two- to fourfold. The action of Be is highly stereospecific. The isotacticity index of polypropylene is ≫ 95% in the presence of Be but ≪ 68% without it. Addition of Be decreases nonspecific [Ti*]a by about (11 ± 2)-fold; there is only about a twofold reduction of the isospecific [Ti*]i. It decreases kp,a about three times but has no effect on kp,i, so that the latter is (21 ± 4) times the former. Be decreases kAtr,i for transfer with aluminum alkyl much more than it does to kAtr,a; but it does not affect the rates of chain transfer with monomer and by β-hydride elimination or the rate of catalyst deactivation. The number of active sites without Be is [Ti*]i = 15% and [Ti*]a = 55% for a total of 70%. In the presence of Be they are both about 6%. Optimum performance in propylene polymerizations requires both Bi and Be in the case of the CW-catalyst.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080251020
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  • 8
    Electronic Resource
    Electronic Resource
    Superactive and stereospecific catalysts. I. Structures and productivity (1988)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 26 (1988), S. 2003-2018 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two series of catalysts were made, one from MgCl2-A solution containing MgCl2, EH (2-ethylhexanol), and EB (ethyl benzoate) dissolved in decane and another from MgCl2-B solution containing MgCl2, EH, and phthalic anhydride which reacted to form the corresponding phthalic ester. Reactions of these solutions with TiCl4 with or without another ester produced a family of eight catalysts. They form two groups, one having monoesters as modifiers, and the other containing diesters as modifiers. The surface area, pore volume, x-diffractions, polymerization activity, and catalytic stereospecificity of these catalysts have been compared. The diester catalysts differ from the monoester catalysts in every respect. By comparison the corresponding member of the diester catalysts have half as much Ti per Mg, more than 10 times the pore volume, more than a 100-fold the surface area, about 50% more productivity, and greatly increased steroespecificity.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1988.080260802
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  • 9
    Electronic Resource
    Electronic Resource
    Metallocene-methylaluminoxane catalysts for olefin polymerization. I. Trimethylaluminum as coactivator (1988)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 26 (1988), S. 3089-3102 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ethylene was polymerized by Cp2ZrCl2-methylaluminoxane (MAO) catalysts where a portion of the MAO was replaced with trimethyl aluminum (TMA). At a total Al to Zr ratio of 1070, there is neither appreciable loss of productivity nor change in polymerization profile for TMA/MAO ≤ 10. The productivity is reduced only by two- to three-fold for TMA/MAO ≤ 100 accompanied by a 10 min induction period. Aging of this catalyst did not affect the induction period, but improves its productivity. The kinetic isotope effect for radiolabeling with tritiated methanol is 2.0. About 40% of the Zr is active for the catalyst with {99 [TMA] + 1[MAO]} to Zr ratio of 100. The rate constants for propagation and chain transfer were obtained. The mechanisms for the mixed TMA and MAO cocatalyst system are discussed. The results of this work have important practical significance. MAO is a hazardous material to synthesize and only in low yields. The replacement of 〉 90% of MAO with TMA represents a substantial saving since as much as 0.1M of the former is commonly used for a polymerization.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1988.080261117
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  • 10
    Electronic Resource
    Electronic Resource
    Superactive and stereospecific catalysts. II. Kinetics of propylene polymerizations (1988)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 26 (1988), S. 2973-2989 
    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 propylene polymerization by superactive CH-catalyst prepared from toluene solution of MgCl2 · EH/PA/TiCl4-TEA/PES was investigated. The results are compared with CW-catalyst prepared from crystalline MgCl2/EB/PC/TEA/TiCl4-TEA/MPT (abbreviations given in the text). The former is four times more active than the latter and produces more isotactic polypropylene. The CH-catalyst has 25% of the Ti as isospecific sites as compared to 6.7% for the CW-catalysts. These sites have the same rate constant of propagation so that the higher polymerization activity of the CH-catalyst is attributable simply to a greater number of active sites. Differences in the kinetics of deactivation and of chain transfer for the two catalysts are described.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1988.080261109
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