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  • 1
    Electronic Resource
    Electronic Resource
    Effects of Regiochemical and Stereochemical Errors on the Course of Isotactic Propene Polyinsertion Promoted by Homogeneous Ziegler-Natta Catalysts (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 7538-7543 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00104a006
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  • 2
    Electronic Resource
    Electronic Resource
    Polymerization of 3-methyl-1-butene promoted by metallocene catalysts (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 589-597 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 3-Methyl-1-butene was polymerized in the presence of a number of homogeneous metallocene catalysts (co-catalyst methylalumoxane). Contrary to literature reports, it was found that even the simplest C2-symmetric metallocenes promote the isotactic polymerization of this monomer with reasonable productivities. Quite surprisingly, a prevailingly isotactic polymer was also obtained in the presence of Cs-symmetric metallocenes, which are instead syndiotactic-specific in propene polymerization.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1996.030170813
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of polymerization temperature on the microtacticity of isotactic poly(propylene) prepared using heterogeneous (MgCl2-supported) Ziegler-Natta catalysts (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1873-1878 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A study of the effect of polymerization temperature on the microtacticity of poly(propylene) prepared using various MgCl2-supported catalysts has shown that, in almost all cases, an increase in temperature leads not only to higher proportions of isotactic polymer but also to increased stereoregularity of the isotactic fraction. The results indicate a greater relative increase in productivity, with increasing temperature, for highly isospecific as opposed to moderately isospecific centres. It is suggested that easier propagation after the occasional regioirregular (2,1-) insertion may contribute to this effect.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Propene polymerization with MgCl2-supported catalysts: effects of using a diether as external donor (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 1181-1188 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 13C NMR analysis of poly(propylene) fractions of different tacticity, obtained using a catalyst system of type MgCl2/TiCl4/diisobutyl phthalate - AlEt3 - diether, has provided further evidence that the active species in this system are similar to those in which the ether is used as “internal” rather than “external” donor. Chain-end analysis of relatively low molecular weight polymer fractions indicated, for polymers of similar molecular weight, similar proportions of butyl-terminated chain-ends, indicative of chain transfer with hydrogen following regioirregular (2,1-) insertion. The relatively high hydrogen response of diether-containing catalyst systems can therefore be largely ascribed to this phenomenon, irrespective of whether the diether is used as internal or external donor. At relatively low hydrogen concentrations, chain transfer to hydrogen takes place predominantly after the occasional secondary insertion, while the additional presence of vinylidene chain-ends in certain xylene-soluble fractions indicates that chain transfer via β-H transfer takes place mainly after primary insertion.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980419
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  • 5
    Electronic Resource
    Electronic Resource
    Isotactic 1-butene polymerization promoted by C2-symmetric metallocene catalysts (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 1257-1270 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1-Butene polyinsertion promoted by two typical C2-symmetric zirconocene catalysts (i.e. rac-ethylenebis(1-indenyl)ZrCl2 (1) and rac-dimethylsilylbis(1-indenyl)ZrCl2) (2) was investigated under both hydrooligomerization and polymerization conditions and compared with that of propene. It was found that, in spite of a similar regiospecificity for the two monomers, the fraction of “dormant” sites is higher in 1-butene polymerization, as a result of a (much) lower reactivity of a 2,1 last-inserted unit. Accordingly, in the investigated cases, 2,1 units of 1-butene were not incorporated in the growing chains but either isomerized to 4,1 units or remained at the chain end until they underwent chain transfer via β-hydrogen elimination. Experimental evidence is also presented of an epimerization reaction of the growing poly(1-butene) chain with a 1,2 last-inserted unit, leading to a decrease of polymer stereoregularity with decreasing monomer concentration.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021980427
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of procatalyst composition on the stereospecificity of a Ziegler-Natta catalyst systemRevised manuscript of December 20, 1991. (1992)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 1463-1468 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In propylene polymerization with MgCl2/TiCl4/phthalate ester catalysts, using 2,2,6,6-tetramethylpiperidine as external donor, it has been found that the fraction of atactic polymer formed increased with decreasing ester content in the catalyst. At the same time, however, the stereoregularity of the isotactic polymer fraction, as measured by 13C NMR, increased. Polymerization in the absence of the external donor led to lower polymer yield and a lower stereoregularity of the isotactic fraction. The results indicate that the external donor is actively involved in the generation of isospecific sites, particularly in catalysts having relatively low ester contents.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1992.021930622
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  • 7
    Electronic Resource
    Electronic Resource
    Probabilistic multi-site modelling of propene polymerization using markov models (1993)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Theory and Simulations 2 (1993), S. 399-420 
    Details
    ISSN: 1018-5054
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Possible propagation mechanisms in propene polymerization using heterogeneous catalysts are described by combinations of Bernoulli and first- or even second-order Markov models. Both NMR-measured pentad fractions and GPC Gel permeation chromatography.-measured molecular weight distributions are directly taken into account to fit an appropriate propagation model for a specific catalyst. The analytical data so obtained have been used for an examination of the applicability of multi-site propagation models and for estimation of the main parameters in each model. The propagation and termination probabilities are estimated, as are “mix” parameters giving the fraction of the polymer population stemming from each kind of propagation mechanism. In this way the subpopulation produced by each site is characterized in terms of tacticity and molecular weight distribution. A three-site model is required to explain the measured data properly.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1993.040020310
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  • 8
    Electronic Resource
    Electronic Resource
    Application of conservation law to NMR measurements of poly(propylene) stereoregularity (1993)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Theory and Simulations 2 (1993), S. 385-398 
    Details
    ISSN: 1018-5054
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new method is presented for data reconciliation in the 13C NMR determination of the pentad distribution in regioregular poly(propylene). Deviations of experimentally measured data from mathematically derived conservation laws are corrected by a maximum-likelihood method. In this method some assumptions are made about the structure of the erros to obtain better estimates of the correct data. The validity of this procedure was demonstrated with Monte Carlo simulation, after which the method has been applied to real 13C NMR data to show what corrections may be obtained. Conservation laws for hexads and heptads are derived as well, for possible future use.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1993.040020309
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  • 9
    Electronic Resource
    Electronic Resource
    Hydrogen activation in propene polymerization with MgCl2-supported Ziegler-Natta catalysts: the effect of the external donor (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 167-172 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 13C NMR analysis of relatively low-molecular-weight polypropylenes prepared using the catalyst system MgCl2/TiCl4/phthalate ester-AlEt3-external Lewis base has revealed the presence of up to around 20% butyl (n-Bu) chain ends, indicative of regioirregular (2,1-) monomer insertion followed by chain transfer with hydrogen. The effect of hydrogen on catalyst activity depends on the nature of the external donor, and the results indicate that at least part of the observed increase in catalyst activity in the presence of hydrogen can be ascribed to the regeneration of active species via chain transfer at dormant (2,1-inserted) sites.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950114
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  • 10
    Electronic Resource
    Electronic Resource
    Regio- and stereospecificity in propene polymerization with MgCl2-supported Ziegler-Natta catalysts: effects of hydrogen and the external donor (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 1431-1437 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Investigation of the effects of hydrogen and different external donors on the stereoregularity and chain-end distribution of polypropylene prepared using MgCl2/TiCl4/phthalate ester-AlEt3-alkoxysilane catalyst systems has not only confirmed the importance of regiospecificity in relation to hydrogen activation but has also indicated a significant effect of stereospecificity. Alkoxysilanes giving high isospecificity also give high molecular weight polypropylene. Polymer stereoregularity also increases with increasing hydrogen concentration in polymerization. These effects indicate that not only regioirregular but also stereoiregular insertion slows down chain propagation. In each case the probability of chain transfer with hydrogen is higher than that following a stereoregular insertion, and in each case chain transfer with hydrogen leads to the regeneration of isospecific propagation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021960506
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