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  • 11
    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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  • 12
    Electronic Resource
    Electronic Resource
    Aspects of hydrogen activation in propene polymerization using MgCl2/TiCl4/diether catalysts (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 2501-2510 
    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 the chain-end distribution of poly(propylenes) prepared using the highly active catalyst system MgCl2/TiCl4/diether - AlEt3 has revealed particularly high proportions of butyl chain-ends in polymers prepared at relatively low hydrogen pressures. This indicates that the high sensitivity of this type of catalyst to hydrogen, both with respect to catalyst activity and polymer molecular weight, can largely be ascribed to chain transfer following regioirregular (2,1-) insertion, such an insertion leading to a species having low activity in chain propagation. Isotactic stereoregularity increases with increasing hydrogen pressure, indicating that a stereoirregular insertion may also slow down the chain propagation, again leading to chain transfer and resulting in the conversion of a potential chain defect into an isobutyl chain-end. Analysis of highly isotactic polymer fractions isolated via temperature rising elution fractionation revealed the presence of both butyl and isobutyl chain-ends, indicating that even the most highly stereo-specific sites in MgCl2-supported catalysts are not totally regiospecific.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1996.021970814
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  • 13
    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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  • 14
    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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  • 15
    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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  • 16
    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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  • 17
    Electronic Resource
    Electronic Resource
    Electron attenuation lengths in Pb metal (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 11 (1988), S. 144-147 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Electron attenuation lengths have been measured for Pb metal in the energy range 300-1200 eV. The measurements were carried out by observing the attenuation produced in a substrate (Cu, Ag or Pd) XPS signal following adsorption of a single Pb monolayer. Attenuation lengths were estimated from these attenuation factors by means of a Lambert-Beer expression. The data are represented well by the least-squares expression λ = 0.78(±0.08)E1/2 (in Å).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740110304
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  • 18
    Electronic Resource
    Electronic Resource
    Isopiestic measurements of electrolyte activity - sky blue FF and sodium polymethacrylate (1958)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 28 (1958), S. 355-358 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Isopiestic measurements have been made on aqueous solutions of Sky Blue FF and of sodium polymethacrylate, and the relevant activity coefficients estimated.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1958.1202811710
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  • 19
    Electronic Resource
    Electronic Resource
    Relation between free radicals and ultraviolet absorption in poly(methyl methacrylate) (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 1679-1685 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A correlation between the radiation-induced nine-line electron spin resonance signal and the unstable component of the optical absorption in the near ultraviolet in poly(methyl methacrylate) is made on the basis of the radiation dose relationship, the dependence of production on irradiation temperature at a constant radiation dose, and on the fading of both signals on oxygen diffusion into the poly(methyl methacrylate) after irradiation. It is concluded that this correlation is applicable only immediately after irradiation and the stability of the initial radical is discussed with respect to the fading results. A process of radical decay and conversion is suggested to account for differences found in the fading characteristics of the two signals.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.150100609
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