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The role of intermediate chain migration in propene polymerization using substituted { i Pr(CpFlu)}ZrCl 2 /MAO catalysts
Author(s) -
Angermund Klaus,
Fink Gerhard,
Jensen Vidar R.,
Kleinschmidt Ralph
Publication year - 2000
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/(sici)1521-3927(20000201)21:2<91::aid-marc91>3.0.co;2-1
Subject(s) - tacticity , steric effects , alkyl , propene , catalysis , polymerization , polymer , polymer chemistry , chemistry , atmospheric temperature range , epimer , kinetic energy , activation energy , thermodynamics , materials science , crystallography , physics , stereochemistry , organic chemistry , quantum mechanics
Comparison of pentad distributions obtained from NMR spectra and from a molecular mechanics‐based modeling approach is performed for the catalysts { i Pr(3‐X‐CpFlu)}ZrCl 2 (X = H, Me, Et, i Pr, t Bu) at a range of different temperatures. In order to model the temperature dependency of the pentad distributions the variation in steric influence along with the change of the rotational energy level for catalysts with substituents displaying relatively low barriers to rotation is treated approximately by calculating energy profiles of 360° rotation of the alkyl groups. The temperature at which intermediate chain migration (back‐skip) or chain epimerization starts to be important seems to be rather constant (30–50°C) among the five catalysts. Even in the case of X = t Bu, back‐skip seems to be unimportant for explaining the formation of isotactic polymer at room temperature.