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A stereochemical and statistical analysis of metallocene‐promoted polymerization
Author(s) -
Farina Mario,
Di Silvestro Giuseppe,
Terragni Alberto
Publication year - 1995
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1995.021960125
Subject(s) - tacticity , metallocene , catalysis , polymerization , polymer chemistry , steric effects , chemistry , polymer , materials science , organic chemistry
The metallocene catalysts active in propylene polymerization can be divided into five classes, depending on whether the catalytic sites are chirotopic or not, and on the symmetry relationship between the catalytic sites bound to the same metal atom. Under the hypothesis of a purely alternating mechanism for propagation, class III and class IV catalysts, respectively, give rise to prevailingly isotactic and syndiotactic polymers. Four probabilistic schemes have been developed for interpreting the stereosequence distribution of polypropylene in terms of pentads. They take into account the two sources of steric control, chirotopicity of the catalyst site and configuration of the chain end, and the presence, besides the alternating mechanism, of successive addition steps at the same catalytic site.