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Molecular mechanics and mechanisms of regulation of the stereospecificity in Ziegler‐Natta catalysis
Author(s) -
Guerra Gaetano,
Corradini Paolo,
Cavallo Luigi,
Vacatello Michele
Publication year - 1995
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19950890130
Subject(s) - natta , stereospecificity , polymerization , catalysis , metallocene , homogeneous , propene , chemistry , monomer , mechanism (biology) , polymer chemistry , homogeneous catalysis , materials science , polymer science , thermodynamics , organic chemistry , polymer , physics , quantum mechanics
The model catalytic sites, proposed in our group for the homogeneous and heterogeneous stereospecific Ziegler‐ Natta polymerizations of olefins, are reviewed. For all the homogeneous metallocene‐based as well as for the heterogeneous catalytic models, a common mechanism of enantioselectivity is indicated by the study of the non‐bonded interactions. This mechanism of enantioselectivity, which involves a chiral orientation of the growing chain , is in agreement with a large number of experimental results for these catalytic systems. The model sites for the homogeneous isospecific polymerization of propene are also able to account for the observed enantioselectivities in the regioirregular placements. Recent calculations relative to a peculiar catalytic model site, which should present a polymerization mechanism involving a regular back‐skip of the chain, to the starting position after each monomer insertion, are shortly reviewed. The relevance of this polymerization mechanism to the comprehension of the stereospecificity of some homogeneous and heterogeneous catalytic systems is also briefly discussed.