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Advances in propene polymerization using MgCl 2 ‐supported catalysts. Fundamental aspects and the role of electron donors
Author(s) -
Chadwick John C.
Publication year - 2001
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 - 10.1002/1521-3900(200108)173:1<21::aid-masy21>3.0.co;2-a
Subject(s) - tacticity , propene , catalysis , polymer , polymerization , stereoselectivity , polymer chemistry , hydrogen , molar mass distribution , ziegler–natta catalyst , copolymer , materials science , polypropylene , chemistry , organic chemistry
The fundamental factors determining the performance of state‐of‐the‐art MgCl 2 ‐supported catalysts for polypropylene are becoming increasingly evident. Polymer yield, isotacticity, molecular weight and molecular weight distribution are dependent on the regio‐ and stereoselectivity of the active species. Chain transfer with hydrogen after the occasional regioirregular (2,1‐) insertion has a strong effect on molecular weight and is the main reason for the high hydrogen response shown by high‐activity catalysts containing diether donors. Hydrogen response is also dependent on stereoselectivity. The probability of a stereo‐ or regioirregular insertion can be related to the lability of donor coordination in the vicinity of the active species. Results with different catalyst systems can be interpreted on the basis of a propagation model involving interconverting active species, such that polypropylene produced using MgCl 2 ‐supported catalysts can be regarded as a stereoblock polymer comprising (highly) isotactic sequences, moderately isotactic (isotactoid) sequences and syndiotactoid sequences. Strongly coordinating donors will give stereoregular polymers in which highly isotactic sequences predominate.