8.
In this contribution, the stereochemistry of propylene insertion/propagation reactions with a variety of
C
1 symmetric metallocene catalysts, containing bridged cyclopentadienyl-fluorenyl ligand for the preparation of highly stereoregular
polypropylene is presented. The impact of the distal substitutent’s size and composition and changes that the catalytic sites
undergo upon such substitution is elaborated. A comprehensive mechanism is proposed to explain the resulting catalytic changes
that bring about the irreversible
C
s/
C
1 site transformation and tactic behavior inversion. Furthermore the cyclopentadienyl’s combined distal/proximal and fluorenyl’s
frontal substituent effects on molecular weight, regio-, and stereoregularity of the final polymers are discussed. Finally,
stereoselectivities of
C
2 and
C
1 symmetric catalyst systems are compared. It is shown that current high performance
C
1 symmetric catalyst systems with central site chirality can be isotactic selective as well or even better in certain aspects
than the
C
2 symmetric bridged bisindenyl-based metallocene catalysts.
The text was submitted by the authors in English.
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