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article
meso- and rac-diastereomers of 1- and 2-tert-butyldimethylsiloxy-substituted ethylenebis(indenyl)zirconium dichlorides for formation of short- and long-chain branched polyethene
Abstract
Ethene was homo- and copolymerized over the methylaluminoxane (MBO) activated meso-and rac-diastereomers of 1- and 2-tert-butyldimethylsiloxy-substituted ethylenebis(indenyl)zirconium dichlorides (meso-1, rac-1, meso-2, rac-2) at 40 degreesC in toluene. Homopolyethenes produced at low ethene concentration under slurry conditions revealed significantly modified melt rheological properties resulting from long-chain branching (LCB). In addition, a small amount of ethyl branching was found in polyethenes produced with meso-1, rac-1, and meso-2. The meso-catalysts were found to have an excellent comonomer response; in the copolymerization of ethene with 1-hexene r(E)(meso-1) = 10 +/- 1 and r(E)(meso-2) = 11 +/- 1. Comonomer reactivity ratios indicate a strong preference toward formation of isolated comonomer units in the polymer chain. Chain termination occurs preferentially after regular 1,2-insertion of the comonomer, although irregular 2,1-insertions also inflict some chain terminations with the racemic catalysts but not with the meso-catalysts. In ethene homopolymerization, chain transfer to monomer is the prevailing chain transfer mechanism for all studied catalysts and results in a high vinyl end group selectivity.