Catalyst systems for improved stereoselectivity and broader mole

Details Catalyst systems for improved stereoselectivity and broader mole Catalyst systems for improved stereoselectivity and broader mole

1994-04-06

2000-10-17

Wu, David W.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

526351, 5261243, 502125, C08F 464

Patent

active

061333859

ABSTRACT:
The present invention provides a catalyst system and a process for the polymerization of olefin that exhibits improved selectivity and broader molecular weight distribution in the polymer product. The catalyst system includes a conventional supported Ziegler-Natta catalyst in combination with a mixture of at least two electron donors, both having the general formula SiR.sub.m (OR').sub.4-m where R is selected from the group consisting of an alkyl group, a cycloalkyl group, an aryl group and a vinyl group; R' is an alkyl group; and m is 0-3, wherein when R is an alkyl group, R may be identical with R'; when m is 0, 1 or 2, the R' groups may be identical or different; and when m is 1, 2 or 3, the R groups may be identical or different. Preferably, one electron donor is described by the formula: ##STR1## wherein R.sub.1 and R.sub.4 are both an alkyl or cycloalkyl group containing a secondary or tertiary carbon atom attached to the silicon atom, R.sub.1 and R.sub.4 being the same;; R.sub.2 and R.sub.3 are alkyl or aryl groups, R.sub.2 and R.sub.3 being the same or different;
and the other electron is described by the formula: ##STR2## wherein R'.sub.1 is an alkyl or cycloalkyl group containing at least one primary, secondary or tertiary carbon atom attached to the silicon atom, R'.sub.2 and R'.sub.3 are an alkyl or aryl group, R'.sub.2 and R'.sub.3 being the same or different; and R'.sub.4 is an alkyl group with a primary carbon attached to the silicon atom, R'.sub.1 and R'.sub.4 being the same or different. This catalyst system produces polypropylene having xylene solubles of 1-7 to 5.1 wt % and a molecular weight distribution of about 10.

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