Patent ID: 6252019
Filing Date: 2001-06-26
Classification: C08F,Y10S

Abstract:
A process comprising the step of contacting, in a condensed phase, at least one alpha olefin monomer with at least one hafnocene catalyst/catalyst precursor of formula (I):ZR""Z'HfQ.sub.k A.sub.1 (I)where:(a) Z and Z' are the same or different and are a cyclopentadienyl containing ligand, at least one of which is a cyclopentadienyl containing ligand having at least one aromatic ring fused to the central cyclopentadienyl ring or a hetero atom analog of a cyclopentadienyl containing ligand;(b) R"" is structural bridge;(c) Q is a linear or branched alkyl radical, an aryl radical, an alkenyl radical, an alkylaryl radical, an arylalkyl radical or a halogen atom;(d) A is a counterion;(e) k is an integer having a value from 1 to 3;(f) l is an integer having a value from 0 to 2; and(g) Z and Z' have at least one .beta. substituent sterically larger than a hydrogen atom;(h) the ZR""Z' ligand system has C.sub.2 or near C.sub.2 symmetry; and(i) the process generates isotactic polymers having a melting point within about 5% of the value for a pure isotactic polymer and an isotactic selectivity above 90% for monomers capable of forming isotactic polymer units at a temperature greater than or equal to 50.degree. C. and at a pressure sufficient to maintain the contacting in the condensed phase.