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Abstract

The invention provides a metallocene catalyst for use in preparing syndiotactic polyolefins. The catalyst comprises a bridged metallocene in which one of the cyclopentadienyl rings is substituted in a substantially different manner from the other ring. It was discovered that this type of catalyst is highly syndiospecific, and it also produces a polymer with a novel microstructure. The invention further includes the use of one or more of the catalysts in a polymerization process. The catalyst is generally described by the formula R'(CpR.sub.n)(CpR'.sub.m)MeQ.sub.k wherein each Cp is a cyclopentadienyl or substituted cyclopentadienyl ring; each R.sub.n and R'.sub.m is the same or different and is a hydrocarbyl radicals having 1-20 carbon atoms; R' is a structural bridge between the two Cp rings imparting stereoigidity to the catalyst; Me is a group 4b, 5b, or 6b metal from the Periodic Table of Elements; each Q is a hydrocarbyl radical having 1-20 carbon atoms or is a halogen; 0.ltoreq.k.ltoreq.3; 0.ltoreq.n.ltoreq.4; 1.ltoreq.m.ltoreq.4; and wherein R'.sub.m is selected such that (CpR'.sub.m) is a sterically different ring than (CpR.sub.n).

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First Claim