| 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 sec (CpRn)(CpR min m)MeQk wherein each Cp is a cyclopentadienyl or substituted cyclopentadienyl ring; each Rn and R min m is the same or different and is a hydrocarbyl radicals having 1-20 carbon atoms; R sec is a structural bridge between the two Cp rings imparting stereorigidity 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 </= k </= 3; 0 </= n </= 4; 1 </= m </= 4; and wherein R min m is selected such that (CpR min m) is a sterically different ring than (CpRn). |