| abstract |
The invention provides a metallocene catalyst for use in preparing syndiotactic/isotactic block 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 and the cyclopentadienyl rings have lack of bilateral or pseudo-bilateral symmetry. The catalyst comprises a metallocene compound generally described by the formula R''(C5R4)(C4R'4C5C4R'4)MeQp wherein (C5R4) is a substituted cyclopentadienyl ring; (C4R'mC5C4R'n) is a fluorenyl ring or substituted fluorenyl ring; each R and R' is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, and alkoxy alkyl or an alkylamino radical, each R and R' may be the same or different; (C5R4) has a lack of bi-lateral symmetry; R'' is a structural bridge between the (C5R4) and (C4R'4C5C4R'4) rings to impart stereorigidity and, preferably, is a hydrocarbyl biradical having at least one carbon atom to form the bridge; Q is a hydrocarbyl radical, such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements; and p is the valence of Me minus 2. This catalyst is syndio-/iso-specific and produces a syndiotactic/isotactic block polymer. |