Process for preparation of syndiotactic vinyl aromatic polymers

Claim 1

A process for preparing polymers of vinyl aromatic monomers having a high degree of syndiotacticity comprising contacting one or more vinyl aromatic monomers under polymerization conditions with a catalytically effective amount of a catalyst comprising a metal complex containing compound the formula: [Cp.sub.m MX.sub.n X'.sub.p ].sup.+ A.sup.- wherein: Cp is a single η 5 -cyclopentadienyl or η 5 -substituted cyclopentadienyl group, the substituted cyclopentadienyl group being optionally also bonded to M through a substituent: M is a metal of Group 3, 4, 5, 6, 8, 9, 10 or the Lanthanide Series of the Periodic Table; X each occurrence is an inert anionic ligand, with the proviso that at least one X is R: X' is an inert, neutral, donor ligand: R is hydride, hydrocarbyl, silyl, a combination thereof or a halo or alkoxy substituted derivative thereof having up to 20 carbon, silicon or carbon and silicon atoms: m and p are independently 0 or 1; n is an integer greater than or equal to 1, the sum of m and n is one less than the valence of M, or when Cp is optionally bonded to M through the substituent, the sum of m and n is two less than the valence of M; and A - is a noncoordinating, compatible anion of a Bronsted acid salt.