Process for preparation of syndiotactic vinyl aromatic polymers

Claim 1

A process for preparing a syndiotactic polymer of a vinyl aromatic monomer said process comprising contacting a polymerizable vinyl aromatic monomer under polymerization conditions with a catalyst characterized. in that the catalyst comprises a metal complex of the formula: [Cp m MX n X′ p ]⁺A⁻ wherein: Cp is a single η⁵-cyclopentadienyl group which may optionally also be 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; each X independently is an inert anionic ligand or a group of formula R, with the proviso that at least one X is R; X′ is an inert, neutral donor ligand; each R independently is hydride, or ls hydrocarbyl or silyl, optionally substituted with one or more halogen atoms or alkoxy groups, and having up to 20 carbon and/or 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.