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Abstract

A process for preparing syndiotactic vinyl aromatic polymers comprising contacting one or more aromatic monomers under polymerization conditions with a catalyst corresponding to the formula: [Cp.sub.m MX.sub.n X'.sub.p ].sup.+ A.sup.- wherein: Cp is a single .eta..sup.5 -cyclopentadienyl or .eta..sup.5 -substituted cyclopentadienyl group; 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 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 equal to the valence of M; and A.sup.- is a noncoordinating, compatible anion of a Bronsted acid salt.

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