Process and catalyst for producing syndiotactic polymers

A process for the syndiotactic propagation of a polymer chain derived from an ethylenically unsaturated monomer comprising:

• (a) providing a catalyst comprising an unbalanced metallocene cation and a stable noncoordinating counter anion for said metallocene cation, said metallocene cation being characterized by a cationic metallocene ligand having sterically dissimilar ring structures joined to a positively charged coordinating transition metal atom;
• and each of said ring structures being a substituted cyclopentadienyl group and one of said ring structures being a substituted cyclopentadienyl group which is sterically different from the other cyclopentadienyl group, and both of said substituted cyclopentadienyl groups being in a sterically hindered relationship which each other providing a stereorigid relationship relative to said coordinating transition metal atom to prevent rotation of said rings.
• (b) contacting said catalyst in a polymerization reaction zone with an ethylenically unsaturated monomer which contains 3 or more carbon atoms or which is a substituted vinyl compound and maintaining said reaction zone under polymerization conditions to produce syndiospecific polymerization of said monomer.