Catalyst composition for preparation of syndiotactic vinyl aromatic polymers

A catalyst composition for preparing polymers of vinyl aromatic monomers having high stereo-regularity comprising:

• 1) a metal complex of the formula:
• [Cp.sub.m MX.sub.n X'.sub.p ].sup.+ A.sup.-
• wherein:
• Cp is a single .eta..sup.5 -cyclopentadienyl group or a .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;
• 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 R' or hydride, wherein R' is hydrocarbyl, silyl or a mixture thereof, optionally substituted with one or more halogen atoms or alkoxy groups, said R' 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;
• and
• the sum of m and n is one less than the valence of M;
• and
• A- is a noncoordinating, compatible anion of a Bronsted acid salt;
• and
• 2) an aluminum, magnesium or zinc metal hydrocarbyl, the molar ratio of the metal complex:
• metal hydrocarbyl being 1:1 to 1:1000;
• said metal complex and metal hydrocarbyl being combined prior to contacting of the metal complex with a vinyl aromatic monomer.