Olefin polymerization catalysts

A catalyst system comprising:

• (A) a Group IV B transition metal component of the formula:
• ##STR5## wherein M is Zr, Hf or Ti;
• (C.sub.5 H.sub.5-y-x R.sub.x) is a cyclopentadienyl ring which is substituted wit from zero to five groups R, "x" is 0, 1, 2, 3, 4 or 5 denoting the degree of substitution, and each R is, independently, a radical selected from a group consisting of C.sub.1 -C.sub.20 hydrocarbyl radicals, C.sub.1 -C.sub.20 substituted hydrocarbyl radicals wherein one or more hydrogen atoms are replaced by a halogen atom, C.sub.1 -C.sub.20 hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from the Group IV A of the Periodic Table of Elements and halogen radicals or (C.sub.5 H.sub.5-y-x R.sub.x) is a cyclopentadienyl ring in which two adjacent R-groups are joined forming C.sub.4 -C.sub.20 ring to give a saturated or unsaturated polycyclic cyclopentadienyl ligand;
• (JR'.sub.z-l-y) is a heteroatom ligand in which J is an element with a coordination number of three from Group V A or an element with a coordination number of two from Group VI A of the Periodic Table of Elements, each R' is, independently a radical selected from a group consisting of C.sub.1 -C.sub.20 hydrocarbyl radicals, substituted C.sub.1 -C.sub.20 hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen atom, and "z" is the coordination number of the element J;
• each Q is, independently any univalent anionic ligand or two Q's are a divalent anionic chelating agent;
• "y" is 0 or 1 when w is greater than 0;
• y is 1 when w is 0, when "y" is 1, T is a covalent bridging group containing a Group IV A or V A element;
• L is a Lewis base where "w" denotes a number from 0 to 3;
• and
• (B) an alumoxane.