Process and catalyst for polyolefin density and molecular weight control

Claim 1

A catalyst suitable for the polymerisation of an olefin comprising (a) the carbene represented by the formula and its derivative of the formula and the carbene represented by the formula and the derivatives of this carbene wherein Cp is a cyclopentadienyl or substituted cyclopentadienyl radical, and R'" is an alkyl, aryl or alkylaryl radical having from 1-18 carbon atoms; or a compound of the formula (C 5 R' m ) p R" s (C 5 R' m )MeQ 3 _ p or R" s (CSR' m ) 2 MeQ'. wherein Me is a Group 4b, 5b or 6b metal, (C s R' m ) is cyclopentadienyl or substituted cyclopentadienyl, each R' which can be of the same or different, is hydrogen, an alkyl, alkenyl, aryl, alkylaryl or arylalkyl radical having from 1 to 20 carbon atoms or two R' substituents together form a fused C 4 -C B ring, R" is a C l -C 4 alkylene radical, a dialkyl germanium or silicone or an alkyl phosphine or amine radical bridging two (C s R' m ) rings, each Q which can be the same or different, is aryl, alkyl, alkenyl, alkylaryl or arylalkyl radical having from 1 to 20 carbon atoms or halogen, Q' is an alkylidene radical having from 1 to 20 carbon atoms, s is 0 or 1, p is 0, 1 or 2; provided that s is 0 when p is 0; m is 4 when s is 1; m is 5 when s is 0; and that at least one R' is a hydrocarbyl radical when s= 0 and Q is an alkyl radical or halogen and (b) an alumoxane.