Novel trialkyl aluminum cocatalyst

A catalyst composition which comprises a mixture of:

• (a) at least one alkyl metal compound having the formula R.sub.3 '''M, wherein M=Al, Ga, or In, R''' is selected from the group consisting of C.sub.1 to C.sub.20 primary, branched primary, secondary, or tertiary alkyl, cycloalkyl, alkenyl and aralkyl groups and hydride and mixtures thereof;
• (b) a Group IVB-VIII transition metal compound on a layer lattice support, a molar ratio of said R.sub.3 '''M to said transition metal compound being about 0.5:1 to 200:1;
• (c) at least one hindered Lewis base, said Lewis base not causing excessive cleavage of metal-carbon bonds or loss of active sites, under polymerization conditions hindered Lewis bases being those whose complexing ability toward the cocatalyst is hindered sufficiently by steric and/or electronic effects to cause appreciable dissociation of the trialkyl metal Lewis base complex under polymerization conditions;
• (d) A Group IA to Group IIIA metal salt selected from the group consisting of sterically hindered carboxylates, alkoxides and aryloxides;
• and
• (e) at least one unhindered Lewis base, said unhindered base not causing excessive cleavage of metal-carbon bonds or loss of active sites under polymerization conditions.