Process for ethylene-propylene-diene terpolymers using VCl{hd 4 {b as catalyst and as cocatalyst (1) R{HD 3{B Al and (2) RAlCl{hd 2 {b in admixture

This invention is directed to a process for preparing copolymers of ethylene with certain alpha olefins and nonconjugated dienes. The novel aspect of this invention relates to a catalyst system comprising a vanadium tetrachloride catalyst in conjunction with a cocatalyst comprising equimolar quantities of ethyl aluminum dichloride and tri-isobutyl aluminum. Isobutyl aluminum dichloride may be substituted for the ethyl aluminum dichloride. The product prepared by this process has a high number average molecular weight and is high in tensile strength when compounded with carbon blacks or mineral fillers and extender oils. Additionally, the polymer of this invention exhibits a rapid cure rate. Since the product further exhibits a narrow molecular weight distribution and low crystallinity, there is a greatly reduced die swell upon extrusion. The combination of the high molecular weight, narrow molecular weight distribution and low crystallinity produce a vulcanized product of low compression set.