In the copolymerization of ethylene, propylene and 5-ethylidene-2-norbornene (ENB) in the presence of the catalytic system VOCl 3Al 2(C 2H 5) 3Cl 3 when the temperature of polymerization is raised from 20 to 50°C and the concentration of ENB in the reaction mixture is increased, the possibility of secondary reactions taking place at the copolymer double bonds increases. Increase in polymerization temperature widens the molecular weight distribution (MWD) and increases the crystallinity of copolymer gels. On adding hydrogen and increasing catalyst concentration, the MWD becomes still wider. The amount of gel in copolymers increases with an increase of the duration of polymerization. Polymers obtained at temperatures of 20 to 50° with an unsaturation of 1·0–1·5% dissolve almost completely in toluene at 80° and are free from crosslinked structures.