Abstract: The effects of the catalyst system and composition of ethylene-propylene copolymers onthe crystallization rates of the copolymer have been studied by dilatometry. It is shownthat for the same catalyst system, the maximum crystallisation rate 1/t_1/2(max) of thecopolymer increased with the increase of the ethylene content in it.The maximum crystal-lization rates of ethylene-propylene copolymers obtained with various catalyst systemswere found in the following order:(VOCl₃-)> (V_5-9) > (V(acac)₃-)The order of 1/t_1/2(max) for the catalyst system with addition of an active agent ETCA was:(VOCl₃-ETCA) > (V_5-9-ETCA) > (V(acac)₃-ETCA)The results of the crystallinity and glass transition temperature of the coplymers, aswell as the composition of copolymers of differnt sequence suggested that the ethylene-propylene copolymer obtained with VOCl₃-had longer PE species and those obtained with V_5-9- had shorter PE species. More irregular structure was formed when the copolymer isobtained with V _(acac)3-catalyst system.

Key words: Ethylene-propylene copolymer, Crystallisation rate, Sequence structure, Dilatometry