The structure and properties of commercial ethylene-propylene block copolymers have been studied by a series of techniques. The results obtained show that the ethylene-propylene block copolymers may be a mixture of PP

PP-b-EPR

EPR and PE

and the thermal properties of the ethylene-propylene block copolymers are influenced by the random copolymeriza-tion of ethene with residual propene in the sequential copolymerization process. Meanwhile

the multi-phase structure of ethylene-propylene block copolymers was revealed by DMA and SEM.