Crystalline alternating ethylene‐butadiene copolymers

The copolymerization of ethylene with butadiene at −25°C. in the presence of co‐ordinated anionic catalytic systems, prepared at −78°C. from a vanadium compound, organometallic compounds of aluminum and a weak LEWIS base, yields copolymers with particular crystalline structure. By fractionation of crude products, crystalline ethylene‐butadiene copolymers were obtained, the crystalline structure of which was attributed to a succession of ethylene units regularly alternating with trans‐buta‐1,4‐dienic units.