Mercaptan, dialkyl xanthogen disulfide or sulfur modified chloroprene based copolymers are disclosed. At least 92% of the chloroprene derived units present in the copolymer have a l,4-trans configuration. The copolymer comprises units derived from chloroprene, up to 20 parts and preferably 2 or more parts per l00 parts chloroprene derived units of units derived from 2,3-dichloro-l,3-butadiene, and 2 to 25 parts per l00 parts of chloroprene and 2,3-dichlor-1,3-butadiene of randomly distributed units derived from vinyl monomer. |