Emulsion copolymerization of chloroprene and isoprene initiated by potassium persulphate has been investigated. When chloroprene and isoprene were copolymerized to approximately 80% conversion

only a small amount of gel occurred. The peak in the viscosity-conversion curve

followed by a marked drop

is usually a sign of gel formation

since the insoluble gel does not contribute to the viscosity of the solution. The product thus obtained has a markedly decreased rate of crystallization

and the brittle-point of the vulcanizates is 5℃lower than those of the corresponding vulcanizates from Neoprene type GN-A.