AbstractBy the consecutive oxidation of graft copolymer with perbenzoic acid and with periodic acid, the trunk of polyisoprene degraded throughly into low molecular compounds and remained the branch of polystyrene alone. The polystyrene extracted was similarly oxidized. Measurements of [η] showed that both the polystyrene branch and the polystyrene generated freely have the same molecular weights. Assuming that the rubber hydrocarbon molecule did not suffer any degradation, the numbers and the length of the grafted branches of polystyrene were computed