Abstract: A process for forming a copolymer of styrene and butadiene is disclosed including providing an aqueous phase comprising an aqueous mixture comprising water, styrene monomer, butadiene monomer, a suspension stabilizing agent, and a chain propogating amount of one or more free radical polymerization initiators, the ratio of the styrene monomer and the butadiene monomer being between about 80:20 and about 95:5 by weight, the weight proportion of water to the combination of styrene monomer and butadiene monomer being between about 0.8:1 and about 2:1 and a vapor phase comprising an inert gas and butadiene monomer, heating the aqueous phase and the vapor phase to a temperature between about 50.degree. C. and about 130.degree. C.