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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. at a pressure between about 20 psi and about 140 psi, removing butadiene monomer from the vapor phase after at least about 75 percent by weight of the butadiene monomer and the styrene monomer in the aqueous phase are converted to a copolymer and prior to conversion of more than about 98 percent by weight of the butadiene monomer and the styrene monomer to a copolymer in the aqueous phase, and heating the aqueous phase at a temperature between about 50.degree. C. and about 130.degree. C. at a pressure between about 20 psi and about 140 psi until at least about 90 percent by weight of the styrene monomer and butadiene monomer are copolymerized to form an aqueous suspension of discrete copolymer particles.

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