Dispersion copolymerization in liquid aliphatic hydrocarbons

A process for the dispersion copolymerization of 35 to 70% by weight of vinyl substituted aromatic monomer and 30 to 65% by weight of conjugated diene monomer comprising carrying out the copolymerization in a reaction mixture comprising a dispersing medium comprising at least 75 percent by weight of a liquid aliphatic hydrocarbon, an anionic catalyst system, and a block copolymer dispersing agent comprising at least two polymer blocks wherein at least one of the polymer blocks is soluble in the dispersing medium and at least another of the polymer blocks is insoluble in the dispersing medium and the dispersing agent acts to disperse a random copolymer of vinyl substituted aromatics and conjugated dienes formed in the presence of the dispersing agent and wherein the random copolymer has a solubility parameter of at least 1.9 greater than the solubility parameter of the dispersing medium.