The dispersibility of the initial polystyrene block in forming a S-B-S type of copolymer is improved by first preparing a small block of homopolydiene such as homopolybutadiene as a dispersing agent. Onto this small block of homopolybutadiene, the first block of polystyrene is formed and affixed and thereby made dispersible in a mixture of alkanes and 15 to 60% by weight of cycloalkanes, preferably hexane and cyclohexane. After the preparation of the dispersing agent and the first styrene block, the remaining monomer charges to the reactor are fed in aliphatic hydrocarbon diluents, preferably hexane or technical hexane, thereby greatly reducing the final percentage of cycloalkanes including cyclohexane in the reactor to less than 25% of total dispersing medium. The block copolymers produced according to the present process display a narrow molecular weight distribution and improved tensile strength over block copolymers produced in the absence of the additional cycloalkanes in the solvent system.