Process for producing block copolymer from conjugated diene and vinyl aromatic

Claim 1

A process for producing a clear block copolymer resin according to a suspension polymerization process which comprises block copolymerizing a mixture of 70 to 90 parts by weight of an aromatic vinyl compound monomer and 10 to 30 parts by weight of a conjugated diene monomer in two stages using an organolithium compound as a polymerization initiator, characterized by using an aliphatic hydrocarbon selected from the group consisting of propane, butane, pentane, hexane, heptane, nonane, decane, and mixtures thereof as a solvent, adding, in the first polymerization stage, a mixture of 10 to 60 parts by weight of the aromatic vinyl compound monomer out of the total amount thereof and the total amount of the conjugated diene monomer to the reaction system to polymerize all the monomers substantially for the formation of an elastomeric copolymer block, and continuously adding, subsequently in the second polymerization stage, all the remaining aromatic vinyl compound monomer to the reaction system at a polymerization rate that the added monomer is substantially polymerized at once and that no unreacted monomer is substantially present in the reaction system, and continuing the polymerization to polymerize all the monomer substantially for the formation of a non-elastomeric block, said polymerization being carried out at a temperature of from about 20° C. to about 80° C.