Abstract: A process for producing a high impact polystyrene characterized by polymerizing a conjugated diene (preferably, 1,3-butadiene) by the use of an organolithium-based catalyst containing a polyfunctional organolithium compound (preferably, said organolithium-based cataylst is a mixture of a polyfunctional organolithium compound and a monofunctional organolithium compound at such a mixing ratio that the amount of lithium atom in the polyfunctional organolithium compound is 5% by weight or more based on the total sum of the lithium atoms in the respective compounds), coupling the resulting polymer molecules with a polyfunctional treating agent having at least two (preferably, 2-4 on the average) reactive sites capable of reacting with the active lithium terminal of the polymer, dissolving in styrene the conjugated diene polymer thus obtained, which has substantially a network structure and is substantially soluble in styrene, preferably in a proportion of 2-30% by weight, and then radical-polymerizing the resultin

Abstract: Process for producing a completely random copolymer of a conjugated diene and a monovinyl substituted aromatic compound having the same composition as that of the starting monomeric mixture which comprises copolymerizing a conjugated diene and a monovinyl substituted aromatic compound in the presence of lithium catalyst in a polymerization medium at a temperature not higher than 150.degree. C and at which the resulting copolymer is substantially phase-separated, said temperature being dependent upon the type of medium, and type, composition and concentration of the monomer used.

Abstract: A polymerization process for producing rubbery polymers or random copolymers having excellent physical properties as well as good processability, and completely freed from a flow at normal temperature. The process, which may be called as "Low-temperature Pretreatment Polymerization process," comprises polymerizing conjugated dienes or copolymerizing conjugated dienes and monovinyl substituted aromatic compound under a specific polymerization conditions in the presence of an alkyllithium catalyst to produce a polymer or random copolymer of the desirably controlled structure of branches to afford such excellent properties mentioned above.