Abstract: A stable and non-polar solvent soluble alpha-methylstyrene-conjugated diene oligomer dilithium as a polymerization initiator is obtained by preparing a dilithium initiator solution by reacting lithium metal with alpha-methylstyrene in a polar solvent at low temperature, thereafter adding gradually a small amount of a conjugated diene to the dilithium initiator solution to consume completely the alpha-methylstyrene, and then adding additional conjugated diene in a certain amount so as to prepare the stable and non-polar solvent soluble alpha-methylstyrene-conjugated diene oligomer dilithium.

Abstract: A process for producing a film or sheet of a tapered styrenebutadiene copolymer or mixture thereof, which comprises:Melt extruding and then biaxially stretching a tapered styrenebutadiene copolymer with a molecular weight of 40,000 - 250,000, a total styrene content of 50 - 90 wt. %, and a total butadiene content of 40 - 10 wt. %, wherein said tapered styrene-butadiene copolymer contains: (a) more than 5% of the chain portion having a tapering rate of 0.3 - 4 and a styrene content of 30 - 70 wt. %, (b) more than 35% of the chain portion with a styrene content of more than 80 wt. %, and (c) more than 10% of the chain portion with a styrene content from at least 5 wt. % to less than 50 wt. % between high styrene content chain portions which have a styrene content greater than 80 wt. %.

Abstract: First polymerization of a mixture of styrene-type monomers and conjugated diene monomers containing 30 to 70% by weight of styrene-type monomers is carried out, and when 40 or more of the diene monomers have been converted to a copolymer, there are then added styrene-type monomers in such an amount that the content of styrene units accounts for a proportion of 70 to 85% by weight of the finally obtained block copolymers, followed by completion of the polymerization. Alternatively, when all the diene monomers added have been converted to the copolymer, the second polymerization of styrene type monomers is carried out in the presence of a small amount of conjugated dienes as a polymerization retardant. Block copolymers obtained thus are useful for sheet or film molding having good low-temperature impact strength.