Abstract: A conjugated diene rubber composition for tires comprising (I) 2-100 weight parts of a high-cis conjugated diene polymer rubber, which is a polymer of conjugated diene monomer alone or with a copolymerizable monomer, and has a cis-bond unit content of at least 40% in the conjugated diene monomer units, and a weight average molecular weight (Mw) of 20,000-10,000,000, and in which the ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) and the weight average molecular weight (Mw) satisfy the formula: log(Mw/Mn)<0.162×log(Mw)−0.682, and (II) 0-98 weight parts of other polymer rubber. A tire comprising at least a tread composed of the above-mentioned conjugated diene rubber composition has very high rebound resilience.

Abstract: A conjugated diene polymer rubber composition for modifying a resin comprising a conjugated diene homopolymer or copolymer in which the content of cis-bond units in the total conjugated diene monomer units is at least 40%; the weight average molecular weight (Mw) is 20,000 to 10,000,000; and the Mw and the number average molecular weight (Mn) satisfy the formula: log(Mw/Mn)<0.162×log(Mw)−0.682, (i) A resin composition comprising a resin and the conjugated diene polymer rubber composition, and (ii) a polyaromatic vinyl resin composition prepared by polymerizing an aromatic vinyl monomer in the presence of the conjugated diene polymer rubber composition have balanced and good low-temperature resistance and surface luster.