To provide a branched conjugated diene-aromatic vinyl copolymer, of which the processability when processed into a vulcanizate is good and the vulcanizate has satisfying low hysteresis loss while exhibiting excellent wet skid resistance, thereby having an excellent balance between them, satisfies practically sufficient abrasion resistance and destructive characteristics, and further has excellent productivity, and a method for producing the same.
The conjugated diene-aromatic vinyl copolymer (C) is a random copolymer. A bonding amount of the aromatic vinyl in the conjugated diene-aromatic vinyl copolymer (C) is 38-45 mass%, and a bonding amount of vinyl in the total bonding units of the conjugated diene is more than 43 mol% and equal to or less than 50 mol%. A weight-average molecular weight (Mw-C) of the conjugated diene-aromatic vinyl copolymer (C) is 700,000-1,000,000, and a ratio of the weight-average molecular weight (Mw-C) to a number-average molecular weight (Mn-C), ((Mw-C)/(Mn-C)), is 1.7-3.0. Mooney viscosity (ML-C) and Mooney relaxation rate (MSR-C) measured at 120°C satisfy relation in formula (1): ä195-(ML-C)}/300≤(MSR-C)≤ä235-(ML-C)}/300, wherein 90≤(ML-C)≤125.
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Toshifumi Onuki
Kazuhiko Naito