Nippon Zeon Company, Ltd.

Souichi Suzuki

Tetsu Ohishi

Akio Ueda

Nagatoshi Sugi

Hiroshi Horino

Keiji Komuro

Tetsuo Waku

A rubber composition for tire treads includes (Ia) an oil-extended rubber having a Mooney viscosity (ML.sub.1+4, 100.degree. C) of 20 to 70 which is prepared by adding 20 to 80 parts of a hydrocarbon oil to 100 parts by weight of a rubber terpolymer which is composed of 2 to 13% by weight of combined styrene, 15 to 70% by weight of combined 1,3-butadiene and 17 to 83% by weight of combined 1,3-pentadiene with the dienes having a total 1,4-bond content of at least 65 mole%, (II) vulcanization additives, and (III) 30 to 110 parts by weight, per 100 parts by weight of the oil-extended rubber (Ia), of a carbon black for rubber having an average particle diameter of not more than 60 m.mu. the rubbery copolymer has a glass transistion temperature of -70.degree. to -20.degree. C., and is produced by emulsion-polymerization at 0.degree. to 30.degree. C.

Rubber composition for tire treads

A radical polymerization initiator comprising as an active ingredient a hydroperoxide of disproportionated or hydrogenated rosin acid or its alkali metal or ammonium salt. The initiator is prepared by contacting disproportionated or hydrogenated rosin acid or its alkali metal or ammonium salt with molecular oxygen in water or an organic solvent at a temperature of 0.degree. to 150.degree.C. to form its hydroperoxide.

Radical polymerization initiator andd process for its preparation

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Yokohama, Japan

Souichi Suzuki