PURPOSE: To provide a tire tread rubber compa. which can constitute a tire having improved wet skid resistance without sacrificing rolling resistance or tread abrasion resistance.

CONSTITUTION: A soln. or styrene, isoprene, and butadiene in hexane is placed in a reactor. A soln. of tripiperidinophosphine oxide(TPPO) in hexane and a soln. of n-butyllithium in hexane are added to the soln. to initiate polymn. The temp. of the reactor is maintained at 10 to 14°C. After polymn. for 5 hr, methanol is added to terminate the polymn. An antoxidant is added to the resultant terpolymer (SIBR) cement, and the solvent hexane is evaporated in a vacuum oven. The SIBR thus obtd. is then dried. According to DSC, this SIBR has a first glass transition temp. of -21°C and a second glass transition temp. of -8°C and possesses excellent properties for use in tire treads.