| abstract |
Styrene-butadiene random copolymers having an average vinyl content of at least 70%, a breadth of the distribution of vinyl contents of at least 20%, a Mooney viscosity (ML1+4, 100 DEG C.) of 10 to 150, and a styrene content of about 3 to 30% by weight. They are prepared by copolymerizing styrene and butadiene in a hydrocarbon solvent in the presence of an organolithium initiator and a Lewis base and, if necessary, an anionic surface active agent containing -SO3M or -OSO3M (wherein M is Na, K, Rb or Cs) under temperature-raising conditions. They are rubber materials having low rolling resistance and high wet skid resistance. |