Styrene-Butadiene or Styrene-Butadiene-Rubber (SBR) is a synthetic rubber copolymer consisting of styrene and butadiene.
It has good abrasion resistance and good aging stability when protected by additives, and is widely used in car tires, where it is blended with natural rubber. It was originally developed prior to World War II in Germany[1], but during the War was used extensively by the USA to replace natural rubber supplies from the far-east, that had been captured by the Japanese.
SBR can be produced from solution or as emulsion. In both instances, the reaction is via free radical polymerization. Pressure reaction vessels are required and usually charged with the two monomers, a free radical acid and a chain transfer agent such as an alkyl mercaptan. The latter prevents high molecular weight and high viscosity product from forming. High styrene-content rubbers are hard, since the Tg (glass transition temperature) of butadiene is extremely low. The production process is initiated by sodium.
It is not to be confused with a thermoplastic elastomer made from the same monomers, styrene-butadiene block copolymer.