Styrene-Butadiene Rubber (SBR)

Styrene-butadiene rubber (SBR) is the most widely used synthetic rubber. It can be produced by the copolymerization of butadiene (≈ 75%) and styrene (≈ 25%) using free radical initiators. A random copolymer is obtained. The micro structure of the polymer is 60–68% trans, 14–19% cis, and 17–21% 1,2–. Wet methods are normally used to characterize polybutadiene polymers and copolymers. Solid state NMR provides a more convenient way to determine the polymer micro structure.

Currently, more SBR is produced by copolymerizing the two monomers with anionic or coordination catalysts. The formed copolymer has better mechanical properties and a narrower molecular weight distribution. A random copolymer with ordered sequence can also be made in solution using butyllithium, provided that the two monomers are charged slowly.

 Block copolymers of butadiene and styrene may be produced in solution using coordination or anionic catalysts. Butadiene polymerizes first until it is consumed, then styrene starts to polymerize. SBR produced by coordinaton catalysts has better tensile strength than that produced by free radical initiators.

The main use of SBR is for tire production. Other uses include footwear, coatings, carpet backing, and adhesives. The l997 U.S. production of SBR was approximately 940 million pounds.