Styrene-butadiene rubber (SBR)

SBR is the highest volume synthetic elastomer produced globally. The structure of SBR is given in Fig. 1.2. During the Second World War production was set up on a large scale in US and in Germany. It can be produced by solution and emulsion polymerization of styrene and butadiene. Free radical emulsion polymerization is carried out at two different temperatures: 50°C (hot emulsion grade) and 5–10°C (cold emulsion grade). In the hot process an initiator such as potassium peroxydisulfate is used and in the cold process a redox initiator is used. Tg (−55 to −35°C) depends on the styrene and butadiene ratio, and the density is 0.94 g/cm3