Styrene-butadiene
Identifiers
CAS number	9003-55-8
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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.

Contents 1 Buna S 2 Properties 3 Applications 4 See also 5 References

[edit] Buna S

The material was initially marketed with the brand name Buna S. It derives this name from: Bu for butadiene, Na for sodium (natrium in Latin), and S for styrene.^[2][3]

[edit] Properties

• Glass transition temperature approximately −55 °C (−67.0 °F), but varies with styrene content^[4]
• Possible temperature range of use: approximately −40 to 100 °C (-40 to 212 °F)
• Chemical Type: styrene-butadiene (copolymer)
• Trade names (common): GRS, Buna S, SBR
• Elongation (%): 450-500
• Shore A hardness: 50-90^[5]
• Major application characteristics: good physical properties; excellent abrasion resistance; but sensitive to oil, wastewater and ozone; electrical properties good, but not outstanding

[edit] Applications

The elastomer is used widely in pneumatic tires, shoe heels and soles, gaskets and even chewing gum. It is a commodity material which competes with natural rubber. Latex (emulsion) SBR is extensively used in coated papers, being one of the most cost-effective resins to bind pigmented coatings. It is also used in building applications, as a sealing and binding agent behind renders as an alternative to PVA, but is more expensive. In the latter application, it offers better durability, reduced shrinkage and increased flexibility, as well as being resistant to emulsification in damp conditions.

Additionally, it is used in some rubber cutting boards.

[edit] See also

• elastomer
• ozone cracking
• tyre
• synthetic rubber

[edit] References