Styrene-butadiene rubber competition

Butadiene and styrene may be polymerised in any proportion. The Tfs of the copolymers vary in an almost linear manner with the proportion of styrene present. Whereas SBR has a styrene content of about 23.5% and is rubbery, copolymers containing about 50% styrene are leatherlike whilst with 70% styrene the materials are more like rigid thermoplastics but with low softening points. Both of these copolymers are known in the rubber industry as high-styrene resins and are usually used blended with a hydrocarbon rubber such as NR or SBR. Such blends have found use in shoe soles, car wash brushes and other mouldings but in recent times have suffered increasing competition from conventional thermoplastics and to a less extent the thermoplastic rubbers. 

Whilst the peroxide-initiated emulsion polymerized polybutadiene had disappointing properties it was found in 1929 that copolymerization of butadiene with styrene and in 1930 with acrylonitrile led to the production of interesting materials. The butadiene-styrene rubber. Buna S, was potentially a general purpose rubber but at that time not competitive with natural rubber. On the other hand the butadiene-acrylonitrile rubber. Buna N, now commonly known as nitrile rubber had certain properties such as oil resistance not shown by natural rubber and commercial production was started about 1935. Commercial production of butadiene-styrene rubber did not commence until 1937 and many things were to happen before it became the world s most used rubber. 

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