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Unformatted text preview: 4.3 Poly(styrene-co-acrylonitrile) Copolymer (SAN) Many copolymers of styrene have been investigated, very often in the hope of finding a material which has greater heat resistance and toughness than straight polystyrene whilst retaining the low cost, rigidity and transparency of the PS homopolymer. Up to the present time results have been rather disappointing, with the exception of acrylonitrile-containing materials, styrene copolymers have not achieved much commercial importance as rigid materials. Commercial styrene-acrylonitrile copolymers (SAN) generally contain 20-30% acrylonitrile. They are random amorphous copolymers and are produced by bulk or suspension polymerization using techniques similar to those described previously for the homopolymer. (x: 70-80% y: 30-20%) Free Radical Initiator y x N C + N C CH 2 =CH CH 2 =CH -(CH 2-CH) (CH 2-CH) - Compared to straight polystyrene, styrene-acrylonitrile copolymers have a higher softening point and improved impact strength. (See Table 3.1.) They are also transparent but tend to have a slight yellow tint. improved impact strength....
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