Styrene acrylonitrile is a copolymer plastic consisting of styrene and acrylonitrile. It is also known as SAN. It is widely used in place of polystyrene owing to its greater thermal resistance. The chains of the polymer show alternating repeat units of styrene and acrylonitrile, and it is a copolymer, Styrene Acrylonitrile (SAN) - Styrene and Acrylonitrile monomers can be copolymerized to form a random, amorphous copolymer that has improved weatherability, stress crack resistance, and barrier properties. The copolymer is called Styrene Acrylonitrile or SAN.