There are various other important plastics which are related to polystyrene, for example, toughened polystyrene (a mixture of polystyrene and rubber), ABS (a polymerized mixture of styrene, acrylonitrile and nitrile rubber), SAN (a polymerized mixture of styrene and acrylonitrile) and ASA (a polymer of styrene with a methacrylate ester). Polymers composed of more than one type of monomer, for example, SAN, are usually called copolymers. Polystyrene plastics are used to make moldings and in various electric components. Expanded polystyrene, foams such as Styropor, are used as heat and sound insulation materials and in packaging to absorb mechanical shock. Of this family, only polystyrene, ASA and SAN are transparent; TPS and ABS are opaque.
PVC
Another important modern plastic is polyvinyl chloride (PVC), which was first produced commercially in Germany in 1931. The raw materials for PVC production are ethylene and chlorine, which are reacted to give vinyl chloride (CH2=CHC1). This is polymerized to give PVC, which can be represented as follows:
-CHCl-CH2-CHC1-CH2-CHC1-CH2-
PVC is used to make a wide range of molded products, and it is often mixed with a plasticizer which softens it and makes it more flexible. Plastic pipes and gutters, and flexible plastic sheets are frequently made of PVC. Copolymers of vinyl chloride with vinyl acetate (CH2=CHCOOCH3), or vinylidene chloride (CH2=CC12), are also important commercial plastics.