STYRENE

liquid hydrocarbon that belongs to the family of aromatic organic compounds and is important chiefly for its marked tendency to undergo polymerization. Styrene is used in the manufacture of plastics, resins, and rubbers, which are composed of very large molecules (polymers) formed by combination of smaller ones (monomers). It is also used to make polyesters and latex paints. Pure styrene is clear, colourless, flammable, and slightly toxic; it boils at 145 C (293 F) and freezes at -30.6 C (-23.1 F). Its molecular formula is C8H8. Its isolation from storax (a natural balsam) and its polymerization were reported before 1850, but its industrial manufacture and utilization were not begun until the late 1930s. It is produced by dehydrogenation of ethylbenzene, most of which is made from ethylene and benzene, both derived from petroleum. Production increased rapidly during World War II because of the importance of styrene as a component of synthetic rubbers; by the late 20th century, more than 9,000,000 metric tons per year were being made. Free-radical catalysts cause the rapid conversion of styrene into polystyrene (q.v.), a plastic widely used in molded or extruded articles. The synthetic rubber called SBR, GR-S, or Buna S is made from mixtures of styrene and butadiene, which react to form a copolymer, the molecules of which contain units of both compounds. Several other monomers (e.g., acrylonitrile) may be copolymerized with styrene to produce useful plastics or resins with qualities superior to that of polystyrene.