Polystyrene is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum. At room temperature, polystyrene is normally a solid thermoplastic, but can be melted at higher temperature for molding or extrusion, then resolidified. Styrene is an aromatic monomer, and polystyrene is an aromatic polymer.
Polystyrene was first manufactured by BASF in the 1930s, and is used in numerous plastic products. Pure solid polystyrene is a colorless, harder plastic with limited flexibility which can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various colors. It is economical and is used for producing plastic model assembly kits, plastic cutlery, and many other objects where a fairly rigid, economical plastic of any of various colors is desired. Polystyrene fabricated into a sheet can be stamped (formed) into economic, disposable cups, glasses, bowls, lids, and other items, especially when high strength, durability, and heat resistance are not essential. A thin layer of transparent polystyrene is often used as an infra-red spectroscopy standard.
Polystyrene's most common use, however, is as expanded polystyrene, which is a mixture of about 5% polystyrene and 95% air. This is the lightweight material of which coffee cups and takeaway food containers are made. The voids filled with trapped air give expanded polystyrene low thermal conductivity. It is also used as insulation in building structures, as packing material for cushioning inside boxes, and also in crafts and model building, particularly architectural models.
In the USA it is made by the Dow Chemical Company under the tradename Styrofoam. The word styrofoam is often used by the general public to indicate any brand of polystyrene foam (see genericized trademark).
Expanded polystyrene contains CFCs.
Because it is an aromatic hydrocarbon, polystyrene is flammable and burns with an orange-yellow flame giving off soot, as opposed to non-aromatic hydrocarbon polymers such as polyethylene, which burn with a light yellow flame (often with a blue tinge) and no soot.
The symbol for polystyrene developed by the Society of the Plastics Industry so that items can be labeled for easy recycling is .
The Unicode character is ♸, which will appear here if you have a suitable font installed: ♸.
Pure polystyrene is brittle, but hard enough that a fairly high-performance can be made by giving it some of the properites of a stretchier material, such as polybutadiene rubber. The two materials can't normally be mixed due to the amplified effect of intermolecular forces on polymer solubility, but if polybutadiene is added during polymerization, it can become chemically bonded to the polystyrene, forming a graft copolymer which helps to incorporate normal polybutadiene into the final mix, resulting in high impact polystyrene or HIPS, often called "high impact plastic" in advertisements.
Acrylonitrile butadiene styrene or ABS plastic is similar to HIPS: a copolymer of acrylonitrile and styrene, toughened with polybutadiene. Most electronics cases are made of this form of polystyrene.
Styrene can be copolymerized with other monomers; for example, divinylbenzene for cross-linking the polystyrene chains.