Structure and PropertiesThe chemical make up of polystyrene is a long chain hydrocarbon with every other carbon connected to a phenyl group (the name given to the aromatic ring benzene, when bonded to complex carbon substituents). Polystyrene's chemical formula is (C8H8)n; it contains the chemical elements carbon and hydrogen. Because it is an aromatic hydrocarbon, it 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. Complete oxidation of polystyrene produces only carbon dioxide and water vapor. Because of its chemical inertness, polystyrene is used to fabricate containers for chemicals, solvents, and foods.
This addition polymer of styrene results when vinyl benzene (styrene) monomers (which contain double bonds between carbon atoms) attach to form a polystyrene chain (with each carbon attached with a single bond to two other carbons and a phenyl group).
Polystyrene is generally flexible and can come in the form of mouldable solids or viscous liquids. The force of attraction in polystyrene is mainly due to short range van der Waals attractions between chains. Since the molecules and long hydrocarbon chains that consist of thousand of atoms, the total attractive force between the molecules is large. However, when the polymer is heated (or, equivalently, deformed at a rapid rate, due to a combination of viscoelastic and thermal insulation properties), the chains are able to take on a higher degree of conformation and slide past each other. This intermolecular weakness (versus the high intra-molecular strength due to the hydrocarbon backbone) allows the polystyrene chains to slide along each other, rendering the bulk system flexible and stretchable. The ability of the system to be readily deformed above its glass transition temperature allows polystyrene (and thermoplastic polymers in general) to be readily softened and molded with the addition of heat.
A 3-D model would show that each of the chiral backbone carbons lies at the center of a tetrahedron, with its 4 bonds pointing toward the vertices. Say the -C-C- bonds are rotated so that the backbone chain lies entirely in the plane of the diagram. From this flat schematic, it is not evident which of the phenyl (benzene) groups are angled toward us from the plane of the diagram, and which ones are angled away. The isomer where all of them are on the same side is called isostatic polystyrene, which is not produced commercially.
Ordinary atactic polystyrene has these large phenyl groups randomly distributed on both sides of the chain. This random positioning prevents the chains from ever aligning with sufficient regularity to achieve any crystallites, so the plastic has a very low melting point, Tm<<TRT. But metallocene-catalyzed polymerization can produce an ordered syndiotactic polystyrene with the phenyl groups on alternating sides. This form is highly crystalline with a Tm of 270 °C (518 °F).
Extruded polystyrene is about as strong as unalloyed aluminium, but much more flexible and much lighter (1.05 g/cm3 vs. 2.70 g/cm3 for aluminium).