Polycarbonate

a polyester of carbonic acid and dihydroxy compounds of the following general formula:

Polycarbonates may be aliphatic, mixed, or aromatic, depending on the nature of A and A′. Only aromatic polycarbonates have gained practical importance; they are produced commercially by interphase polycondensation, phosgenation of aromatic dihydroxy compounds in a pyridine medium, or transesterification of diaryl carbonates (for example, diphenylcarbonate) by aromatic dihydroxy compounds. The most commonly used dihydroxy compound is 4,4′ -isopropylidenediphenyl, also called dian or bisphenol A. Polycarbonates based on the bisphenol A have the formula

These polycarbonates are thermoplastic linear polymers (molecular weight, 35,000–70,000) that are characterized by very high impact strength (250–500 kilojoules per sq m, or kilograms-force per cm per sq cm [kgf.cm/cm²]), yield strength (strength in flexure, 77–120 meganewtons per sq m [MN/m²], or 770–1,200 kgf/cm²), and very good dielectric properties (dissipation factor, 0.0009 at 50 hertz). Polycarbonates are optically transparent, cold-resistant (stable at temperatures slightly below – 100°C), and self-extinguishing; they dissolve in most organic solvents such as methylene chloride and chloroform, and are resistant to acids, salt solutions, and oxidizing agents.

Polycarbonates are processed by all the standard methods used for thermoplastic resins (for example, injection molding, extrusion, and compression molding). They are used in the preparation of films, fibers, and various products in many sectors of industry, mainly in electric engineering. In 1973, world production of polycarbonates (mainly in the Federal Republic of Germany, the USA, and Japan) was 100,000 tons.