Polyesters

Polyester polymers join their repeating units through an ester linkage. The commercially most important polyester fibre is terylene (also called dacron), made by condensation polymerization of ethylene glycol (HO-CH2-CH2-OH) with terephthalic acid (a benzene ring bearing two -COOH groups) in the presence of a catalyst (zinc acetate-antimony trioxide) at high temperature (420-460 K), with elimination of water at each ester linkage, giving the repeating structure -[O-CH2-CH2-O-CO-C6H4-CO]n-. Terylene has a relatively high melting point (265 degC) and resists both chemicals and water; blended with cotton it gives wrinkle-free 'terycot' fabric, and blended with wool it gives 'terywool', and it is also used as a glass-reinforcing material in safety helmets. PET (polyethylene terephthalate) is another trade name for essentially the same class of polyester and is the most common thermoplastic polyester, used to make bottles, jam jars and packaging containers. Polycarbonates are a re …