Polyester: Terylene (Dacron)

Polyesters are condensation polymers in which the repeating linkage joining the monomer units is an ester group, $-\text{CO--O}-$, formed by the reaction of a carboxylic acid group with a hydroxyl (alcohol) group, releasing a molecule of water at each linkage -- the same condensation logic used for nylon-6,6's amide linkages, but built from a diol and a diacid instead of a diamine and a diacid.

Terylene (marketed in some countries as Dacron, and known generically as PET, polyethylene terephthalate) is the polyester prescribed by name in this syllabus. It is manufactured by heating ethylene glycol, $\text{HO--CH}_2\text{CH}_2\text{--OH}$ (a diol), with terephthalic acid, $p\text{-HOOC--C}_6\text{H}_4\text{--COOH}$ (a benzene-1,4-dicarboxylic acid, a diacid), in the presence of a catalyst such as zinc acetate/antimony trioxide, at around $420$--$460\ \text{K}$. At each step one $-\text{OH}$ of the glycol condenses with one $-\text{COOH}$ of the diacid to form an ester linkage and release water:

giving the repeat unit $\big[-\text{O--CH}_2\text{CH}_2\text{--O--CO--C}_6\text{H}_4\text{--CO--}\big]_n$, in which the rigid, flat benzene ring of the terephthalate unit alternates with the flexible two-carbon glycol bridge along the chain. …