Polyethers and Polyesters

polymers containing functional groups of ethers (polyethers) or esters (polyesters) in the main chain of the macromolecule; they may be saturated or unsaturated.

Polyethers,

HO— [— R— O —]_n — H

(where R is a hydrocarbon radical of various structure, containing no fewer than two carbon atoms), are produced by polymerization of cyclic oxides (for example, propylene oxide, ethylene oxide) or by polycondensation of glycols. Linear polyesters,

H—[—OAO—CO —A′ —CO —]_n—OH

where A is a hydrocarbon radical and A’ is an organic or inorganic acid radical (for example, polyethylene terephthalate, nucleic acids), are prepared by polycondensation of glycols with dibasic acids or their anhydrides, or hydroxy acids. Branched polyesters (for example, alkyd resins) or cross-linked polyesters are produced by using polyhydric alcohols (more than two OH groups; for example, glycerol, pentaerythritol and various po-lyols).

The highly diverse properties of polyethers and polyesters depend on chemical composition, structure, and molecular weight, and also on the presence of functional groups (—OH and —COOH). Polyethers are usually more elastic than polyesters. Polyethers and polyesters may enter into chemical reactions at the end functional groups, with an increase in molecular weight; unsaturated polyethers and polyesters undergo cross-linking to form three-dimensional structures. Polyesters are hydrolyzed in the presence of acids and alkalies, whereas polyethers are considerably more resistant to hydrolysis.

The properties of polyethers and polyesters determine their uses. For example, low-molecular-weight unsaturated polyethers and polyesters are used as components for adhesives, paints, and varnishes, and also for impregnation. High-molecular-weight polyesters are used in the manufacture of plastics (for example, polycarbonates), films, and polyester fibers.