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(or polyurethane), a polymer containing urethan groups, —NH—CO—O—, in the main chain of the macromolecule; the general formula for linear polyurethans is
[— A—OCOHN — A′ — NHCOO —]n
Polyurethans are usually produced by polycondensation of diisocyanates or polyisocyanates (A’ is a diisocyanate residue in the general formula) with compounds containing active hydrogen atoms, for example, dihydric and trihydric alcohols (A is a hydrocarbon residue). This process is often called polymerization or polycombination. The substances most commonly used in polyurethan synthesis include hexamethylene-l, 6-diisocya-nate, toluene-2,4- and 2,6-diisocyanates, tri(p-isocyanate phe-nyl)methane, aliphatic or aromatic polyethers and polyesters, glycols, and glycerol.
The properties of polyurethans vary over an extremely wide range, depending on the nature and length of chain segments between urethan groups and on the structure (linear or cross-linked), molecular weight, crystallinity and so on. Polyurethans may be viscous liquids or amorphous or crystalline solids, ranging from highly elastic soft rubbers to rigid plastics (Shore hardness from 15 on scale A to 60 on scale D, respectively). Polyurethans are resistant to acids, mineral and organic oils, gasoline and oxidizing agents; they surpass polyamides in resistance to hydrolysis. Linear polyurethans are soluble in certain polar solvents—for example, dimethylformamide and dimethyl sulfoxide.
Polyurethans are used as foams, rubbers, thermoplasts, fibers, varnishes, adhesives and latices for the preparation of potting compounds. Polyurethan articles are produced by direct liquid-phase molding from base monomers or from previously prepared polymers (prepolymers). World production of polyurethan was estimated at 1.2 million tons in 1973.
REFERENCESSaunders, J. H., and K. C. Frisch. Khimiia poliuretanov. Moscow, 1968. (Translated from English.)
See also references under .
IU. L. MOROZOV