Urethane Elastomers

polyurethanes possessing rubberlike properties. The urethane elastomers produced industrially include vulcanized millable rubbers, casting systems, and thermoplastic elastomers. Vulcanized millable rubbers are linear or branched solid polymers (molecular weight ~30,000). They are processed using conventional technology, with separate steps for the preparation of the rubber mixture and vulcanization. Casting systems are urethane polymers that are converted into end items directly from a liquid or semiliquid state. During the production of the end items, casting is combined with the synthesis of a solid, cross-linked polymer. Thermoplastic elastomers are solid polymers (molecular weight, 15,000–18,000); the methods used in their processing are the same as those used in producing items from thermoplastics. Urethane elastomers are all synthesized through the same production scheme, with variations in the relative amounts of the starting materials, that is, diisocyanates (toluene 2,4-diisocyanate) and polyethers having terminal hydroxyl groups (polyethyleneglycol adipinate).

The density of urethane elastomers is 0.93–1.26 g/cm³, and the temperature of glass transition varies from –35° to –44°C. A characteristic feature of these elastomers is a high specific energy of cohesion (378–588 kilojoules/mole [90–140 kilocalories/ mole]). Because of this feature, rubbers based on urethane elastomers possess unique mechanical properties; their tensile strength is 30–50 meganewtons/m² (300–500 kilograms-force/cm²), and their abrasion resistance is 50–100 cm³/kilowatt-hour. The rubbers resist the effects of oils, fuels, solvents, ultraviolet light, gamma radiation, and ozone. Drawbacks include low hydrolytic stability and comparatively low thermal stability.

Casting systems are widely used in industry for making solid tires for intrafactory transport, parts for the sifters used in the classification of coal, conveyer belts, driving belts, packing and shock absorbers, shoe soles, carpet pads, and wallpaper. Thermoplastic elastomers are used mainly for automotive parts, and vulcanized millable rubbers are used in making shoe uppers and articles having complex shapes.

Trade names for urethane elastomers include SKU (USSR), Adiprene, Texin, Genthane, and Elastothane (United States), Vulkollans, Durethan, Desmophen, and Urepan (Federal Republic of Germany), and Sispur (German Democratic Republic). World production of urethane elastomers in 1974 was approximately 80,000 tons.