In the reinforced state, these rubbers offer moderate tensile strength but relatively low elongation properties. They resist oxidation and ozone, and they do not support combustion. Postcuring is required to develop optimum properties. Typical applications are seals, gaskets, diaphragms, pump impellers, tubing, and vacuum and radiation equipment. These rubbers, combinations of polyesters or polyethers and diisocyanates, are unusual in that physical properties do not depend on compounding materials.
Urethanes crosslink and undergo chain extension to produce a wide variety of compounds.
They are available as castable or liquid materials and as solids or millable gums. Urethane polymers have outstanding abrasion resistance, excellent tensile strength and load-bearing capacity, and elongation potential, accompanied by high hardness. Other properties include low-temperature resistance, high tear strength, either high or low coefficient of friction, good radiation resistance, and good elasticity and resilience, even in very hard stocks. Typical applications include seals, bumpers, metal-forming dies, valve seats, liners, coupling elements, rollers, wheels, and conveyor belts, especially where abrasive conditions are present.