Substitution of from 5 to 50 equivalent percent of an ultra-low unsaturation polyoxypropylene diol for PTMEG in isocyanate-terminated prepolymers used in spandex production is found to lower considerably both prepolymer viscosity and hysteresis while substantially retaining other desirable physical properties. Such products may offer higher fiber production rates than are possible while employing an all PTMEG-derived polymer.
