Phase separating polyurethane prepolymers and elastomers prepared by reacting a polyol having a molecular weight of 600-3500 and isocyanate and a low molecular weight chain extender in which the ratios of reactants have a limited range

A reactive, 100 percent solids, storage stable segmented, phase-separating polyurethane prepolymer having soft segments and suitable hard segments comprising the reaction product of:

• (i) a polyol (A) having a number average molecular weight of from about 600 to about 3500 and having a functionality of at least 2;
• (ii) an isocyanate (B) having a functionality of at least 2;
• and
• (iii) a low molecular weight chain extender (C) having a molecular weight in a range lower than about 500 and having a functionality of at least 2, wherein the reactants are employed in such proportions so as to satisfy the following equations:
• ##EQU5##
• Eq.sub.OH .gtoreq.Eq.sub.CE (b)
• Eq.sub.CE >O, (c)
• wherein Eq.sub.NCO denotes the equivalents of the isocyanate species employed, and Eq.sub.OH and Eq.sub.CE denote the respective molar equivalents of the polyol and chain extender employed, said soft segments provided by the polyol and said suitable hard segments provided by the reaction product of the isocyanate and chain extender and which induce phase-separation of said hard and soft segments in said prepolymer as a result of thermodynamic incompatibility between said hard and soft segments, said prepolymer being an opaque solid at room temperature.