Polyurethane-25 is a complex polymer formed by the reaction of dihydroxypolyoxobutylene (degree of polymerization 12-30), dimethylol propionic acid, meta-tetramethylenexylenediisocyanate, isophoronediisocyanate and trimethoylpropane. The prepolymer is neutralized with triethylamine and chain extended with C0-8 alkyl diamine.