Unsymmetrical polyurethane polyol prepolymers are disclosed for use in the formation of coating compositions. The prepolymers are prepared as a reaction product of a diisocyanate with a short chain aliphatic diol and a long chain polymeric diol. The prepolymers are intended as the first component for reaction with a second component polyisocyanate in a two-component coating composition. The coating compositions exhibit excellent abrasion resistance and weatherability, and are particularly useful as coatings for polymeric window transparencies.