This invention relates to a moisture curable, isocyanate terminated, branched prepolymer which is the reaction product of (a) an alcohol having two or three --OH groups, (b) a hydrophobic polymeric diol or triol and (c) at least one polyisocyanate, said prepolymer having an NCO content in the range 0.3 to 1.0 meq/q. Exposure of the prepolymer as a coating on a substrate to moisture under atmospheric conditions results in a cured coating having excellent adhesion to the substrate and excellent abrasion resistance.