39 diisocyanate toluene diisocyanate 3 3 39 dimethyl 4 4 biphenylene diisocyanate 1 4 tetramethylene diisocyanate 1 6 hexamethylene diisocyanate 2 2 4 trimethylhexane 1 6 diisocyanate methylene bis phenyl isocyanate 1 5 naphthalene diisocyanate bis isocyanatoethyl fumarate isophorone diisocyanate ipdi and methylene bis 4 cyclohexylisocyanate there can also be employed isocyanate terminated adducts of diols such as ethylene glycol 1 4 butylene glycol polyalkylene glycols etc these are formed by reacting more than one more of a diisocyanate such as those mentioned with one mole of a diol to form a longer chain diisocyanate alternatively the diol can be added along with the diisocyanate while diisocyanates are preferred other multi functional isocyanates can be utilized examples are 1 2 4 benzene triisocyanate and polymethylene polyphenyl isocyanate it is preferred to employ an aliphatic diisocyanate since it has been found that these provide better color stability in the finished coating examples include 1 6 hexamethylene diisocyanate 1 4 butylene diisocyanate methylene bis 4 cyclohexyl isocyanate and isophorone diisocyanate mixtures of diisocyanates can also be employed the proportions of the diisocyanate and the polyester are chosen so as to provide a hydroxyl containing product this can be accomplished by utilizing a less than stoichiometric amount of polyisocyanate i e less than one isocyanate group per hydroxyl and carboxyl group in the polyester higher e g stoichiometric or excess isocyanate levels can be present if the reaction is terminated at the desired stage as by addition of a compound which reacts with the residual isocyanate groups water alcohols and amino alcohols are examples of such compounds in one especially desirable embodiment of the invention a multi functional alcohol is used to terminate the reaction at the desired stage determined by the viscosity thereby also contributing residual hydroxyl groups.