Hydroxy functional urethane polyester with polymerized lactones

The solvent based, thermosetting coating composition comprising

• (I) hydroxy functional urethane modified polyester resin which resin has a number average molecular weight (M.sub.n) of between about 2,000 and about 20,000, said resin being the product of polymerization at about 50.degree.-300.degree. C. of a reaction mixture of lactone monomers in the presence of hydroxy-containing urethane modified polyester precursor (i) having a number average molecular weight (M.sub.n) between about 1,000 and about 10,000 (ii) having a hydroxyl number between about 30 and about 300, and (iii) containing between about 1 and about 10 urethane groups per molecule;
• wherein pendant hydroxyl terminated polycaprolactone moieties are formed and attached to the polyester precursor and wherein said lactone monomers are selected from those represented by the general formula:
• ##STR5## in which n is at least 4, at least n+2 R's are hydrogen, and the remaining R's are substituents selected from the group consisting of alkyl, cycloalkyl, alkoxy and single ring aromatic hydrocarbon radicals, and wherein said hydroxy-containing urethane modified polyester precursor consists of the reaction product of:
• (A) urethane modified diol being the reaction product of:
• (a) diol and (b) diisocyanate, wherein said diol and said diisocyanate are reacted in a molar ratio from about 4:1 to about 4:3, respectively:
• (B) polyol comprising at least about 5 weight percent triol;
• and
• (C) acid component selected from dicarboxylic acids and anhydrides thereof;
• and wherein the reaction mixture comprises between about 10 and 80 weight percent of said precursor and between about 90 and about 20 weight percent of said lactone monomers;
• and
• (II) a blocked polyisocyanate crosslinking agent comprising the reaction product of:
• (A) the reaction product of (i) organic diisocyanate represented by the formula:
• OCN--R--NCO
• wherein R is selected from the group consisting of aliphatic, cycloaliphatic and aromatic radicals and combinations thereof and wherein one of the isocyanate groups thereof is a more reactive isocyanate group than the other isocyanate group and (ii) sufficient active hydrogen containing blocking agent to react with substantially all of said more reactive isocyanate groups;
• and
• (B) sufficient polyol to react with substantially all of said other isocyanate groups.