Diblocked diisocyanate urea urethane oligomers and coating compositions comprising same

A solvent based resin composition comprising:

• A. a chain-extendable, crosslinkable diblocked diisocyanate urea urethane oligomer of number average molecular weight about 300 to about 1500 comprising the reaction product of primary or secondary alkanolamine of molecular weight about 60 to 300 with half-blocked organic diisocyanate in molar ratio of about 1:2, respectively, whereby both the hydroxy and amine functionality react with free isocyanate groups to form urethane and urea linkages respectively, said oligomer being substantially free of unreacted hydroxy and amino functionality, said half-blocked diisocyanate having number average molecular weight of about 120 to about 600 and comprising the reaction product of the organic diisocyanate of molecular weight less than about 250, with an approximately equal molar amount of monofunctional blocking agent selected from the group consisting of primary alcohol, secondary alcohol, amide, phenol, ketoxime and a mixture of any of them, wherein said diblocked diisocyanate urea urethane oligomer has a de-blocking temperature of about 150.degree. C. to about 220.degree. C.;
• B. Bisphenol A epichlorohydrin epoxy resin of epoxide equivalent weight about 180 to about 200, wherein said oligomer and said epoxy resin are present in weight ratio of about 1:1 to about 2:1, respectively;
• and
• C. organic solvent in amount sufficient to provide a volatile organic content (calculated) of less than about 400 g/l.