Catalysis of the epoxy-carboxyl reaction

We have investigated the reactions of glycidyl ether, glycidyl ester, and other oxirane functional resins with carboxyl or anhydride functional compounds and polymers in the presence of a wide range of amine, phosphonium, and metal catalysts. We confirmed that both amine and phosphonium compounds can catalyze the reaction of epoxy groups with carboxyl and anhydride groups. There are certain deficiencies with these catalysts, such as a tendency to yellow and a reduction in stability at ambient or elevated temperatures. We also observed that many of the known amine catalysts contribute to poorer humidity resistance and exterior durability. Several metal salts were found to effective catalysts, but they also contributed to a reduction in chemical resistance or they led to paint instability. We have discovered a group of metal chelates that overcome these problems and provide stable formulation in a single package that do not yellow during cure and that give improved resistance properties. The new catalysts have been evaluated in high-solids epoxy/carboxyl coatings, automotive clearcoats, and powder coatings.