Crosslinking reactions of acrylic polymers containing carboxyl groups with melamine resins

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Abstract
The mechanism of cure has been studied in coating systems comprising blends of ammonium salts of acrylic acid–acrylic ester copolymers and alkoxymethylmelamines. Experiments were conducted both on the resin components themselves and on model compounds having analogous chemical structures. Curing of the resin begins with loss of ammonia to regenerate free carboxyl groups, rather than loss of water to form amides. The alkoxy group is eliminated, and ester crosslinks are formed between the carboxyl and the methylolmelamine. Base binding studies on cured films show that the extent of crosslinking depends on the exact composition of the resin system and the presence or absence of an acidic catalyst. These variables can be adjusted to provide essentially quantitative crosslinking in the cured coating, as shown by the complete disappearance of unreacted carboxyl groups.

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