NEW CROSS-LINKING SYSTEM USING BLOCKED CARBOXYLIC-ACID

A new crosslinking reaction between carboxylic acids blocked by alkyl vinyl ethers and epoxides was studied. Carboxylic acids were converted into hemiacetal eaters by the reaction with vinyl ethers. The blockin g reaction was accelerated in the presence of a relatively weak acid, phosphoric acid, without cationic polymerization of the vinyl ether. T he blocked carboxylic acids had good solubility in various kinds of or ganic solvents. Although the blocked carboxylic acids were stable unde r storage conditions, they regenerated carboxylic acids by heating at 140 degrees C, eliminating vinyl ethers. Both the deblocking reaction of the blocked carboxylic acid and esterification of the regenerated c arboxylic acid with epoxide were accelerated in the presence of a rela tively weak Lewis acid, zinc 2-ethylhexanoate, without polyetherificat ion of epoxide. Curing of this system proceeded through a sequence of three-step reactions consisting of deblocking, esterification, and add ition of 2-hydroxyalkyl ester to vinyl ether. The main product of this system was 2-acetalalkyl ester. This system with the Lewis acid can b e stabilized under practical storage conditions by adding triethanolam ine as a stabilizer for the catalyst. This system offers one-component high solid coating solutions and cured films with excellent acid rain resistance. (C) 1997 Elsevier Science S.A.