Abstract
A new crosslinking reaction between carboxylic acids blocked by alkyl vinyl ethers and epoxides was studied. Carboxylic acids were converted into hemiacetal esters by the reaction with vinyl ethers. The blocking reaction was accelerated in the presence of a relatively weak acid, phosphoric acid, without cationic polymerization of the vinyl ether. The blocked carboxylic acids had good solubility in various kinds of organic solvents. Although the blocked carboxylic acids were stable under storage conditions, they regenerated carboxylic acids by heating at 140 °C, eliminating vinyl ethers. Both the deblocking reaction of the blocked carboxylic acid and esterification of the regenerated carboxylic acid with epoxide were accelerated in the presence of a relatively weak Lewis acid, zinc 2-ethylhexanoate, without polyetherification of epoxide. Curing of this system proceeded through a sequence of three-step reactions consisting of deblocking, esterification, and addition of 2-hydroxyalkyl ester to vinyl ether. The main product of this system was 2-acetalalkyl ester. This system with the Lewis acid can be stabilized under practical storage conditions by adding triethanolamine as a stabilizer for the catalyst. This system offers one-component high solid coating solutions and cured films with excellent acid rain resistance.
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