A blocking method of carboxylic acids using alkyl vinyl ethers was studied. In this method, carboxylic acids were converted into hemiacetal esters.
The vinyl ether blocked carboxylic acid was prepared by the addition of carboxylic acid to an excess of alkyl vinyl ether (×1.5 mol) in the presence of trace amounts of acidic phosphate (0.4 equiv%) at 25°C for 17 h.
The deblocking reaction of the vinyl ether blocked carboxylic acid occurred readily at temperatures over 140°C. The activation energy of the deblocking reaction (1. 06 × 10
5 J/mol) was higher than that of the esterification between carboxylic acid and epoxide (7.91 × 10
4 J/mol). This result indicated that the deblocking reaction was the rate-determining step in the curing of the vinyl ether blocked carboxylic acid/epoxide system.
The blocked carboxylic acid was stable at 50°C up to 30 days. The vinyl ether blocked carboxylic acid/epoxide system was also stable under the same storage condition.
By using the vinyl ether blocked carboxylic acids with epoxides, useful one-component coatings can be obtained.
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