Photopolymerization Maleimides and Vinyl Ethers

Clearcoats based on combinations of various maleimides (MI) and vinyl ethers (VE) or VE blends were tested with respect to their UV-photocuring in air [175]. It was found that MI/VE binders and reactive thinners could be cured without additional photoinitiators. Moreover, the equimolar MI/VE blends could be used as photoinitiators for acrylate systems, although their reactivity compared with commercial Norrish type I initiators proved to be poor. The observed limitations, e.g. changes in the properties of cured UPRs, limited reactivity in the air and irritation effects, could be ehminated using aliphatic MI types with further increased reactivity, higher functionality and/or molecular weight and lower irritation. 

Allyl ethers were used as built-in monomers in UPRs [176]. High hardness of the coatings cured in air using photoinitiators was achieved. Following polyfunctional allyl ethers were incorporated into polyester molecules  

1- allyloxy-5,6-hexanediol, trimethylolpropane monoallyl ether, pentaerythri-tol diallyl and triallyl ether, glycerol monoallyl ether, and diallyl ether of propoxylated czs-2-butene-l,4-diol. The allyl ether monomers with hydroxyl groups were reacted with a mixture of fumaric acid, adipic acid and 1,2-propylene glycol, thus forming a maleic unsaturated polyester with terminal and pendant allyl ether groups. 

UV-curable UPRs are mainly used in coatings, waterborne ones in particular. Por that purpose, imsaturated polyesters were synthesized from ethylene glycol, diethylene glycol and 1,2-propylene glycol combined with dicarboxylic acids or acid anhydrides fumaric acid, tetrahydrophthalic anhydride, tereph-thahc acid and trimelUtic anhydride [177] trimethylolpropane diallyl ether was incorporated into the polyester as an air inhibitor of cure. Moreover, tri-ethylamine was added to neutralize the unreacted carboxyUc groups, whereas 

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