Photoinitiated polymerization of vinyl ether and acrylate monomer mixtures

The photoinitiated cationic polymerization of vinyl ether (VE) monomers has been studied by real-time infrared spectroscopy. For the divinyl ether of triethylene glycol, the chain reaction was shown to develop rapidly and extensively, with kinetic chain lengths on the order of 10,000. Interpenetrating polymer networks have been produced by UV curing of a vinyl ether/acrylate mixture in the presence of a cationic photoinitiator. The acrylate double bond polymerizes faster than the vinyl ether double bond and reaches 95% conversion in triacrylate monomers. Vinyl ether/acrylate hybrids were also found to polymerize readily upon UV exposure in the presence of a radical photoinitiator, according to a cross-propagation mechanism which generates a copolymer with isolated VE units. Acrylate radicals were shown to be twice as reactive toward the acrylate double bond than toward the vinyl ether double bond, thus leading to a UV-cured polymer which contains a relatively large amount of unreacted double bonds. The residual unsaturation content was markedly reduced by the addition of a cationic photoinitiator and by exposing the sample successively to filtered and unfiltered UV radiation.