Synthesis and photopolymerization of novel multifunctional vinyl esters

Novel mono- and multifunctional vinyl ester monomers containing thioether groups were synthesized via an amine-catalyzed Michael addition reaction between vinyl acrylate and multifunctional thiols. Using photo-differential scanning calorimetry and real-time Fourier transform infrared (RTIR) spectroscopy, the polymerization kinetics and oxygen inhibition of the homopolymerizations of the vinyl ester monomers were investigated. The effect of the vinyl ester and thioether group on acrylate/vinyl ester and thiol/vinyl ester copolymerizations was determined using realtime IR spectroscopy to monitor polymerization rates of acrylate, vinyl, and thiol groups simultaneously. Polymerization of the vinyl esters used was found to be relatively insensitive to oxygen inhibition. We propose that the thioether group is responsible for reducing oxygen inhibition by a series of chain transfer/oxygen-scavenging reactions. In polymerization of a acrylate/vinyl ester mixture both in nitrogen and in air, the vinyl ester monomer significantly enhances the polymerization rates and the conversion of the acrylate double bonds via plasticization of the crosslinked matrix and reduction of inhibition by oxygen. Ultimately, the vinyl ester monomer is incorporated into the polymer network. Thiol/vinyl ester free-radical copolymerization is much faster than either thiol/allylether copolymerization or vinyl ester homopolymerization. The electron-rich vinyl ester double bonds ensure rapid copolymerization with thiol. (C) 2004 Wiley Periodicals, Inc.