Photoinitiated polymerization of vinyl ether-based systems

Abstract

The photoinitiated polymerization of vinyl ether (VE)-based coatings has been studied by real-time infrared (RTIR) spectroscopy. In the presence of diaryliodonium or triarylsulfonium photoinitiators, the cationic polymerization occurs rapidly upon UV-exposure and continues to proceed upon storage in the dark. Increasing the formulation viscosity by introduction of telechelic VE oligomers was found to have a strong slowing down effect on the UV-curing, because of the reduced mobility of the reactive species. VEs proved to be very effective monomers to achieve a fast and extensive curing of dicycloaliphatic epoxides. Similar polymerization profiles have been recorded by RTIR spectroscopy for the two monomers upon UV-exposure, which argues in favor of a copolymerization process between VEs and epoxides. When associated to electron acceptor monomers, like unsaturated esters or N-substituted maleimides, VEs undergo a radical-type copolymerization upon UV-exposure. For the maleate/VE combination, the two monomers were found to disappear at the same rate, whatever the monomer feed composition. The resulting alternating copolymer was shown to be formed by homopolymerization of a donor/acceptor complex. A similar conclusion was drawn from the kinetic data obtained for the maleimide/VE combination which polymerizes readily upon UV-exposure, even in the absence of any added photoinitiator.