Effect of reactive oxygen species on the kinetics of free radical photopolymerization

The kinetic profile for free radical photopolymerization of a low viscous acrylate resin was found to exhibit an unusual behaviour under atmospheric conditions: two successive waves of polymerization were observed and characterized by RT-FTIR and confocal Raman microscopy. The first wave is merely attributed to the conventional photoinitiation process with a good depth curing but a surface layer which is strongly inhibited by molecular oxygen. During this inhibition process, hydroperoxides are generated at a relatively high concentration. After full consumption of the photoinitiator, these hydroperoxides are further responsible for the second polymerization wave. Depth profiling experiments and determination of the variation of hydroperoxide concentration with time confirm this assumption.