Effects of polymerizable organoclays on oxygen inhibition of acrylate and thiol-acrylate photopolymerization

Oxygen inhibition is of great concern in radical photopolymerization. This research investigates the effects of polymerizable organoclays on oxygen inhibition of acrylate and thiol-acrylate systems. Without use of thiol monomers, oxygen inhibition is difficult to overcome, although adding acrylated polymerizable organoclays slightly enhances polymerization in air. By incorporating thiols, on the other hand, polymerization rates and conversion continue to increase until thiol concentration reaches 30 mol% reaching rates and conversions approximately 80% of those observed in nitrogen. Further improvements have been observed by adding suitable polymerizable organoclays. Addition of only 5 wt% thiolated organoclays into the thiol-acrylate systems including 20 mol% thiol enhances the conversion in air to almost identical levels of that achieved under nitrogen. Interestingly, addition of either non-reactive or acrylated organoclays usually decreases the polymerization. In addition, higher thiol conversions are achieved by adding thiolated organoclays due to increased thiol-ene reaction induced by the functional groups on the clay surfaces.