Radical photopolymerizations are typically triggered by the capacity of some molecules (photoinitiators) to be exited upon light irradiation, and to then form initiating radicals that add to reactive groups of a polymerizable mixture (formulation). Since polymers are present in all aspects of our society, developing new photoinitiators is industrially relevant. In Light-COAT, we have developed novel acyl - dithiocarbamates (DTCs), which have proven to homolytically cleave to provide radicals (Type I photoinitiators) upon irradiation with low energy visible light (405 to 460 nm). The formed radicals can trigger radical polymerization of monomers containing double bonds, particularly acrylate esters and acrylamides. One initial DTC photoinitiator was identified as the most promising one, and proven safe against genotoxicity and acute toxicity tests. The DTC was formulated and tested in coating applications by us and also by industrial contacts against benchmark commercial photoinitiators. The coatings were characterized according to industrial standards. The developed photoinitiators offered adequate coatings with good adhesion, albeit they could not outperform commercial ones. We also investigated the performance of our visible-light activated initiators in other applications, including 3D-printing, dental composites, adhesives, hydrogels (e.g. used in contact lenses) and polymeric matrices for structural composites. In the last application, one DTC derivative provided materials with improved properties with respect to commercial benchmark photoinitiators. The improved properties include the formation of tougher materials and a higher elongation at break. In addition, we could achieve a much better control of the polymerization because of the remarkable ON/OFF activation of the photoinitiator with light. We are currently in contact with industrial partners to closely evaluate if these improved attributes may find a real application and commercial niche.
