N-phenylmaleimides as comonomers and photoinitiators in ultraviolet-visible photopolymerizable formulations
One of the fastest growing areas in coatings technology is radiation-curable materials. Radiation curing offers several distinct advantages compared to typical solvent-borne or thermoset materials including reduced volatile organic compound emissions, reduced energy requirements, and increased speed of cure. Conventional free radical photoinitiators provide the advantage of fast, controllable rates of photocuring; however, they typically also have several major disadvantages. In light of the difficulties associated with the use of most conventional free radical photoinitiators, an alternative class of copolymerizable photoinitiators is of interest. Based upon literature reports on the photochemical hydrogen abstraction reactions of phthalimides, succinimides, and α, β-unsaturated ene-ones, maleimides were chosen as likely candidates for a new family of copolymerizable photoinitiators. Due to the relative ease of synthesis, and potentially reduced toxicity compared to the N-alkylmaleimides, N-phenylmaleimides were chosen as the focus of this dissertation research. A series of photopolymerization studies was performed in order to ascertain the utility of N-phenylmaleimides as free-radical photoinitiators for acrylic-based UV-curable formulations. Supplementarily to the photopolymerization studies, a battery of small-molecule structural, photophysical, and photochemical studies was performed to further elucidate the small-molecule photophysics and photochemistry of N-phenylmaleimides. These small-molecule chemistry studies were performed with the goal of determining and understanding the photochemical processes that occur upon direct excitation and triplet sensitization of N-phenylmaleimides in UV-curable formulations, as well as the structure-reactivity relationships operative among N-phenylmaleimides in these formulations.