Silyl Glyoxylates as a New Class of High Performance Photoinitiators: Blue LED Induced Polymerization of Methacrylates in Thin and Thick Films

Silyl glyoxylates are proposed here as a new class of high performance type I photoinitiators for free radical polymerization under air or in laminate (e.g., (meth)­acrylates) upon exposure to different near-UV (at 395 nm; at 405 nm) and blue (at 477 nm) LEDs. The new proposed photoinitiators can also be used in the presence of additives that can enhance their initiating ability: an iodonium salt and an amine or a phosphine. The silyl glyoxylate-based photoinitiating systems exhibit excellent polymerization performances upon blue LED light (at 477 nm) with exceptional bleaching properties compared to camphorquinone (CQ)-based systems. This can be highly worthwhile for the preparation of colorless polymers upon visible light. Real-time Fourier transform infrared spectroscopy (RT-FTIR) experiments are used to monitor the polymerization profiles. The involved chemical mechanisms are investigated by fluorescence, laser flash photolysis, electron spin resonance (ESR), and steady state photolysis experiments. Molecular orbital calculations are also carried out. The overall excited state processes and the chemical mechanisms involved in the initiation step are detailed