On-Demand Visible Light Activated Amine/Benzoyl Peroxide Redox Initiating Systems: A Unique Tool To Overcome the Shadow Areas in Photopolymerization Processes

A novel way to counterbalance the drawbacks and advantages of photo polymerization and redox polymerization is proposed. Photoinitiating systems based on charge transfer complexes (CTC) between a phosphine and an iodonium salt as well as an amine and iodonium salt are checked for the free radical polymerization of methacrylates. Polymer materials as thick as 8.5 cm can be produced under air upon exposure to a LED at 405 nm using an amine/phosphine/iodonium three-component photoinitiating system. When combined with benzoyl peroxide (BPO), these systems are active in photoinduced redox polymerization; i.e., the CTC is used to absorb the light and generates initiating radicals and the amine/BPO couple allows a redox polymerization. Therefore, a fast/slow time control of the radical reaction is feasible under air, and an excellent monomer conversion is obtained both at the top layer and in the core of the sample. The efficiency of this photoactivated redox system is assessed in terms of monomer conversion (followed by FTIR and RAMAN analysis) and time control. The chemical mechanisms are studied using UV-vis absorption spectroscopy, steady-state photolysis, P-31 NMR, and ESR-spin trapping experiments.