Visible and long-wavelength photoinitiated cationic polymerization

A new system for efficiently carrying out cationic photopolymerizations wit h visible and long-wavelength UV light is described. This system is based o n the principle that certain onium salt cationic photoinitiators can be red uced by free radicals produced by the hydrogen abstraction reactions of pho toexcited ketones. Thus, when camphorquinone, benzil, 2-isopropylthioxantho ne, and 2-ethylanthraquinone are irradiated in the presence of a monomer th at can serve as a hydrogen donor, the resulting monomer-bound radical rapid ly reduces a diaryliodonium salt or a dialkylphenacylsulfonium salt, and th e resulting monomer-centered cations initiate the polymerizations of epoxid es, vinyl ethers, and heterocyclic compounds. Onium salts with high reducti on potentials, such as triarylsulfonium salts, do not undergo sensitization by this new system. (C) 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 343-356, 2001.