Radical-Promoted Visible Light Photoinitiated Cationic Polymerization of Epoxides

Herein is described the development of a three-component photoinitiator system that employs the free radical promoted decomposition of diaryliodonium salts for the visible light induced cationic polymerization of epoxides. A long wavelength, titanium-complex free radical photoinitiator is used to generate radicals that abstract hydrogen atoms from benzyl alcohol synergists. The resulting benzyl radical species efficiently reduce diaryliodonium salts thereby generating oxycarbenium ions that spontaneously fragment to form the corresponding aldehyde and a Br⊘nsted superacid. The superacid subsequently initiates the cationic ring-opening polymerization of a wide variety of epoxide monomers.