One-Component Stilbene-Based Iodonium Photoinitiators with Increased Photoacid Quantum Yield for Cationic Vat 3D Printing

New advanced iodonium salts based on stilbene chromophores with significantly improved photoinitiating properties are presented. The extended conjugated double bond system provides major improvement in quantum yield of superacid generation (up to 10 times higher compared to benzylidene-based iodonium salts) while maintaining absorption properties in UV-A and visible light. The newly developed iodonium salts exhibit photoinitiating activity toward cationically polymerizable monomers such as cyclic epoxy monomers (e.g., 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane-carboxylate (CADE)), oxetanes (e.g., bis[1-ethyl(3-oxetanyl)]methyl ether (OXT-221)) and glycidyl ether monomers (e.g., diglycidyl ether of bisphenol A (DGEBA)) under the irradiation by light-emitting diodes (LEDs) emitting at 365, 405 and even 430 nm, with no additives. Commonly used diaryliodonium photoinitiators are inactive under those irradiation wavelengths. Moreover, some of the new iodonium salts are also able to photoinitiate free radical photopolymerization of the acrylate monomers, such as trimethylolpropane triacrylate (TMPTA). Such high photoinitiating activity allows these salts to be used as one-component photoinitiators in cationic vat 3D printing of nanocomposites at ambient temperature. The resolution of the cationic prints was limited mainly by the DLP 3D printer and monomers, with slight signs of overpolymerization.