Coumarin derivatives as amphiphilic photoinitiators for free radical and cationic Photopolymerizations with UV-Vis LED irradiation

Three coumarin-3-oxoacetic acids (COXAs), which are amphiphilic photoinitiators (PIs) used in photocuring technology, were synthesized and studied. These PIs exhibited strong ultraviolet visible absorption in the range 300-500 nm. Real-time fourier transform infrared (RT-FTIR) and photo-differential scanning calorimet (photoDSC) experiments showed that these materials could be used as type I PIs and type II PIs to initiate free radical polymerization (FRP) of acrylate monomers. Notably they can sensitize iodonium and sulfonium salts to initiate cationic polymerization (CP) of epoxy and oxetane monomers. Furthermore, COXAs could initiate deep curing of Tri-(propylene glycol) diacrylate (TPGDA) at very low concentrations which was 0.01 wt%. The curing depth exceeded around 9 cm when the sample was irradiated with a 415 nm LED (100 mW & sdot;cm- 2) for 5 min. The COXAs also initiated deep curing of the water-soluble monomer polyethylene glycol (400) diacrylate (PEG(400)DA) at the same depth as TPGDA under the same irradiation conditions, even in various proportions of water. Moreover, the COXAs exhibited acceptable photobleaching and lower cytotoxicity.