Single-component thioxanthone-based photoinitiator for free-radical photopolymerization of acrylates via UV-LED irradiation

In this study, three new efficient one-component type II photoinitiators (PIs) for free-radical polymerization of acrylate-type monomers under ultraviolet (UV) light-emitting diode (UV-LED) irradiation were synthesized by covalently linking different coinitiators with a thioxanthone chromophore using a methyl ester linker. UV-visible spectroscopy and electron spin resonance analysis confirmed the generation of free radicals through intramolecular reactions between hydrogen donor coinitiators and the thioxanthone moiety. Real-time Fouriertransform infrared spectroscopy was used to investigate the kinetics of photopolymerization of the prepared PIs. TX-A2 with benzodioxole as a coinitiator showed conversions of 90 % within 20 s for C--C double bonds and a polymerization rate of 10.9 %/s, performing considerably better than a commercial PI 2-isopropylthioxanthone and the prepared PIs with anisole and thioanisole coinitiators. These results highlight the significance of intramolecularly incorporated coinitiator moieties in enhancing the performance of efficient single-component type II PIs. In addition, TX-A2 was successfully used for curing color photoresist films, which could be patterned via photolithography and improved the stability of color pigments in the films toward light and heat, indicating its considerable potential in advanced manufacturing.