Methods A photopolymerizable methacrylate phenacyl phenothiazinium salt (Acry-P-PTh) was synthesized by incorporating acrylic ester groups. Its structure, photophysical properties, photochemical behavior, migration ratio, and thermal stability were investigated using ultraviolet-visible absorption (UV-Vis) spectroscopy, real-time infrared (RT-IR) spectroscopy, and differential scanning calorimetry (DSC).

Results and Discussion UV-Vis analysis revealed that Acry-P-PTh was responsive to ultraviolet(UV), visible, and near-infrared (NIR) light, with the peak absorption wavelength shifting to 520 nm, a 5 nm redshift compared to phenacyl phenothiazinium salt (P-PTh). Photopolymerization kinetics demonstrated that Acry-P-PTh effectively initiated both free radical and cationic polymerization. Under 365 nm, 405 nm, and 850 nm irradiation, Acry-P-PTh generated benzoyl radicals and Brønsted superacids through C-S bond homolysis. This dual initiation mechanism enabled the polymerization of both acrylate monomers, trimethylolpropane triacrylate (TMPTA), and cationic monomers, EPOX, achieving excellent initiation performance in hybrid systems compared to single-monomer resin systems. Specifically, under 365 nm light irradiation, the final free radical conversion rate exceeded 50%, and the final cationic conversion rate exceeded 40%; under 405 nm light irradiation, the final free radical conversion rate exceeded 45%, and the final cationic conversion rate exceeded 45%. Notably, under 850 nm light, EPOX cationic polymerization achieved a 40% conversion rate within 30 min. Migration studies confirmed that Acry-P-PTh exhibited low migration, with post-curing migration ratios lower than those of P-PTh, measuring 4. 9% for the free radical system and 3. 5% for the cationic system. Thermal stability analysis further revealed high thermal resistance, with polymerization temperatures for free radical and cationic polymerization being 233 ℃ and 78 ℃, respectively. These properties make Acry-P-PTh a promising material for various applications, such as food packaging and biomedicine manufacturing.

Conclusion The synthesized Acry-P-PTh demonstrates broadband absorption across the ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrum. Compared to P-PTh, Acry-P-PTh shows reduced low migration ratio. When mixed with Acry-P-PTh with TMPTA and EPOX monomers, the photocurable system is able to resist higher thermal polymerization temperatures, demonstrating excellent thermal stability. In conclusion, Acry-P-PTh, as an advanced photoinitiator, holds significant potential for practical applications.