A novel sulfur-containing photoinitiator based on benzophenone derivatives for rapid photopolymerization

In this study, a series of benzophenone (BP)-based photoinitiators (PIs), designated as BP-Sn, were synthesized by the integration of small molecule hydrogen donors into the BP scaffold. This design aims to minimize reliance on co-initiators, reduce potential odors and toxicities, and enhance initiation efficiency of PIs under LED irradiation. Additionally, the incorporation of thioether linkages imparts a distinctive dual functionality to PIs, enabling them to exhibit both hydrogen-abstracting (Type II) and bond-breaking (Type I) characteristics. The photophysical and photoinitiation properties of BP-Sn were evaluated using electron paramagnetic resonance, UV-visible spectrophotometry, and real-time Fourier-transform Infrared spectroscopy. The findings demonstrate that BP-Sn exhibit remarkable efficacy as a single-component PI for free-radical polymerization, achieving a final conversion efficiency approaching 95% and a photoinitiation rate exceeding 20% s^-1 for the polymerization of tripropylene glycol diacrylate without the need for additional co-initiators. Furthermore, the polymerization experiment revealed that exposure to 365 nm LED light for just 2 min results in the formation of a colorless and well-defined patterned texture, with a thickness of 5 mm and a diameter of 7 cm, demonstrating its potential practical applications.