Novel Acyl Phosphine Oxides as Low-Migration Type I Photoinitiators for Radical Polymerization

TPO-L (Ethyl(2,4,6-trimethylbenzoyl) phenylphosphinate) is a liquid high-efficiency photoinitiator, which is widely used in the UV-LED photopolymerization reaction field. After TPO-L participates in the photopolymerization reaction, the TPO-L that did not participate in the reaction will migrate to the surface of a coating, causing the coating surface to turn yellow and accelerating the aging process of the coating. This issue has attracted increasing attention. To address the high migration issue of TPO-L, in this experiment, three new type I photoinitiators were designed and synthesized, namely TPOLs with acylphosphine oxide structures. The structure of TPOLs can be modified by different lengths of methyl-terminal ethoxy chains. The properties of TPOLs were systematically evaluated through migration experiments, monomer solubility tests, absorption spectra, photopolymerization kinetics, photolysis, free radical trapping experiments, and cellular cytotoxicity. The results show that the absorption maxima of the TPOLs are located at around 372 nm. TPOLs have good solubility in acrylic monomers, and TPOL-2 and TPOL-3 in particular exhibit high photopolymerization efficiency. At a concentration of 50 μM, the cell survival rates of TPOL-1 and TPOL-3 are approximately 90%. It is noteworthy that the migration rate of TPOL-3 in the cured film is as low as 0.02%, significantly lower than the 0.98% of TPO-L, indicating that TPOL-3 has higher migration stability and better environmental compatibility. In summary, these results indicate that TPOL-3 has high initiation efficiency during LED curing, good solubility in monomers, and a low migration rate, making it a promising candidate material for low-migration photopolymerization applications.