Monoacylphosphine oxides with substituents in the phosphonyl moiety as Norrish I photoinitiators: Synthesis, photoinitiattion properties and mechanism

In order to study the effect of the substituents in the phosphonyl moiety of monoacylphosphine oxide (MAPO) on its stability and initiation performance, (2,4,6-trimethylphenyl)(phenyl)(benzoyl)phosphine oxide (TMBPO), (4-tolyl)(phenyl)(2,4,6-trimethylbenzoyl)phosphine oxide (4-MTPO) and (2,4-xylyl)(phenyl)(2,4,6-trimethylbenzoyl)phosphine oxide (2,4-DMTPO) were designed and prepared. Studies on TMBPO showed that the introduction of methyl groups into the phosphonyl moiety of MAPO significantly enhanced its stability and light absorption abilities. The photopolymerization of trimethylolpropane triacrylate (TMPTA) showed that the initiation efficiency of 4-MTPO and 2,4-DMTPO were higher than that of TPO, regardless of whether it was initiated upon LED at 385 nm or 420 nm. In addition, the migration rates of 4-MTPO and 2,4-DMTPO in cured TMPTA were approximately 1/2 and 1/4 that of TPO, respectively.