Photoreactivity study of photoinitiated free radical polymerization using Type II photoinitiator containing thioxanthone initiator as a hydrogen acceptor and various amine-type co-initiators as hydrogen donors

In this work, free radical photopolymerization of trimethylolpropane trimethacrylate (TMPTMA) is initiated. We investigated the corresponding photoreactivity by using Type II photoinitiator (PI) systems based on thioxanthone (TX) as a hydrogen acceptor and five amine-type molecules, such asN-phenylglycine (NPG), triethylamine (TEA), triethanolamine (TEOA), 2,2 '-(4-methylphenylimino)diethanol (p-TDEA), andN-phenyldiethanolamine (n-PDEA), as hydrogen donors. Their photochemical and photophysical properties are studied. The TX hydrogen acceptor displayed rather red-shifted compared to all the hydrogen donor compounds. The hydrogen donor compounds exhibited the absorption band at lower than 300 nm, which followed the trend ofp-TDEA > n-PDEA > NPG > TEOA > TEA. All the packages exhibit good electron-transfer ability by the calculation of the free energy changes (Delta G(ET)) through cyclic voltammetry (CV) measurement. However, the hydrogen donors with different steric hindrance, secondary, and tertiary amines have a decisive influence on the photoreactivity; that is, the TX/TEOA package shows the best double-bond conversion (DC) efficiency than other formulations under similar weight ratios (hydrogen acceptor: hydrogen donor = 1:2 wt%). We then conduct the photoreactivity based on TX/TEOA formulation with different weight ratios. The DC values are in the order of 1:2 wt% > 1.5:1.5 wt% > 2:1 wt%. Under suitable amount of hydrogen donor, the TX/TEOA-based formulation also exhibits stable DC value at air atmosphere.