Photoreactivity study of photoinitiated free radical polymerisation
Researchers have studied photoinitiated free radical polymerisation using Type II photoinitiator containing thioxanthone initiator as a hydrogen acceptor and various amine-type co-initiators as hydrogen donors.
In the work, free radical photopolymerisation of trimethylolpropane trimethacrylate (TMPTMA) was initiated. The scientists 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 as N-phenylglycine (NPG), triethylamine (TEA), triethanolamine (TEOA), 2,2′-(4-methylphenylimino)diethanol (p-TDEA), and N-phenyldiethanolamine (n-PDEA), as hydrogen donors. Their photochemical and photophysical properties have been studied.
Good electron-transfer ability
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 of p-TDEA > n-PDEA > NPG > TEOA > TEA. All the packages exhibited good electron-transfer ability by the calculation of the free energy changes (ΔGET) through cyclic voltammetry (CV) measurement. However, the hydrogen donors with different steric hindrance, secondary, and tertiary amines had 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%).
The researchers then conducted the photoreactivity based on TX/TEOA formulation with different weight ratios. The DC values were 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 exhibited stable DC value at air atmosphere.
The study has been published in Journal of Coatings Technology and Research, Volume 18, 2021.
