Photoreactivity study of photoinitiated free radical polymerization using Type II photoinitiator containing thioxanthone
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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 Yung-Chung Chen , Ting-Yu Liu, Yan-Heng Li
American Coatings Association 2020 Abstract 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 as N-phenylglycine (NPG), triethylamine (TEA), triethanolamine (TEOA), 2,2¢-(4-methylphenylimino)diethanol (p-TDEA), and N-phenyldiethanolamine (nPDEA), 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 of pTDEA > n-PDEA > NPG > TEOA > TEA. All the packages exhibit good electron-transfer ability by the calculation of the free energy changes (DGET) 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 Y.-C. Chen (&), T.-Y. Liu, Y.-H. Li Department of Chemical and Materials Engineering, National Kaohsiung University of Science and Technology, Kaohsiung City 80778, Taiwan, ROC e-mail: [email protected] Y.-C. Chen Photo-SMART (Photo-sensitive Material Advanced Research and Technology Center), National Kaohsiung University of Science and Technology, Kaohsiung City 80778, Taiwan, ROC
wt%. Under suitable amount of hydrogen donor, the TX/TEOA-based formulation also exhibits stable DC value at air atmosphere. Keywords Type II photoinitiator, Thioxanthone hydrogen acceptor, Amine-type hydrogen donors, Photopolymerization
Introduction The photopolymerization process has attracted considerable attention owing to its 5E characteristics including efficient, enabling, economical, energy saving, and environmentally friendly. This technique of converting unsaturated monomers into polymers after light irradiation has been widely used in coatings, adhesives, 3D printing, microlithography, optics, medicine, nanotechnology, and so on.1–6 Generally, the photopolymerization reacted through three steps: (1) a photoinitiator (PI) absorbed the light irradiation, (2) PI dissociated and generated the active free radicals, and (3) the initiation and propagation of the monomer occurred for polymerization.7–9 Therefore, this implies the PI is the most critical compon
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