One-component thioxanthone-based polymeric photoinitiators

The photochemical and photophysical properties of new polymeric photoinitiators (PPIs) containing pendant thioxanthone (TX) and amine moieties are studied. The PPIs are synthesized by copolymerization of tert-butyl 2-((9-oxo-9H-thioxanthen-2-yloxy)methyl)acrylate (TX1) with N,N-dimethylaminoethyl methacrylate (DMAEM) at two different ratios using free radical polymerization. UV-vis spectra indicate that PPIs possess similar absorption characteristics to TX1 in the violet range (approximate to 400 nm; absorption red-shift 20 nm). The photochemical mechanisms are studied by electron spin resonance (ESR), steady state photolysis, laser flash photolysis, and cyclic voltammetry. ESR studies indicate formation of two different aminoalkyl radicals on the hydrogen donor amine. The triplet state of the PPIs is short-lived compared to isopropyl thioxanthone and TX1, due to the built-in amine functionality. Photopolymerization of trimethylolpropane triacrylate (TMPTA) initiated by these photoinitiators under LED exposure at 385 and 405 nm using real-time FTIR spectroscopy shows that they exhibit higher efficiency than TX/N-methyldiethanolamine (MDEA) and TX1/MDEA systems with the advantage of a much higher molecular weight that can be very helpful to overcome migration issues. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3370-3378