Today, polymeric photoinitiators are good choice for initiation mechanism of UV-curable printing inks with their low migration potential. In this study, new thioxanthone-styrene polymeric photoinitiators were synthesized. Polystyrene that was synthesized by atom transfer radical polymerization (ATRP) was functionalized by cyclohexeneoxide and then reacted with thioxanthone-thioacetic acid. Piperazine was reacted with bromine chain end of polystyrene and final polymeric photoinitiator was obtained. Proton Nuclear Magnetic Resonance (1H NMR), Attenuated Total Reflectance- Fourier Transform Infrared Spectroscopy (ATR-FTIR), Gel Permeation Chromatography (GPC) and Ultraviolet-Visible Spectroscopy (UV–vis) analyses were confirmed the expected structures. The curing property of new polymeric photoinitiator was compared with a conventional thioxanthone printing formulation that is used in flexographic varnish. The photopolymerization kinetics were determined by Photo Differential Scanning Calorimetry (Photo-DSC) and the results showed that 83% of conversion was reached for thioxanthone-styrene polymeric photoinitiator with MW = 4200. The migration behavior was identified with Liquid Chromatography–Mass Spectrometry LC–MS. It was shown that thioxanthone based polymeric photoinitiator is usable in flexographic varnish and thioxanthone migration level is reduced with macrophotoinitiation.
Volume 119, June 2018, Pages 36–43