Water-Soluble Photoinitiators From Dimethylamino-Substituted Monoacylphosphine Oxide For Hydrogel And Latex Preparation

In order to respond to the growing demand for radiation-curable waterborne products like hydrogels or inks, there is a need for water-soluble radical photoinitiators exhibiting absorption in the near UV to visible range. Herein the synthesis of a novel type-I diphenylphosphine oxide photoinitiator bearing a 2,6-dimethyl-4-dimethylaminobenzoyl group is described. The presence of a tertiary amino group in the para position of the benzoyl group results in an increased absorption in the visible range and its facile conversion into water-soluble derivatives after a subsequent protonation or quaternization reaction. Quaternization with methyl triflate (MeOTf) yields a water-soluble monoacylphosphine oxide compound displaying a quaternary ammonium group -N(CH3)(3)(+) OTf-. The main characteristics are water-solubility, shelf-stability, absorption in near-UV range, low cytotoxicity, and efficient alpha-scission as evidenced by steady-state photolysis experiments. Its photopolymerization efficiency has been evaluated by real-time Fourier transform infrared spectroscopy at 385 and 420 nm using an aqueous solution of poly(ethylene glycol) acrylate. The polymerization rate is comparable to that obtained with the conventional water-soluble monoacylphosphine oxide TPO-Li. Using this new photoinitiator, 3D-printed hydrogels, and aqueous polymer dispersions can be prepared.