Bisphosphonic Acid-Functionalized Water-Soluble Photoinitiators

The first bisphosphonic acid-functionalized benzophenone (BP) and thioxanthone (TX) photoinitiators (PIs), BPBP and TXBP, are synthesized as a new class of water-soluble PIs for free radical polymerization. BPBP shows excellent solubility (28 g L-1) in water at ambient temperature, compared to TXBP (0.05 g L-1) and also the commercial PI Irgacure 2959 (5 g L-1). BPBP and TXBP show UV-vis absorption at approximate to 260 (epsilon = 12912) and 405 (epsilon = 3314) nm in water. Photopolymerization results demonstrate that they can successfully initiate the photopolymerization of poly(ethylene glycol) diacrylate (M-n = 250 D) in the presence of bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate (Iod). The photochemical mechanisms are investigated by electron-spin resonance-spin trapping, fluorescence, and steady-state photolysis techniques.