A water soluble and highly reactive bisphosphonate functionalized thioxanthone-based photoinitiator

A new water soluble bisphosphonate functionalized thioxanthone (TXBP2) is synthesized from aza-Michael addition reaction of 2-(2-aminoethoxy)-9H-thioxanthen-9-one and tetraethyl vinylidene bisphosphonate. This photoinitiator shows excellent water-solubility of 86 g L-1 compared to Irgacure 2959 (5 g L-1). It has a lambda(max) in the near UV-visible region, similar to 400 nm. The photoinitiation effectiveness of TXBP2 is studied by photo-DSC for photopolymerization of trimethylolpropane triacrylate and poly(ethylene glycol) diacrylate (PEGDA, M-n = 575 D). It shows very high polymerization rates and conversions with bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate or ethyl 4-(dimethylamino)benzoate, compared to thioxanthone. The photochemical mechanisms investigated by laser flash photolysis and fluorescence indicate that the reaction involves both singlet and triplet pathway. Water solubility, biocompatibility and high reactivity make this photoinitiator a promising candidate for biomedical applications.