Water soluble polymeric photoinitiator for dual-curing of acrylates and methacrylates

A novel water soluble polymeric (photo)initiator is designed for efficient dual curing of mixtures of acrylates and methacrylates. The initiator (PAATX) functionalized with thioxanthone (10 wt %) was synthesized from the aza-Michael addition reaction of a poly(amido amine) (prepared from the reactions of 1,4-diamino butane with N,N'-methylene bisacrylamide) to 9-oxo-9H-thioxanthen-2-yl acrylate. It was used for polymerization of a mixture of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) diacrylate (PEGDA, M-n = 575 D). The first curing stage is the aza-Michael addition between PEGDA and the amines of PAATX; and the second is visiblelight-initiated radical polymerization (PAATX has an absorption maximum in the near UV-vis region, similar to 400 nm) of HEMA and remaining acrylates. The kinetics of the curing reactions were investigated using FTIR and photo-DSC. The steady state photolysis results show that PAATX/bis-(4-tert-butylphenyl)-iodonium hexafluorophosphate (Iod) system has the highest photolysis rate which signifies that PAATX forms radicals more efficiently by a photooxidation mechanism. The excited state reactivity has been studied by steady state photolysis, time resolved and steady state fluorescence as well as laser flash photolysis experiments. Remarkably, contrary to the usual behavior of thioxanthone derivatives, the new reported structure exhibits a singlet state reactivity.