Design, synthesis and properties of carbazole-indenedione based photobleachable photoinitiators for photopolymerization

Abstract

In order to investigate the properties of carbazole-indenedione based photoinitiators for photopolymerization, two visible light-sensitive photoinitiators (CAs) were designed and synthesized. Their structures were confirmed by nuclear magnetic resonance (NMR) and high resolution mass spectrometry (HR-MS). Additionally, their properties concerned photophysical/photochemical and photoinitiating were determined by electron paramagnetic resonance (EPR), UV–vis spectrophotometer and real-time FT-IR spectroscopy. The results have showed that CA-2 could be regarded as an effective one-component photobleachable photoinitiator for free-radical polymerization (FRP). Meanwhile, its photoinitiating property could be enhanced or optimized by adding the additional hydrogen donor or iodonium salt, and the interpenetrated polymer networks (IPN) were synthesized by the hybrid polymerization of TMPTA (trimethylolpropane triacrylate)/EPOX (3,4-epoxycyclohexylmethyl 3,4-epoxycycohexanecarboxylate) initiated by two-component CA-2/Iod (iodonium salt). The results of theoretical calculation experiments showed that it is also an effective way to improve the photoinitiating efficiency by the introduction of the electron-donating piperidine group in the ortho-position of the double bond on carbazole skeleton. The curing depth experiments showed that the photobleaching performance could be enhanced by introduction of Iod in acrylic/epoxy resin and a colorless polymer with the thickness of 5.8 mm was obtained under visible LED light irradiation for 6 min. Thus, the carbazole-indenedione based photobleachable dye CA-2 has great potential in deep curing materials (e.g. dental materials, biomedical materials and 3D printing).