A synergistic effect of a ferrocenium salt on the diaryliodonium salt-induced visible-light curing of bisphenol-A epoxy resin

The interactions of diaryliodonium and ferrocenium (FC) salts during photopolymerization under visible light were systematically studied. Spectroscopic, electrochemical, and calculation results indicate that electron transfer occurs between diaryliodonium and FC salts and that FC can be used as a photosensitizer for diaryliodonium salt photoinitiation systems under visible light. Thus, the activity of a two-component photoinitiator system composed of different proportions of diaryliodonium and FC salts was investigated for induction of cationic polymerization of bisphenol-A epoxy resin A (DGEBA) and cationic/free radical hybrid polymerization of a DGEBA/tripropylene glycol diacrylate (TPGDA) mixture under visible light. Cationic polymerization of DGEBA achieved high epoxy conversion, while hybrid polymerization of DGEBA and TPGDA achieved synchronous curing. The proposed two-component photoinitiator system may meet the special needs of applications such as 3D printing. Hybrid polymerization may improve the performance of light-cured polymers. Diaryliodonium and ferrocenium salts undergo photo-electron transfer (PET) to initiate photopolymerizations under a halogen lamp.