Improvement on curing performance and morphology of E5I/TPGDA mixture in a free radical-cationic hybrid photopolymerization system

Abstract

A visible light-induced free radical-cationic hybrid photopolymerization system co-initiated by diphenyliodonium hexafluorophosphate (IOPF) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO). IOPF and TPO rapidly induced a mixture of diglycidyl ether of bisphenol-A epoxy resin (E51) and tripropylene glycol diacrylate (TPGDA) under a halogen lamp (λ = 380–580 nm). The curing rate of epoxy resin is significantly accelerated. The effect of weight ratio of IOPF/TPO, proportion of E51/TPGDA, benzoyl peroxide (BPO), 3,4-epoxycyclohexylmethyl-3′,4’epoxycyclohexyl carboxylate (ERL4221) on IOPF/TPO/TPGDA/E51 hybrid systems (HSs1–11) were studied by near infrared (NIR) spectroscopy. Free radical and cationic photopolymerization for TPO/TPGDA and IOPF/TPO/E51 were also investigated. TPO shows a sensitization effect to accelerate the curing of E51. Scanning electron microscopy (SEM) was used to observe the morphology of cured films, including surface and cross section. The film of hybrid system with BPO (HS-6) has the advantage of smooth surface and uniform cross section, while that of free radical system is obviously plicate. The acceleration of epoxy conversion is up to 85%, when ERL4221 was added.