In situ monitoring of photopolymerization by photoinitiator with luminescence characteristics

Abstract

Judging functional groups’ conversion of polymers during the photopolymerizaiton is of vital importance no matter in academic research or in industry for the conversion of functional groups directly determining the performance of polymers. Many methods used to judge the conversion like (Fourier Transform IR)FT-IR and Photo-DSC are so limited and mainly applied into the lab instead of being applied in industry. Herein, providing a visible and direct strategy to monitor the photopolymerization in industry remains a great challenge. In this work, a strategy of utilizing type II photoinitiator 2,6-bis(furan-2-ylmethylidene) cyclohexan-1-one (BFC)’s luminescence characteristics to monitor both free radical and cationic photopolymerization was reported. In the free radical photopolymerization of photoinitiator BFC and monomer polyethylene glycoldiacrylate (PEGDA), BFC emits intensely with yellow fluorescence under irradiation firstly. Then BFC/PEGDA produces radicals to initiate the polymerization based on hydrogen transfer interaction, which makes π-conjugated structure of BFC be destroyed and the fluorescence of BFC disappears gradually. While in the cationic photopolymerization of photosensitizer thioxanthone (ITX), initiator Iod, epoxy monomer TTA21 and BFC, BFC shows photostability and aggregation-induced emission (AIE) character. As cationic photopolymerization was carried out, the fluorescence of BFC got bright with the viscosity of epoxy monomer increased based on the restriction of intramolecular motion (RIM) mechanism. Both phenomenons allowed BFC to be served as probe to monitor free radical and cationic photopolymerization respectively. Combined with photoluminescence (PL) intensity of BFC being linear relationship with conversion of functional groups, it’s easy to judge the conversion through PL intensity. This visible and direct strategy achieving the visualization of photopolymerization shows great potential to be applied in industry.