![]() Beyond epoxides, which were the first monomers polymerized by a cationic ring-opening polymerization (CROP), the photopolymerization of other cyclic monomers has recently spread out thanks to the emergence of novel initiating systems. This polymerization route has been largely developed using radical polymerization of vinyl monomers, but to a lesser extent by ring-opening polymerization (ROP). Photopolymerization is the subject of a growing interest both at industrial and academic levels because it provides high reaction kinetics, low emissions of volatile organic solvents and in some cases, low shrinking stress. This work show that the peripheral group strongly affect the initiation ability of enone photoinitiator. Accordingly, it is proposed that C3PY and C3ID tend to photolyze through intramolecular hydrogen abstraction. To decipher these phenomenon, steady state photolysis, cyclic voltammetry and theoretical calculation were jointly performed. Polymerization profiles show that C3s could initiate the polymerization and TEOA significantly promote the initiation efficiency of C3CZ, while this acceleration effect is relatively small for C3PY and C3ID. Under 405/460 nm LED irradiation, the polymerization kinetics of a diacrylate monomer in the presence of one-component C3s or bimolecular C3s/triethanolamine (TEOA) were investigated by Real-time FT-IR technology. C3s display good light absorption in the region of 300 - 500 nm. In this work, three enone dyes (C3s) bearing N-alkylated pyrrole (C3PY), indole (C3ID) and carbazole (C3CZ) group were synthesized and characterized to explore the effect of peripheral group on their photoinitiation ability. The possibility of extending wavelength sensitivity of photopolymerizations by excited state complexes (exciplexes) is also discussed. Also, low optical density of the CTC in resins allowed to access extremely thick samples and composites. ![]() Interestingly, CTC can act as dual photo/thermal photoinitiators both in cationic and free radical photopolymerizations. In the present review, an update on CTCs as photoinitiating systems for photopolymerization applications will be provided with examples of CTC-specific structure/reactivity/efficiency relationships. In these cases, the ground state intimate association of a donor and acceptor creates a new structure that can result in (bathochromic) visible light absorption compared to the separated compounds. Beyond these strategies, charge transfer complexes (CTCs), also referred to as electron donor acceptor (EDA) complexes, were also reported to be the visible light initiating species. Visible light induced synthesis generally involves i) dyes or chromophores with potential photocleavable bonds (Type I photoinitiator), ii) hydrogen abstractions (Type II photoinitiator) by dyes/chromphores and iii) photoredox catalysis using metal-based or metal-free dyes.
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