Radical Cations in Versatile High Performance Initiating Systems for Thermal, Redox, and Photopolymerizations

Highly versatile initiating systems for thermal, redox, and photopolymerization processes are proposed. The photopolymerization using the multifunctional amine tris[4-(diethylamino)phenyl]amine (t4epa) and iodonium salt (Iod) as photoinitiating system (PIS) is presented. Methacrylate function conversion up to 84% was reached under LED@850 nm using t4epa/Iod/phosphine PIS when only 60% was possible for the same resin using a commercial camphorquinone/amine/phosphines blue light (470 nm) PIS showing that longer wavelengths can be used with high final performances. Estimation of the balance between photothermal vs photoinduced electron transfer processes to initiate polymerization was performed exhaustively thanks to thermal imaging, Raman confocal microscopy, FTIR, cyclic voltammetry, UV-vis-NIR spectroscopy, ESR, ESR-ST photolysis, DSC, photo-DSC, and molecular modeling. This method can be used in further works interested in photochemical/thermal processes as it allowed to highlight two unusual reactivity features: (i) the in situ creation of a bicomponent thermal initiator (potentially occurring in several other systems) and (ii) the estimation of light-induced heating rates. Remarkably, a NIR light-absorbing radical cation is responsible for the photoreaction and the high photoinitiating performance. Interestingly, in parallel and without light, the first pure organic peroxide-free redox radical initiating system based on the proposed t4epa/Iod combination will be presented; that is, performances similar to or better than harmful/unstable peroxide-based redox (or thermal) initiating systems are obtained.