Radical Cations in Versatile High Performance Initiating Systems for Thermal, Redox, and Photopolymerizations Patxi Garra, †,‡ Alexandre Baralle, †,‡ Bernadette Graff, †,‡ Gautier Schrodj, †,‡ Fabrice Morlet-Savary, †,‡ Ce ́ line Dietlin, †,‡ Jean-Pierre Fouassier, †,‡ and Jacques Laleve ́ e* ,†,‡ † Université de Haute-Alsace, CNRS, IS2M UMR 7361, F-68100 Mulhouse, France ‡ Université de Strasbourg, Strasbourg, France * S Supporting Information ABSTRACT: 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. 1. INTRODUCTION Today, free radical polymerization (FRP) is of high academic/ industrial interest (roughly 45% of the total polymer production). 1 For polymerization in eco-friendly conditions (at room temperature (RT) and under air; without purification of monomers), two strategies are generally relevant: redox polymerization 2-4 and photopolymerization. 5-13 Many ex- haustive reviews begin with a clear distinction between these techniques and thermal polymerization (heating of the reaction media). First, redox polymerization is occurring when an oxidizing agent (e.g., bearing a weak O-O or S-S bond 14 ) is mixed with a reducing agent (or system), 15,16 leading to the polymerization of the surrounding resin through the generation of initiating radicals in a redox process. This type of process is very convenient for filled sample polymerization (e.g., for the access to composites), but commercial systems still show some huge drawbacks due to the current toxicity/ instability of oxidizing agents (e.g., peroxides 17 ). One important challenge for redox polymerization is to use less harmful/toxic metal-free oxidizing agents (e.g., iodonium salts that are safe as used in dental applications 18 ). In parallel, free radical photopolymerization is occurring when actinic light is absorbed by photoinitiating systems (PIS), leading to the formation of radicals that initiate FRP. One of the most important challenge is the shift of actinic wavelengths toward visible to near-infrared (NIR) wave- lengths, particularly for the access to composites 19,20 (these latter NIR wavelengths showing much better penetrations in Received: September 13, 2018 Revised: October 8, 2018 Article pubs.acs.org/Macromolecules Cite This: Macromolecules XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.macromol.8b01975 Macromolecules XXXX, XXX, XXX-XXX Downloaded via UNIV OF SUNDERLAND on November 5, 2018 at 01:06:53 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.