EXPLORING THE POTENTIAL OF PHOTOTHERMAL POLYMERIZATION – EXPO-PHOTO

Photopolymerization is a room temperature process allowing both a temporal and a spatial control of the polymerization that finds application in various areas such as coatings, inks, and additive manufacturing. Nevertheless, most photopolymerization systems employed today at the industrial and academic levels usually rely on the in-situ generation of active species under UV or visible light to trigger the polymerization. While this strategy is very effective to initiate or catalyze the polymerization of various monomers at room temperature, several drawbacks remain: 1) the low penetration depth of photons in the UV and visible range limits the production of thick or composites materials; 2) short wavelengths associated with UV-irradiation are harmful for the operator; 3) because photopolymerization takes place at room temperature, access to a large range of polymer materials that require overpassing high-energy barriers is impossible.
There is thus a high demand for a technology that would provide a spatial and a temporal control of the polymerization, like photopolymerization, while employing safer irradiation wavelengths (i.e. near infra-red) and affording the benefits of thermal polymerization (i.e. temperature increase). In this respect, the use of photothermal effect has emerged over the past ten years as an efficient strategy to convert a near infra-red (NIR) radiation into heat with a high spatial (nanometers) and a temporal (picoseconds) resolution and with a high depth of cure. However, in most instances, photothermal polymerization has been achieved using gold nanoparticles that bring high cost to the technology and potential compatibility issues with organic formulations.
Accordingly, The EXPO-PHOTO project aims at synthesizing organic near infra-red absorbing dyes having a strong photothermal effect (WP1) to be subsequently employed as efficient “heaters” for the development of new photothermal polymerization processes. To this end, a comprehensive study will be conducted to determine and model the structure/photothermal effect relationship. The potential of this approach will be exploited in three key technological areas: functional and patterned surfaces by nitroxide-mediated polymerization (WP2), epoxy-anhydride composites (WP2) and polyhydroxyurethane adhesives and coatings (WP3).
To reach these objectives, the EXPO-PHOTO project gathers a cohesive group of three academic partners with acknowledged and well-defined skills in the fields of organic synthesis (ICR, D. Gigmes), photochemistry (IS2M, J. Lalevée) and polymer synthesis (ICGM, J. Pinaud and S. Caillol).