PHOTOlatent N-hétérocyclic carbenes for Delayed Ring-Opening Polymerization – PHOTONDROP

Photopolymerization is a well-established technology showing a growing interest because of significant economical and environmental advantages. Nevertheless, more than 95% of films and coatings derived wherefrom are based on a radical process strongly inhibited by atmospheric oxygen. There is thus a high demand for novel non-radical photoinitiators. In this respect, N-Heterocyclic Carbenes (NHCs) have emerged as versatile ligands for organometallic catalyst (Grubbs’ 2nd generation) but also as powerful organocatalysts for polymerization reactions (ring-opening, step-growth, anionic) over the past decade. NHCs are usually synthesized by deprotonation of an azolium salt with a strong base, but their generation in situ and “on demand” from thermally labile progenitors has attracted a lot of interests in the past few years. Interestingly, the generation of NHCs by a photochemical process has never been reported and an efficient photolatent NHCs has yet to be fully developed.

PHOTON DROP project thus aims at developing a simple synthetic pathway to robust photolatent NHCs (WP1). They will be subsequently used as photoligands and photocatalysts in ring-opening metathesis and anionic polymerizations for key applications: film UV-curing (WP2) and latex production (WP3).
To prepare the photolatent NHCs we propose a simple anion exchange between azolium salts and photosensitive salts, which was successfully supported by preliminary experiments. As pre-organocatalysts, they will be subsequently used for the ring-opening anionic polymerization (ROAP) of bio-based cyclic esters, like macrolactones. The photo-ROAP will be performed in bulk in the form of a film or in aqueous miniemulsion, leading to biodegradable films or latexes respectively. Polyesters films prepared wherefrom are expected to find application in single-use packaging items whereas polyesters latexes should be the first step to biodegradable paints. In a more original manner, photolatent-NHCs will be also used as pre-ligands for the in-situ generation of Ru-based catalysts subsequently employed for the ring-opening metathesis polymerization (ROMP) of cyclic olefins (norbornene, dicyclopentadiene…), or/and resins derived wherefrom. Photo-ROMP will be also explored either in bulk, to form weathering resistant and hard coatings, or in aqueous miniemulsion to form cargo particles for “bioactive” coatings. We believe that the photolatent formulations developed in PHOTON DROP will be also the premise of new 3D-printing materials (stereolithography) able to impart higher resistance to static and fatigue stress (ROMP polymers) or biodegradability (polymacrolactone) to final objects.

In order to reach these objectives, the research program has been divided in 5 Work Packages (WP1-5):
WP 1: Synthesis and characterization of Photolatent NHCs
WP 2: Next-generation UV coatings based on Photo-ROMP and -ROAP
WP 3: Novel Latexes via photo-ROMP and ROAP in Miniemulsion
WP 4: Project Management
WP 5: Industrial Exploitation of research results

Following a product-led approach, all these WPs have a list of deliverables achieved by different partners, and translated to two individual PhD research projects (PhD1 already funded in IAM-ICGM, PhD2 in IS2M) and to two 18-months postdoc projects (Postdoc1 in IAM-ICGM, Postdoc2 in LCPO).
PHOTON DROP is a 42-month collaborative research project supported by three academic partners, Partner 1: Ingénierie et Architecture Macromoléculaires team of Institut Charles Gerhardt de Montpellier (IAM-ICGM), Partner 2: Institut de Science des Matériaux de Mulhouse (IS2M) and Partner 3: Laboratoire de Chimie des Polymères Organiques (LCPO), with acknowledged and well-defined skills in the field of NHC, organocatalyzed polymerizations (IAM-ICGM), photopolymerization (IS2M) and ROMP (LCPO).
It must be emphasized that promising preliminary results, detailed and described thereafter, account for the project feasibility.