Peroxide-Free (Photo)Initiating Systems – NoPerox

The project involved :
i) establishing chemical structure/reactivity relationships for the new AMILB redox initiation systems and their polymerisation efficiency (conversion, polymerisation speed, range of accessible monomers);
ii) to demonstrate the possibility of activating the AMILB process using light, for unique access to «dual cure« systems (highly original polymerisation using two modes: redox and photochemical),
iii) to develop purely organic approaches without peroxide or metal
iv) apply these photoactivated redox systems to bio-based monomers (Task 3) and for industrial applications (Task 4).

In the end, the new radical polymerisation initiation approaches proposed outperformed all the systems used in redox and photopolymerisation.

The results of this study are clear: phosphine oxides are actively involved in the redox system and therefore play both a photoinitiator and a chelating agent role. These results led to a feasibility study involving this new system for filament winding applications (P2, P4). In addition, very recently, efficient systems based on lactone derivatives (synthesised by P1) have shown promise and could also be the subject of further investigation (P2).

The preliminary results of this study are without appeal, The discovery of the direct involvement of phosphines oxides (photoinitiator Norrish type I) in a redox mechanism remains to date the major advance of this project (never postponed before). Efficient systems based on lactone derivatives synthesised by P1 could also be the subject of significant recovery.

As part of the ANR PRCE programme, the use of patents was preferred (currently being analysed by the industrial partner). A specific redox system was selected and transferred to the industrial partner (P4), which is currently testing this approach on a pilot scale. This new system is the subject of a feasibility study for filament winding. For the more academic approach (non-patented part), remarkable results have been obtained (11 publications in international peer-reviewed journals).

During the last decade, photopolymerization has witnessed intense research efforts due to the constant growth of industrial applications associated with the synthesis of new photoinitiators and monomers. However, this technique is limited to the polymerization of thin films. On the opposite, redox initiating systems (2-Cartridges) can efficiently initiate the polymerization of thick films but their sensitivity to oxygen and their instability/toxicity adversely affect their potential use. Very recently, the consortium involved in this project has proposed a new chemical mechanism called MABLI (for Metal Acetylacetonates – Bidentate Ligand Interaction) – in full agreement with this submission in Domaine 2-axe 3. In this approach, new redox initiating systems based on metal complexes comprising a remarkably stable oxidizing agent are capable to liberate an acac radical by ligand exchange while changing its oxidation degree. The development of high-performance amine-free and peroxide-free redox initiating systems is now possible through the new proposed MABLI process that can overcome the current issues of both redox and photochemical systems. Pure organic peroxide-free systems will also be proposed. The possibility to activate these systems by light can also be expected (redox photoactivated polymerization). On the basis of these preliminary results, we propose to investigate and shed some light on: i) the structure/reactivity relationships for the new proposed MABLI redox initiating systems and their efficiency in polymerization (conversion, curing rate, range of monomers); ii) the possible light activation of the MABLI process for a unique access to dual cure systems (through photochemical and redox modes), iii) the development of pure-organic peroxide-free and metal-free approaches and iv) applicability of these proposed redox photoactivated systems for biosourced monomers (Task 3) and on an industrial scale (Task 4). Altogether, the new proposed initiation approaches for radical polymerization is potentially a way to outrank all the redox and photopolymerization systems as: oxidizing agent is stable (metal acetylacetonates), bidentate ligand is stable, thick (filled) samples can be polymerized and photoactivation can enhance surface curing and polymerization rates. Due to the high potential versatility of the new peroxide-free initiation systems, this proposal is submitted in PRCE as: i) a better understanding of the key factors governing the reactivity and the chemical mechanisms is urgently needed and ii) for the development of an organic peroxide-free approach. In this context, the industrial partner (P4) has very recently developed a new methacrylic liquid thermoplastic resin range (www.elium-composites.com) for the manufacture of continuous fiber reinforced composites (CFRC). The development of peroxide-free (photoactivated) redox initiating system should be the next generation of CFRC as well as the photopolymerization in the composite processes for better control of the on-demand activation and fast polymerization.