Modeling of Diels-Alder reversible network formation under diffusion-controlled conditions for the construction of cure diagrams

Description

In the recent years, thermoreversible networks based on Diels-Alder (DA) cycloadditions have been widely investigated as self-healing materials. The DA reaction leads to two competing equilibria forming endo or exo cycloadducts for which the opening of the DA covalent bonds is favored at high temperatures, while the (re)formation of the cycloadducts is preferred at low temperatures.1 These dynamic bonds, apart from conferring self-healing properties, lead to extended material lifetimes, improved stability, reliability, and sustainability. In addition, this enhancement addresses limitations often observed in classical network-forming materials, providing increased recyclability, reprocessability, and reshapeability.2 Such properties make them attractive for numerous potential applications where mechanical robustness is required to insure thermomechanical stability. This implies the necessity of a (partially) vitrified network with a sufficiently high glass transition temperature (Tg). Self-healing as well as forward and retro-DA reaction will thus occur, at least partially, in diffusion-controlled conditions for most application temperatures.3–6
This work focuses thus on studying the effect of vitrification on DA reaction kinetics for a reversible thermosetting network based on a furan-maleimide chemistry. Starting from a classical two equilibria model, a novel mechanistic model describing this vitrifying system was derived by inserting a diffusion controlled encounter pair formation as intermediary step.7 Using calorimetric data and long-term Tg evolutions, the kinetic, thermodynamic and diffusion parameters were optimized. This led to a set of parameters that can describe well the system in both kinetically-controlled and diffusion-controlled conditions. Using these parameters, the Time-Temperature-Transformation and Continuous-Heating-Transformation diagrams of this thermoset were simulated and experimentally confirmed by Modulated Temperature Differential Scanning Calorimetry (for vitrification/de-vitrification phenomena) and dynamic rheometry (for gelation/de-gelation phenomena). Through their particular shape, these diagrams allowed to visually describe the differences between the cure process of these reversible networks with those of classical irreversible thermosets. This is particularly relevant in the context of designing and processing these materials, especially in view of their potential applications in self-healing.

Period	15 Apr 2024 → 18 Apr 2024
Event title	IMP days Thermosets 2024
Event type	Conference
Location	Lyon, France