Modeling of Diels–Alder Reversible Network Formation in Diffusion-Controlled Conditions

A novel mechanistic model is developed for a vitrifying covalent adaptable polymer network based on the thermoreversible furan-maleimide Diels–Alder (DA) cycloaddition. To account for the effect of diffusion limitations on the reaction rates, a diffusion-controlled encounter pair formation mechanism is introduced, with the related rates of formation and separation calculated using the Williams–Landel–Ferry equation. The kinetic, thermodynamic, and diffusion parameters are optimized using calorimetric data and the variation of the glass transition temperature (T_g) with time and/or temperature, leading to a set of parameters that can describe a specific thermosetting system in vitrifying conditions. These parameters are shown to be also valid for a second, chemically similar, reversible network having a comparable T_g. Lastly, the parameters obtained are used to simulate time–temperature-transformation (TTT) and continuous-heating-transformation (CHT) diagrams of these systems, including also the vitrified sections. With these results, this model proves to be a versatile tool suitable for the prediction of the effect of diffusion limitations for any time–temperature cure program, aiding in the accurate interpretation of analytical results related to these reversible networks. This is of particular interest for the design and processing of these self-healing and reprocessable materials.