Reaction-Diffusion Model for Thermosetting Polymer Dissolution through Exchange Reactions Assisted by Small-Molecule Solvents

Thermosetting polymers involving dynamic bonds or exchange reactions (also known as vitrimers) can be fully dissolved in a solvent utilizing a small-molecule participated bond-exchange reaction (BER). The dissolution of the polymer network is achieved by selectively cleaving chemical bonds on polymer chains into short segments or clusters through the participation of BER by small molecules. However, the dissolution is a complex process that couples chemical reactions with the diffusion featured by varied diffusivity both in time and dimension. Here, a reaction diffusion model is developed for the vitrimer dissolution in alcohol via transesterification. We developed a mathematical model involving both mass transport by diffusion and transesterification kinetics to trace the dissolution behavior of vitrimer samples for various temperatures and solvents. By following the concentration of functional groups and using classical gel theory, the evolution of the mass loss can be obtained. The numerical simulations lead to a quantitative description of the diffusion and dissolution processes. Simulation results are consistent with experimental results, showing good prediction for the size and mass evolution using different dissolution times, temperatures, and solvent choice. This work provides a deep insight into the reaction-diffusion process, which can be used to guide the future development and optimize recycling processes using dynamic bonds.