Self-Healing in Mobility-Restricted Conditions Maintaining Mechanical Robustness: Furan-Maleimide Diels-Alder Cycloadditions in Polymer Networks for Ambient Applications

Two reversible polymer networks, based on Diels-Alder cycloadditions, are selected to discuss the opportunities of mobility-controlled self-healing in ambient conditions for which information is lacking in literature. The main methods for this study are (modulated temperature) differential scanning calorimetry, microcalorimetry, dynamic rheometry, dynamic mechanical analysis, and kinetic simulations. The reversible network 3M-3F630 is chosen to study the conceptual aspects of diffusion-controlled Diels-Alder reactions from 20 to 65 degrees C. Network formation by gelation is proven and above 30 degrees C gelled glasses are formed, while cure below 30 degrees C gives ungelled glasses. The slow progress of Diels-Alder reactions in mobility-restricted conditions is proven by the further increase of the system's glass transition temperature by 24 degrees C beyond the cure temperature of 20 degrees C. These findings are employed in the reversible network 3M-F375PMA, which is UV-polymerized, starting from a Diels-Alder methacrylate pre-polymer. Self-healing of microcracks in diffusion-controlled conditions is demonstrated at 20 degrees C. De-gelation measurements show the structural integrity of both networks up to at least 150 degrees C. Moreover, mechanical robustness in 3M-F375PMA is maintained by the poly(methacrylate) chains to at least 120 degrees C. The self-healing capacity is simulated in an ambient temperature window between -40 and 85 degrees C, supporting its applicability as self-healing encapsulant in photovoltaics.