Cross-Linking Vitrimers after Melt Processing Using Supramolecularly Masked Dynamic Cross-Linkers

Vitrimers are permanent polymer networks with dynamic covalent bonds that allow them to be reshaped and recycled. Although they are often promoted as an ideal class of materials situated between thermosets and thermoplastics, vitrimers are usually far more difficult to process than thermoplastics because their melt viscosity gradually decreases with increasing temperature. They are thus subject to a challenging trade-off between processability and mechanical performance, limiting their practical utility. Herein, we report the concept of a supramolecularly masked cross-linker that enables a vitrimer precursor to be processed as a thermoplastic before being thermally cured to form a vitrimer. The cross-linker features hydrogen bonding groups that promote aggregation and phase separation, allowing for it to be melt-blended with a functional thermoplastic at low temperature with minimal cross-linking. After shaping, the loaded thermoplastic is heated to a suitably high curing temperature to disassemble the aggregated cross-linker, thereby unmasking the cross-linker for reacting with the functionalized matrix. The resulting cured elastomeric vitrimers exhibit excellent thermomechanical properties along with mechanical and chemical recyclability. The latter consists of recovering the vitrimer precursor, which can be further reprocessed as a thermoplastic and converted back to a vitrimer after melt processing.