Azine-Based dynamic covalent polyurethane elastomers with excellent mechanical and Creep-Resistant properties

Dynamic covalent bonds have received tremendous attention since they endowed classical crosslinked polymers with new properties, including self-healing, stimuli-responsive, anti-bacterial, and recycling properties. The dynamic crosslinked polymers combined the merits of thermoset and thermoplastic elastomers. However, the dynamic nature also compromised the heat resistance of dynamic crosslinked polymers, especially the creep resistance at high temperatures. Herein, a hexahydroxy azine crosslinker was synthesized and used to prepare a range of azine-based polyurethane elastomers (PUEs). The exchange reactions of small molecular model compounds revealed that the azine moieties could exchange fast at 150 °C. The resulting azine-based PUEs showed outstanding thermal stabilities and mechanical properties owing to the conjugated structure and related hydrogen bonds of azine. The obtained azine-based PUEs also exhibited a high creep temperature of 150 °C thanks to the relatively higher exchange temperature of azine moieties and high functionality of the azine crosslinker. The degradation process of azine-based PUEs displayed solvent and acid strength dependence. The excellent reprocessing properties of azine-based PUEs were attributed to the distribution of the azine moieties both in the backbone and crosslinking points. This study provides an alternative way to solve the creep resistance of dynamic crosslinked polyurethanes and a feasible method for the industrialization of the recyclable thermoset polyurethane elastomers.