Synthesis of Dynamic Polyurethanes by Utilizing Low-Transition-Temperature Mixtures of Pyrogallol and Poly(ethylene glycol)

Dynamic covalent networks exhibit intriguing reprocessing and self-healing properties, but they usually require complex synthesis procedures and frequently use hazardous solvents. Herein, we proposed a green synthesis strategy for dynamic polyurethane that was conducted in a one-pot, solvent-free manner that addresses the aforementioned problems. A new type of low-transition-temperature mixture (LTTM) was prepared by blending pyrogallol and poly(ethylene glycol), which allowed the reagents to remain as liquids at room temperature. The formation of LTTMs was ascribed to the presence of intermolecular hydrogen-bonding and van der Waals interactions between the molecules of the two reagents. Self-healing and reprocessable dynamic polyurethane with dissociative exchangeable phenol–carbamate bonds was synthesized by incorporating a hexamethylene diisocyanate trimer as the third component into the LTTMs, followed by thermal curing. The properties of the dynamic polyurethane could be adjusted by modifying the pyrogallol content in the LTTMs. The preparation of LTTMs and dynamic polyurethane did not require any purification steps and solvents, which provides an innovative approach to polymer synthesis that is efficient and environmentally friendly.