Epoxy vitrimer based on borate ester bond for green degradation, closed-loop recycling, and ready reprocessing

The three-dimensional network of traditional epoxy resin endows it with suitable properties, but it also presents challenges in reprocessing and recycling. Recent years have witnessed the development of novel epoxy resins crosslinked via dynamic bonds. However, a milder and greener degradation process is still urgently needed. In this study, phenylboric acid (PBA) was selected as the curing agent for the epoxy resin (E44) to prepare an epoxy vitrimer (PBAE) containing borate ester bonds. Then properties of prepolymer and cured resin were characterized in detail, which manifested that the borate ester bond in PBAE endowed it with green degradation mode and convenient closed-loop recycling process, while maintaining good solvent resistance; besides, PBAE resin exhibited good thermal properties with a glass transition temperature of 148 °C, a temperature with 5% mass loss of 290 °C and mass residual rate at 800 °C is higher than 25%; the PBAE composite possessed good mechanical properties with a flexural strength of 499 MPa and an interlaminar shear strength of 46 MPa; in addition, upon heating and application of pressure, the PBAE resin readily showed self-healing or reprocessing properties.