Reprocessable and chemically recyclable poly(acylhydrazone–imine) covalent adaptable networks with enhanced mechanical strength and creep resistance

Abstract

Chemical recycling of thermosetting resins represents a sustainable solution to deal with end-of-life polymer products in an energy-saving and easy-to-conduct way. However, it remains a major challenge to fabricate easy-to-achieve chemically recyclable thermosets that possess superior mechanical strength, high fracture toughness, and desirable creep resistance. Herein, a new chemically recyclable poly(acylhydrazone–imine) covalent adaptable network (CAN) is reported by systematically tailoring the intramolecular dynamic interactions of polymer networks. The introduction of acylhydrazone bonds endowed PAI_x-CANs with both high mechanical strength and fracture toughness through the formation of synergistic hydrogen-binding interactions. For example, PAI₁-CANs exhibit a high Young's modulus of ∼1.58 GPa, a yield strength of ∼83.7 MPa, a tensile strength of ∼73.6 MPa, and also a high fracture toughness of ∼19.7 MJ m⁻³. Meanwhile, owing to the strong intermolecular hydrogen-binding interactions, the obtained PAI_x-CANs also exhibit good creep resistance. Interestingly, the PAI_x-CANs can be depolymerized into the starting monomers in high purity under acidic conditions at room temperature. The recovered monomers can be further utilized to fabricate new PAI_x-CANs with comparable mechanical properties to the original PAI_x-CANs. This work provides a new method for the construction of high-performance chemically recyclable thermosets as next-generation substitutes for conventional thermosetting resins.