γ-Ray-sensitive motif-driven versatile epoxy thermoset: Highly efficient radiation degradation, intrinsic flame resistance and sustainable synthesis

With the growing awareness of energy consumption and environmental pollution, the development of γ-radiation-degradable technology derived from clean energy is of great concern. However, radiation-induced degradation for thermoset materials is limited because γ-radiation-induced radicals are prone to recombination rather than controlled cleavage. Herein, via introducing the radiation-sensitive groups, phenyl imine conjugated N[sbnd]N bonds, we synthesized a radiation-sensitive epoxy monomer from vanillin (a renewable source) and 4-hydroxybenzhydrazide. The thermoset was formed by crosslinking this bio-based epoxy monomer with our reported hardener bearing phenyl imine conjugated N[sbnd]N bonds. When treated by a stimulus of γ-ray radiation, the resulting epoxy thermoset with high contents of sensitive groups could be efficiently degraded at a dose of 10 kGy. Degradation of the thermosets are realized through the controlled cleavage of phenyl imine conjugated N[sbnd]N bonds. Benefiting from this stable conjugated structural design, the epoxy thermosets exhibit excellent mechanical performance and intrinsic flame resistance with a tensile strength over 70 MPa and a limited oxygen index (LOI) of 35.1 %, which are higher than those of traditional robust thermosets made from bisphenol A. This work not only renders a pioneering paradigm of bio-based γ-ray-degradable thermosets but also develops an effective approach to simplify the manufacturing process of fire-safe thermosets, which significantly enhance the versatility of polymer materials.