Sustainably sourced Schiff base vitrimeric epoxy networks with intrinsic flame retardancy, degradability and shape-memory capabilities

The three-dimensional cross-linking network endows epoxy thermosets with outstanding application performance, rendering epoxy thermosets indispensable in the field of materials. It also makes epoxy thermosets insoluble and immiscible. Moreover, epoxy thermosets are derived mainly from non-renewable fossil resources, causing an environmental crisis. In addition, epoxy thermosets are flammable and pose a significant fire hazard. To address these problems, three Schiff base curing agents were prepared in this work by utilizing p-hydroxybenzaldehyde, vanillin and syringaldehyde. Three structurally distinct curing agents were utilized to prepare epoxy vitrimers incorporating dynamic imine bonds. The epoxy vitrimers exhibited outstanding mechanical properties. The incorporation of the Schiff base structure into the cross-linking network greatly enhanced the fire safety of the epoxy vitrimers. The epoxy vitrimers demonstrated excellent chemical resistance and can be degraded selectively in an acetone solution of hydrochloric acid. In addition, the epoxy vitrimers demonstrated excellent shape memory properties and significant stress relaxation. This work provides a novel strategy for the preparation of intrinsically flame-retardant bio-based epoxy vitrimers and innovatively investigates the influence of methoxy groups on the properties of epoxy vitrimers.