A phosphonate‐derived epoxy vitrimer with intrinsic flame retardancy and catalyst‐free reprocessability

Abstract Phosphonate, as an effective flame‐retardant group, has a dynamic phosphonate exchange behavior similar to the transesterification of carboxylate; and introducing it into the network of epoxy resin (EP) is beneficial for solving the fire risk and waste disposal problems of EP in the meantime. Herein, a reprocessable and flame‐retardant epoxy vitrimer (EV) with dual dynamic covalent reactions of phosphonate and carboxylate transesterifications is constructed by introducing a phosphonate‐containing diol named GHPP into an epoxy‐anhydride curing system. The presence of the phosphonate makes the EV intrinsically flame‐retardant; meanwhile, both of the dynamic phosphonate and carboxylate transesterifications are accelerated by the abundant primary hydroxyl groups, which show much higher activity than the as‐generated β‐hydroxyls during curing, leading to enhanced dynamic properties of the EV. As a result, on the one hand, the EV achieves the UL‐94 V‐0 rating with a high limiting oxygen index value of 37.3%; and it shows a 41% reduction for the peak heat release rate and a 39% reduction for the total heat release in the cone calorimetry test. On the other hand, such EV exhibits rapid stress relaxation and is reprocessed easily to maintain its mechanical properties, thermal properties and flame retardancy to the hilt.