Thermo-healing and recyclable epoxy thermosets based on dynamic phenol-carbamate bonds

In recent years, the reversible addition reaction of isocyanates and active hydrogen compounds has aroused wide concern. The synthesis of a novel dynamic covalent system based on phenol-carbamate bonds (PCBs) and its application in the preparation of thermo-healing and recycled epoxy resins have become a research hotspot. Herein, a compound with a phenolic hydroxyl group was designed and synthesized, which was used to react with isocyanate to obtain the dynamic covalent system of PCBs. Based on PCBs, a cross-linked polyurethane curing agent and the epoxy thermosetting resin with recyclability and thermo-healing ability were prepared. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), stress relaxation analysis and tensile test were carried out on the synthesized epoxy resins based on PCBs (PCBs-EP). The results showed that the dynamic PCBs endow epoxy thermosets with outstanding reprocessability, thermo-healing, welding, recycling and shape memory properties. Based on the reversible dynamic phenol-carbamate bonds, PCBs-EP can be thermally healed within 2 h under 100 °C, and the thermo-healing effect is obvious. More surprisingly, the tensile strength of PCBs-EP reaches 95.89 (±1.06) MPa, and its tensile strength still maintains 74.13% of the original after healed and 70.6% of the original after welded. Therefore, the strategies for incorporating dynamic covalent PCBs into thermosetting epoxy resins provide a feasible strategy for preparing cross-linked epoxy thermosets with high thermo-healing efficiency and high mechanical strength in a cost-effective manner.