Self-healable, reprocessable and anti-flammable eugenol-derived covalent adaptable thermosets based on dynamic covalent boronic esters and thiol-ene click chemistry

Thermosetting polymer materials have been widely used in many fields due to their excellent properties. Due to the restriction of the crosslinking network, traditional thermosetting polymer materials exhibit insolubility and immiscibility. Therefore, reprocessing of thermosetting polymer materials is a great challenge. With the depletion of petroleum-based resources, the utilization of natural resources for the preparation of bio-based thermosetting polymer materials is a major trend. In this study, eugenol-based covalent adaptable thermosets were prepared by UV curing and thermal curing according to thiol click chemistry. The mechanical properties of the eugenol-based covalent adaptable thermosets could be regulated according to the components, which were better than those of the control sample. The eugenol-based covalent adaptable thermosets exhibited excellent transparency and UV shielding properties. The introduction of dynamic covalent boronic ester (BSH) promoted the formation of residual char and enhanced the fire safety of eugenol-based covalent adaptable thermosets. Because of the dynamic borate ester bonds in the cross-linked network, the eugenol-based covalent adaptable thermosets exhibited significant stress relaxation behavior, excellent shape memory function and self-healing properties. The samples could be reprocessed at 100 °C several times. After three cycles of pulverizing and hot pressing, the recovery ratio of the tensile strength for the reprocessed samples remained above 85%. This study provides a novel strategy for preparing self-healable, reprocessable and anti-flammable covalent adaptable thermosets with tunable mechanical properties.