A Tough and Self-Healing Polymer Enabled by Promoting Bond Exchange in Boronic Esters with Neighboring Hydroxyl Groups

B–O bonds are effective for constructing self-healing polymers, because of their unique combination of high thermodynamic stability and kinetic tunability. However, it is still challenging to develop boron-containing polymers that show simultaneously high mechanical strength, good hydrolytic stability, and autonomous self-healing ability. Herein, we designed and synthesized a phenol compound with three hydroxyls, two of which form boronic ester with boronic acid while the other one can promote the dynamic exchange of B–O bonds. Taking advantage of the new boronic esters as the cross-linking sites, a series of strong and tough elastomers with outstanding self-healing capacities at room temperature were successfully fabricated. The new design concept provides a novel type of dynamic covalent boronic esters as the platform for synthesizing durable and functional self-healing materials. Moreover, phenol compounds with three hydroxyl groups are abundant in the natural product, tannic acid (TA), which can also form dynamic boronic esters with boronic acid and be used to derive polymers with excellent recyclability. Therefore, this new system might facilitate the commercialization of boron-based dynamic covalent polymers as viable alternatives to contemporary commodity thermosets.