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.