Cross-linked polymers constructed with dynamic-covalent boronic esters were synthesized via photoinitiated radical thiol-ene click chemistry. Because the reversibility of the boronic ester cross-links was readily accessible, the resulting materials were capable of undergoing bond exchange to covalently mend after failure. The reversible bonds of the boronic esters were shown to shift their exchange equilibrium at room temperature when exposed to water. Nevertheless, the materials were observed to be stable and hydrophobic and absorbed only minor amounts of water over extended periods of time when submerged in water or exposed to humid environments. The facile reversibility of the networks allowed intrinsic self-healing under ambient conditions. Highly efficient self-healing of these bulk materials was confirmed by mechanical testing, even after subjecting a single site to multiple cut-repair cycles. Several variables were considered for their effect on materials properties and healing, including cross-link density, humidity, and healing time.
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