A seawater triggered dynamic coordinate bond and its application for underwater self-healing and reclaiming of lipophilic polymer.

In this work, water triggered dynamic catechol-Fe3+ coordinate bonds are revealed and studied at atomic, molecular and macroscopic levels using Mössbauer spectroscopy, rheological analysis, etc. DOPA-iron complexation is found to be dynamic in the presence of water, and this dynamic manner is immobilized after removing water. Accordingly, a water saturated lipophilic polymer containing catechol-Fe3+ crosslinks, rather than the dry version, exhibits dynamic coordination-dissociation behavior. In addition, a migration of iron proves to be enabled in the catechol-Fe3+ crosslinked polymer immersed in seawater. Rearrangement of the dynamic catechol-Fe3+ coordinate bonds among different molecules is thus favored. Based on these results, we develop a bulk lipophilic polymer solid capable of repeated autonomic recovery of strength in seawater without manual intervention. When the polymer is damaged in seawater, reshuffling of the mobile hyperbranched polymer networks across the crack interface, owing to the dynamic catechol-Fe3+ crosslinkages activated by the alkaline circumstances, rebinds the damaged site. By taking advantage of the same mechanism, the polymer can be remolded with the help of seawater and this recycled polymer is still self-healable in seawater. Unlike in the case of conventional polymers where water would shield macromolecules from interacting, here, seawater is a necessary environmental assistant for the material interaction to take effect. The outcomes are beneficial for deepening the understanding of coordinate bonds, and the development of robust underwater self-healing lipophilic polymers.