Catalyst-free dynamic exchange of aromatic Schiff base bonds and its application to self-healing and remolding of crosslinked polymers†
The present work reveals that catalyst-free dynamic reversible exchange of aromatic Schiff base bonds is enabled at room temperature. Attachment of aryl groups to both nitrogen and carbon atoms of carbon–nitrogen double bonds is a critical structural factor that contributes to the dynamic characteristics and complete reaction between aromatic aldehyde and aromatic amine. The exchange mechanism is studied by model compounds, and free radical intermediates are found to be involved in the non-equilibrium stage of the exchange reaction. By taking advantage of the dynamic equilibrium of aromatic Schiff base bonds, infusible and insoluble crosslinked polyacrylate is self-healed and reprocessed through rearrangement of macromolecular networks. The reprocessed polymer is still self-healable. Either the self-healing or reprocessing is completed in air without heating. Considering that Schiff base polymers have shown diverse properties and stimulus–response behaviors, activation of the dynamic exchange of the inherent Schiff base bonds would result in a series of novel functionalities. More interestingly, traditional crosslinked polymers might thus be provided with a facile way of being smarter.