Crack-localization in elastomeric self-healing enabled by one supermolecule-analogous molecule

Abstract

Residual invisible cracks make perfect material self-healing difficult to achieve. In principle, cracks could be visualized by luminescent indicators; however, high-energy fluctuations associated with rapid healing kinetics interfere with the electronic transitions of luminophores. Here, grouped secondary bonds are combined in a phenylborate-derived chain extender (BOB-1) in the structural form of supermolecule-analogous dimer, inhibiting conformation perturbation to enhance radiative transition. Asymmetric intramolecular O → B coordination affords a dynamic-exchange activation energy as low as 32.88 kJ·mol−1, enabling second-level healing at room-temperature and minute-level healing at 0 °C. Incorporated into polyurethane elastomers through a facile chain-extension procedure, this dynamic motif produces a distinguishable photoluminescent redshift upon O → B coordination, thereby localizing cracks. The material achieves near-100% mechanical recovery and retains at least 95% strength, over twice that of apparently flaw-free controls. Notably, only a 12.5 mol% BOB-1 fraction is required for chain-extending functionality, the engineering crack-visualization of self-healing integrity verification is expected. Self-healing residual cracks in polymeric materials are usually hard to visualise. Here the authors develop a phenylborate-derived molecule, that not only provides good self-healing properties to PU but also makes cracks distinguishable by photoluminescent redshift upon O → B coordination.