Autonomous self-healing of polymeric gels cross-linked by diarylbibenzofuranone-based dynamic covalent bonds

Self-healing materials attract a lot of attention because of their ability to repair the internal and external damage, thereby extending the lifetime of the material in numerous applications that we cannot repair easily. Diarylbibenzofuranone (DABBF), which is a novel dynamic covalent bond unit, can reach a state of radically thermodynamic equilibrium under air at room temperature without any stimuli. Furthermore, DABBF and radical species formed from cleaved DABBF are tolerant of oxygen. Here we report that gels cross-linked by DABBF show autonomous selfhealing under air at room temperature. Cross-linked polymers with DABBF as a cross-linker were prepared by polyaddition of tetrahydric DABBF and tolylene-2,4-diisocyanate-terminated poly(propylene glycol) (PPG). To confirm whether or not DABBF units in the cross-linked polymers were a state of equilibrium and could exchange their bonds, de-cross-linking reaction was performed in DMF under air at room temperature by adding excess DABBF. After decross- linking for 24 h, a THF-soluble high-molecular-weight component was detected by GPC measurement. It was expected to be linear polymers and/or cross-linked oligomers. 1H-NMR spectrum of the solution without fractionation after de-crosslinking clearly indicated the presence of soluble PPG, which had constituted a threedimensional network. In contrast, these results were not observed in the case of the usual cross-linked polymers (control experiment). Consequently, we confirmed that the reorganization of the cross-linked polymers was due to the autonomously exchangeable DABBF units. The self-healing property of the polymeric gels swollen with DMF was also investigated under air at room temperature. The gels were cut with a razor blade and the cut pieces were brought together immediately without pressing them strongly. After 24 h, self-healing of the contacted samples could be observed and the scars had almost disappeared. This self-healing behavior was also verified from the almost complete recovery of mechanical properties.