Double Reversible Networks: Improvement of Self-Healing in Hybrid Materials via Combination of Diels-Alder Cross-Linking and Hydrogen Bonds

Intrinsic self-healing materials rely on a reversible bond formation after failure. In this study we report hybrid materials that contain two intrinsic self-healing forces: The reversible covalent bond formation of DielsAlder groups is supported by intrinsic hydrogen bonds, which form supramolecular interactions and contribute to the mobility and proximity of the DA groups. This concept was realized by a combination of urea group containing spherosilicates with butyl methacrylate based polymers bearing both DA moieties and self-assembling hydrogen bonds. Multifunctional one-component polymers were synthesized and studied regarding their application in self-healing hybrid materials. The self-healing behavior was investigated following the signals for bond release and formation of DA groups in the material using IR, UV-vis, and CP-MAS NMR spectroscopy. Furthermore, DSC and rheological measurements were performed and revealed that the materials are superior compared to previously studied systems concerning their healing capacity. The self-healing behavior of the formed hybrid materials was proven by a cut healing test of several millimeters using microscope images. We can conclude that it is advantageous to combine several reversible functions in one material to promote the self-healing capacity particularly in nanocomposites where the flexibility of the network is restricted.