Supramolecular Polymer Networks with Enhanced Mechanical Properties: The Marriage of Covalent Polymer and Metallacycle†

Main observation and conclusion Supramolecular polymer networks (SPNs) have always been the focus of research due to their novel features of good processability, stimuli-responsiveness, self-healing, and recyclability. Herein, we report the preparation of a metallacycle-linked supramolecular gel via orthogonal metal-ligand interactions and host-guest interactions. A triangular metallacycle with three appended 21-crown-7 (21C7) units was obtained by the metal coordination of nickel(II)-salen-based dipyridyl ligands and platinum(II) acceptors. The integration of this metallacycle and traditional copolymer bearing secondary ammonium salts constructed a SPN via host-guest recognition between 21C7 units and ammonium salts, and a supramolecular gel further formed at high concentration. Multiple stimulus responsiveness and self-healing properties of gel were observed. The gel exhibited better stretchability compared to relative gel formed by copolymer alone owing to the synergistic effect of covalent bonds and supramolecular interactions. Moreover, compared to the model gel without metallacycles, the gel showed higher storage and loss moduli, and exhibited stronger stiffness in the self-healing tests performed with rheometer, indicating the metallacycle played an important role in improving the stiffness and self-healing of the gel. Therefore, the feasible approach to the formation of SPNs by the marriage of covalent polymers and metallacycles is expected to open a new way to design novel SPNs.