A Supramolecular Hydrogel Based on Copolymers of Acrylic Acid and Maleic Anhydride Derivatives with Terpyridine Motifs.

A kind of terpyridine derivative () in which the amino was incorporated by a short alkyl chain was synthesized. Through grafting of terpyridine units into the hydrophilic copolymers of maleic anhydride and acrylic acid via the reaction of the amino groups in and the maleic anhydride units, a series of gelator polymers-, , and -containing different contents of terpyridine units was synthesized. Under coordination of Ni and terpyridine ligands in linear polymers, the supramolecular hydrogels , , and with different cross-linking degrees were prepared. The linear polymers - had a strong absorption peak at about 290 nm in the UV-vis spectra which was attributed to π-π* transition, and there was a new peak at about 335 nm led by the metal-to-ligands charge transfer (MLCT) when coordinated with Ni ions. According to the rheological behaviors, the storage modulus (G') was larger than the loss modulus (G''). These hydrogels showed typical gel-like characteristics when the terpyridine content of the hydrogels exceeded 10%, and the hydrogels showed liquid-like characteristics when the terpyridine content of the hydrogels was less than 7%. The results of the micromorphological investigation of the xerogels from SEM illustrated the metal-terpyridine coordination cross-linking could have an important influence on the microstructures of the resulting hydrogels. Furthermore, these hydrogels based on supramolecular cross-links exhibited reversible solution-gel transition at different environmental temperatures. At the same time, the equilibrium swelling of the supramolecular hydrogels was 8.0-12.3 g/g, which increased with the decrease in the content of the terpyridine units in the resulting hydrogels.