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

A kind of terpyridine derivative (NH2-Tpy) 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 PAAMa via the reaction of the amino groups in NH2-Tpy and the maleic anhydride units, a series of gelator polymers-P1, P2, and P3-containing different contents of terpyridine units was synthesized. Under coordination of Ni2+ and terpyridine ligands in linear polymers, the supramolecular hydrogels H1, H2, and H3 with different cross-linking degrees were prepared. The linear polymers P1-P3 had a strong absorption peak at about 290 nm in the UV-vis spectra which was attributed to pi-pi* transition, and there was a new peak at about 335 nm led by the metal-to-ligands charge transfer (MLCT) when coordinated with Ni2+ 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.

Automated summary

A series of gelator polymers containing different contents of terpyridine units were synthesized by grafting terpyridine units into hydrophilic copolymers PAAMa. Supramolecular hydrogels with different cross-linking degrees were prepared by coordination of Ni2+ and terpyridine ligands in linear polymers. These hydrogels exhibited reversible solution-gel transition and adjustable swelling properties.