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

• Published in: Polymers Vol. 14; no. 14; p. 2857
• Main Authors: Chi, Zheng, Ma, Chenchen, He, Ziyuan, Ma, Zihan, Chen, Xuegang, Huang, Zhaoge
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 13.07.2022; MDPI
• Subjects: Acids; Acrylic acid; Aqueous solutions; Charge transfer; Coordination; coordination interaction; Copolymers; Crosslinking; Equilibrium; Graft copolymers; Hydrogels; Ligands; Loss modulus; Maleic anhydride; Metals; Morphology; Polymers; Rheological properties; Solvents; Storage modulus; supramolecular hydrogel; terpyridine; Xerogels
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym14142857

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 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 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.