Preparation and properties of Schiff base fluorescent hydrogels with high strength and toughness based on multiple hydrogen bonding and hydrophobic association

The preparation of hydrogels with excellent mechanical properties by the synergistic interaction of various non-covalent bonds is one of the research focuses. However, the emerging applications put forward requirements on the function, in addition to the mechanical properties. Therefore, we prepared a physically cross-linked Schiff base fluorescent hydrogel Poly(methacrylic acid-co-poly(ethylene glycol) methyl ether acrylate-co-(Z)-N-(4-(2-((1H-indol-3-yl)methylene)hydrazino-1-carbonyl)phenyl)methacrylamide) (P(MAA-PEGA-IHPMA)) by solvent exchange method, which greatly improved the mechanical properties of the hydrogel, and realized the versatility of the hydrogel. The hydrogel improved the binding energy and crosslinking density through the synergistic effects of non-covalent bonds such as hydrophobic association, hydrogen bonding and metal complexation. Therefore, the hydrogel had excellent mechanical properties (the maximum tensile fracture stress and strain are 1.45 MPa and 401%, respectively, and the maximum toughness was 3.41 MJ/m 3 ), and could be regulated by changing the content of IHPMA. Moreover, its fluorescence properties could be controlled by the concentration of Zn 2+ . In addition, P(MAA-PEGA-IHPMA) hydrogel also showed temperature response, solvent-responsive fluorescence, antibacterial properties and shape memory function. The fluorescent hydrogel with high strength and toughness had potential applications in temperature control materials, anti-fatigue materials and flexible sensors.