A Multiresponsive Hydrophobic Associating Hydrogel Based on Azobenzene and Spiropyran

Summary of main observation and conclusion Stimuli‐responsive hydrogels crosslinked by weak noncovalent bonds such as hydrogen bonds, ionic interactions, host‐guest interactions and hydrophobic interactions have been extensively investigated. Herein, azobenzene and spiropyran acting as two hydrophobic pendant groups were introduced into a hydrophilic polyacrylamide (PAM) via free radical copolymerization to construct a hydrophobic interaction based thermo‐, light‐ responsive polymer hydrogel. Its viscosity and color could be reversibly regulated by heating and cooling. Meanwhile, its color could be specifically switched by light without obvious viscosity change. The gel was also capable of being transited to sol by addition of β‐cyclodextrin (β‐CD), which encaged the hydrophobic groups and then increased the solubility of polymer in water. The hydrogel could be regained after UV irradiation at λ = 365 nm, and after irradiation at λ = 440 nm, the hydrogel changed into a clear sol again.