Preparation and Characterization of Thermal and pH Dual Sensitive Hydrogel Based on 1,3‐Dipole Cycloaddition Reaction

Abstract

In this study, thermal and pH dual sensitive hydrogels were prepared via Cu-free 1,3-dipole cycloaddition between two copolymers which were modified by azide and maleimide functional groups, respectively. First, the thermally sensitive terpolymers were fabricated via conventional free-radical polymerization of N-isopropylacrylamide, hydroxyethyl methacrylate (HEMA), and N,N-dimethylacrylamide (DMA). Then, polymeric dipolarophiles were synthesized via the esterification between the above terpolymers and N-maleoyl alanine. Similarly, the pH-sensitive terpolymers were also fabricated via conventional free-radical polymerization of 4-vinylpyridine, HEMA, and DMA, and then, polymeric dipoles were acquired via the decoration of the as-prepared terpolymers with 2-azidoacetic acid. Afterward, the smart hydrogels were fabricated via the aqueous 1,3-dipole cycloaddition reaction between the as-prepared polymeric dipolarophiles and dipoles without the use of catalysts. The results of swelling measurements confirm that the hydrogels possessed thermal and pH dual sensitivity. Moreover, the investigation of the behavior of oscillatory swelling shrinking indicates their sensitivity to temperature and pH was reversible and repeatable, which is of great significance for the repeated use of the prepared hydrogels. The proposed strategy demonstrates a great application prospects in the preparation of hydrogels as there were no catalysts and organic solvents employed. POLYM. ENG. SCI., 60:917-924, 2020.

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