Poly(N-isopropylacrylamide-co-benzo-12-crown-4-acrylamide) Hydrogels with Dual Molecular-/Ion-Recognition Responsive Properties

A novel poly(N-isopropylacrylamide-co-benzo-12-crown-4-acrylamide) (poly(NIPAM-co-B₁₂C₄Am)) hydrogel with dual molecular-/ion-recognition responsive properties is prepared by using 12-crown-4 as both guest unit for molecular-recognition and host unit for ion-recognition.  This smart hydrogel exhibits high responsivity toward γ-cyclodextrin (γ-CD) and Na⁺.  Due to the stable formation of 1:1 γ-CD/B₁₂C₄ host-guest complexes, the volume phase transition temperature (VPTT) of poly(NIPAM-co-B₁₂C₄Am) hydrogel shifts to a higher value at the presence of γ-CD; while, the VPTT shifts to a lower value when crown ethers capture Na²⁺ and form 2:1 “sandwich” complexes of B₁₂C₄/Na⁺. The results provide valuable guidance for designing and applying poly(NIPAM-co-B₁₂C₄Am) smart hydrogels in various applications such as chemical valves, sensors and actuators.