Thermosensitive Phase Behavior of Benzo-21-crown-7 and Its Derivatives.

For designing water-soluble responsive materials, utilizing crown ethers as main building blocks has been rarely explored in contrast to their linear poly(ethylene glycol) counterparts. In the current study, we report the robust thermoresponsive properties of the benzo-21-crown-7 (B21C7) family with lower critical solution temperature (LCST) and upper critical solution temperature (UCST) behavior. Different substituent groups on the benzene ring exhibit significant effects on water solubility and thermoresponsiveness. B21C7 and its cyano derivative display LCST phenomena, while B21C7-based carboxylic acid derivative presents UCST followed by LCST phase behavior. Supramolecular interactions with KCl provide an additional tuning approach for this crown ether system. These results demonstrate that B21C7s can serve as an easily accessible toolbox to develop new thermosensitive systems and prepare thermally responsive materials.