Nonionic cyclodextrin based binary system with upper and lower critical solution temperature transitions via supramolecular inclusion interaction

A nonionic binary aqueous interaction system consisting of β-cyclodextrin trimer (β-CD₃) and naphthalene-terminated poly(ethylene glycol) (PEG-NP₂), which has tunable upper critical solution temperature (UCST) behavior around room temperature and lower critical solution temperature (LCST) behavior at high temperature, was investigated. In the UCST transition, gel-like aggregates form because of supramolecular inclusion complexation between β-CD₃and PEG-NP₂. During LCST transition, PEG-NP₂becomes insoluble in water, which results in its precipitation. The effects of concentration, stoichiometry of the two components, and electrolyte on UCST behavior are discussed. This study provides a new nonionic thermoresponsive material.