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 beta-cyclodextrin trimer (beta-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 beta-CD3 and PEG-NP2. During LCST transition, PEG-NP2 becomes 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.