Thermally-responsive properties of a polyrotaxane consisting of β-cyclodextrins and a poly(ethylene glycol)-poly(propylene glycol) triblock-copolymer

A polyrotaxane, in which many beta-cyclodextrin molecules (beta-CDs) are threaded onto a triblock-copolymer of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) capped with fluorescein-4-isothiocyanate (FITC), was synthesized as a model of stimuli-responsive molecular assemblies for nano-scale devices. The interaction between the beta-CDs and the terminal FITC moieties was significantly observed at low temperature in the diluted condition. However, the interaction of the beta-CDs with the PPG segment was observed with increasing temperature. From these results, it is considered that the majority of the beta-CDs move toward the PPG segment with increasing temperature. Intermolecular association behavior of the polyrotaxane was characterized by static and dynamic light scattering measurements above critical association concentration. The polyrotaxane associated at lower temperature showed dissociation behavior above a specific temperature. Based on these results, it is suggested that the dissociation of the associated polyrotaxane molecules is closely related to the thermally-induced localization of beta-CDs onto the PPG segment.