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

A polyrotaxane, in which many beta-cyclodextrin molecules (beta-CDs) are th readed onto a triblock-copolymer of poly(ethylene glycol) (PEG) and poly(pr opylene 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 m oieties was significantly observed at low temperature in the diluted condit ion. However, the interaction of the beta-CDs with the PPG segment was obse rved with increasing temperature. From these results, it is considered that the majority of the beta-CDs move toward the PPG segment with increasing t emperature. Intermolecular association behavior of the polyrotaxane was cha racterized by static and dynamic light scattering measurements above critic al association concentration. The polyrotaxane associated at lower temperat ure showed dissociation behavior above a specific temperature. Based on the se results, it is suggested that the dissociation of the associated polyrot axane molecules is closely related to the thermally-induced localization of beta-CDs onto the PPG segment.