Thermally induced localization of cyclodextrins in a polyrotaxane consisting of β-cyclodextrins and poly(ethylene glycol)-poly(propylene glycol) triblock copolymer

A polyrotaxane, in which many beta-cyclodextrins (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 nanoscale devices. Coupling of FITC with the terminal amino groups in the polypseudorotaxane was performed in DMF at 5 degrees C. Under these conditions, a side reaction between the hydroxyl groups of beta-CD and FITC was prevented. The interaction of the beta-CDs with terminal FITC moieties in the polyrotaxane was significantly observed at low temperature. However, the interaction of the beta-CDs with the PPG segment was observed with increasing temperature. On the basis of these results, it is concluded that the majority of the beta-CDs move toward the PPG segment with increasing temperature although some beta-CDs may reside on the PEG segments.