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

A polyrotaxane, in which many beta-cyclodextrins (beta-CDs) are threaded on to a triblock copolymer of poly(ethylene glycol) (PEG) and poly(propylene g lycol) (PPG) capped with fluorescein-4-isothiocyanate (FITC), was synthesiz ed as a model of stimuli-responsive molecular assemblies for nanoscale devi ces. Coupling of FITC with the terminal amino groups in the polypseudorotax ane was performed in DMF at 5 degrees C. Under these conditions, a side rea ction between the hydroxyl groups of beta-CD and FITC was prevented. The in teraction of the beta-CDs with terminal FITC moieties in the polyrotaxane w as significantly observed at low temperature. However, the interaction of t he 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 bet a-CDs move toward the PPG segment with increasing temperature although some beta-CDs may reside on the PEG segments.