SUMMARY: A polyrotaxane in which many b-cyclodextrins (b-CyDs) 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. bCyDs threaded onto the triblock copolymer enhance the solubility of the polyrotaxane and presumably contribute to the prevention of aggregation between PPG segments. The interaction of b-CyDs with a terminal FITC moiety was observed to be significant at 10 8C, however, with increasing temperature, the interaction of b-CyDs with a PPG segment becomes prominent. From these results, it is concluded that the majority of bCyDs move toward the PPG segment with increasing temperature although some b-CyDs may reside on PEG segments.

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Cover: The figure shows the formation of a block-selective polyrotaxane composed of PEI-b-PEG-b-PEI copolymer by pH-controlled threading of cyclodextrins (CDs) onto the copolymer. While the CD threads indiscriminately at high pH onto the entire block copolymer, lowering the pH to 4.4 in the presence of 9-anthraldehyde results in expulsion of the macrocycles from the PEI blocks and capping of the rotaxane by a one-pot sequence.