Solvent- and thermoresponsive polyrotaxanes with beta-cyclodextrin dispersed/aggregated structures on a pluronic F127...

A series of polyrotaxane-based triblock copolymers comprising beta-cyclodextrins (beta-CDs) threaded onto a distal 2-bromopropionyl end-capped Pluronic F127 as a central block and poly(N-isopropylacrylamide) outer blocks as end-stoppers were prepared via ATRP of N-isopropylacrylamide in aqueous solution. The structure of the resulting copolymers was characterized in detail by (1)H NMR, (13)C NMR, GPC, and WXRD techniques. Unlike those CD-based polyrotaxanes exhibiting the characteristic tunnel-type crystal structure, these copolymers precipitated from DMF with anhydrous ether preserve a dispersed-state structure in which the beta-CDs are loosely distributed along the Pluronic F127 chain, while they present an aggregated structure in which the beta-CDs are densely stacked one by one along the polymer backbone, holding the typical tunnel-like crystal structure after incubation in water and freeze-drying. The beta-CD dispersed and aggregated states are convertible by the incubation or precipitation treatments. Furthermore, annealing at various temperatures manifests them having the thermoresponsibility in the solid state. These copolymers containing the beta-CD dispersed structure possess an imperfect crystal PEO domain, while those with the beta-CD aggregated structure hold both a microcrystal and an imperfect crystal PEO domain. Hence, the as-prepared polyrotaxane-based triblock copolymers are not only solvent-sensitive but also thermoresponsible supramolecular materials.