Solvent- and thermoresponsive polyrotaxanes with β-cyclodextrin dispersed/aggregated structures on a pluronic F127 backbone

A series of polyrotaxane-based triblock copolymers comprising β-cyclodextrins (β-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 ¹H NMR, ¹³C 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 β-CDs are loosely distributed along the Pluronic F127 chain, while they present an aggregated structure in which the β-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 β-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 β-CD dispersed structure possess an imperfect crystal PEO domain, while those with the β-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.