Acetylation of Cyclodextrin-Threaded Polyrotaxanes Yields Temperature-Responsive Phase Transition and Coacervate Formation Properties.

Stimuli-responsive materials have received considerable attention for their application in biomedical fields. Herein, the temperature-dependent phase transition behavior of acetylated polyrotaxanes (Ac-PRXs) consisting of acetylated cyclodextrins threaded onto a linear axle polymer in aqueous solution is investigated. The aqueous solutions of Ac-PRXs exhibit temperature-dependent transmittance changes when the degree of acetylation is 30-40%. Upon increasing the temperature, Ac-PRXs are dehydrated and acetyl groups are subsequently associated through hydrophobic interactions. Interestingly, the Ac-PRXs form coacervate droplets with a diameter of ≈2-3 µm above their cloud points. These temperature-responsivities of Ac-PRXs are observed for other PRXs with different axle polymer molecular weights and compositions. Consequently, the acetylation of PRXs is an attractive chemical modification for yielding temperature-responsivities, and Ac-PRXs can be applied as temperature-responsive supramolecular materials.