Effect of Alkyl Chain Length of Acylated α‐Cyclodextrin‐Threaded Polyrotaxanes on Thermoresponsive Phase Transition Behavior

The temperature‐dependent phase transition behavior of acetylated polyrotaxanes (PRXs) consisting of acylated α‐cyclodextrins threaded onto a poly(ethylene glycol) chain in an aqueous solution is investigated. Acetyl (Ac), propionyl (Pr), and butyryl (Bu) group‐modified PRXs with different degrees of substitution are synthesized to elucidate the effect of the alkyl chain length of the acyl groups on temperature responsivity. Ac‐PRXs, Pr‐PRXs, and Bu‐PRXs are dissolved in water and exhibit temperature‐dependent transmittance changes accompanied by coacervate formation. However, the temperature responsivity of acylated PRXs is seen in limited degree of substitution range (≈10%). The maximum degree of substitution to show temperature responsivity of acylated PRXs decreases with increasing alkyl chain length of the acyl groups. Transmittance measurements of acylated PRXs in the presence of urea reveal that the alkyl chain length of the acyl groups determines the predominant force involved in the temperature‐induced phase transition. During the temperature‐induced phase transition of Pr‐PRXs and Bu‐PRXs, hydrophobic interactions are predominant; however, hydrogen bond formation may occur in Ac‐PRXs. These fundamental findings related to acylated PRXs will facilitate the application of PRXs as thermoresponsive supramolecular materials. Temperature‐induced phase transition of acylated polyrotaxanes (PRXs) in water is investigated. The alkyl chain length of the acyl groups governs the intermolecular forces involved in the phase transition of acylated PRXs. Hydrophobic interaction is predominant in the phase transition of propionylated and butyrylated PRXs, whereas hydrogen bonding is expected to be involved in the phase transition of acetylated PRX.