OEGylated Cyclodextrin-Based Polyrotaxanes Showing Remarkable Thermoresponsive Behavior and Photocontrolled Degradation

Abstract

OEGylated cyclodextrin-threaded polyrotaxanes (PRXs) capped with UV-cleavable stoppers were synthesized, and their thermoresponsive and degradable behavior were investigated. These PRXs in aqueous solutions exhibit fast thermally induced phase transitions and small hysteresis as well as tunable phase transition temperatures, which are quite distinct from previous methylated PRXs. Based on the mechanically interlocked architecture, PRXs are stable in solutions but can be completely degraded into hydrophilic components upon UV cleavage of stoppers. As a consequence, the thermoresponsive behavior of PRXs was switched off. Furthermore, micrometer-scale globular aggregates were formed from thermoresponsive PRXs above their phase transition temperatures but disaggregated quickly upon cooling or UV irradiation. This phenomenon was utilized to take these PRXs as unique carriers for guests with dually controlled release by both temperature and light. The present work provides efficient synthesis of a new class of thermoresponsive interlocked polymers with on-demand degradation, and the findings illustrate the prominent effect of PRX architecture on the remarkable thermoresponsive and degradable behavior.

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

“…[ 22 ] The temperature‐dependent coacervation of PRXs in aqueous solutions has also been observed in other modified PRXs, including Me‐PRXs and OEG‐modified PRXs. [ 16,17,19 ] Therefore, to investigate the coacervate formation of Pr‐PRX and Bu‐PRX, microscopic observations of these solutions were performed at various temperatures across the T CP ( Figure A). All acylated PRXs formed coacervate droplets once the temperature increased above the T CP .…”

“…[ 16,17 ] Additionally, the chemical modification of oligo(ethylene glycol) (OEG) carbamate or ethyl carbamate can also induce temperature responsivity in PRXs. [ 18–20 ]…”

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

“…[16,17] Similar temperature-dependent phase transitions and coacervate formation behaviors were also observed for other chemically modified PRXs, such as oligoethylene glycol (OEG) and alkyl carbamate modified PRXs. [18][19][20] We have previously investigated that the aqueous solubility of PRXs was improved by the acylation of the hydroxy groups of the threading α-CDs. [21,22] The acetylated PRXs (Ac-PRXs) dissolve in aqueous solutions when the degree of acetylation (DA) is less than ≈40%.…”

“…In the case of Me-PRXs and OEG-modified PRXs, the temperature-induced phase transition occurs within narrow temperature ranges (less than 10 °C). [13,16,18,19] Therefore, the contribution of acetyl groups on the temperature-dependent phase transition behaviors of Ac-PRXs might be different from those of Me-PRXs and OEG-modified PRXs.…”

“…Next, the 1 H NMR spectra of 36Ac-PRX 10k in D 2 O were recorded at various temperatures to identify the functional groups involved in the temperature-dependent phase transition. [19] Figure 2C shows enlarged 1 H NMR spectra of the ethylene oxide backbone of the PEG axle (3.65 ppm) and acetyl groups (2.08 ppm) in 36Ac-PRX 10k (full range spectra are shown in Figure S4, Supporting Information). The peak area of the ethylene oxide backbone in 36Ac-PRX 10k was roughly constant at all temperatures.…”