Photodimerization-Mediated Intramolecular Cross-Linking of Thermoresponsive Dendronized Cyclodextrin-Based Polyrotaxanes.

Intramolecular cross-linking of mechanically interlocked polyrotaxanes (PRXs) is promising to create novel single-chain nanoparticles with distinct architectures and properties. Here, we report intramolecular cross-linking of thermoresponsive dendronized cyclodextrin-based PRXs through photodimerization mediated by dendritic confinement. These PRXs are based on polyethylene glycol axle, which are dendronized with cinnamate-cored threefold dendritic oligo(ethylene glycol)s (OEGs) to contribute dually thermoresponsive and photo-cross-linkable functions. The cinnamates confined by dendritic OEGs undergo efficient photodimerization in aqueous solutions to afford intramolecularly cross-linked PRXs, and their photoreaction behavior is controlled by the PRX architecture and solvation. Dendronized PRXs exhibit characteristic thermoresponsive behavior in water because of thermally induced dehydration and aggregation of dendritic OEGs. Remarkably, phase transition temperatures of intramolecularly cross-linked dendronized PRXs are increased significantly with the photodimerization of the hydrophobic cinnamate moieties, and thermally induced aggregation is retarded to form smaller coacervates irrespective of dehydration of the dendritic OEGs. These intramolecularly cross-linked dendritic PRXs with unique architectures and thermoresponsiveness serve as a new class of stimuli-responsive interlocked polymers for diverse applications.