2.2. Main Chain Polyrotaxane with Crown Ethers (CEs) 5985 2.3. Main Chain Polyrotaxanes with Other Wheel Compounds 5987 2.3.1. Cucurbit[n]uril-Based System 5987 2.3.2. Cyclobisparquat/Cyclophane-Based Systems 5988 2.3.3. Metal Coordination Systems 5989 2.3.4. Calixarene-Based System 5990 2.4. Applications of Main Chain Polyrotaxanes 5990 2.4.1. Biodegradable Polyrotaxanes and Hydrogels 5990 2.4.2. Molecular Tubes Prepared from Polyrotaxanes 5993 2.4.3. Supramolecular Light-Harvesting Antenna 5993 2.4.4. Insulated Polymers 5993 2.4.5. Stimuli-Responsive Molecular Shuttles Using Polyrotaxanes or Polypseudorotaxanes 5993 3. Side Chain Polyrotaxanes and Polypseudorotaxanes 5995 3.1. Background of Side Chain Polyrotaxanes and Polypseudorotaxanes 5995 3.2. Categories of Side Chain Polyrotaxanes and Polypseudorotaxanes 5997 3.3. Rotor/Polyaxis Systems (See Scheme a and b) 5997 3.3.1. CD-Based Systems 5997 3.3.2. Crown Ether-Based Systems 6003 3.3.3. Cucurbituril-Based Systems 6003 3.4. Polyrotor/Axis Systems (See Scheme c and d) 6004 3.4.1. CD-Based Systems 6004 3.4.2. Crown Ether-and Cyclophane-Based Systems

The development of stimulus-responsive polymeric materials is of great importance, especially for the development of remotely manipulated materials not in direct contact with an actuator. Here we design a photoresponsive supramolecular actuator by integrating host–guest interactions and photoswitching ability in a hydrogel. A photoresponsive supramolecular hydrogel with α-cyclodextrin as a host molecule and an azobenzene derivative as a photoresponsive guest molecule exhibits reversible macroscopic deformations in both size and shape when irradiated by ultraviolet light at 365 nm or visible light at 430 nm. The deformation of the supramolecular hydrogel depends on the incident direction. The selectivity of the incident direction allows plate-shaped hydrogels to bend in water. Irradiating with visible light immediately restores the deformed hydrogel. A light-driven supramolecular actuator with α-cyclodextrin and azobenzene stems from the formation and dissociation of an inclusion complex by ultraviolet or visible light irradiation.

Molecular recognition plays an important role in nature, with perhaps the best known example being the complementarity exhibited by pairs of nucleobases in DNA. Studies of self-assembling and self-organizing systems based on molecular recognition are often performed at the molecular level, however, and any macroscopic implications of these processes are usually far removed from the specific molecular interactions. Here, we demonstrate that well-defined molecular-recognition events can be used to direct the assembly of macroscopic objects into larger aggregated structures. Acrylamide-based gels functionalized with either host (cyclodextrin) rings or small hydrocarbon-group guest moieties were synthesized. Pieces of host and guest gels are shown to adhere to one another through the mutual molecular recognition of the cyclodextrins and hydrocarbon groups on their surfaces. By changing the size and shape of the host and guest units, different gels can be selectively assembled and sorted into distinct macroscopic structures that are on the order of millimetres to centimetres in size.

The formation of effective and precise linkages in bottom-up or top-down processes is important for the development of self-assembled materials. Self-assembly through molecular recognition events is a powerful tool for producing functionalized materials. Photoresponsive molecular recognition systems can permit the creation of photoregulated self-assembled macroscopic objects. Here we demonstrate that macroscopic gel assembly can be highly regulated through photoisomerization of an azobenzene moiety that interacts differently with two host molecules. A photoregulated gel assembly system is developed using polyacrylamide-based hydrogels functionalized with azobenzene (guest) or cyclodextrin (host) moieties. Reversible adhesion and dissociation of the host gel from the guest gel may be controlled by photoirradiation. The differential affinities of α-cyclodextrin or β-cyclodextrin for the trans-azobenzene and cis-azobenzene are employed in the construction of a photoswitchable gel assembly system.

Ein supramolekulares Hydrogel entsteht aus einem wasserlöslichen Polymer, das über Wirt‐Gast‐Einschlusskomplexe zwischen Cyclodextrin und Ferrocen vernetzt ist. Die Dissoziation und Neubildung von Einschlusskomplexen durch Redoxstimuli führte zur makroskaligen Ausdehnung und Kontraktion des Hydrogels. Das Gel wird als redoxaktiver Aktuator verwendet, und die mechanische Arbeit konnte ermittelt werden.

Common adhesives stick to a wide range of materials immediately after they are applied to the surfaces. To prevent indiscriminate sticking, smart adhesive materials that adhere to a specific target surface only under particular conditions are desired. Here we report a polymer hydrogel modified with both β-cyclodextrin (βCD) and 2,2′-bipyridyl (bpy) moieties (βCD–bpy gel) as a functional adhesive material responding to metal ions as chemical stimuli. The adhesive property of βCD–bpy gel based on interfacial molecular recognition is expressed by complexation of metal ions to bpy that controlled dissociation of supramolecular cross-linking of βCD–bpy. Moreover, adhesion of βCD–bpy gel exhibits selectivity on the kinds of metal ions, depending on the efficiency of metal–bpy complexes in cross-linking. Transduction of two independent chemical signals (metal ions and host–guest interactions) is achieved in this adhesion system, which leads to the development of highly orthogonal macroscopic joining of multiple objects.

Aggregates formed from amphiphilic alternating copolymer samples of sodium maleate and dodecyl vinyl ether (MAL/C12) of different molecular weights or (weight-average) degrees of polymerization N w1 (= 76−5000) were characterized by light scattering and fluorescence techniques in 0.05 M aqueous NaCl at pH 10 to investigate the molecular weight dependence of the micellar structure of amphiphilic polyelectrolytes. The light scattering and fluorescence data demonstrated a unicore−multicore transition of the MAL/C12 micelle at N w1 ≈ 300. The structures of unicore and multicore micelles of MAL/C12 copolymers formed were analyzed using the flower micelle model and the flower necklace model, respectively. The data points for unicore micelles formed from the three low-molecular-weight MAL/C12 fractions were in good agreement with the flower micelle model of the minimum loop size determined by the rigidity of the polymer main chain, which we proposed previously [ Kawata Kawata Macromolecules20074011741180]. On the other hand, the data points for the four high-molecular-weight MAL/C12 fractions were nicely fitted to the flower necklace model, the conformation of which was represented as the touched bead model.

Summary: We have successfully constructed a redox‐responsible hydrogel system by combination of β‐cyclodextrin (β‐CD), dodecyl‐modified poly(acrylic acid) [p(AA/C12)], and a redox‐responsive guest, ferrocenecarboxylic acid (FCA). In the reduced state of FCA, the ternary mixture exhibited a gel‐like behavior, whereas, in its oxidized state, the mixture exhibited a sol behavior.Conceptual illustration for the redox‐responsive hydrogel system.magnified imageConceptual illustration for the redox‐responsive hydrogel system.