Highly Elastic Supramolecular Hydrogels Using Host–Guest Inclusion Complexes with Cyclodextrins

Supramolecular hydrogels, which are cross-linked via host–guest interactions, show high-performance physical properties, such as elasticity and toughness. Herein we prepare a supramolecular hydrogel without chemical cross-linker. The supramolecular hydrogel was prepared by polymerization of the inclusion complexes between β-cyclodextrin acrylamide and adamantane acrylamide monomers. The β-cyclodextrin–adamantane gel (βCD–Ad gel) shows a high stretching property (990%). The initial strain (0%) is restored in several minutes for a βCD–Ad gel stretched to 180% of the initial strain without altering the physical history. However, chemically cross-linked poly­(acrylamide) does not show the reversible stretching property. These results indicate that host–guest interaction inside the supramolecular hydrogel plays an important role in the shape recovery properties

Movable Cross-Linked Polymeric Materials from Bulk Polymerization of Reactive Polyrotaxane Cross-Linker with Acrylate Monomers

Topological cross-linked polymers attract much attention from their unique mechanical properties derived from their cross-linking structure. Here, we have fabricated a polymeric material (Acryl-AcO-PRx) incorporating topological cross-links into various universal acrylate polymers by using a modified polyrotaxane as a polymerizable cross-linking agent. Acryl-AcO-PRx obtained by a simple photocuring technique under bulk conditions showed a distinctly higher extensibility compared with the chemical cross-linked polymers. In addition, Acryl-AcO-PRx materials showed high stress relaxation and deformation hysteresis. These results indicate that the topologically cross-linked structure composed of polyrotaxane plays an important role in mechanical properties even in bulk state

Macroscopic Self-Assembly Based on Molecular Recognition: Effect of Linkage between Aromatics and the Polyacrylamide Gel Scaffold, Amide versus Ester

The interactions of polyacrylamide- (pAAm-) based gels possessing cyclodextrin (CD) residues (CD-gels) with pAAm-based gels modified with aromatic residues through amide and ester linkages (ArA-gels and ArE-gels, respectively) were investigated to examine the effect of linkage (i.e., amide and ester) between aromatic residues and the pAAm gel scaffold. In the present study, benzyl (Bz), 2-naphthylmethyl (Np), 9-phenanthrylmethyl (Ph), and 1-pyrenylmethyl (Py) residues were chosen as a series of aromatic residues. αCD-gel did not interact notably with the ArA-gels and ArE-gels in water. βCD-gel interacted with the ArA-gels and ArE-gels possessing smaller aromatic residues (i.e., Bz and Np residues) in water to form gel assemblies. γCD-gel showed different tendencies of its interactions with the ArA-gels and with the ArE-gels; γCD-gel interacted with the ArA-gels carrying larger aromatic residues (i.e., Ph and Py residues), while γCD-gel formed stable gel assemblies only with NpE-gel among the ArE-gels examined. This is because γCD residues in γCD-gel included favorably dimeric aromatic residues in the ArA-gels and ArE-gels. Reflection fluorescence spectra for the ArA-gels and ArE-gels possessing fluorescent aromatic residues (i.e., Np, Ph, and Py residues) in the presence of 10 mM γCD were indicative of weak selectivities of γCD toward NpE, PhA, and PyA residues. Such weak selectivities may be largely enhanced in the macroscopic observation of interaction of CD-gels with the ArA-gels and ArE-gels presumably because of multivalency

Temperature-Sensitive Macroscopic Assembly Based on Molecular Recognition

The interaction of polyacrylamide­(pAAm)-based gel modified with benzyl (Bz) moiety (Bz­(<i>x</i>)-gel, where <i>x</i> denotes the mol % content of Bz moiety) with a pAAm-based gel possessing cyclodextrin (CD) moieties (αCD-gel, βCD-gel, and γCD-gel) was investigated at various temperatures to elucidate the effect of temperature on the formation of macroscopic assembly. The interaction of Bz­(<i>x</i>)-gel with CD-gels was stronger at a lower temperature, consistent with the binding constants for the model system of pAAm modified with 1 mol % Bz moiety and native CDs. Bz(15)-gel interacted only with βCD-gel at a higher temperature

Journalists’ orientations toward objectivity and emotionality in the coverage of the nuclear power plant accident and the tsunami-afflicted Tohoku area.

<p>Journalists’ orientations toward objectivity and emotionality in the coverage of the nuclear power plant accident and the tsunami-afflicted Tohoku area.</p

Supramolecular Materials Cross-Linked by Host–Guest Inclusion Complexes: The Effect of Side Chain Molecules on Mechanical Properties

Functional polymeric materials constructed by noncovalent bonds have attracted considerable attention due to their beneficial stretching and self-healing properties. We chose host–guest interactions using cyclodextrins (CDs) as host molecules to realize supramolecular materials with stretching and self-healing properties. Notably, an inclusion complex of a CD and a guest molecule functions as a reversible bond in a material. Herein, we studied the relationship between the mechanical properties of the materials and host–guest interactions based on the association constants of CDs with guest molecules and molecular structures of the guest molecules. A chemically cross-linked poly­(acrylamide) gel showed high rupture stress, although the rupture strain was noticeably low. However, the host–guest hydrogels (CDAAmMe-R hydrogels) exhibited a higher rupture stress and strain of approximately 1000%. These rupture stress and strain values were related to the association constants of the CDs with guest units on the polymer side chain and the structure of the guest molecules. In particular, the αCDAAmMe-Dod hydrogel with a dodecyl group with a long, rod-like structure showed better rupture stress and strain (1250%). The βCDAAmMe-AdAAm hydrogel with a spherical adamantyl acrylamide (AdAAm) group showed better self-healing properties. To realize a practical self-healing process under dry conditions, a poly­(methyl triethylene glycol acrylate) xerogels with βCDAAmMe and AdAAm (βCDAAmMe-AdAAm TEGA xerogel) was prepared. The βCDAAmMe-AdAAm TEGA xerogel exhibited self-healing properties, regaining 61% of its initial material strength at 100 °C

A Photoresponsive Polymeric Actuator Topologically Cross-Linked by Movable Units Based on a [2]Rotaxane

A photoresponsive polymeric material, in which [2]­rotaxane units with α-cyclodextrin threading onto an azobenzene derivative is used as a topological cross-link for the main chains of the polymeric material in aqueous media, was achieved. [2]­Rotaxane structures were found to act as movable links in the polymer network, and the mechanical properties of the material were enhanced to show a rupture strain of 2800%. The materials were reversibly deformed by irradiation with UV or visible light in aqueous media, which caused photoisomerization of the azobenzene moiety and changed the structure of the [2]­rotaxane linker, leading to deformation of the polymer network. Surprisingly, the dry materials, which had been uniaxially extended in air, showed a faster response than the hydrogel. The orientation of the polymeric network in the materials enables the efficient response. This dry material (5.6 mg) performed 5.6 μJ of mechanical work within 10 s, which is approximately 50 times higher than that achieved in our previous work

Coding categories and prevalence in TV program contents (percentage).

<p>Coding categories and prevalence in TV program contents (percentage).</p

pH- and Sugar-Responsive Gel Assemblies Based on Boronate–Catechol Interactions

The interaction between poly­(acrylamide) gels carrying phenylboronic acid (PB gel) and catechol moieties (CAT gel) respectively is investigated. The PB gel forms an assembly with the CAT gel on a macroscopic scale in basic aqueous media. The adhesion strength is estimated by stress–strain measurements. The assembly and disassembly of the gels are reversibly switched by varying the pH of the medium. The adhesion strength is tunable by competitive monosaccharide molecules in accordance with the association constant with PB moieties

Coding categories and prevalence in newspaper contents (percentage).

<p>Coding categories and prevalence in newspaper contents (percentage).</p