Stimuli-sensitive hydrogels changing their volumes and shapes in response to various stimulations have potential applications in multiple fields. However, these hydrogels have not yet been commercialized due to some problems that need to be overcome. One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle. Here we prepare extremely stretchable thermosensitive hydrogels with good toughness by using polyrotaxane derivatives composed of α-cyclodextrin and polyethylene glycol as cross-linkers and introducing ionic groups into the polymer network. The ionic groups help the polyrotaxane cross-linkers to become well extended in the polymer network. The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains. In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers.

The thermal decomposition of smithsonite (ZnCO 3 ) was studied to obtain a universal kinetic description of the process applicable to a range of reaction conditions. A synthesized ZnCO 3 was subjected to thermoanalytical measurements under various heating and atmospheric conditions in a flow of dry N 2 gas, or N 2 −CO 2 or N 2 −H 2 O mixed gases. Systematic shifts of the reaction temperature to higher or lower values by the effects of CO 2 or H 2 O, respectively, were identified as specific characteristics of the system. With reference to the physicogeometrical kinetic behavior of the reaction in a flow of dry N 2 gas, the retardation effect of CO 2 was demonstrated in the scheme of the physicogeometrical consecutive surface reaction (SR) and phase boundary-controlled reaction (PBR). The individual kinetics of SR and PBR were universally described over different CO 2 partial pressures using an accommodation function (AF) obtained by considering the consecutive elementary steps of SR and PBR. The catalytic effect of water vapor was assumed to result from contributions of water molecules to the consecutive elementary steps of SR and to the crystal growth of the solid product of the reaction (ZnO). An alternative AF derived considering the adsorption of water molecules on solid surfaces allowed us to obtain the universal kinetic description of the thermal decomposition over different water vapor pressures.

A synthetic lipid A of Helicobacter pylori strain 206-1 (compound HP206-1), which is similar to its natural lipid A, exhibited no or very low endotoxic activities as compared to Escherichia coli-type synthetic lipid A (compound 506). Furthermore, compound HP206-1 as well as its natural lipid A demonstrated no or very low mitogenic responses in murine spleen cell. On the other hand, compound HP206-1 showed a weaker but significant production of interleukin-8 in a gastric cancer cell line, MKN-1, in comparison with compound 506. Furthermore, compound HP206-1 exhibited induction of tumor necrosis factor-alpha production in human peripheral blood mononuclear cells and the cytokine production was clearly inhibited by mouse anti-human Toll-like receptor (TLR) 4 monoclonal antibody HTA125. Our findings indicate that the chemically synthesized lipid A, mimicking the natural lipid A portion of lipopolysaccharide from H. pylori strain 206-1, has a low endotoxic potency and immunobiological activities, and is recognized by TLR4.

We investigated the structure, thermal properties, and dynamics of polyrotaxane (PR), composed of poly(ethylene glycol) (PEG) and α-cyclodextrins (CDs), and PR derivatives comprising hydroxypropylated CDs, that is, hydroxypropylated PRs (HyPRs), in the solid state by using wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and viscoelastic spectroscopy. It was observed that HyPRs with high chemical modification ratios show a WLF-type viscoelastic relaxation that can be ascribed to the cooperative segmental motion of several CD molecules, whereas HyPRs with a lower modification ratio and PR with a highly ordered packing structure of CDs do not exhibit any mechanical relaxation mode. A comparison between the relaxation temperatures of HyPRs with different modification and inclusion ratios suggested that the hydrogen bond between CDs primarily dominates the viscoelastic properties of solid-state PR. Our experimental results indicate a close relationship between the crystallinity and fluctuation of cyclic molecules in solid-state PR, which is the first evidence of the dynamic softening of the glassy state formed by assembled cyclic molecules in solid-state PR.

The concentration-induced conformational change in hydroxypropylated polyrotaxane (H-PR) composed of poly(ethylene glycol) (PEG) and hydroxypropylated R-cyclodextrins (CDs) was investigated at various concentrations from the overlap concentration c* to the semidilute regime by using the small-angle neutron scattering technique. We employed the generalized Zimm plot with the wormlike chain model to analyze the scattering functions of H-PR since they deviated from the Ornstein-Zernike equation particularly in the high-Q range. It was found that the persistence length of H-PR decreased with increasing polymer concentration c p , while those of PEG remained unchanged in the same molar concentration regime. This unusual concentration dependence of polymer conformation for H-PR may indicate that CDs in H-PR could slide freely and rapidly over the whole range of PEG chains in the neighborhood of c*, but their mobility was suppressed as c p increased due to some molecular interaction among CDs.

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We prepared building blocks with the ability to form a polymer network, a polyrotaxane (PR) structure that enhances the flexibility of the polymer network, and thermosensitive dangling chains that impart the polymer network with rapid sensitivity. First, thermosensitive poly­(N-isopropyl­acrylamide) (PNIPA) was grafted from α-cyclodextrin, a cyclic molecule of PR, via controlled radical polymerization. The terminal chlorinated alkyl group of the grafted PNIPA was then modified with azide or alkyne. As a result, we obtained two types of PNIPA-grafted PR molecules with different terminations of PNIPA as building blocks. We then prepared a polymer network in which PR molecules with several dangling PNIPA chains were connected by PNIPA chains using a click reaction. Because of the presence of the dangling PNIPA chains, the obtained hydrogel exhibits rapid responses to changes in water temperature; it also exhibits flexibility due to the presence of the PR structure.