Yasushi Okumura

Supramolecules with topological characteristicshave attracted great interest both experimentally and theoretically. A new kind of gel has been obtained by chemically cross-linking polyrotaxane molecules in solution. The polymer chains are topologically interlocked by figure-of-eight cross-links (see Figure), which can pass along the polymer chains freely to equalize the “tension” of the threaded polymer chains just like pulleys.

Abstract An anomalously large dielectric permittivity of ≈10 4 is found in the mesophase temperature range (MP phase) wherein high fluidity is observed for a liquid‐crystal compound having a 1,3‐dioxane unit in the mesogenic core (DIO). In this temperature range, no sharp X‐ray diffraction peak is observed at both small and wide Bragg angles, similar to that for a nematic phase; however, an inhomogeneous sandy texture or broken Schlieren one is observed via polarizing optical microscopy, unlike that for a conventional nematic phase. DIO exhibits polarization switching with a large polarization value, i.e., P = 4.4 µC cm −2 , and a parallelogram‐shaped polarization–electric field hysteresis loop in the MP phase. The inhomogeneously aligned DIO in the absence of an electric field adopts a uniform orientation along an applied electric field when field‐induced polarization switching occurs. Furthermore, sufficiently larger second‐harmonic generation is observed for DIO in the MP phase. Second‐harmonic‐generation interferometry clearly shows that the sense of polarization is inverted when the +/− sign of the applied electric field in MP is reversed. These results suggest that a unidirectional, ferroelectric‐like parallel polar arrangement of the molecules is generated along the director in the MP phase.

Poly(ethylene glycol) (PEG)-substituted cyclodextrin (CD) with an azobenzene group at the terminal of the PEG chain (6-Az-PEG600-HyCiO-β-CD) was synthesized. The conformation of 6-Az-PEG600-HyCiO-β-CD in aqueous solution could be controlled thermally and photochemically. At low concentration, 6-trans-Az-PEG600-HyCiO-β-CD formed different types of self-inclusion complexes or existed in a dethreading form depending on the temperature, while at high concentration, an intermolecular complex was formed. Moreover, UV-light irradiation induced a conformational change to a self-inclusion complex where the CD cavity included the azobenzene part regardless of the concentration.

The deformation mechanism of “slide-ring” (SR) gels was investigated with small-angle neutron scattering (SANS). The SR gels were prepared by coupling α-cyclodextrin (CD) molecules on polyrotaxane chains consisting of poly(ethylene glycol) and CD. Because of a hollow structure of CD molecules, the cross-links made of CD molecules in a figure-of-eight shape can slide along the polymer chain. A normal butterfly pattern was observed for the first time in two-dimensional SANS isointensity profiles for the SR gels under uniaxial deformation, where the normal butterfly pattern means a prolate isointensity pattern in the direction perpendicular to the stretching direction. However, by either increasing the cross-link density or increasing the stretching ratio, the normal butterfly patterns changed to abnormal butterfly patterns as are commonly observed in conventional covalent-bonded chemical gels. The difference in the deformation mechanism as well as the cross-linking inhomogeneities between the SR gels and the covalent-bonded chemical gels is discussed by focusing on the unique architecture of the SR gels.