The University of Tokyo · Materials Science
Professor Kazuaki Kato's research lab specializes in the design and synthesis of advanced polyrotaxane-based materials, with a focus on slide-ring gels and stimuli-responsive soft materials. The lab explores the unique viscoelastic behavior arising from sliding dynamics of cyclic molecules along polymer chains, aiming to understand and control the mechanical properties of these systems through molecular architecture. Key research directions include the development of novel cyclodextrin-based polyrotaxanes, precise control of cross-link density and ring density, and the creation of gels with tunable mechanical responses and dynamic behavior.
Figures are computed from collected data and may differ slightly.
A systematic study of the viscoelastic relaxation of slide-ring gels revealed the dynamics of chains sliding through the cross-links, based on a precise assignment of the plateau moduli and on detailed consideration of the correlation between relaxation times and the molecular weights between cross-links. The slide-ring gels exhibit finite equilibrium moduli that are much smaller than those of the rubbery plateau, indicating a significant contribution of the ring components’ entropy to the elast
Modification of the guest polymer ends efficiently and substantially decreases the density of the threaded rings. The minimized ring density drastically facilitates chain sliding through the cross-links in polyrotaxane gels. This molecular design is like regulating the "pressure" of the rings confined in the interlocked architecture, which counteracts the sliding.
The universal relationship between the elastic modulus and the cross-link density of a conventional rubber/gel has been demonstrated experimentally to be inapplicable to gels with slidable cross-links. Herein, we describe the synthesis of slide-ring (SR) gel networks devoid of intramolecular cross-links by the cross-coupling of two differently functionalized polyrotaxanes. The cross-link density was determined from the characteristic UV absorption attributed to the asymmetric cross-linked moiety
Double-digit relaxation of the elastic modulus and a previously unknown plateau are observed in a new class of slide-ring gels. Detailed consideration of the assignment of the two observed plateaus and the relaxation dynamics reveals that the relaxation is attributable to the sliding dynamics of partial chains through cross-links. This suggests a transition between one state where the cross-links behave as fixed ones and another where they slide freely.
A novel polyrotaxane consisting of poly(dimethylsiloxane) (PDMS) and γ-cyclodextrin (γ-CD) is synthesized, and the threaded γ-CDs of polyrotaxane are intermolecularly cross-linked in solution to yield a new class of slide-ring gel. Synthesis of the polyrotaxane is achieved by an end-capping reaction of pseudo-polyrotaxane whose both ends are preliminarily activated as p-nitrophenyl ester with p-methoxytritylamine derivatives. The obtained polyrotaxane is soluble in N,N-dimethylformamide (DMF) an
We report herein a versatile synthesis of cyclodextrin-based polyrotaxanes (CD-PRs). Three different CD-PRs were synthesized from different linear polymers and different CDs with relatively good yields by a novel single method. This method requires no additional capping reagents, because CDs play a dual role as both the cyclic components and the end-capping groups. The end-capping is achieved by transesterification with excess CDs at both ends of pseudopolyrotaxanes activated with p-nitrophenyl
A new class of ductile glasses is created from a thermoplastic polyrotaxane. The hard glass, which has a Young's modulus of 1 GPa, shows crazing, necking, and strain hardening with a total elongation of 330%. Stress concentration is prevented through a unique stretch-induced intramolecular phase separation of the cyclic components and the exposed backbone. In situ synchrotron X-ray scattering studies indicate that the backbone polymer chains slip through the cyclic components in the regions wher
The molecular dynamics of condensed polymers are directly linked to practically important mechanical properties, such as glass transition behavior and impact strength. We present a unique viscoelastic glass-forming polyrotaxane that is comprised of a main chain polymer and threaded cyclodextrins. The abnormally broad glass transition phase is attributed to the segment motion, which is unprecedentedly insusceptible to cooperative motion with neighboring chains until vitrification is completed. Ev
Topological constraints in polyrotaxanes significantly affected their glass transition dynamics. The effects of the constraints were systematically studied using a series of different coverage glass-forming polyrotaxanes consisting of a common polymer and threaded ring molecule of varying ratios. Although their ratios were similar and hence exhibited similar <i>T</i><sub>g</sub> values by differential thermal analysis, mechanical relaxation was considerably prolonged with increasing coverage. Th
A simple molecular design based on the size of the cyclic components of polyrotaxanes achieved a significant variation of mechanical relaxation dynamics of polyrotaxane gels.
A series of polyrotaxane glasses composed of poly(ethylene glycol) backbones and threaded α-cyclodextrins (α-CDs) with different substituents were found to exhibit unique viscoelasticities attributed to their interlocked structures, beyond a mere miscible blend of the different components. Differences in the interactions between CDs, which occupied 80 wt % or more of the materials, brought about wide variations in the glass transition temperature and also influenced the cooperativity of segmenta
Pure (2R,3S)-3-methyl-2-pentanol is resolved from the racemates by a steroidal host; the interpretation of the recognition mechanism based on the crystal structure reveals that CH/O interaction between the host and guest plays a decisive role in enantio-selective enclathration of the small aliphatic secondary alcohol.
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