Strain-Induced Orientation of Host Rings that Determines the Sliding of Guest Polymers and Plasticity of Glassy Polyrotaxane.

The unique motility of mechanically interlocked polymers enables their mechanical properties to profoundly transform. This property has been exploited less in glassy materials than in rubbery materials. This study demonstrated that in the glassy state the rings must orient before sliding and clarified the requisite structural changes by the synchrotron microbeam X-ray diffraction mapping of a ductile cyclodextrin (CD)-based glassy polyrotaxane.

Marked Sensitivity of Ultimate Elongation to Loading Axiality in Polyrotaxane Gels with Largely Slidable Cross Links.

Polyrotaxane (PR) gels with low ring densities have figure-of-eight cross links that can slide along network strands. The slidable cross links have a unique ability to increase the network strand length between adjacent cross links in the loading direction via chain supply from the stress-free direction, thereby enhancing the ultimate elongation (λ) of the gels. We reveal that this enhancement of λ due to the slidable cross links is pronounced specifically in uniaxial stretching, while it is considerably modest in biaxial stretching.

Direct enhancement of intercomponent interactions in polyrotaxane and its pronounced effects on glass state properties.

Strong interactions between the host cyclodextrin and the threading guest polymer were introduced by selective modifications to the polymer of a polybutadine-based polyrotaxane. The changes in the intercomponent interactions influenced the mobility of the threading polymer that was confined in the glassy host framework, resulting in different mechanical properties.

Anisotropic Amorphous X-ray Diffraction Attributed to the Orientation of Cyclodextrin.

The beauty of cyclic molecules is reflected in their host-guest complexation reactions, as well as their unique X-ray diffraction patterns. Cyclodextrins, the longest known host molecules with rigid ring structures, show anisotropic X-ray diffraction characteristic of their single-molecule structure, rather than their intermolecular relationships. Amorphous derivatives of α-cyclodextrin exhibit broad and strong halo diffractions in the solid, melted, and dilute solution states.

Analysis of High-Molecular-Weight Polyrotaxanes by MALDI-TOF-MS Using 3-Aminoquinoline-Based Ionic Liquid Matrix.

Polyrotaxane (PR) is a necklace-like supramolecule composed of cyclic components, such as cyclodextrin (CD), and a threading polymer capped with bulky end groups. PR exhibits peculiar mechanical properties attributed to the intermolecular cross-links with CD. Various CD molecules threaded on a linear PEG chain are often modified with chemical groups to add specific physicochemical properties.

Prolonged Glass Transition due to Topological Constraints in Polyrotaxanes.

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 values by differential thermal analysis, mechanical relaxation was considerably prolonged with increasing coverage.

Direct Determination of Cross-Link Density and Its Correlation with the Elastic Modulus of a Gel with Slidable Cross-Links.

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.

Drastic Change of Mechanical Properties of Polyrotaxane Bulk: ABA-BAB Sequence Change Depending on Ring Position.

Polyrotaxane (PR), consisting of many ring molecules and an axis polymer, is a typical supramolecular structure with unique topological characteristics. In this study, we demonstrated the drastic change of the macroscopic mechanical properties depending on the ring position of PR in bulk. Poly(ethylene oxide)--poly(propylene oxide)--poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer was employed as an axis polymer to control the position of β-cyclodextrin (β-CD).

Polyrotaxane Brushes Dynamically Formed at a Water/Elastomer Interface.

Dense polymer brushes with closely packed rotaxane structures were formed at the interface of water and a styrene-butadiene elastomer by spontaneous segregation of an amphiphilic polyrotaxane (PR), a mechanically interlocked polymer consisting of hydrophobic polybutadiene threading through multiple hydrophilic γ-cyclodextrin (γ-CD) derivatives. Segregation of PR at the water/elastomer interface was suggested by X-ray photoelectron spectroscopy. The polymer brush structure at the water interface was investigated using neutron reflectometry.

Pronounced effects of the densities of threaded rings on the strain-dependent Poisson's ratio of polyrotaxane gels with movable cross-links.

The density of threaded ring molecules (fCD) in polyrotaxane (PR) chains has pronounced effects on the strain-induced swelling of PR gels where the cross-linked ring molecules are slidable along the network strands. The equilibrium Poisson's ratio (μ∞), which is a measure of the strain-induced volume change, for the PR gel increases with an increase in elongation (λ) at moderate λ but becomes a constant value () at sufficiently large λ. When the modulus exceeds a threshold value (Ec), the λ dependence of μ∞ disappears due to the loss of the slidability of the cross-links.

Unusual Fracture Behavior of Slide-Ring Gels with Movable Cross-Links.

In this study, the quasi-static fracture behavior of slide-ring gels (SR gels), in which movable cross-links can slide on polymer chains, is for the first time investigated and compared to that of conventional polymer gels with fixed cross-links (FC gels). For the usual FC gels, there is a trade-off relation between toughness (fracture energy [Formula: see text]) and stiffness (Young's modulus ): with increasing cross-linking density, the Young's modulus increases, while fracture energy [Formula: see text] decreases. However, SR gels show an unusual fracture behavior that contradicts this trade-off relation.

Ductile Glass of Polyrotaxane Toughened by Stretch-Induced Intramolecular Phase Separation.

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.

One-Pot Synthesis and Characterization of Polyrotaxane-Silica Hybrid Aerogel.

A novel kind of polyrotaxane-silica hybrid aerogel is successfully prepared via one-pot sol-gel synthesis in this work. The polyrotaxane can chemically interpenetrate with Si particles homogeneously in nanoscale, so as to shorten the gelation time and construct a flexible and mechanically strong skeleton. The supramolecular effect ascribable to the sliding motion of cyclic components in polyrotaxane is introduced into the hybrid aerogel for the first time.

Volume Phase Transitions of Slide-Ring Gels.

The volume phase transition of slide-ring gels with freely-movable cross-linking junctions was investigated. Ionic chemical gels with fixed cross-linking junctions undergo volume phase transitions when they have higher than the critical degree of ionization. However, the experimentally-observed critical ionization value for slide-ring gels is much higher than theoretical values for chemical gels.

Polyrotaxane Glass: Peculiar Mechanics Attributable to the Isolated Dynamics of Different Components.

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.

Synthesis, structure, and mechanical properties of silica nanocomposite polyrotaxane gels.

A significantly soft and tough nanocomposite gel was realized by a novel network formed using cyclodextrin-based polyrotaxanes. Covalent bond formation between the cyclic components of polyrotaxanes and the surface of silica nanoparticles (15 nm diameter) resulted in an infinite network structure without direct bonds between the main chain polymer and the silica. Small-angle X-ray scattering revealed that the homogeneous distribution of silica nanoparticles in solution was maintained in the gel state.

A significant impact of host-guest stoichiometry on the extensibility of polyrotaxane gels.

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.

Synthesis of graft polyrotaxane by simultaneous capping of backbone and grafting from rings of pseudo-polyrotaxane.

Graft polyrotaxanes, with poly(ε-caprolactone) (PCL) graft chains on the ring components were synthesized by the simultaneous ring-opening polymerization of ε-caprolactone from both ends of the backbone polymer, an end-functionalized polyethylene glycol (PEG) and the formation of inclusion complexes with α-cyclodextrin (α-CD). PEG with multiple functional groups at each end was prepared by the condensation of PEG-amine and D-gluconic acid; the PEG derivative formed an inclusion complex with α-CD. The polymerization of multiple hydroxy groups at the backbone ends resulted in a star-shaped end group, which served as a bulky capping group to prevent dethreading.

Cooperativity and selectivity in chemomechanical polyethylenimine gels.

Gel particles obtained from polyethylenimine (PEI) cross-linked with 10% ethylene glycol diglycidyl ether show considerable selectivity in size changes if exposed to solutions of different effector compounds. Monocarboxylic acids induce contractions of, e.g.

Chemomechanical Polymers as Sensors and Actuators for Biological and Medicinal Applications.

Changes in the chemical environment can trigger large motions in chemomechanical polymers. The unique feature of such intelligent materials, mostly in the form of hydrogels, is therefore, that they serve as sensors and actuators at the same time, and do not require any measuring devices, transducers or power supplies. Until recently the most often used of these materials responded to changes in pH.

Microtubule-cyclodextrin conjugate: functionalization of motile filament with molecular inclusion ability.

A microtubule-beta-cyclodextrin conjugate was prepared on a kinesin-adsorbed glass surface by chemical and biochemical means. Fluorescence microscope observation and a motility assay indicated that the conjugate simultaneously expressed an inherent motor function and an inclusion property.

Excellent enantio-selective enclathration of (2R,3S)-3-methyl-2-pentanol in channel-like cavity of 3-epideoxycholic acid, interpreted by the four-location model for chiral recognition.

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.

Interpretation of enantioresolution in nordeoxycholic acid channels based on the four-location model.

Nordeoxycholic acid (NDCA) forms three kinds of host frameworks, M1, M2, and M3, with channels where aliphatic alcohols (1-7) are accommodated. (13)C-NMR studies clarified that racemic alcohols 1- or 2-6 are enclosed in the M1- or M2-type channel with lower than 15% enantiomeric excess, respectively, while 3-methyl-2-pentanol (7) is done in the M3-type with 47% ee. These inclusion phenomena can be explained due to the Difference Fourier maps of electron densities of their enantiomers in the channels.