Polyrotaxane Structure Research Articles

Highly Tough Slide‐Crosslinked Gel Polymer Electrolyte for Stable Lithium Metal Batteries

AbstractGel polymer electrolytes (GPEs) hold great promise for the practical application of lithium metal batteries. However, conventional GPEs hardly resists lithium dendrites growth and maintains long‐term cycling stability of the battery due to its poor mechanical performance. Inspired by the slide‐ring structure of polyrotaxanes (PRs), herein we developed a dynamic slide‐crosslinked gel polymer electrolyte (SCGPE) with extraordinary stretchability of 970.93 % and mechanical strength of 1.15 MPa, which is helpful to buffer the volume change of electrodes and maintain mechanical integrity of the battery structure during cycling. Notably, the PRs structures can provide fast ion transport channels to obtain high ionic conductivity of 1.73×10−3 S cm−1 at 30 °C. Additionally, the strong polar groups in SCGPE restrict the free movement of anions to achieve high lithium‐ion transference number of 0.71, which is favorable to enhance Li+ transport dynamics and induce uniform Li+ deposition. Benefiting from these features, the constructed Li|SCGPE‐3|LFP cells exhibit ultra‐long and stable cycle life over 1000 cycles and high‐capacity retention (89.6 % after 1000 cycles). Even at a high rate of 16 C, the cells deliver a high capacity of 79.2 mAh g−1. The slide‐crosslinking strategy in this work provides a new perspective on the design of advanced GPEs for LMBs.

Composite materials based on slide‐ring polyrotaxane structures for optoelectronics

AbstractComposite material based on polyethylene glycol (PEG) and polypyrrole (PPy) polyrotaxanes both encapsulated into α‐cyclodextrins (α‐CDs) macrocycle molecules was synthesized by cross‐linking reaction. The effect of PPy‐αCD polyrotaxane incorporation into the PEG‐αCD polyrotaxane matrix, on the structural, morphological, thermal, and dielectric properties was evaluated and compared to the reference material. Scanning electron microscopy spectroscopy indicates different surface morphologies of this material in comparison to the reference one. In addition, the contact angle measurements and surface free energy attest a hydrophilic surface, while the reference material exhibits a hydrophobic surface. More than that, the presence of the PPy‐αCD cross‐linked into the matrix has a beneficial effect on the thermal properties. The composite material shows an enhanced dielectric constant value of 31,365 at 10 Hz frequency compared to the 38.2 of the reference material, and higher dielectric loss (62,398 vs. 80 at 10 Hz, respectively). The conductivity measurements at 10 Hz frequency indicated for the reference material the value 4.5 × 10−11, while for the material with PPy‐αCD polyrotaxane, the conductivity is three orders of magnitude higher (3.5 × 10−8) confirming the improvements of the electrical properties.

Highly Tough Slide-Crosslinked Gel Polymer Electrolyte for Stable Lithium Metal Batteries.

Gel polymer electrolytes (GPEs) hold great promise for the practical application of lithium metal batteries. However, conventional GPEs hardly resists lithium dendrites growth and maintains long-term cycling stability of the battery due to its poor mechanical performance. Inspired by the slide-ring structure of polyrotaxanes (PRs), herein we developed a dynamic slide-crosslinked gel polymer electrolyte (SCGPE) with extraordinary stretchability of 970.93 % and mechanical strength of 1.15 MPa, which is helpful to buffer the volume change of electrodes and maintain mechanical integrity of the battery structure during cycling. Notably, the PRs structures can provide fast ion transport channels to obtain high ionic conductivity of 1.73×10-3 S cm-1 at 30 °C. Additionally, the strong polar groups in SCGPE restrict the free movement of anions to achieve high lithium-ion transference number of 0.71, which is favorable to enhance Li+ transport dynamics and induce uniform Li+ deposition. Benefiting from these features, the constructed Li|SCGPE-3|LFP cells exhibit ultra-long and stable cycle life over 1000 cycles and high-capacity retention (89.6 % after 1000 cycles). Even at a high rate of 16 C, the cells deliver a high capacity of 79.2 mAh g-1. The slide-crosslinking strategy in this work provides a new perspective on the design of advanced GPEs for LMBs.

Facile Preparation of Tough, Puncture-Resistant Antibacterial Polyrotaxane Hydrogel.

Slide-ring hydrogels containing polyrotaxane structures have been widely developed, but current methods are more complex, in which modified cyclodextrins, capped polyrotaxanes, and multistep reactions are often needed. Here, a simple one-pot method dissolving the pseudopolyrotaxane (pPRX) in a mixture of acrylamide and boric acid to form a slide-ring hydrogel by UV light is used to construct a tough, puncture-resistant antibacterial polyrotaxane hydrogel. As a new dynamic ring cross-linking agent, boric acid effectively improves the mechanical properties of the hydrogel and involves the hydrogel with fracture toughness. The polyrotaxane hydrogel can withstand 1 MPa compression stress and maintain the morphology integrity, showing 197.5 mJ puncture energy under a sharp steel needle puncture. Meanwhile, its significant antibacterial properties endow the hydrogel with potential applications in the biomedical field.

β-cyclodextrin encapsulation of anthracene-based polymer: a versatile approach for photoluminescence recovery and improved thin film performance

In this study, we present the synthesis of a novel host-guest polyrotaxane (PR1) using a microwave-assisted threading approach. The polyrotaxane structure involves the encapsulation of an anthracene-based conjugated polymer (P1) within β-cyclodextrin (β-CD) cavities. The successful formation of PR1 and P1 was confirmed using various spectroscopic and thermal techniques. Optimized geometry and vibrational frequencies of the polymer P1 conducted using DFT calculations at the DFT/B3LYP/6–311+G(d) level of theory showed good agreement with experimental results. Physicochemical and electrical properties of PR1 and the free polymer P1 revealed significant improvements resulting from the encapsulation process. Particularly, enhanced solubility in DMF and DMSO and processability, improved thermal stability, surface homogeneity, and smoothness in PR1 compared to the free polymer. Additionally, the encapsulation process led to an enhanced redox potential of PR1 in comparison to the free polymer. Interestingly, the photoluminescence of thin films of P1 was found to be quenched due to a phenomenon known as aggregation caused quenching (ACQ). However, the encapsulation of the polymer using β-CD rings reduced the formation of aggregates, effectively suppressing the ACQ process. This resulted in the recovery of photoluminescence. Notably, the charge carrier mobility of the encapsulated polymer was maintained at a similar order of magnitude.

Rapid shape recovery and remodeling by tuning the topology of polycaprolactone-based polymer networks

Shape memory polymers (SMPs) designed with desired performance depend on a deeper understanding of network topology and macro characteristics. Although photoreversible dynamic covalent bonds are used for permanent shape reconstruction of SMPs due to their economical and rapid, the disordered network structure limits the ability to improve shape memory performance through structural adjust. In this work, the polycaprolactone networks with sliding structural components (polyrotaxane) and photoreversible components (coumarin) were prepared by preprogrammed precursors. The SMPs network topology is controlled by adjusting the length of molecular chain and sliding distance. Reversible bonding can realize complex shape designability and solid remodeling. Furthermore, the supramolecular structure of polyrotaxane can adjust the uneven stress distribution caused by network topology defects, so the material can instantly return to its original shape under more than 300 % strain, and its elongation at break is over 1600 %. Especially the thermo-mechanical properties of materials can be adjusted by simple preliminary monomer synthesis steps. The results revealed the material has excellent shape memory and controllable thermodynamic properties, which provides a new paradigm for the preparation of high performance SMPs.

Creation of Molecular Gel Materials Using Polyrotaxane-Derived Polymeric Organogelator.

Molecular gels, which are soft and flexible materials, are candidates for healthcare, cosmetic base, and electronic applications as new materials. In this study, a new polymeric organogelator bearing a polyrotaxane (PR) structure was developed and could induce the gelation of N',N″-dimethylformamide (DMF), a known solvent for dissolving polymeric materials and salts. Furthermore, the resulting DMF molecular gels exhibited thixotropic properties, observed by the inversion method using vials, which are essential for gel spreading. The scanning electron microscopy of the xerogels suggested that the gel-forming ability and thixotropic property of gels were imparted by the network of the laminated aggregates of thin layer material similar to those of other gels made of clay materials. This thin layer material would be formed by the aggregation of polymeric organogelators. The dynamic viscoelasticity measurements of the obtained gels revealed the stability and pseudo-thixotropic behaviors of the obtained gels, as well as a specific concentration effect on the mechanical behavior of the gels attributed to the introduction of the PR structure. Additionally, the preparation of the polymer organogelator/polymer composites was investigated to improve the mechanical properties via the filler effect induced by the agglomerates of organogelator. Moreover, the tensile tests confirmed that the introduction of the gelator enhanced the mechanical properties of the composites.

Quadruple H-Bonding and Polyrotaxanes Dual Cross-linking Supramolecular Elastomer for High Toughness and Self-healing Conductors.

Tough and self-healable substrates can enable stretchable electronics long service life. However, for substrates, it still remains a challenge to achieve both high toughness and autonomous self-healing ability at room temperature. Herein, a strategy by using the combined effects between quadruple H-bonding and slidable cross-links is proposed to solve the above issues in the elastomer. The elastomer exhibits high toughness (77.3 MJ m-3 ), fracture energy (≈127.2 kJ m-2 ), and good healing efficiency (91 %) at room temperature. The superior performance is ascribed to the inter and intra crosslinking structures of quadruple H-bonding and polyrotaxanes in the dual crosslinking system. Strain-induced crystallization of PEG in polyrotaxanes also contributes to the high fracture energy of the elastomers. Furthermore, based on the dual cross-linked supramolecular elastomer, a highly stretchable and self-healable electrode containing liquid metal is also fabricated, retaining resistance stability (0.16-0.26 Ω) even at the strain of 1600 %.

A series of coordination polymers constructed by 2-phenylsuccinic acid and flexible bis(imidazole) ligands: Syntheses, structures, and photoluminescent properties

Eight coordination polymers (CPs), namely, [Co(μ-phsuc)(μ-obix)]n(1), {[Co2(μ-phsuc)2(μ-pbix)1.5]⋅2H2O}n(2), [Zn(μ-phsuc)(μ-obix)]n(3), {[Zn(μ-phsuc)(μ-mbix)]⋅H2O}n(4), {[Zn(μ-phsuc)(μ-pbix)]⋅H2O}n(5), {[Zn(μ-phsuc)(μ-pbix)]⋅1.5H2O⋅CH3OH}n(6), [Cd(μ-phsuc)(μ-obix)]n(7) and [Cd(μ3-phsuc)(μ-pbix)0.5]n(8) (phsucH2 = 2-phenylsuccinic acid, obix = 1,2-bis((imidazol-1-yl)methyl)benzene, mbix = 1,3-bis((imidazol-1-yl)methyl)benzene, pbix = 1,4-bis((imidazol-1-yl)methyl)benzene), were solvothermally synthesized and characterized by IR spectroscopy, elemental analysis, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), and thermal analyses. The structural analyses revealed that the compounds were 2D coordination polymers, in which metal ions were in tetrahedral coordination geometries in 1-6 and in octahedral coordination geometries in 2, 7 and 8. Compounds 1, 3, 4, 5, 7 and 8 displayed 4-connected 2D wave sheets with the point symbol of {44.62}. Compound 2 was rare example exhibiting a 2D polyrotaxane structure. Compound 6 showed a two-fold interpenetrated 2D structure with hcb topology (the point symbol of {63}). In the compounds, the neighboring 2D layers were further assembled by π⋅⋅⋅π stacking and weak C–H⋅⋅⋅π interactions into the 3D supramolecular framework. The effects of the bis(imidazole) linkers and metals ions on the framework assemblies have been discussed. In addition, thermal and photoluminescent and optical properties of the compounds were investigated.

Neutron Scattering Studies on Structure and Dynamics of Polyrotaxane

Neutron Scattering Studies on Structure and Dynamics of Polyrotaxane

Thermal and Physical Properties of Polyurethanes Crosslinked by Polyrotaxanes—Influence of Polyrotaxane structures and Isocyanate Index—

Thermal and Physical Properties of Polyurethanes Crosslinked by Polyrotaxanes—Influence of Polyrotaxane structures and Isocyanate Index—

Highly Conductive and Thermostable Grafted Polyrotaxane/Ceramic Hybrid Polymer Electrolyte for Solid-State Lithium-Metal Batteries.

Although polymer electrolytes have been regarded as potential separator materials for high energy density solid-state lithium-based batteries, their applications were significantly restricted by the low ionic conductivity, poor mechanical strength, and thermostability. Herein, a highly conductive and thermostable hybrid polymer electrolyte was developed by combining poly(vinylidene fluoride-co-hexafluoropropylene)-grafted polyrotaxane and nano-Al2O3 particles. In this unique hybrid, not only the Lewis acid-type Al2O3 and the fluorine groups of polyrotaxane branches exhibited strong integration with ionic species to accelerate the dissociation of lithium salt, improving the Li ionic conductivity, but also the abundant hydroxy functional groups on the surface of Al2O3 hydrogen-bonded with fluorine-containing branches, enhancing the mechanical strength. More importantly, the hybrid electrolyte exhibited superior thermal stability due to the heat resistance of the ceramic filler and the unique bead string structure of polyrotaxane. Consequently, a polymer electrolyte with a comprehensively improved performance was obtained, including high ionic conductivity and Li+ transfer number and superior tensile strength and thermostability. The hybrid electrolyte provided a dendrite-free lithium anode with a long life up to 1800 h and stable solid-state lithium-metal batteries at a high temperature of 80 °C.

Polyrotaxane: New generation of sustainable, ultra-flexible, form-stable and smart phase change materials

The development of thermal energy storage materials is the most attractive strategy to harvest the solar energy and increase the energy utilization efficiency. Phase change materials (PCMs) have received much attention in this research field for several decades. Herein, we reported a new kind of PCM micro topological structure, design direction, and the ultra-flexible, form-stable and smart PCMs, polyrotaxane. The structure of polyrotaxane was fully confirmed by 1H nuclear magnetic resonance, attenuated total reflection-fourier transform infrared and X-ray diffraction. Then the tensile properties, thermal stability in the air, phase change energy storage and shape memory properties of the films were systematically analyzed. The results showed that all the mechanical performance, thermal stability in air and shape memory properties of polyrotaxanes were enhanced significantly compared to those of polyethylene oxide (PEO). The form stability at temperatures above the melting point of PEO significantly increased with the α-CD addition. Further with the high phase transition enthalpy and excellent cycle performance, the polyrotaxane films are therefore promising sustainable and advanced form-stable phase change materials for thermal energy storage. Notably, its ultra-high flexibility, remolding ability and excellent shape memory properties provide a convenient way for the intelligent heat treatment packaging of complex and flexible electronic devices. In addition, this is a totally novel insight for polyrotaxane application and new design method for form-stable PCMs.

Molecular dynamics and structure of polyrotaxane in solution

Polyrotaxane (PR) is a supramolecular assembly in which ring molecules are threaded onto an axial polymer chain. This paper reviews the molecular structure and dynamics of a PR composed of polyethylene glycol (PEG) and α-cyclodextrin (CD) based on data obtained from X-ray and neutron scattering experiments on PR solutions. The dynamics of CD and the PEG monomers in the PR were evaluated separately by quasielastic neutron scattering with deuterium labeling. Inclusion complex formation with CD increases the stiffness of the PEG backbone and restricts the diffusion of the PEG monomers that are covered by or in close proximity to the CD molecules. The sliding motion of the CD molecules along the PEG axis was explored using full atomistic molecular dynamics (MD) simulations, showing that the sliding dynamics were retarded by the interaction between the CD cavities and PEG. This paper reviews our X-ray and neutron scattering experiments on the molecular structure and dynamics of a supramolecular assembly, polyrotaxane (PR) composed of polyethylene glycol (PEG) and α-cyclodextrin (CD). Inclusion complex formation with CDs increases the stiffness of the PEG backbone and restricts the diffusion of the PEG monomers that are covered by or in close proximity to the CD molecules.

Polyrotaxane: New Generation of Sustainable, Ultra-Flexible and Form-Stable Phase Change Materials

The development of thermal energy storage materials is the most attractive strategy to harvest the solar energy and increase the energy utilization efficiency. Phase change materials (PCMs) have received much attention in this research field for several decades. Herein, we reported a new kind of PCM micro topological structure, design direction, and the ultra-flexible form-stable PCMs, polyrotaxane. The structure of polyrotaxane was fully confirmed by 1H Nuclear Magnetic Resonance, Attenuated Total Reflection-Fourier Transform Infrared and X-ray diffraction. Then the tensile properties, organic solvent resistance, thermal stability, fire safety and phase change energy storage properties of the films were systematically analyzed. The results showed that all the mechanical performance, organic solvent resistance, thermal stability and fire safety of PLRs were enhanced significantly compared to those of PEO. Nevertheless, the form stability at temperatures above the melting point of PEO significantly increased with the α-CD addition. Further with the high phase transition enthalpy and excellent cycle performance, the polyrotaxane films are therefore promising sustainable and advanced solid-solid phase-change materials for thermal energy storage.

Precise synthesis of polyrotaxane and preparation of supramolecular materials based on its mobility

This review describes (1) the precise synthesis of polyrotaxane (PRx) and (2) materials using PRx. PRx has a necklace-like structure in which a linear molecule penetrates the cavity of a cyclic molecule and both ends of the linear molecule are capped with a bulky substituent. The supramolecular structure of PRx can be formed with cyclic molecules used as building blocks. PRx exhibits many features (e.g., cyclic molecule slippage) that are not found in other supramolecular structures. In this review, we report that the number of cyclic molecules, the length (molecular weight) of the linear molecules, and the combination of the cyclic molecules and linear molecules in PRx can be precisely controlled to maximize cyclic molecule slippage. In addition, we created a material that quickly recovers its material strength because of the cyclic molecule slippage of PRx. Polyrotaxane (PRx) has a necklace-like structure, which exhibits many features (e.g., cyclic molecule slippage) that are not found in other supramolecular structures. In this review, we report that the number of cyclic molecules, the length (molecular weight) of the linear molecules, and the combination of the cyclic molecules and linear molecules in PRx can be precisely controlled to maximize cyclic molecule slippage. In addition, we created a material that quickly recovers its material strength because of the cyclic molecule slippage of PRx.

Polyrotaxane crosslinked modified EC/PVDF composite membrane displaying simultaneously enhanced pervaporation performance and solvent resistance for benzene/cyclohexane separation

A new strategy was proposed that simultaneously improves the pervaporation (PV) performance and solvent resistance via the construction of a movable crosslinked structure in ethyl cellulose/polyvinylidene fluoride (EC/PVDF) composite membrane for the purpose of benzene/cyclohexane separation. Based on the molecular design of the macrocyclic compound cyclodextrin, polyrotaxane crosslinking agent (PR=) with a special sliding/rotating property and cavity structure was successfully synthesized. Furthermore, for convenient comparative study, cyclodextrin crosslinking agent (CD=) with cavity structure bereft of a sliding/rotating property and pentaerythritol triacrylate (PETA) without sliding/rotating property and cavity structure were prepared. The composite membranes were fabricated with crosslinking modified EC as active layer, together with PVDF support layer. The molecular structure and microstructure were confirmed. The pervaporation and swelling performance of the fabricated membranes for benzene/cyclohexane were investigated. PR= modified membranes showed good solvent resistance and exhibited a flux of 4332 g·m−2·h−1 and separation factor of 6.26, which was higher than CD= and PETA modified membranes. The results were attributed to the facilitated transport behavior, which was markedly related with the sliding/rotating property and cavity structure of polyrotaxane (PR). The related research provides interesting suggestions for PV membrane design for the separation of organic mixtures.

Hydrogen-Bonded Polyrotaxane Cation Structure in Nickel Dithiolate Anion Radical Salts: Ferromagnetic and Semiconducting Behavior Associated with Structural Phase Transition.

The pseudo-polyrotaxane structure of [(H-bpy+ )- (DB-24-crown-8)]∞ (H-bpy+ = monoprotonated 4,4-bipyridinium; DB-24-crown-8 = dibenzo-24-crown-8) has been incorporated into the anion radical salt [Ni(dmit)2 ]- (dmit2- = 1,3-dithiole-2-thione-4,5-dithiolate). (H-bpy+ )(DB-24-crown-8)[Ni(dmit)2 ]- crystallized as two polymorphs, crystals 1 and 2. Crystal 1 was found to have a lower density and looser packing structure in which H-bpy+ forms a one-dimensional hydrogen-bonding chain that passes though the crown ether ring of DB-24-crown-8. DB-24-crown-8 adopts a U-shaped conformation in which two phenylene rings sandwich one of the pyridyl rings of H-bpy+ to stabilize the structure. The [Ni(dmit)2 ]- anions are arranged in a layer parallel to the (10) plane with uniform side-by-side interactions. A structural phase transition was observed at 235 K, accompanied by ordering of the polyrotaxane structure. In crystal 1, at 173 K, H-bpy+ is twisted around the central C-C bond, which perturbs the arrangement of [Ni(dmit)2 ]- through short C-H⋅⋅⋅S contacts. As a result, the semiconducting behavior, with an activation energy of 0.21 eV, becomes insulating below 235 K. The crystal exhibits ferromagnetic interactions because of the weak side-by-side interactions between [Ni(dmit)2 ]- anions. Crystal 2 has a similar pseudo-polyrotaxane structure but showed no phase transition. This suggests that the looser crystal packing in crystal 1 induces the structural change of the pseudo-polyrotaxane, perturbing the electron system of [Ni(dmit)2 ]- .

Ionothermal Synthesis of Five Keggin-Type Polyoxometalate-Based Metal-Organic Frameworks.

Five unique Keggin-type polyoxometalate (POM)-based metal-organic frameworks (POMFs), namely [CH2L1]2[(CuL12)(PMoVI9MoV3O40)] (1), [Zn0.5(H2O)(L1)][Zn(L1)1.5Cl][H2L1]0.5[PMo12O40]·1.25H2O (2), (TBA)[Cu(H2O)2L12][PMo12O40] (3), [Cu2(H2O)2(L1)3][PMVI11MoVO40] (4), (H2L2)0.5[(CuIL2)2(PMo12O40)]·H2O (5), L1 = 4,4'-bis((1H-1,2,4-triazol-1-yl)methyl)-biphenyl, L2 = 1,4-bis((1H-1,2,4-triazol-1-yl)methyl)-benzene, have been synthesized under ionothermal conditions. According to single-crystal data, 1 exhibits a novel mechanically interlocked molecular architecture (MIMA) constructed by two-dimensional (2D) interpenetrating polyrotaxane layers with unique cyclophanes (tetra-cationic viologen macrocycle cyclobis(paraquat- p-phenylene) (CBPQT4+ system)), resulting in an H-bonded 3D supermolecule, and is the first synthesis of self-assembled cyclophane-PMOFs under ionothermal conditions. 2 shows a novel 2D three-fold interpenetrating polyrotaxane host and guest network. 1 and 2 are presented as the first MIMA polyrotaxane structures to have been synthesized under ionothermal conditions. Electrochemical impedance spectroscopy (EIS) reveals that 2, 4, and 5 show high proton conductivity owing to their unique structural properties. Solid-state diffuse reflection UV-vis-NIR measurements show the title compounds are potentially semiconductor materials. Photocatalytic investigations indicate that 1-5 possess high and stable photocatalytic H2 evolution and rhodamine B (RhB) degradation under visible-light irradiation.

Design of a Well-Defined Polyrotaxane Structure on a Glassy Polymer Surface.

The polymer dynamics at the water interface play a crucial role in the manifestation of biorelated functions. One of the strategies for this is to form inclusion complexes of polymer chains with cyclic compounds. However, such an idea has been limited to bulk materials so far. Here we propose a preparation pathway for a polyrotaxane structure composed of poly(ethylene oxide) (PEO) and α-cyclodextrin (CD) at the outermost surface of a glassy poly(methyl methacrylate) film on the basis of the combination of a click reaction and the Langmuir-Blodgett method. The chain motion of PEO at the water interface could be regulated by threading of CD molecules on PEO and thereby the biological responses such as protein adsorption and platelet adhesion altered depending on the extent of complexation.