Mechanically Robust Skin-like Poly(urethane-urea) Elastomers Cross-Linked with Hydrogen-Bond Arrays and Their Application as High-Performance Ultrastretchable Conductors

3D Printable Supramolecular Viologen-Cationic Polyurethane Ionotronics for Multimodal Sensing and Displays

Ionic polyurethanes with excellent properties have garnered significant attention in flexible wearables. However, it is still challenging to achieve ionic polyurethane ionotronics with both excellent mechanical properties and functionalization. Here, a series of hydroxypropyl viologen (HDPV) cationic-based supramolecular polyurethane with tunable strength (7.6-76.6 MPa), toughness (29.1-285.3 MJ m-3), and elongation (499.8%-1102.3%) are developed by balancing HDPV cations and dynamic sextuple hydrogen bonds into the polyurethane. Dynamic modulation of the mechanical and electrochromic properties of the polyurethane can be achieved by adjusting the content of HDPV cations and dynamic sextuple bonds. Strong electrostatic interactions between the HDPV cationic-based polyurethane and the ionic liquid resulted in the preparation of ionogels with excellent pressure/strain and temperature sensing properties. Additionally, benefiting from the redox properties of the polycationic backbone, electrochromic devices fabricated from HDPV cationic-based polyurethane demonstrated a high modulation range of 79.1%, a certain degree of color memory effect, and excellent cycling stability. Shape customization of flexible electrochromic devices of HDPV cationic-based polyurethane can be achieved by 3D printing technology. The study paves a new avenue for the fabrication of flexible visual ionotronics with high stability and versatility.

Strong and Anti-Impact Multi-Functional Elastomer via Hierarchical Hydrogen Bonding Design

Despite extensive research on enhancing the strength, toughness, or impact resistance of elastomers, materials that simultaneously integrate these properties remain elusive. In this work, a multifunctional elastomer is developed with high strength, superior toughness, and excellent impact resistance by designing multiscale structures. The synergistic coupling of strong and weak hydrogen bonds, rigid ring-flexible chain coordination, and precise control of hard/soft block ratio enabled the development of an optimized multiscale architecture tailored for superior performance, achieving a tensile strength of 84 MPa and a toughness of 450 MJ m⁻3, while maintaining excellent impact resistance across varying strain rates. Additionally, the incorporation of hindered urea dynamic covalent bonds and hydrogen bond-induced localized conjugation effect impart thermal adhesion and fluorescence capabilities, broadening the material's functional application scenarios. This multiscale molecular design strategy not only facilitates the tailoring of high-performance materials but also provides new insights into the structure-property relationships in elastomers.

Engineering Hydrophobic Hierarchical Supramolecular Interactions in Reversibly Cross-Linked Elastomers for Outstanding Water Resistance

Achieving outstanding water resistance in reversibly cross-linked elastomers (RCEs) remains challenging due to the presence of polar and hydrophilic groups within polymer chains. In this study, we present the fabrication of mechanically robust, healable, and recyclable RCEs with exceptional water resistance by incorporating hydrophobic hierarchical supramolecular interactions into poly(tetramethylene ether glycol) (PTMEG)-based polyurethane elastomers. These hierarchical supramolecular interactions, consisting of hydrogen bonding and π-π stacking, exhibit high binding energy, facilitating the in situ formation of phase-separated hydrophobic nanostructures that significantly enhance the water resistance of the elastomers. Consequently, the elastomers exhibit outstanding water resistance, with a water absorption as low as 1.1 wt % even after 40 days of immersion in water. In addition to their superior water resistance, the elastomers exhibit excellent mechanical properties, including a tensile strength of ∼67.8 MPa, toughness of ∼633 MJ m-3, and fracture energy of ∼160 kJ m-2. These mechanical properties are attributed to the synergistic effects of phase-separated nanostructures and strain-induced crystallization of PTMEG segments. Furthermore, the reversibility of the hydrophobic hierarchical supramolecular interactions enables the convenient healing and recycling of the elastomers, allowing the healed and recycled elastomers to restore their original mechanical performance. These elastomers were further demonstrated to be effective in encapsulating flexible electrochromic devices for underwater applications.

Robust Mechanically Interlocked Network Ionogels

Ionogels have attracted considerable attention as versatile materials due to their unique ionic conductivity and thermal stability. However, relatively weak mechanical performance of many existing ionogels has hindered their broader application. Herein, we develop robust, tough, and impact-resistant mechanically interlocked network ionogels (IGMINs) by incorporating ion liquids with mechanical bonds that can dissipate energy while maintain structural stability. Profiting from the dynamic yet stable nature of the mechanically interlocked networks, IGMINs exhibit high tensile strength (9.6 MPa), fracture energy (39 kJ/m2), and toughness (25.9 MJ/m3), along with a high elongation rate (473 %) and excellent impact resistance and shape memory, resulting in overall performance that surpasses most reported ionogels. Furthermore, in the application of strain sensors for monitoring the gait of crawling robots, the toughness and robustness of IGMINs ensure their ability to consistently output stable electrical signals during the stretching and contraction processes, thereby highlighting their practical application potential. Our work provides a new research strategy for toughening ionogels and promotes the development of mechanically interlocked materials.

Healable, Recyclable, and Ultra-Tough Waterborne Polyurethane Elastomer Achieved through High-Density Hydrogen Bonding Cross-Linking Strategy

With the increasing popularity of elastomers in industry and daily life, their high performance and functionality have attracted widespread attention. However, it is a great challenge for them to possess both high mechanical properties and excellent healing and recovery capabilities due to the limitations of the preparation methods and the intrinsic microstructure of the elastomers. In this study, a strategy of ice-controlled interfacial stepwise cross-linking was proposed to prepare the waterborne polyurethane-based elastomers with ultrahigh-density hydrogen bonding interaction achieved by enhancing the utilization rate of phenol hydroxyl groups of tannic acid to the maximum extent. The elastomers have incredible mechanical properties, including ultrahigh toughness of 1.03 GJ m-3 (which represents the highest level among polyurethane elastomers prepared through common processing techniques to date), extremely high true fracture stress of ∼1.9 GPa, world-record fracture energy of 520 kJ m-2, and exciting multiple functional characteristics, such as highly efficient self-healing ability of 10 min, high resistance to physical damage and chemical corrosion, broad temperature and frequency damping effects, good shape memory effect, and excellent melt-processing recyclability and solvent recyclability. These robust multifunctional elastomers represent considerable potential in various fields, from defense and military industry and civil transportation to precision manufacturing, etc.

Tailoring dual cross-linked polymer-ionic liquid composites by blending co-crystallizable polymers for stretchable electronics

Facile adjustment of the behavior of dual cross-linked polymer-ionic liquid composites (PICs) for stretchable electronics was achieved via solution blending of two copolymers having the same monomer pairs. Two poly(docosyl acrylate-r-tert-butyl acrylate) (poly(A22-r-tBA)) copolymers with different molar ratios were synthesized and solution-cast with ionic liquids (ILs) to fabricate ternary PICs. The phase behavior and the thermal and structural properties of the composites were investigated by varying the mixing ratio, providing insights into the cross-linking mechanisms. The observed changes enabled systematic modulation of the stretchability, thermal stability, and self-healing capability of PICs, which are crucial attributes of wearable devices. Mechanically tough and conductive PICs were utilized in fabricating strain sensors capable of detecting human motion.

Sea Cucumber-Inspired Polyurethane Demonstrating Record-Breaking Mechanical Properties in Room-Temperature Self-Healing Ionogels

Practical applications of existing self-healing ionogels are often hindered by the trade-off between their mechanical robustness, ionic conductivity, and temperature requirements for their self-healing ability. Herein, this challenge is addressed by drawing inspiration from sea cucumber. A polyurethane containing multiple hydrogen-bond donors and acceptors is synthesized and used to fabricate room-temperature self-healing ionogels with excellent mechanical properties, high ionic conductivity, puncture resistance, and impact resistance. The hard segments of polyurethane, driven by multiple hydrogen bonds, coalesce into hard phase regions, which can efficiently dissipate energy through the reversible disruption and reformation of multiple hydrogen bonds. Consequently, the resulting ionogels exhibit record-high tensile strength and toughness compared to other room-temperature self-healing ionogels. Furthermore, the inherent reversibility of multiple hydrogen bonds within the hard phase regions allows the ionogels to spontaneously and efficiently self-heal damaged mechanical properties and ionic conductivity multiple times at room temperature. To underscore their application potential, these ionogels are employed as electrolytes in the fabrication of electrochromic devices, which exhibit excellent and stable electrochromic performance, repeatable healing ability, and satisfactory impact resistance. This study presents a novel strategy for the fabrication of ionogels with exceptional mechanical properties and room-temperature self-healing capability.

Squid-Inspired Anti-Salt Skin-Like Elastomers With Superhigh Damage Resistance for Aquatic Soft Robots

Cephalopod skins evolve multiple functions in response to environmental adaptation, encompassing nonlinear mechanoreponse, damage tolerance property, and resistance to seawater. Despite tremendous progress in skin-mimicking materials, the integration of these desirable properties into a single material system remains an ongoing challenge. Here, drawing inspiration from the structure of reflectin proteins in cephalopod skins, a long-term anti-salt elastomer with skin-like nonlinear mechanical properties and extraordinary damage resistance properties is presented. Cation-π interaction is incorporated to induce the geometrically confined nanophases of hydrogen bond domains, resulting in elastomers with exceptional true tensile strength (456.5 ± 68.9 MPa) and unprecedently high fracture energy (103.7 ± 45.7 kJ m-2). Furthermore, the cation-π interaction effectively protects the hydrogen bond domains from corrosion by high-concentration saline solution. The utilization of the resultant skin-like elastomer has been demonstrated by aquatic soft robotics capable of grasping sharp objects. The combined advantages render the present elastomer highly promising for salt enviroment applications, particularly in addressing the challenges posed by sweat, in vivo, and harsh oceanic environments.

Super-Durable, Tough Shape-Memory Polymeric Materials Woven from Interlocking Rigid-Flexible Chains

Developing advanced engineering polymers that combine high strength and toughness represents not only a necessary path to excellence but also a major technical challenge. Here for the first time a rigid-flexible interlocking polymer (RFIP) is reported featuring remarkable mechanical properties, consisting of flexible polyurethane (PU) and rigid polyimide (PI) chains cleverly woven together around the copper(I) ions center. By rationally weaving PI, PU chains, and copper(I) ions, RFIP exhibits ultra-high strength (twice that of unwoven polymers, 91.4 ± 3.3 MPa), toughness (448.0 ± 14.2 MJ m-3), fatigue resistance (recoverable after 10 000 cyclic stretches), and shape memory properties. Simulation results and characterization analysis together support the correlation between microstructure and macroscopic features, confirming the greater cohesive energy of the interwoven network and providing insights into strengthening toughening mechanisms. The essence of weaving on the atomic and molecular levels is fused to obtain brilliant and valuable mechanical properties, opening new perspectives in designing robust and stable polymers.

Filler effects inspired high performance polyurethane elastomer design: segment arrangement control

Elastomers with high strength and toughness are in great demand. Previous research on elastomers focused mainly on the design of new chemical structures, but their complicated synthesis process and expensive monomers have restricted the practical application of these materials. Inspired by general filler effects, a strategy is proposed to remarkably enhance the mechanical properties of thermoplastic polyurethane (TPU) elastomers by designing the arrangement of hard/soft segments using traditional chemical compositions. By utilizing the synergetic effect of weak hard segments, normal TPU elastomers are upgraded into advanced elastomers. Combining experiments and simulations, it is demonstrated that a suitable sequence length can achieve considerably enhanced strength and toughness by maximizing the relative surface area of hard domains. Mixing the obtained elastomer with an ionic liquid can result in a durable ionogel sensor with balanced mechanical strength and ionic conductivity. This easy-to-implement strategy offers a new dimension for the development of high-performance elastomers.

Highly Durable Silicone-Based Elastomers Achieved Through the Synergy of Bi-Incompatible Soft Segments and Multi-Scale Hydrogen Bonds

Developing a silicone elastomer with high strength, exceptional toughness, good crack tolerance, healability, and recyclability, poses significant challenges due to the inherent trade-offs between these properties. Herein, the design of silicone-based elastomers with a nanoscopic microphase separation structure and comprehensive mechanical properties is achieved by combining bi-incompatible soft segments and multi-scale hydrogen bonds. The formation of multi-scale hydrogen bonds involving urethane, urea, and 2-ureido-4[1H]-pyrimidinone (UPy) facilitates efficient reversible crosslinking of the synthesized polymer containing thermodynamically incompatible poly(dimethylsiloxane) (PDMS) and poly(propylene glycol) (PPG). The dynamic dissociation and recombination of hydrogen bonds, coupled with the forced compatibility and spontaneous separation of bi-incompatible soft segments, can effectively dissipate energy, particularly in the crack region during the stretching process. The obtained silicone-based elastomer exhibits a high break strength of 8.0 MPa, good elongation at break of 1910%, ultrahigh toughness of 67.8 MJ m-3, and unprecedented fracture energy of 31.8 kJ m-2 while maintaining their thermal stability, hydrophobicity, healability, and recyclability. This resilient and long-lasting silicone-based elastomer exhibits significant potential for use in flexible electronic devices.

Imparting Ultrahigh Strength to Polymers via a New Concept Strategy of Construction of up to Duodecuple Hydrogen Bonding among Macromolecular Chains

Interconnecting macromolecules via multiple hydrogen bonds (H-bonds) can simultaneously strengthen and toughen polymers, but material synthesis becomes extremely difficult with increasing number of H-bonding donors and acceptors; therefore, most reports are limited to triple and quadruple H-bonds. Herein, this bottleneck is overcome by adopting a quartet-wise approach of constructing H-bonds instead of the traditional pairwise method. Thus, large multiple hydrogen bonds can be easily established, and the supramolecular interactions are further reinforced. Especially, when such multiple H-bond motifs are embedded in polymers, four macromolecular chains-rather than two as usual-are tied, distributing the applied stress over a larger volume and more significantly improving the overall mechanical properties. Proof-of-concept studies indicate that the proposed intermolecular multiple H-bonds (up to duodecuple) are readily introduced in polyurethane. A record-high tensile strength (105.2 MPa) is achieved alongside outstanding toughness (352.1 MJ m-3), fracture energy (480.7 kJ m-2), and fatigue threshold (2978.4 J m-2). Meantime, the polyurethane has acquired excellent self-healability and recyclability. This strategy is also applicable to nonpolar polymers, such as polydimethylsiloxane, whose strength (15.3 MPa) and toughness (50.3 MJ m-3) are among the highest reported to date for silicones. This new technique has good expandability and can be used to develop even more and stronger polymers.

Bionic Artificial Skin Based on Self-Healable Ionogel Composites with Tailored Mechanics and Robust Interfaces

Bionic artificial skin which imitates the features and functions of human skin, has broad applications in wearable human-machine interfaces. However, equipping artificial materials with skin-like mechanical properties, self-healing ability, and high sensitivity remains challenging. Here, inspired by the structure of human skin, an artificial skin based on ionogel composites with tailored mechanical properties and robust interface is prepared. Combining finite element analysis and direct ink writing (DIW) 3D printing technology, an ionogel composite with a rigid skeleton and an ionogel matrix is precisely designed and fabricated, realizing the mechanical anisotropy and nonlinear mechanical response that accurately mimic human skin. Robust interface is created through co-curing of the skeleton and matrix resins, significantly enhancing the stability of the composite. The realization of self-healing ability and resistance to crack growth further ensure the remarkable durability of the artificial skin for sensing application. In summary, the bionic artificial skin mimics the characteristics of human skin, including mechanical anisotropy, nonlinear mechanical response, self-healing capability, durability and high sensitivity when applied as flexible sensors. These strategies provide strong support for the fabrication of tissue-like materials with adaptive mechanical behaviors.

Regulation of Hard Segment Cluster Structures for High-performance Poly(urethane-urea) Elastomers

Elastomers are widely used in daily life; however, the preparation of degradable and recyclable elastomers with high strength, high toughness, and excellent crack resistance remains a challenging task. In this report, a polycaprolactone-based poly(urethane-urea) elastomer is presented with excellent mechanical properties by optimizing the arrangement of hard segment clusters. It is found that long alkyl chains of the chain extenders lead to small and evenly distributed hard segment clusters, which is beneficial for improving mechanical properties. Together with the multiple hydrogen bond structure and stress-induced crystallization, the obtained elastomer exhibits a high strength of 63.3 MPa, an excellent toughness of 431 MJ m-3 and an outstanding fracture energy of 489 kJ m-2, while maintaining good recyclability and degradability. It is believed that the obtained elastomer holds great promise in various application fields and it contributes to the development of a sustainable society.

Upcycling of Carbon Fiber/Thermoset Composites into High-Performance Elastomers and Repurposed Carbon Fibers

Recycling of carbon fiber-reinforced polymer composites (CFRCs) based on thermosetting plastics is difficult. In the present study, high-performance CFRCs are fabricated through complexation of aromatic pinacol-cross-linked polyurethane (PU-AP) thermosets with carbon fiber (CF) cloths. PU-AP thermosets exhibit a breaking strength of 95.5 MPa and toughness of 473.6 MJ m-3 and contain abundant hydrogen-bonding groups, which can have strong adhesion with CFs. Because of the high interfacial adhesion between CF cloths and PU-AP thermosets and high toughness of PU-AP thermosets, CF/PU-AP composites possess a high tensile strength of >870 MPa. Upon heating in N,N-dimethylacetamide (DMAc) at 100 °C, the aromatic pinacols in the CF/PU-AP composites can be cleaved, generating non-destructive CF cloths and linear polymers that can be converted to high-performance elastomers. The elastomers are mechanically robust, healable, reprocessable, and damage-resistant with an extremely high tensile strength of 74.2 MPa and fracture energy of 149.6 kJ m-2. As a result, dissociation of CF/PU-AP composites enables the recovery of reusable CF cloths and high-performance elastomers, thus realizing the upcycling of CF/PU-AP composites.

Flexible Cages Enable Robust Supramolecular Elastomers

Advances in modern industrial technology continue to place stricter demands on engineering polymeric materials, but simultaneously possessing superior strength and toughness remains a daunting challenge. Herein, a pioneering flexible cage-reinforced supramolecular elastomer (CSE) is reported that exhibits superb robustness, tear resistance, anti-fatigue, and shape memory properties, achieved by innovatively introducing organic imide cages (OICs) into supramolecular networks. Intriguingly, extremely small amounts of OICs make the elastomer stronger, significantly improving mechanical strength (85.0 MPa; ≈10-fold increase) and toughness (418.4 MJ m-3; ≈7-fold increase). Significantly, the cooperative effect of gradient hydrogen bonds and OICs is experimentally and theoretically demonstrated as flexible nodes, enabling more robust supramolecular networks. In short, the proposed strengthening strategy of adding flexible cages effectively balances the inherent conflict between material strength and toughness, and the prepared CSEs are anticipated to be served in large-scale devices such as TBMs in the future.

Strain-Induced Phase Separation and Mechanomodulation of Ionic Conduction in Anisotropic Nanocomposite Ionogels

Ionogels have great potential for the development of tissue-like, soft, and stretchable ionotronics. However, conventional isotropic ionogels suffer from poor mechanical properties, low efficient force transmission, and tardy mechanoelectric response, hindering their practical utility. Here, we propose a simple one-step method to fabricate bioinspired anisotropic nanocomposite ionogels based on a combination of strain-induced phase separation and mechanomodulation of ionic conduction in the presence of attapulgite nanorods. These ionogels show high stretchability (747.1% strain), tensile strength (6.42 MPa), Young's modulus (83.49 MPa), and toughness (18.08 MJ/m3). Importantly, the liquid crystalline domain alignment-induced microphase separation and ionic conductivity enhancement during stretching endow these ionogels with an unusual mechanoelectric response and dual-programmable shape-memory properties. Moreover, the anisotropic structure, good elasticity, and unique resistance-strain responsiveness give the ionogel-based strain sensors high sensitivity, rapid response time, excellent fatigue resistance, and unique waveform-discernible strain sensing, which can be applied to real-time monitoring of human motions. The findings offer a promising way to develop bioinspired anisotropic ionogels to modulate the microstructure and properties for practical applications in advanced ionotronics.

Hybrid Cross-Linking to Construct Functional Elastomers

ConspectusElastomers have been extensively used in diverse industrial sectors such as footwear, seals, tires, and cable jacketing and have attracted more and more attention in emerging fields such as regenerative medicine, soft robotics, and stretchable electronics. Global consumption of natural and synthetic elastomers amounted to nearly 27 million metric tons in 2020. In addition, to further enhance the common properties of elastomers, it is highly desired to endow elastomers with functionalities such as reprocessability, biomimetic mechanical properties, self-healing ability, bioactivity, and electrical conductivity, which will significantly broaden their applications. The covalent or noncovalent cross-linked structure is the essential factor for the elasticity of elastomers. Traditional elastomers usually comprise a single type of cross-linked molecular network, for which it is difficult to modulate the properties and introduce functionalities. Inspired by the simultaneous existence of multiple cross-linked structures in proteins, researchers have employed a hybrid cross-linking strategy to construct elastomers. Various noncovalent interactions (e.g., hydrogen bonds, metal-ligand coordination, ionic interactions, and chain folding) and dynamic covalent bonds (e.g., disulfide bonds, oxime-urethane bonds, and urea bonds) have been integrated in elastomers. Accordingly, the properties and functionalities of elastomers can be tuned by regulating the types, ratios, and distributions of cross-links. The hybrid cross-linking strategy provides a versatile and effective way to construct diverse functional elastomers for broad applications in various important fields.In this Account, we present our recent progress on functional elastomers constructed by a hybrid cross-linking strategy, including their design, preparation, properties, and diverse applications. First, we provide a brief introduction of the basic concept of functional elastomers and outline general strategies and mechanics for functional elastomers constructed by hybrid cross-linking. Then, we classify hybrid cross-linked elastomers by their design strategies, including multiple cross-linking, topological design, chemical coupling, and multiple networks. The relationships between the functionalities and hybrid cross-linked structures are summarized. At the same time, we also introduce diverse applications of these hybrid cross-linked elastomers in biomedicine, flexible electronics, soft robotics, 3D printing, and so on. Finally, we discuss our perspective on open challenges and future development trends of this rapidly evolving field. This Account highlighting the diverse hybrid cross-linked elastomers not only provides insights into strategies for elastomer functionalization but also provides new ideas for material design and inspires a variety of new applications.

A strain-reinforcing elastomer adhesive with superior adhesive strength and toughness

Strong and ductile adhesives often undergo both interfacial and cohesive failure during the debonding process. Herein, we report a rare self-reinforcing polyurethane adhesive that shows the different phenomenon of only interfacial failure yet still exhibiting superior adhesive strength and toughness. It is synthesized by designing a hanging adhesive moiety, hierarchical H-bond moieties, and a crystallizable soft segment into one macromolecular polyurethane. The former hanging adhesive moiety allows the hot-melt adhesive to effectively associate with the target substrate, providing sufficient adhesion energy; the latter hierarchical H-bond moieties and a crystallizable soft segment cooperate to enable the adhesive to undergo large lap-shear deformations through sacrificing weak bonds and mechano-responsive strength through the fundamental mechanism of strain-induced crystallization. As a result, this polyurethane adhesive can keep itself intact during the debonding process while still withstanding a high lap-shear strength and dissipating tremendous stress energy. Its adhesive strength and work of debonding are as high as 11.37 MPa and 10.32 kN m-1, respectively, outperforming most reported tough adhesives. This self-reinforcing adhesive is regarded as a new member of the family of strong and ductile adhesives, which will provide innovative chemical and structural inspirations for future conveniently detachable yet high-performance adhesives.

A stretchable, mechanically robust polymer exhibiting shape-memory-assisted self-healing and clustering-triggered emission

Self-healing and recyclable polymer materials are being developed through extensive investigations on noncovalent bond interactions. However, they typically exhibit inferior mechanical properties. Therefore, the present study is aimed at synthesizing a polyurethane-urea elastomer with excellent mechanical properties and shape-memory-assisted self-healing behavior. In particular, the introduction of coordination and hydrogen bonds into elastomer leads to the optimal elastomer exhibiting good mechanical properties (strength, 76.37 MPa; elongation at break, 839.10%; toughness, 308.63 MJ m-3) owing to the phased energy dissipation mechanism involving various supramolecular interactions. The elastomer also demonstrates shape-memory properties, whereby the shape recovery force that brings damaged surfaces closer and facilitates self-healing. Surprisingly, all specimens exhibite clustering-triggered emission, with cyan fluorescence is observed under ultraviolet light. The strategy reported herein for developing multifunctional materials with good mechanical properties can be leveraged to yield stimulus-responsive polymers and smart seals.

Engineering of Chain Rigidity and Hydrogen Bond Cross-Linking toward Ultra-Strong, Healable, Recyclable, and Water-Resistant Elastomers

High-performance elastomers have gained significant interest because of their wide applications in industry and our daily life. However, it remains a great challenge to fabricate elastomers simultaneously integrating ultra-high mechanical strength, toughness, and excellent healing and recycling capacities. In this study, ultra-strong, healable, and recyclable elastomers are fabricated by dynamically cross-linking copolymers composed of rigid polyimide (PI) segments and soft poly(urea-urethane) (PUU) segments with hydrogen bonds. The elastomers, which are denoted as PIPUU, have a record-high tensile strength of ≈142 MPa and an extremely high toughness of ≈527 MJ m^-3 . The structure of the PIPUU elastomer contains hydrogen-bond-cross-linked elastic matrix and homogenously dispersed rigid nanostructures. The rigid PI segments self-assemble to generate phase-separated nanostructures that serve as nanofillers to significantly strengthen the elastomers. Meanwhile, the elastic matrix is composed of soft PUU segments cross-linked with reversible hydrogen bonds, which largely enhance the strength and toughness of the elastomer. The dynamically cross-linked PIPUU elastomers can be healed and recycled to restore their original mechanical strength. Moreover, because of the excellent mechanical performance and the hydrophobic PI segments, the PIPUU elastomers are scratch-, puncture-, and water-resistant.

Tough Ionogels: Synthesis, Toughening Mechanisms, and Mechanical Properties-A Perspective

Polymeric ionogels are polymer networks swollen with ionic liquids (i.e., salts with low melting points). Ionogels are interesting due to their unique features such as nonvolatility, high thermal and electrochemical stability, excellent ionic conductivity, and nonflammability. These properties enable applications such as unconventional electronics, energy storage devices (i.e., batteries and supercapacitors), sensors and actuators. However, the poor mechanical performance of ionogels (e.g., fracture strength < 1 MPa, modulus < 0.1 MPa, and toughness < 1000 J m^-2) have limited their use, thus motivating the need for tough ionogels. This Perspective summarizes recent advances toward tough ionogels by highlighting synthetic methods and toughening mechanisms. Opportunities and promising applications of tough ionogels are also discussed.

Molecularly Engineered Unparalleled Strength and Supertoughness of Poly(urea-urethane) with Shape Memory and Clusterization-Triggered Emission

To address the challenge of realizing multifunctional polymers simultaneously exhibiting high strength and high toughness through molecular engineering, ultrastrong and supertough shape-memory poly(urea-urethane) (PUU) is fabricated by regulating: i) the reversible cross-links composed of rigid units and multiple hydrogen bonds, and ii) the molecular weight of soft segments. The optimal material exhibits an unparalleled strength of 84.2 MPa at a large elongation at a break of 925.6%, a superior toughness of 322.8 MJ m^-3 , and remarkable fatigue resistance without fracture. The repeated stretching of this material induces an irreversible deformation, which, however, can be rapidly recovered by heating. Moreover, all samples are capable of temporary shape fixation at -40 °C (recovering the original shape at 30 °C) and exhibit blue fluorescence when excited at the optimum wavelength, which is ascribed to clusterization-triggered emission (CTE) due to the formation of microphase-separation structures. Thus, the adopted approach provides a solution to a long-standing problem and paves the way to the realization of intrinsically luminescent shape-memory materials exhibiting both ultrahigh strength and ultrahigh toughness.