Healable, Recyclable, and Mechanically Tough Polyurethane Elastomers with Exceptional Damage Tolerance

Chemically recyclable polyvinyl chloride-like plastics

Polyvinyl chloride (PVC) is the world's third-most widely manufactured thermoplastic, but has the lowest recycling rate. The development of PVC-like plastics that can be depolymerized back to monomer contributes to a circular plastic economy, but has not been accessed. Here, we develop a series of chemically recyclable plastics from the reversible copolymerization of cyclic anhydride with chloral. The copolymerization is highly efficient through the anionic or cationic mechanism under mild conditions, yielding polyesters with tunable structure and properties from multiple commercial monomers. Notably, these polyesters manifest mechanical properties comparable to PVC and polystyrene. Meanwhile, such polyesters are flame-retardant like PVC due to high chloride content. Of significance, these polyesters can be depolymerized back to starting monomers at high temperatures owing to the reversibility of the copolymerization, leading to a circular economy. Overall, the readily available monomers, simple synthesis, advantageous performance, and practical recyclability make the polymers promising for applications.

Direct Ink Writing 3D Printing Elastomeric Polyurethane Aided by Cellulose Nanofibrils

3D printing of a flexible polyurethane elastomer is highly demandable for its potential to revolutionize industries ranging from footwear to soft robotics thanks to its exceptional design flexibility and elasticity performance. Nevertheless, conventional methods like fused deposition modeling (FDM) and vat photopolymerization (VPP) polyurethane 3D printing typically limit material options to thermoplastic or photocurable polyurethanes. In this research, a water-borne polyurethane ink was synthesized for direct ink writing (DIW) 3D printing through the incorporation of cellulose nanofibrils (CNFs), enabling direct printing of complex, monolithic elastomeric structures at room temperature that can maintain the designed structure. Additionally, a solvent-induced fast solidification (SIFS) method was introduced to facilitate room-temperature curing and enhance mechanical properties. The 3D-printed WPU structures demonstrated strong interfacial adhesion, exhibiting high ultimate tensile strength of up to 22 MPa and an elongation at break of 951%. The 3D-printed WPU structures also demonstrated outstanding resilience and durability, capable of enduring more than 100 cycles of compression and tension as well as withstanding vehicle crushing and heavy lifting. This method also shows suitability for 3D printing complex structures such as a vase and an octopus.

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.

Mechanochemically accelerated deconstruction of chemically recyclable plastics

Plastics redesign for circularity has primarily focused on monomer chemistries enabling faster deconstruction rates concomitant with high monomer yields. Yet, during deconstruction, polymer chains interact with their reaction medium, which remains underexplored in polymer reactivity. Here, we show that, when plastics are deconstructed in reaction media that promote swelling, initial rates are accelerated by over sixfold beyond those in small-molecule analogs. This unexpected acceleration is primarily tied to mechanochemical activation of strained polymer chains; however, changes in the activity of water under polymer confinement and bond activation in solvent-separated ion pairs are also important. Together, deconstruction times can be shortened by seven times by codesigning plastics and their deconstruction processes.

A robust bio-based polyurethane employed as surgical suture with help to promote skin wound healing

Designing bio-based polyurethane materials with excellent mechanical, biocompatibility, and self-healing properties simultaneously is currently a significant challenge due to the increasing demands for high-performance materials. In this study, we propose an asymmetric backbone strategy utilizing bio-based polycarbonate as the soft segment, equimolar ratios of lysine diisocyanate and isophorone diisocyanate as asymmetric hard segments, and isophorone diamine as the chain extender. The resulting polyurethane elastomers exhibit excellent mechanical properties, including high tensile stress (46.1 MPa), toughness (213.9 MJ/m3), and fracture energy (98.47 kJ/m3). The polyurethane elastomers demonstrate good self-healing and recyclable properties under simple heat treatment. Furthermore, biological experiments confirm the degradability and bio-safety of the bio-based polyurethane elastomers, which have shown potential in accelerating wound healing in mice when used as surgical sutures. These findings highlight the promising prospects of the obtained polyurethane elastomers in various applications, including biomedicine, flexible sensing, and electronic components.

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.

Strong and Healable Elastomers with Photothermal-Stimulus Dynamic Nanonetworks Enabled by Subnano Ultrafine MoO3-x Nanowires

One-dimensional nanomaterials have become one of the most available nanoreinforcing agents for developing next-generation high-performance functional self-healing composites owing to their unique structural characteristics and surface electron structure. However, nanoscale control, structural regulation, and crystal growth are still enormous challenges in the synthesis of specific one-dimensional nanomaterials. Here, oxygen-defective MoO3-x nanowires with abundant surface dynamic bonding were successfully synthesized as novel nanofillers and photothermal response agents combined with a polyurethane matrix to construct composite elastomers, thus achieving mechanically enhanced and self-healing properties. Benefiting from the surface plasmon resonance of the MoO3-x nanowires and interfacial multiple dynamic bonding interactions, the composite elastomers demonstrated strong mechanical performance (with a strength of 31.45 MPa and elongation of 1167.73%) and ultrafast photothermal toughness self-healing performance (20 s and an efficiency of 94.34%). The introduction of MoO3-x nanowires allows the construction of unique three-dimensional cross-linked nanonetworks that can move and regulate interfacial dynamic interactions under 808 nm infrared laser stimulation, resulting in controlled mechanical and healing performance. Therefore, such special elastomers with strong photothermal responses and mechanical properties are expected to be useful in next-generation biological antibacterial materials, wearable devices, and artificial muscles.

Ultratough Supramolecular Polyurethane Featuring an Interwoven Network with Recyclability, Ideal Self-Healing and Editable Shape Memory Properties

Developing multifunctional polymers with excellent mechanical properties, outstanding shape memory characteristics, and good self-healing properties is a formidable challenge. Inspired by the woven cross-linking strategy, a series of supramolecular polyurethane (PU) with an interwoven network structure composed of covalent and supramolecular cross-linking nodes have been successfully synthesized by introducing the ureido-pyrimidinone (UPy) motifs into the PU skeleton. The best-performing sample exhibited ultrahigh strength (∼77.2 MPa) and toughness (∼312.7 MJ m-3), along with an ideal self-healing efficiency (up to 90.8% for 6 h) and satisfactory temperature-responsive shape memory effect (shape recovery rates up to 96.9%). Furthermore, it ensured recyclability. These favorable properties are mainly ascribed to the effective dissipation of strain energy due to the disassembly and reconfiguration of supramolecular nodes (i.e., quadruple hydrogen bonds (H-bonds) between UPy units), as well as the covalent cross-linking nodes that maintain the integrity of the polymer network structure. Thus, our work provides a universal strategy that breaks through the traditional contradictions and paves the way for the commercialization of high-performance multifunctional PU elastomers.

Mechanically Ultra-Robust Fluorescent Elastomer for Elaborating Auxetic Composite

Fluorescent elastomers are predominantly fabricated through doping fluorescent components or conjugating chromophores into polymer networks, which often involves detrimental effects on mechanical performance and also makes large-scale production difficult. Inspired by the heteroatom-rich microphase separation structures assisted by intensive hydrogen bonds in natural organisms, an ultra-robust fluorescent polyurethane elastomer is reported, which features a remarkable fracture strength of 87.2 MPa with an elongation of 1797%, exceptional toughness of 678.4 MJ m-3 and intrinsic cyan fluorescence at 445 nm. Moreover, the reversible fluorescence variation with temperature could in situ reveal the microphase separation of the elastomer in real time. By taking advantage of mechanical properties, intrinsic fluorescence and hydrogen bonds-promoted interfacial bonding ability, this fluorescent elastomer can be utilized as an auxetic skeleton for the elaboration of an integrated auxetic composite. Compared with the auxetic skeleton alone, the integrated composite shows an improved mechanical performance while maintaining auxetic deformation in a large strain below 185%, and its auxetic process can be visually detected under ultraviolet light by the fluorescence of the auxetic skeleton. The concept of introducing hydrogen-bonded heteroatom-rich microphase separation structures into polymer networks in this work provides a promising approach to developing fluorescent elastomers with exceptional mechanical properties.

Hierarchical Supramolecular Aggregation of Molecular Nanoparticles for Granular Materials with Ultra High-Speed Impact-Resistance

The high-speed impact-resistanct materials are of great significance while their development is hindered by the intrinsic tradeoff between mechanical strength and energy dissipation capability. Herein, the new chemical system of molecular granular material (MGM) is developed for the design of impact-resistant materials from the supramolecular complexation of sub-nm molecular clusters (MCs) and hyper-branched polyelectrolytes. Their hierarchical aggregation provides the origin of the decoupling of mechanical strengths and structural relaxation dynamics. The MCs' intrinsic fast dynamics afford excellent high-speed impact-resistance, up to 5600 s-1 impact in a typical split-Hopkinson pressure bar test while only tiny boundary cracks can be observed even under 7200 s-1 impact. The high loadings of MCs and their hierarchical aggregates provide high-density sacrificial bonding for the effective dissipation of the impact energy, enabling the protection of fragile devices from the direct impact of over 200 m s-1 bullet. Moreover, the MGMs can be conveniently processed into protective coatings or films with promising recyclability due to the supramolecular interaction feature. The research not only reveals the unique relaxation dynamics and mechanical properties of MGMs in comparison with polymers and colloids, but also develops new chemical systems for the fabrication of high-speed impact-resistant materials.

Towards higher load capacity: innovative design of a robotic hand with soft jointed structure

In this paper, the innovative design of a robotic hand with soft jointed structure is carried out and a tendon-driven mechanism, a master-slave motor coordinated drive mechanism, a thumb coupling transmission mechanism and a thumb steering mechanism are proposed. These innovative designs allow for more effective actuation in each finger, enhancing the load capacity of the robotic hand while maintaining key performance indicators such as dexterity and adaptability. A mechanical model of the robotic finger was made to determine the application limitations and load capacity. The robotic hand was then prototyped for a set of experiments. The experimental results showed that the proposed theoretical model were reliable. Also, the fingertip force of the robotic finger could reach up to 10.3 N, and the load force could reach up to 72.8 N. When grasping target objects of different sizes and shapes, the robotic hand was able to perform the various power grasping and precision grasping in the Cutkosky taxonomy. Moreover, the robotic hand had good flexibility and adaptability by means of adjusting the envelope state autonomously.

Self-healing photoluminescent polymers with photosensitive behavior for information storage and multiple-level dynamic encryption

Photo-responsive luminescent materials capable of responding to light stimuli are crucial in the realm of sophisticated encryption, anti-counterfeiting, and optical data storage. Yet, the development of such materials that also feature self-healing capabilities, swift reaction times, light weight, fatigue resistance, dynamic display abilities, and enhanced security measures is exceedingly rare and presents considerable challenges. Herein, a novel family of self-healing and photo-stimuli-responsive photoluminescent polymers are reported, which is achieved by interlinking terpyridine- and spiropyran-functionalized polymers through N-Ln coordination bonds and hydrogen bonding among the polymer chains. The resulting polymers exhibit good processability, superior tensile strength, fast self-healing ability, and photo-stimuli-responsive performance. The photo-stimuli-responsive properties include unique color shifts (colorless and purple) and light-controlled time-dependent fluorescence modulation (green-, red-, and yellow-emission), which stem from fine-tuning the isomerization of spiropyran and leveraging the fluorescence resonance energy transfer (FRET) from Ln-Tpy donors to spiropyran acceptors, respectively. Besides, these polymers have been successfully applied in dynamic multi-level information encryption applications. We are convinced that these smart materials, crafted through our innovative approach, hold vast potential for applications in information storage, cutting-edge anti-counterfeiting encryption, UV-sensing, and light-writing technologies, marking a novel strategy in the design of photosensitive luminescent smart materials.

Ultrarobust, Self-Healing Poly(urethane-urea) Elastomer with Superior Tensile Strength and Intrinsic Flame Retardancy Enabled by Coordination Cross-Linking

Poly(urethane-urea) elastomers (PUUEs) have gained significant attention recently due to their growing demand in electronic skin, wearable electronic devices, and aerospace applications. The practical implementation of these elastomers necessitates many exceptional properties to ensure robust and safe utilization. However, achieving an optimal balance between high mechanical strength, good self-healing at moderate temperatures, and efficient flame retardancy for poly(urethane-urea) elastomers remains a formidable challenge. In this study, we incorporated metal coordination bonds and flame-retarding phosphinate groups into the design of poly(urethane-urea) simultaneously, resulting in a high-strength, self-healing, and flame-retardant elastomer, termed PNPU-2%Zn. Additional supramolecular cross-links and plasticizing effects of phosphinate-endowed PUUEs with relatively remarkable tensile strength (20.9 MPa), high elastic modulus (10.8 MPa), and exceptional self-healing efficiency (above 97%). Besides, PNPU-2%Zn possessed self-extinguishing characteristics with a limiting oxygen index (LOI) of 26.5%. Such an elastomer with superior properties can resist both mechanical fracture and fire hazards, providing insights into the development of robust and high-performance components for applications in wearable electronic devices.

Bio-Based Polyurethane-Urea with Self-Healing and Closed-Loop Recyclability Synthesized from Renewable Carbon Dioxide and Vanillin

Developing recyclable and self-healing non-isocyanate polyurethane (NIPU) from renewable resources to replace traditional petroleum-based polyurethane (PU) is crucial for advancing green chemistry and sustainable development. Herein, a series of innovative cross-linked Poly(hydroxyurethane-urea)s (PHUUs) were prepared using renewable carbon dioxide (CO2) and vanillin, which displayed excellent thermal stability properties and solvent resistance. These PHUUs were constructed through the introduction of reversible hydrogen and imine bonds into cross-linked polymer networks, resulting in the cross-linked PHUUs exhibiting thermoplastic-like reprocessability, self healing, and closed-loop recyclability. Notably, the results indicated that the VL-TTD*-50 with remarkable hot-pressed remolding efficiency (nearly 98.0%) and self-healing efficiency (exceeding 95.0%) of tensile strength at 60 °C. Furthermore, they can be degraded in the 1M HCl and THF (v:v = 2:8) solution at room temperature, followed by regeneration without altering their original chemical structure and mechanical properties. This study presents a novel strategy for preparing cross-linked PHUUs with self-healing and closed-loop recyclability from renewable resources as sustainable alternatives for traditional petroleum-based PUs.

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.

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.

Engineering of Reversibly Cross-Linked Elastomers Toward Flexible and Recyclable Elastomer/Carbon Fiber Composites with Extraordinary Tearing Resistance

Carbon fiber (CF)-reinforced polymers (CFRPs) demonstrate potential for use in personal protective equipment. However, existing CFRPs are typically rigid, nonrecyclable, and lack of tearing resistance. In this study, flexible, recyclable, and tearing resistant polyurethane (PU)-CF composites are fabricated through complexation of reversibly cross-linked PU elastomer binders with CF fabrics. The PU-CF composites possess a high strength of 767 MPa and a record-high fracture energy of 2012 kJ m-2. The high performance of the PU-CF composites originates from the well-engineered PU elastomer binders that are obtained by cross-linking polytetrahydrofuran chains with in situ-formed nanodomains composed of hierarchical supramolecular interactions of hydrogen and coordination bonds. When subjected to tearing, the force concentrated on the damaged regions of the PU-CF composites can be effectively distributed to a wider area through the PU binders, leading to a significantly enhanced tearing resistance of the composites. The strong interfacial adhesion between PU binders and the CF fabrics enables the fracture of the CF in bundles, thereby significantly enhancing the strength and fracture energy of the composites. Because of the dynamic nature of the PU elastomer binders, the PU-CF composites can be recycled through the dissociation of the PU elastomer binders.

Tough Self-Healing Materials via In Situ Growth of Zeolitic Imidazolate Framework-8 Nanocrystals in Polymers

Construction of self-healing materials with improved mechanical performance is a great challenge. A strong and tough self-healing composite is fabricated via in situ growth of zeolitic imidazole framework-8 (ZIF-8) nanocrystals in imidazole-containing polymer networks. By adjusting the stoichiometric ratio of the zinc salt to 2-methylimidazole, composites with various mechanical performances are obtained. The existence of ZIF-8 nanocrystals via in situ growth in the polymer networks is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The zinc-imidazole interactions between the ZIF-8 nanocrystals and the polymer are confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The composites can repair themselves under mild conditions owing to dynamic zinc-imidazole interactions. The self-healing efficiency of composites can reach up to 91% under the condition of 60 °C for 48 h. In contrast to the pure zinc cation crosslinking system, the composite containing ZIF-8 nanocrystals prepared via in situ growth exhibited enhanced tensile strength and toughness by 43% and 100%, respectively. This study proves that incorporating the metal-organic frameworks (MOFs) materials into a self-healing system via an in situ growth strategy is highly promising for designing self-healing materials with improved mechanical performance.

Mismatched Supramolecular Interactions Facilitate the Reprocessing of Super-Strong and Ultratough Thermoset Elastomers

Thermoset elastomers have been extensively applied in many fields because of their excellent mechanical strengths and durable characteristics, such as an excellent chemical resistance. However, in the context of environmental issues, the nonrecyclability of thermosets has become a major barrier to the further development of these materials. Here, a well-tailored strategy is reported to solve this problem by introducing mismatched supramolecular interactions (MMSIs) into a covalently cross-linked poly(urethane-urea) network with dynamic acylsemicarbazide moieties. The MMSIs significantly strengthen and toughen the thermoset elastomer by effectively dissipating energy and resisting external stress. In addition, the elastomer recycling efficiency is improved 2.7-fold due to the superior reversibility of the MMSIs. The optimized thermoset elastomer features outstanding characteristics, including an ultrahigh tensile strength (110.8 MPa), an unprecedented tensile toughness (1245.2 MJ m-3), as well as remarkable resistance to chemical media, creep, and damage. Most importantly, it exhibits an extraordinary multirecyclability, and the 4th recycling efficiency remains close to 100%. This scalable method promotes the development of thermosets with both high performance and excellent recyclability, thereby providing valuable guidance for addressing the issue of nonrecyclability from a molecular design standpoint.

A fluorine-based strong and healable elastomer with unprecedented puncture resistance for high performance flexible electronics

There is usually a trade-off between high mechanical strength and dynamic self-healing because the mechanisms of these properties are mutually exclusive. Herein, we design and fabricate a fluorinated phenolic polyurethane (FPPU) elastomer based on octafluoro-4,4'-biphenol to overcome this challenge. This fluorine-based motif not only tunes interchain interactions through π-π stacking between aromatic rings and free-volume among polymer chains but also improves the reversibility of phenol-carbamate bonds via electron-withdrawing effect of fluorine atoms. The developed FPPU elastomer shows the highest recorded puncture energy (648.0 mJ), high tensile strength (27.0 MPa), as well as excellent self-healing efficiency (92.3%), along with low surface energy (50.9 MJ m-2), notch-insensitivity, and reprocessability compared with non-fluorinated counterpart biphenolic polyurethane (BPPU) elastomer. Taking advantage of the above-mentioned merits of FPPU elastomer, we prepare an anti-fouling triboelectric nanogenerator (TENG) with a self-healable, and reprocessable elastic substrate. Benefiting from stronger electron affinity of fluorine atoms than hydrogen atoms, this electronic device exhibits ultrahigh peak open-circuit voltage of 302.3 V compared to the TENG fabricated from BPPU elastomer. Furthermore, a healable and stretchable conductive composite is prepared. This research provides a distinct and general pathway toward constructing high-performance elastomers and will enable a series of new applications.

Biodegradable Polyurethane Derived from Hydroxylated Polylactide with Superior Mechanical Properties

Developing biodegradable polyurethane (PU) materials as an alternative to non-degradable petroleum-based PU is a crucial and challenging task. This study utilized lactide as the starting material to synthesize polylactide polyols (PLA-OH). PLA-based polyurethanes (PLA-PUs) were successfully synthesized by introducing PLA-OH into the PU molecular chain. A higher content of PLA-OH in the soft segments resulted in a substantial improvement in the mechanical attributes of the PLA-PUs. This study found that the addition of PLA-OH content significantly improved the tensile stress of the PU from 5.35 MPa to 37.15 MPa and increased the maximum elongation to 820.8%. Additionally, the modulus and toughness of the resulting PLA-PU were also significantly improved with increasing PLA-OH content. Specifically, the PLA-PU with 40% PLA-OH exhibited a high modulus of 33.45 MPa and a toughness of 147.18 MJ m-3. PLA-PU films can be degraded to carbon dioxide and water after 6 months in the soil. This highlights the potential of synthesizing PLA-PU using biomass-renewable polylactide, which is important in green and sustainable chemistry.

Strength Enhancement of Polyurethane Film by Solution Annealing

Recently, polyurethane elastomer (TPU) has attracted more and more attention depending on its excellent optical, mechanical, and retreatment properties. The high strength of polyurethane has always been pursued, which can enable its application in more fields. In this work, an aliphatic polyurethane elastomer membrane (HRPU6) was successfully synthesized, and its strength was obviously improved by solvent annealing technology. The tensile strength and adhesion strength can reach 64.56 and 2.58 MPa, but 36.55 and 1.57 MPa only before solvent annealing, respectively. The impact strength of laminated glass based on HRPU has also been significantly improved after solvent annealing, confirmed through drop ball impact testing. It has been confirmed that the increase in strength of HRPU6 is attributed to the enhancement of hydrogen bonding and the improvement of the phase separation degree.

Semi-crystalline polymers with supramolecular synergistic interactions: from mechanical toughening to dynamic smart materials

Semi-crystalline polymers (SCPs) with anisotropic amorphous and crystalline domains as the basic skeleton are ubiquitous from natural products to synthetic polymers. The combination of chemically incompatible hard and soft phases contributes to unique thermal and mechanical properties. The further introduction of supramolecular interactions as noncovalently interacting crystal phases and soft dynamic crosslinking sites can synergize with covalent polymer chains, thereby enabling effective energy dissipation and dynamic rearrangement in hierarchical superstructures. Therefore, this review will focus on the design principles of SCPs by discussing supramolecular construction strategies and state-of-the-art functional applications from mechanical toughening to sophisticated functions such as dynamic adaptivity, shape memory, ion transport, etc. Current challenges and further opportunities are discussed to provide an overview of possible future directions and potential material applications.

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.

Sustainable Supramolecular Polymers

Polymer waste is a pressing issue that requires innovative solutions from the scientific community. As a beacon of hope in addressing this challenge, the concept of sustainable supramolecular polymers (SSPs) emerges. This article discusses challenges and efforts in fabricating SSPs. Addressing the trade-offs between mechanical performance and sustainability, the ultra-tough and multi-recyclable supramolecular polymers are fabricated via tailoring mismatched supramolecular interactions. Additionally, the healing of kinetically inert polymer materials is realized through transient regulation of the interfacial reactivity. Furthermore, a possible development trajectory for SSPs is proposed, and the transient materials can be regarded as the next generation in this field. The evolution of SSPs promises to be a pivotal stride towards a regenerative economy, sparking further exploration and innovation in the realm of sustainable materials.

Design of Soft/Hard Interface with High Adhesion Energy and Low Interfacial Thermal Resistance via Regulation of Interfacial Hydrogen Bonding Interaction

Adhesion ability and interfacial thermal transfer capacity at soft/hard interfaces are of critical importance to a wide variety of applications, ranging from electronic packaging and soft electronics to batteries. However, these two properties are difficult to obtain simultaneously due to their conflicting nature at soft/hard interfaces. Herein, we report a polyurethane/silicon interface with both high adhesion energy (13535 J m-2) and low thermal interfacial resistance (0.89 × 10-6 m2 K W-1) by regulating hydrogen interactions at the interface. This is achieved by introducing a soybean-oil-based epoxy cross-linker, which can destroy the hydrogen bonds in polyurethane networks and meanwhile can promote the formation of hydrogen bonds at the polyurethane/silicon interface. This study provides a comprehensive understanding of enhancing adhesion energy and reducing interfacial thermal resistance at soft/hard interfaces, which offers a promising perspective to tailor interfacial properties in various material systems.

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.

Sustainable Polymers with High Performance and Infinite Scalability

Our society has been pursuing high-performance biodegradable polymers made from facile methods and readily available monomers. Here, we demonstrate a library of enzyme-degradable polymers with desirable properties from the first reported step polyaddition of diamines, COS, and diacrylates. The polymers contain in-chain ester and thiourethane groups, which can serve as lipase-degradation and hydrogen-bonding physical crosslinking points, respectively, resulting in possible biodegradability as well as upgraded mechanical and thermal properties. Also, the properties of the polymers are scalable due to the versatile method and the wide variety of monomers. We obtain 46 polymers with tunable performance covering high-Tm crystalline plastics, thermoplastic elastomers, and amorphous plastics by regulating polymer structure. Additionally, the polymerization method is highly efficient, atom-economical, quantitatively yield, metal- and even catalyst-free. Overall, the polymers are promising green materials given their degradability, simple and modular synthesis, remarkable and tunable properties, and readily available monomers.

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.

Dynamic Chemistry Toolbox for Advanced Sustainable Materials

Developing dynamic chemistry for polymeric materials offers chemical solutions to solve key problems associated with current plastics. Mechanical performance and dynamic function are equally important in material design because the former determines the application scope and the latter enables chemical recycling and hence sustainability. However, it is a long-term challenge to balance the subtle trade-off between mechanical robustness and dynamic properties in a single material. The rise of dynamic chemistry, including supramolecular and dynamic covalent chemistry, provides many opportunities and versatile molecular tools for designing constitutionally dynamic materials that can adapt, repair, and recycle. Facing the growing social need for developing advanced sustainable materials without compromising properties, recent progress showing how the toolbox of dynamic chemistry can be explored to enable high-performance sustainable materials by molecular engineering strategies is discussed here. The state of the art and recent milestones are summarized and discussed, followed by an outlook toward future opportunities and challenges present in this field.

Fracture-Resistant Stretchable Materials: An Overview from Methodology to Applications

Stretchable materials, such as gels and elastomers, are attractive materials in diverse applications. Their versatile fabrication platforms enable the creation of materials with various physiochemical properties and geometries. However, the mechanical performance of traditional stretchable materials is often hindered by the deficiencies in their energy dissipation system, leading to lower fracture resistance and impeding their broader range of applications. Therefore, the synthesis of fracture-resistant stretchable materials has attracted great interest. This review comprehensively summarizes key design considerations for constructing fracture-resistant stretchable materials, examines their synthesis strategies to achieve elevated fracture energy, and highlights recent advancements in their potential applications.

High-toughness, extensile and self-healing PDMS elastomers constructed by decuple hydrogen bonding

Elastomers are widely used in traditional industries and new intelligent fields. However, they are inevitably damaged by electricity, heat, force, etc. during the working process. With the continuous improvement of reliability and environmental protection requirements in human production and living, it is vital to develop elastomer materials with good mechanical properties that are not easily damaged and can self-heal after being damaged. Nevertheless, there are often contradictions between mechanical properties and self-healing as well as toughness, strength, and ductility. Herein, a strong and dynamic decuple hydrogen bonding based on carbon hydrazide (CHZ) is reported, accompanied with soft polydimethylsiloxane (PDMS) chains to prepare self-healing (efficiency 98.7%), recyclable, and robust elastomers (CHZ-PDMS). The strategy of decuple hydrogen bonding will significantly impact the study of the mechanical properties of elastomers. High stretchability (1731%) and a high toughness of 23.31 MJ m-3 are achieved due to the phase-separated structure and energy dissipation. The recyclability of CHZ-PDMS further supports the concept of environmental protection. The application of CHZ-PDMS as a flexible strain sensor exhibited high sensitivity.

Wormwood-infused porous-CaCO3 for synthesizing antibacterial natural rubber latex

Wormwood leaf is a traditional Chinese herbal medicine with a high medicinal value and long application history and its essential oil is a high-purity plant oil extracted from Wormwood leaf. Pharmacological research reveals that Wormwood leaf and Wormwood essential oil are a broad-spectrum antibacterial and antiviral drug, which can inhibit and kill many bacteria and viruses. We loaded wormwood extract on porous calcium carbonate (Porous-CaCO3) and introduced it and Wormwood essential oil into Natural rubber latex (NRL), thus synthesizing NRL composites with excellent vitro and in vivo antibacterial effect, cell compatibility and mechanical properties. This NRL material can delay the light aging and thermal oxidation of some mechanical properties, which provides a broader avenue for its commercialization.

Flexible Bioinspired Healable Antibacterial Electronics for Intelligent Human-Machine Interaction Sensing

Flexible electronic sensors are receiving numerous research interests for their potential in electronic skins (e-skins), wearable human-machine interfacing, and smart diagnostic healthcare sensing. However, the preparation of multifunctional flexible electronics with high sensitivity, broad sensing range, fast response, efficient healability, and reliable antibacterial capability is still a substantial challenge. Herein, bioinspired by the highly sensitive human skin microstructure (protective epidermis/spinous sensing structure/nerve conduction network), a skin bionic multifunctional electronics is prepared by face-to-face assembly of a newly prepared healable, recyclable, and antibacterial polyurethane elastomer matrix with conductive MXene nanosheets-coated microdome array after ingenious templating method as protective epidermis layer/sensing layer, and an interdigitated electrode as signal transmission layer. The polyurethane elastomer matrix functionalized with triple dynamic bonds (reversible hydrogen bonds, oxime carbamate bonds, and copper (II) ion coordination bonds) is newly prepared, demonstrating excellent healability with highly healing efficiency, robust recyclability, and reliable antibacterial capability, as well as good biocompatibility. Benefiting from the superior mechanical performance of the polyurethane elastomer matrix and the unique skin bionic microstructure of the sensor, the as-assembled flexible electronics exhibit admirable sensing performances featuring ultrahigh sensitivity (up to 1573.05 kPa-1 ), broad sensing range (up to 325 kPa), good reproducibility, the fast response time (≈4 ms), and low detection limit (≈0.98 Pa) in diagnostic human healthcare monitoring, excellent healability, and reliable antibacterial performance.

High-Toughness and High-Strength Solvent-Free Linear Poly(ionic liquid) Elastomers

Solvent-free elastomers, unlike gels, do not suffer from solvent evaporation and leakage in practical applications. However, it is challenging to realize the preparation of high-toughness (with both high stress and strain) ionic elastomers. Herein, high-toughness linear poly(ionic liquid) (PIL) elastomers are constructed via supramolecular ionic networks formed by the polymerization of halometallate ionic liquid (IL) monomers, without any chemical crosslinking. The obtained linear PIL elastomers exhibit high strength (16.5 MPa), Young's modulus (157.49 MPa), toughness (130.31 MJ m-3 ), and high crack propagation insensitivity (fracture energy 243.37 kJ m-2 ), owing to the enhanced intermolecular noncovalent interactions of PIL chains. Furthermore, PIL elastomer-based strain, pressure, and touch sensors have shown high sensitivity. The linear noncovalent crosslinked network endows the PIL elastomers with self-healing and recyclable properties, and broad application prospects in the fields of flexible sensor devices, health monitoring, and human-machine interaction.

Self-Healing Elastomers with Unprecedented Ultrahigh Strength, Superhigh Fracture Energy, Excellent Puncture Resistance, and Durability Based on Supramolecule Interlocking Networks Formed by Interlaced Hydrogen Bonds

Due to the multiple different properties in self-healing elastomers that are mutually exclusive based on the different and contradictory molecule chain structures, simultaneously achieving the ultrahigh mechanical performance and high durability of self-healing elastomers is a great challenge and the goal that has always been pursued. Herein, we report a novel strategy to fabricate a self-healing elastomer by introducing interlaced hydrogen bonds with superhigh binding energy. Distinguishing from the quadruple hydrogen bonds reported already, the interlaced hydrogen bond with a lower repulsive secondary interaction and higher binding energy is composed of two molecule units with different lengths and steric hindrance. Connected by the interlaced hydrogen bonds, a supramolecule interlocking network is formed to lock the polymer chains at room temperature, endowing the poly(urethane-urea) elastomer with an unprecedented ultrahigh strength (117.5 MPa, even higher than some plastics), the superhigh fracture energy (522.46 kJ m-2), and an excellent puncture resistance (puncture force reached 181.9 N). Moreover, the elastomers also exhibited excellent self-healing properties (healing efficiency up to 95.8%), high transparency (the average transmittance up to 91.0%), and good durability (including thermal decomposition resistance, thermal oxidation aging resistance, water resistance, and solvent resistance), providing a theoretical basis and technical reference in the development and broadening the application prospects of self-healing elastomers.

Ultralong-Term Durable Anticorrosive Coatings by Integration of Double-Layered Transfer Self-Healing Ability, Fe Ion-Responsive Ability, and Active/Passive Functional Partitioning

The application of self-healing polymers in corrosion protection is often limited by their slow and nonautonomous healing ability and poor long-term durability. In this paper, we propose a double-layered transfer self-healing coating constructed by soft and rigid polymer layers. The soft polymer has a fast self-healing rate of 10 min to repair, which was found to accelerate the self-healing of the upper rigid layer. The rigid polymer provided relatively high barrier ability while preserving certain self-healing ability owing to the shear-thinning effect. In this way, the double-layered coating combined rapid self-healing (∼1 h) and high impedance modulus |Z|f-0.01 Hz of 2.58 × 1010 Ω·cm2. Furthermore, the introduction of pyridine groups in B-PEA and polyacrylate-grafted-polydimethylsiloxane (PEA-g-PDMS) induced the Fe ion-responsive ability and shortened the self-healing time to 40 min (100 ppm Fe). Finally, barrier and anode sacrificed layers were introduced to produce multilayered architecture with active/passive anticorrosion performance. In the presence of scratches, the |Z|f-0.01 Hz can be preserved at 1.03 × 1010 Ω·cm2 after 200 days. The created anticorrosive coating technology combines long-term durability with room temperature autonomous rapid self-healing capability, providing a broad prospect for anticorrosive applications.

High Toughness, Multi-dynamic Self-Healing Polyurethane for Outstanding Energy Harvesting and Sensing

Triboelectric nanogenerators (TENGs) are an emerging class of energy harvesting devices with considerable potential across diverse applications, including wearable electronic devices and self-powered sensors. However, sustained contact, friction, and incidental scratches during operation can lead to a deterioration in the electrical output performance of the TENG, thereby reducing its overall service life. To address this issue, we developed a self-healing elastomer by incorporating disulfide bonds and metal coordination bonds into the polyurethane (PU) chain. The resulting elastomer demonstrated exceptional toughness, with a high value of 85 kJ m-3 and an impressive self-healing efficiency of 85.5%. Specifically, the TENG based on that self-healing PU elastomer generated a short circuit current of 12 μA, an open circuit voltage of 120 V, and a transfer charge of 38.5 nC within a 2 cm × 2 cm area, operating in contact-separation mode. With an external resistance of 20 MΩ, the TENG achieved a power density of 2.1 W m-2. Notably, even after self-healing, the electrical output performance of the TENG was maintained at 95% of the undamaged device. Finally, the self-healing TENG was employed to construct a self-powered noncontact sensing system that can be applied to monitor human motion accurately. This research may expand the application prospects of PU materials in future human-computer interaction and self-powered sensing fields.

Healable Ionic Conductors with Extremely Low-Hysteresis and High Mechanical Strength Enabled by Hydrophobic Domain-Locked Reversible Interactions

Extremely low hysteresis, high mechanical strength, superior toughness, and excellent healability are essential for stretchable ionic conductors to enhance their reliability and meet for cutting-edge applications. However, the fabrication of stretchable ionic conductors with such mutually exclusive properties remains challenging. Herein, extremely low-hysteresis and healable ionic conductors with a tensile strength of ≈8.9 MPa and toughness of ≈23.2 MJ m-3 are fabricated through the complexation of 4-carboxybenzaldehyde (CBA) grafted poly(vinyl alcohol) (PVA) (denoted as PVA-CBA) and poly (allylamine hydrochloride) (PAH) followed by acidification and ion-loading steps. The acidification step generates the PVA-CBA/PAH ionic conductors with in situ formed dynamic hydrophobic domains that lock and stabilize noncovalent interactions. This significantly minimizes the energy dissipation of the ionic conductors during cyclic mechanical loading (≤200% strain), resulting in ionic conductors with extremely low hysteresis (≈5%). The fractured ionic conductors can be healed at 60 °C to restore their original properties. Because of the extremely low hysteresis, the PVA-CBA/PAH ionic conductors show a highly stable and reproducible electrical response over 5000 uninterrupted loading-unloading cycles at a strain of 200%. The ionic conductor based sensors exhibit a high sensitivity to a wide range of strains (1-500%).

Enhancement of the mechanical properties of organic-inorganic hybrid elastomers by introducing movable and reversible crosslinks

Organic-inorganic materials have been widely utilized in various fields as multifunctional materials. Poly(dimethyl siloxane) (PDMS), a typical inorganic polymer, has industrially appealing functions, such as transparency, biocompatibility, and gas permeability; however, it has poor mechanical properties. We incorporated organic-inorganic hybrid elastomers (PDMS-γCD-AAl⊃P(EA-HEMA) (x)) with movable crosslinks, and we utilized hydrogen bonds as reversible crosslinks. The organic polymer poly ethyl acrylate-r-hydroxy ethyl methacrylate (P(EA-HEMA)) penetrated the cavity of triacetylated γ-cyclodextrin (γCD), which was introduced into the side chains of PDMS, and it compounded with PDMS at the nanoscale. Structural studies involving visual and X-ray scattering measurements revealed that movable crosslinks improved the compatibility levels of PDMS and acrylate copolymers. However, macroscopic phase separation occurred when the number of reversible crosslinks increased. Furthermore, studies on the mobility levels of acrylate copolymers and movable crosslinks indicated that the relaxation behaviour of PDMS-γCD-AAl⊃P(EA-HEMA) (x) changed with changing numbers of reversible crosslinks. Introducing reversible crosslinks improved the Young's modulus and toughness values. The movable and reversible crosslinks between the organic and inorganic polymers contributed to the high elongation properties. The design of PDMS-γCD-AAl⊃P(EA-HEMA) (x) incorporated cooperatively movable and reversible crosslinks to achieve high compatibility of immiscible polymers and to control the mechanical properties.

Highly Recyclable and Tough Elastic Vitrimers from a Defined Polydimethylsiloxane Network

Despite intensive research on sustainable elastomers, achieving elastic vitrimers with significantly improved mechanical properties and recyclability remains a scientific challenge. Herein, inspired by the classical elasticity theory, we present a design principle for ultra-tough and highly recyclable elastic vitrimers with a defined network constructed by chemically crosslinking the pre-synthesized disulfide-containing polydimethylsiloxane (PDMS) chains with tetra-arm polyethylene glycol (PEG). The defined network is achieved by the reduced dangling short chains and the relatively uniform molecular weight of network strands. Such elastic vitrimers with the defined network, i.e., PDMS-disulfide-D, exhibit significantly improved mechanical performance than random analogous, previously reported PDMS vitrimers, and even commercial silicone-based thermosets. Moreover, unlike the vitrimers with random network that show obvious loss in mechanical properties after recycling, those with the defined network enable excellent thermal recyclability. The PDMS-disulfide-D also deliver comparable electrochemical signals if utilized as substrates for electromyography sensors after the recycling. The multiple relaxation processes are revealed via a unique physical approach. Multiple techniques are also applied to unravel the microscopic mechanism of the excellent mechanical performance and recyclability of such defined network.

Structure and Properties of Metallosupramolecular Polymers with a Nitrogen-Based Bidentate Ligand

The solid-state properties of supramolecular polymers that feature metal-ligand (ML) complexes are, in addition to the general nature of the monomer, significantly affected by the choice of ligand and metal salt. Indeed, the variation of these components can be used to alter the structural, thermal, mechanical, and viscoelastic properties over a wide ranges. Moreover, the dynamic nature of certain ML complexes can render the resulting metallosupramolecular polymers (MSPs) stimuli-responsive, enabling functions such as healing, reversible adhesion, and mechanotransduction. We here report MSPs based on the bidentate ligand 6-(1'-methylbenzimidazolyl) pyridine (MBP), which is easily accessible and forms threefold coordination complexes with various transition metal ions. Thus, a poly(ethylene-co-butylene) telechelic was end-functionalized with two MBP ligands and the resulting macromonomer was assembled with the triflate salts of either Zn2+, Fe2+, or Ni2+. All three MSPs microphase separate and adopt, depending on the metal ion and thermal history, lamellar or hexagonal morphologies with crystalline domains formed by the ML complexes. The melting transitions are well below 200 °C, and this permits facile (re)processing. Furthermore, defects can be readily and fully healed upon exposure to UV-light. While the three MSPs display similar moduli in the rubbery regime, their extensibility and tensile strength depend on the nature of the ML complex, which similarly affects the long-range order and dynamic behavior.

Mechanical property-enhanced thermally conductive self-healing composites: preparation using designed self-healing matrix phase and hyBNNSs

Polymer composites with good thermal conductivity are gaining more and more attention in the current electronics sector, due to their superior heat management capabilities. However, conventional thermally conductive polymer composites are usually subject to interruptions in heat transfer because of physical damage. The present study prepared mechanical property-enhanced thermally-conductive self-healing composites through compositing a self-healing polyurethane matrix with hydroxylated boron nitride (hyBNNSs). The self-healing polyurethane was obtained by incorporating ligands and cerium(III) triflate [Ce(SO3CF3)3] as the metal center into the polyurethane elastomer. An optimal sample (PUp2C) with high tensile strength (6.8 MPa) and stretchability (1053%), ideal toughness (49.2 MJ m-3), and remarkable healing efficiency (97% healing after 48 h at 35 °C) was obtained. An increase in the content of hyBNNSs from 10% to 30% led to a significant increase in the mechanical performance of hyBNNSs20%/PUp2C, which manifested as the increase in the elongation at break (from 1053% to 1302.5%) and stress (from 6.8 MPa to 16.4 MPa). The XRD results revealed that combining PU with hyBNNSs through coordination bonds could significantly promote the crystallization of PUp2C, which was beneficial to enhancing the mechanical properties of the composites. The through-plane (λ⊥) and the in-plane (λ∥) values of the BNNSs30%/PUp2C composite reached 0.41 and 1.42 W mK-1, respectively, which were 195.2% and 507.1% higher than those of the original PUp2C, respectively.

Bioinspired Conductive Enhanced Polyurethane Ionic Skin as Reliable Multifunctional Sensors

Ionogels prepared from ionic liquid (IL) have the characteristics of nonevaporation and stable performance relative to traditional hydrogels. However, the conductivities of commonly used ionogels are at very low relative to traditional hydrogels because the large sizes of the cation and anion in an IL impedes ion migration in polymer networks. In this study, ultradurable ionogels with suitable mechanical properties and high conductivities are prepared by impregnating IL into a safe, environmentally friendly water-based polyurethane (WPU) network by mimicking the ion transport channels in the phospholipid bilayer of the cell membrane. The increase in electrical conductivity is attributed to the introduction of carboxylic acid in the hard segment of WPU; this phenomenon regularly arranges hard segment structural domains by hydrogen bonding, forming ionic conduction channels. The conductivities of their ionogels are >28-39 mS cm-1 . These ionogels have adjustable mechanical properties that make the Young's modulus value (0.1-0.6 MPa) similar to that of natural skin. The strain sensor has an ultrahigh sensitivity that ranges from 0.99 to 1.35, with a wide sensing range of 0.1%-200%. The findings are promising for various ionotronics requiring environmental stability and high conductivity characteristics.

Complexation of Sulfonate-Containing Polyurethane and Polyacrylic Acid Enables Fabrication of Self-Healing Hydrogel Membranes with High Mechanical Strength and Excellent Elasticity

Artificial hydrogel membranes with good biocompatibility are strongly needed in biological fields. The preparation of biocompatible hydrogel membranes simultaneously possessing high mechanical strength, excellent elasticity, and satisfactory self-healing properties remains a challenge. Herein, we demonstrate the preparation of such hydrogel membranes by complexation of sulfonate-containing polyurethane (SPU) and poly(acrylic acid) (PAA) in the presence of Zn²⁺ ions followed by swelling in water (denoted as SPU-PAA/Zn). Originating from the synergy of the coordination and hydrogen-bonding interactions and the reinforcement effect of the in situ formed hydrophobic domains, the SPU-PAA/Zn hydrogel membrane exhibits a high tensile strength of ∼7.1 MPa and a toughness of ∼30.4 MJ m^-3. Moreover, the hydrogel membrane is highly elastic, which can restore to its initial state from an ∼500% strain within 40 min rest at room temperature without any external assistance. The dynamic noncovalent interactions and hydrophobic domains allow the fractured hydrogel membrane to heal and completely regain its original integrity and mechanical properties at room temperature. Both in vitro and in vivo tests confirm that the hydrogel membrane exhibits satisfactory biocompatibility and could be potentially used as a biological barrier membrane in surgical operations or artificial organs.

Room-temperature self-healing polyurethane-cellulose nanocrystal composites with strong strength and toughness based on dynamic bonds

Self-healing materials suffer from a trade-off relationship between their self-healing ability and mechanical strength, which limits their applications. Therefore, we developed a room-temperature self-healing supramolecular composite based on polyurethane (PU) elastomer, cellulose nanocrystals (CNCs), and multiple dynamic bonds. In this system, the abundant hydroxyl groups on the surfaces of the CNCs form multiple hydrogen bonds with the PU elastomer, yielding a dynamic physical cross-linking network. This dynamic network enables self-healing without degrading the mechanical properties. As a result, the obtained supramolecular composites exhibited high tensile strength (24.5 ± 2.3 MPa), good elongation at break (1484.8 ± 74.9 %), favourable toughness (156.4 ± 31.1 MJ m^-3, which is equivalent to that of spider silk and 5.1-times higher than that of aluminium), and excellent self-healing efficiency (95 ± 1.9 %). Notably, the mechanical properties of the supramolecular composites were almost completely retained after reprocessing three times. Further, using these composites, flexible electronic sensors were prepared and tested. In summary, we have reported a method for preparing supramolecular materials having high toughness and room temperature self-healing ability that have applications in flexible electronics.

Tough, Recyclable, and Degradable Elastomers for Potential Biomedical Applications

Elastomers have many industrial, medical and commercial applications, however, their huge demand raises an important question of how to dispose of the out-of-service elastomers. Ideal elastomers that are concurrently tough, recyclable, and degradable are in urgent need, but their preparation remains a rigorous challenge. Herein, a polycaprolactone (PCL) based polyurethane elastomer is designed and prepared to meet this demand. Owing to the presence of dynamic coordination bond and the occurrence of strain-induced crystallization, the obtained elastomer exhibits a high toughness of ≈372 MJ m^-3 and an unprecedented fracture energy of ≈646 kJ m^-2 , which is much higher than natural rubber (≈50 MJ m^-3 for toughness and ≈10 kJ m^-2 for fracture energy). In addition, the elastomer can be recycled at least three times using solvent without losing its mechanical properties and can be degraded by lipase in ≈2 months. Finally, biological experiments demonstrate that the elastomer possesses good biocompatibility and can facilitate wound healing in mice when used as sutures. It is believed that the obtained elastomer meets the requirements for next-generation elastomers and is expected to be used in emerging fields such as biomedicine, flexible electronics, robotics and beyond.

Ambient Environment Adaptive Elastomer Constructed by Microphase Separation and Segment Complexation of Triblock Copolymers

Elastomers with environmental adaption have attracted considerable attention for advanced applications in various areas. Here, we fabricate an ambient environment adaptive elastomer by assembling triblock copolymers polystyrene-b-poly(acrylic acid)-b-polystyrene (SAS) and polystyrene-b-poly(ethylene oxide)-b-polystyrene (SES). Owing to the microphase separation of triblock polymers and hydrogen-bonding complexation of their middle segments, the SAS/SES complex presents dichotomy of vitrified hard PS domains and soft PAA/PEO domains, which presents major relaxation transition in the temperature zone 10-30 °C and relative humidity (RH) 40-60%. The SAS/SES elastomer presents quick adaption to the ambient environment change with temperature and humidity coupling. Moreover, after a loading-unloading cycle training, the SAS/SES elastomer exhibits domain orientation, low energy dissipation, high recovery ratio, and distinct strain stiffening compared with the pristine complex. The SAS/SES elastomer has potential to be used as a sensing and adaption component for complicated intelligent systems.

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.

Extremely Strong and Tough Biodegradable Poly(urethane) Elastomers with Unprecedented Crack Tolerance via Hierarchical Hydrogen-Bonding Interactions

The elastomers with the combination of high strength and high toughness have always been intensively pursued due to their diverse applications. Biomedical applications frequently require elastomers with biodegradability and biocompatibility properties. It remains a great challenge to prepare the biodegradable elastomers with extremely robust mechanical properties for in vivo use. In this report, we present a polyurethane elastomer with unprecedented mechanical properties for the in vivo application as hernia patches, which was obtained by the solvent-free reaction of polycaprolactone (PCL) and isophorone diisocyanate (IPDI) with N,N-bis(2-hydroxyethyl)oxamide (BHO) as the chain extender. Abundant and hierarchical hydrogen-bonding interactions inside the elastomers hinder the crystallization of PCL segments and facilitate the formation of uniformly distributed hard phase microdomains, which miraculously realize the extremely high strength and toughness with the fracture strength of 92.2 MPa and true stress of 1.9 GPa, while maintaining the elongation-at-break of ≈1900% and ultrahigh toughness of 480.2 MJ m^-3 with the unprecedented fracture energy of 322.2 kJ m^-2 . Hernia patches made from the elastomer via 3D printing technology exhibit outstanding mechanical properties, biocompatibility, and biodegradability. The robust and biodegradable elastomers demonstrate considerable potentials for in vivo applications.