Flame-Retardant and Self-Healing Waterborne Polyurethane Based on Organic Selenium

Rationally Designed Binder with Polysulfide-Affinitive Moieties and Robust Network Structures for Improved Polysulfide Trapping and Structural Stability of Sulfur Cathode

Lithium-sulfur batteries (LSBs) have emerged as a promising next-generation energy storage application owing to their high specific capacity and energy density. However, inherent insulating property of sulfur, along with its significant volume expansion during cycling, and shuttling behavior of lithium-polysulfides (LiPSs), hinder their practical application. To overcome these issues, a crosslinked cationic waterborne polyurethane (CCWPU) is rationally designed as a binder for LSBs. The mechanical robustness of CCWPU enables it to withstand the high stress derived from volume expansion of sulfur, facilitating charge-transferring through conserved charge-transfer pathway and promoting interconversion of LiPSs. Additionally, polar urethane groups offer favorable interaction sites with LiPSs, mitigating shuttling behavior of LiPSs via polar-polar interaction. Density functional theory investigations further elucidate that the incorporation of cationic moieties enhances LiPSs immobilization by confining Sn x- (x = 1 or 2) in LiPSs, thereby improving sulfur utilization. Benefiting from these, the cell with CCWPU demonstrates reduced polarization, superior LiPSs conversion rates, and stable cycling performance. Moreover, water-processable nature of CCWPU aligns with environmental consciousness. These diverse functionalities of CCWPU provide valuable insights for the development of advanced binder for LSBs, ultimately improving the electrochemical performances of LSBs.

Flame-Retardant Ionic Conductive Elastomers with Multiple Hydrogen Bonds: Synthesis, Characterization, and Strain Sensing Applications

Flammability is a significant challenge in polymer-based strain sensing applications. In addition, the existing intrinsic flame retardant is not elastic at room temperature, which may potentially damage the flexible equipment. This study presents a series of flame-retardant ionic conductive elastomers (ICEs) (denoted as PCAIPx) containing phosphorus from phytic acid (PA) and nitrogen from choline chloride (ChCl) with multiple hydrogen bonds synthesized using a simple and efficient one-pot UV-initiated radical copolymerization of a polymerizable deep eutectic solvent (PDES). The limiting oxygen index (LOI) value increased from 24.1% for the pure PCAI without PA to 38.3% for PCAIP7.5. The SEM analysis of the residual char shows that the formation of the dense and continuous char layer effectively worked as a shield, preventing further decomposition of the undecomposed polymer inside while hindering the transmission of heat and mass and isolating the oxygen required for combustion. The hydrogen bonds' cross-linked structure and phosphorus-containing elastomer demonstrate a superior elasticity (elongation at break of up to 2109%), durability, and tear resistance and excellent adhesive properties. Application of PCAIPX in strain sensors showed that the elastomer has excellent cyclic stability and exhibited repeatable and stable resistance change signals in response to repetitive bending motions of the wrist, fingers, elbow, and knee. Consequently, this study provides a simple strategy for the development of a flame-retardant ICE which can effectively reduce fire hazards and potentially be applied in other fire-risk fields such as personal protection, firefighting, and sports equipment.

A Visible Light-Responsive, Fast Room-Temperature Self- Healing, Mechanically Robust, Antibacterial Waterborne Polyurethane Based on Triple Dynamic Bonds

Despite the recent rapid advancements in room-temperature self-healing waterborne polyurethanes, imparting fast self-healing ability while concurrently maintaining robust mechanical performance of waterborne polyurethanes remains a formidable challenge. Herein, we propose a molecular structure design strategy for developing visible light-responsive, room-temperature self-healing, and antibacterial waterborne polyurethane (DMZWPU) containing triple dynamic bonds of diselenide bonds, multiple hydrogen bonds, and Zn(II)-carboxylate coordination bonds. This innovative approach effectively balances the tensile stress, fracture toughness, and self-healing ability of the material. Thanks to the synergy of the three dynamic bonds, the resulting DMZWPU film demonstrates a tensile stress of 40.32 MPa and a fracture toughness of 119.29 MJ/m3, respectively. Furthermore, based on the dynamic characteristics of three dynamic bonds and the dual induction of trace ethanol and visible light, the damaged DMZWPU film can recover more than 85% of the tensile stress at room temperature within 2 h. These performances outperform those of most of the currently reported room-temperature self-healable polymers (healing efficiency >80%). Due to the combined action of selenium and zinc ions, the DWZWPU film exhibits excellent antibacterial properties (sterilization rate of 100% in 24 h). Finally, the DMZWPU emulsion is effectively applied for leather finishing processes, and the results show that the DMZWPU coating exhibits excellent folding resistance, wear resistance, and room-temperature self-healing function, as well as enhanced water resistance and dry friction resistance. In summary, this study provides a novel perspective for the development of waterborne polyurethane with high mechanical performances and rapid self-healable ability at room temperature.

Electron-Withdrawing Effects for Tailoring Oxidative-Stress-Mediated Coating in Marine Antifouling

Oxidative stress derived from excess reactive oxygen radicals (ROS) induces cellular damage, apoptosis, and necrosis, thus effective biofouling control by directly inhibiting primary membrane formation. However, the oxidative stress produced that does not rely on additional energy still is a challenge. Herein, an oxidative-stress-mediated marine antifouling polyurea coating is prepared leveraging the strong electron absorption effect of C═N. Given the structure of the urethane bond, the reversible reaction energy barrier of the dynamic urethane bond can be reduced, thereby enabling the urethane bond to be broken without the need for additional energy. The alkyl radical (R·) originating from the oxime-urethane bond can mediate the induction of oxidative stress in cells and microbial death, thus preserving exceptional antifouling properties and resisting most of the organism to adhere on the substrates. Notably, the coating indicates satisfactory antibacterial and antialgae performance and exhibits 8 months of marine field antifouling performance. In addition, the electron structure is investigated by theoretical calculation, and the interface behavior is investigated by molecular dynamics simulation. This work presents a pioneering example of the construction of oxidative-stress-mediated coating, which might be a judicious design strategy for an environmentally friendly marine antifouling coating.

Macrophage-Inspired marine antifouling coating with dynamic surfaces based on regulation of dynamic covalent bonds

Macrophages can kill bacteria and viruses by releasing free radicals, which provides a possible approach to construct antifouling coatings with dynamic surfaces that release free radicals if the breaking of dynamic covalent bonds is precisely regulated. Herein, inspired by the defensive behavior of macrophages of releasing free radicals to kill bacteria and viruses, a marine antifouling coating composed of polyurethane incorporating dimethylglyoxime (PUx-DMG) is prepared by precise regulation of dynamic oxime-urethane covalent bonds. The obtained alkyl radical (R·) derived from the cleavage of the oxime-urethane bonds manages to effectively suppress the attachment of marine biofouling. Moreover, the intrinsic dynamic surface makes it difficult for biofouling to adhere and ultimately achieves sustainable antifouling property. Notably, the PU50-DMG coating not only presents efficient antibacterial and antialgae properties, but also prevents macroorganisms from settling in the sea for up to 4 months. This provides a pioneer broad-spectrum strategy to explore the marine antifouling coatings.

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.

Photochemical Transformations of Peptides Containing the N-(2-Selenoethyl)glycine Moiety

The diselenide bond has attracted considerable attention due to its ability to undergo the metathesis reaction in response to visible light. In our previous study, we demonstrated visible-light-induced diselenide metathesis of selenocysteine-containing linear peptides, allowing for the convenient generation of peptide libraries. Here, we investigated the transformation of linear and cyclic peptides containing the N-(2-selenoethyl)glycine moiety. The linear peptides were highly susceptible to the metathesis reaction, whereas the cyclic systems gave only limited conversion yields of the metathesis product. In both cases, side reactions leading to the formation of mono-, di-, and polyselenides were observed upon prolonged irradiation. To confirm the radical mechanism of the reaction, the radical initiator 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044) was tested, and it was found to induce diselenide metathesis without photochemical activation. The data were interpreted in the light of quantum-chemical simulations based on density functional theory (DFT). The simulations were performed at the B3LYP-D3BJ/def2-TZVP level of theory using a continuum solvation model (IEF-PCM) and methanol as a solvent.

Photoluminescent Self-Healable Waterborne Polyurethane/Mo and S Codoped Graphitic Carbon Nitride Nanocomposite with Bioimaging and Encryption Capability

Creating polymers that combine various functions within a single system expands the potential applications of such polymeric materials. However, achieving polymer materials that possess simultaneously elevated strength, toughness, and self-healing capabilities, along with special properties, remains a significant challenge. The present study demonstrates the preparation of S and Mo codoped graphitic carbon nitride (g-C3N4) (Mo@S-CN) nanohybrid and the fabrication of self-healing waterborne polyurethane (SHWPU)/Mo@S-CN (SHWPU/NS) nanocomposites for advanced applications. Mo@S-CN is an intriguing combination of g-C3N4 nanosheets and molybdenum oxide (MoOx) nanorods, forming a complex lamellar structure. This unique arrangement significantly improves the inborn properties of SHWPU to an impressive degree, especially mechanical strength (28.37-34.11 MPa), fracture toughness (73.65-140.98 MJ m-2), and thermal stability (340.17-348.01 °C), and introduces fluorescence activity into the matrix. Interestingly, a representative SHWPU/NS0.5 film is so tough that a dumbbell of 15 kg, which is 53,003 times heavier than the weight of the film, can be successfully lifted without any significant crack. Remarkably, fluorescence activity is developed because of electronic excitations occurring within the repeating polymeric tris-triazine units of the Mo@S-CN nanohybrid. This fascinating feature was effectively harnessed by assessing the usability of aqueous dispersions of the Mo@S-CN nanohybrid and photoluminescent SHWPU/NS nanocomposites as sustainable stains for bioimaging of human dermal fibroblast cells and anticounterfeiting materials, respectively. The in vitro fluorescence tagging test showed blue emission from 365 nm excitation, green emission from 470 nm excitation, and red emission from 545 nm excitation. Most importantly, in vitro hemocompatibility assessment, in vitro cytocompatibility, cell proliferation assessment, and cellular morphology assessment supported the biocompatibility nature of the Mo@S-CN nanohybrid and SHWPU/NS nanocomposites. Thus, these materials can be used for advanced applications including bioimaging.

Tough and Self-Healing Waterborne Polyurethane Elastomers via Dynamic Hydrogen Bonds Design for Flexible Conductive Substrate Applications

Balancing the mechanical strength and self-healing performance of polyurethane (PU) remains a significant challenge in achieving excellent self-repairing PU materials. In this study, a self-healing waterborne PU elastomer was designed from a bionic concept by incorporating 2'-deoxythymidine (2'-dT) and isophorone diamine (IPDA) into the polymer chain. The loose stacking of IPDA's irregular cycloaliphatic structure resulted in the irregular arrangement of urethane bonds in the hard domain. The formation of sextuple hydrogen bonds between 2'-dT and urethane bonds, as well as quadruple hydrogen bonds between urethane bonds themselves, enhanced the mechanical properties of the material. The multiple hydrogen bonds can dissociate, recombine, and dissipate energy, thereby improving the material's repair capability. The hierarchical self-assembly of hydrogen bonds enabled the PU to achieve a tensile strength of 15.3 MPa and toughness of 100.75 MJ/m3. The prepared PU film is highly transparent and has a transmittance of more than 90%. Additionally, it can undergo rapid repair under high temperatures or under trace solvent conditions. When used as a flexible conductive substrate, it quickly restored the conductivity and enhanced the material's lifespan after surface damage. This environmentally friendly and self-healing waterborne PU elastomer will hold broad application prospects in the field of flexible electronic devices.

Strategy for Constructing Phosphorus-Based Flame-Retarded Polyurethane Elastomers for Advanced Performance in Long-Term

Polyurethane elastomer (PUE), which is widely used in coatings for construction, transportation, electronics, aerospace, and other fields, has excellent physical properties. However, polyurethane elastomers are flammable, which limits their daily use, so the flame retardancy of polyurethane elastomers is very important. Reactive flame retardants have the advantages of little influence on the physical properties of polymers and low tendency to migrate out. Due to the remarkable needs of non-halogenated flame retardants, phosphorus flame retardant has gradually stood out as the main alternative. In this review, we focus on the fire safety of PUE and provide a detailed overview of the current molecular design and mechanisms of reactive phosphorus-containing, as well as P-N synergistic, flame retardants in PUE. From the structural characteristics, several basic aspects of PUE are overviewed, including thermal performance, combustion performance, and mechanical properties. In addition, the perspectives on the future advancement of phosphorus-containing flame-retarded polyurethane elastomers (PUE) are also discussed. Based on the past research, this study provides prospects for the application of flame-retarded PUE in the fields of self-healing materials, bio-based materials, wearable electronic devices, and solid-state electrolytes.

Robust, Flame-Retardant, and Anti-Corrosive Waterborne Polyurethane Enabled by a PN Synergistic Flame-Retardant Containing Benzimidazole and Phosphinate Groups

Waterborne polyurethanes (WPUs) have attracted great interest owing to their environmentally friendly properties, and are wildly applied in production and daily life. However, waterborne polyurethanes are flammable. Up to now, the challenge remains to prepare WPUs with excellent flame resistance, high emulsion stability, and outstanding mechanical properties. Herein, a novel flame-retardant additive, 2-hydroxyethan-1-aminium (2-(1H-benzo[d]imidazol-2-yl)ethyl)(phenyl)phosphinate (BIEP-ETA) has been synthesized and applied to improve the flame resistance of WPUs, which has both phosphorus nitrogen synergistic effect and the ability to form hydrogen bonds with WPUs. The WPU blends (WPU/FRs) exhibited a positive fire-retardant effect in both the vapor and condensed phases, with significantly improved self-extinguishing performance and reduced heat release value. Interestingly, thanks to the good compatibility between BIEP-ETA and WPUs, WPU/FRs not only have higher emulsion stability, but also have better mechanical properties with synchronously improved tensile strength and toughness. Moreover, WPU/FRs also exhibit excellent potential as a corrosion-resistant coating.