Evaluation on Self-healing Mechanism and Hydrophobic Performance of Asphalt Modified by Siloxane and Polyurethane

In order to inhibit and remove the thin ice and extend the lifetime of the damaged bridge, the self-healing mechanism and hydrophobic performance of asphalt modified by siloxane and polyurethane (ASP) were studied by dynamic shear rheology (DSR), fluorescence microscope (FM), atomic force microscope (AFM), the fracture-healing-re-fracture test and molecular simulations. The experimental results indicated that the selfhealing capability of ASP increased with increasing heating time and temperature. Furthermore, the addition of siloxane could improve the reaction energy barrier and complex modulus, and it is believed that the self-healing is a viscosity driven process, consisting of two parts namely crack closure and properties recovery. Contact angle of ASP increased with the increasing siloxane content and it deduced that the siloxane could improve the hydrophobic performance of ASP and the ASP molecule model could simulate well the self-healing mechanism and hydrophobic performance of ASP.

Thermally Reversible,Self-Healing Polyurethane Based on Propyl Gallate and Polyurethane Prepolymers with Varied Isocyanate Content

Thermosetting polyurethanes are widely used in various fields owing to their excellent elasticity,strength and solvent resistance.Three environmental friendly propyl gallate-based self-healing polyurethanes were prepared from polyurethane prepolymers with varying isocyanate content.The thermal stabilities of the polyurethanes were tested using thermogravimetric analysis.Their self-healing and mechanical properties were analyzed using a universal testing machine and dynamic thermomechanical analysis.The polyurethanes were found with high self-healing ability and excellent mechanical properties due to the absence of phenolic carbamate.These qualities improved with increased isocyanate content and the prolonged selfhealing time.We found,therefore,that the propyl gallate-based polyurethane has potential for use in industrial applications as self-healing materials.

BaTiO_(3)/Polyurethane Dielectric Composites with Diels-Alder Bond for Improved Self-Healing Properties

In general,self-healing dielectric composites are mainly composed of polar hydrogen bonds,which have high hydrophilicity and are unsuitable for humid environment.Dielectric composite with Diels-Alder(D-A)bond contains covalent bonds,it can be adopted as an efficient self-healing material.Here,we construct self-healing barium titanate(BT)/polyurethane(PU)dielectric composites by adopting PU with D-A bond as matrix(BT/PU-DA).The prepared 10%BT/PU-DA composite exhibits superior self-healing ability than that of PUDA.Moreover,its dielectric constant can reach 9.3 with a loss of only 0.04 at 1000 Hz and maintain 93%repair efficiency of tensile strength.The experimental analysis suggests the introduction of D-A bond can enhance the thermostability and self-healing ability of BT/PU-DA composite.In addition,the incorporation of BT nanoparticles and D-A bond in the self-healing composite contributes to the lower dielectric loss and excellent tensile strength after healing.The adopted strategy is a promising and facile approach to develop highly efficient selfhealing dielectric material,which will be conducive to reuse and sustainable development of the electronic packaging material in aqueous medium or wet environment.

Microencapsulation of UV-Curable Self-healing Agent for Smart Anticorrosive Coating

UV-curable polyurethane prepolymer and photoinitiator 1173 were facilely encapsulated in a poly（urea-formaldehyde） shell, which was in situ formed by the polymerization of formalde-hyde and urea in an oil-in-water emulsion. The diameters of the microcapsules ranged from 118 μm to 663 μm depending on agitation speed, and were obtained via optical mi-croscopy and scanning electron microscopy analyses. The encapsulation percent and the yield of microcapsules prepared at the agitation speed of 600 r/min can reach 97.52wt% and 65.23wt%, respectively. When the water-borne polyurethane （WPU） coating embedded with the prepared microcapsules were scratched, the healing agent could be released from rup-tured microcapsules and lled the scribed region. The excellent anticorrosion properties of the WPU coating embedded with the prepared microcapsules were con rmed by the results obtained from both electrochemical impedance spectroscopy and Tafel curves.

Synthesis of Lignin-based Nonisocyanate Poly(imine-hydroxyurethane)s Networks.Part II:Self-healing,Reprocessing,and Degradation

This study provides a comprehensive understanding of the polymeric properties of lignin-based non-isocyanate poly(iminehydroxyurethane)s(LNIPUs).The properties of the LNIPUs are affected by changes in the stoichiometric feed ratios of the bis(6-membered cyclic carbonate)(BCC)and levulinate enzymatic hydrolysis lignin(LEHL).The results showed that the LNIPUs exhibited a short relaxation time and excellent thermal repair and degradation properties.With a change in the LEHL content in the LNIPUs to 45.53%,a relaxation time of only 9 s was achieved,and the thermal repair rate of the scratches reached 93%.Furthermore,the tensile strength of the LNIPUs decreased with an increase in the LEHL content after two hot-pressing processes,while a higher than 75% tensile strength was maintained after the second hot-pressing treatment.The LNIPUs exhibited thermoresponsive shape memory property with deformation and shape fixing at 80℃.In addition,the as-synthesized LNIPUs were soluble in ethylene glycol in the absence of any organic solvents.This work demonstrates the synthesis of LNIPUs with self-healing,reprocessing,shape memory,and degradation properties.

Solvent-Free Synthesis of Self-Healable and Recyclable Crosslinked Polyurethane Based on Dynamic Oxime-Urethane Bonds

Polyurethane is widely used for its versatility in design and range of performance.Self-healing and recyclable dynamic polyurethane networks have attracted extensive attention due to their potential to extend service life and ensure safety in use,as well as to promote sustainable use of resources.Developing green and environment-friendly methods to obtain this material is an interesting and challenging task,as the majority of current dynamic polyurethane networks utilize the solution polymerization method.The use of solvents makes the processes complicated,harmful to environment,and increase the cost.Poly(oxime-urethanes)(POUs)are emerging dynamic polyurethanes and show great potential in diverse fields,such as biomaterials,hot melt adhesives,and flexible electronics.In this study,we utilized the solubility properties of dimethylglyoxime in raw material poly(ethylene glycol)to prepare POUs through bulk polymerization for the first time.This method is simple,convenient and cost-efficient.Simultaneously,copper ion coordination improves POUs strength and dynamic properties,with mechanical strength up from 0.54 MPa to 1.03 MPa and self-healing recovery rate up from 85.5%to 91.8%,and activation energy down from 119.6 k J/mol to 95.4 k J/mol.To demonstrate the application of this technology,self-healing and stretchable circuits are constructed from this dynamic polyurethane network.

Visible Light-driven Self-healable Mechanochromic Polyurethanes

Polyurethanes incorporating spiropyran(SP)and diselenide(DiSe)in the main chain,which are confined in different hard segments are developed.Visible light-driven diselenide metathesis and mechanically induced ring opening of SP offer self-healing and mechanochromic properties of the polymers,respectively.Delicate selection of the polymer backbone is found essential to promote the dual functions.In particular for polyurethane with SP coupled into 4,4'-methylenebis(cyclohexyl isocyanate)and DiSe linked with isophorone diisocyanate,excellent mechanical,mechanochromic and self-healing properties are estimated.Moreover,combining self-healing and self-reporting moieties in one chain allows the discrimination of different healing mechanisms,including bond formation and chain entanglement,in a visualized way.

Polyurethane networks based on disulfide bonds:from tunable multi-shape memory effects to simultaneous self-healing

With the prompt development in intellectualization nowadays, the smart materials with multifunctionality or multi-responsiveness are highly expected. But it is a big challenge to integrate the different actuating units into a single system in a synergy pattern. Herein, we put forward a new strategy to develop the polyurethane networks which can present shape-memory effect and self-healing effect in independent way as well as simultaneous acting mode. To realize this goal, poly(tetremethylene ether) glycol was chosen as the soft segment to ensure the polymer chains a good mobility, and disulfide bond as the dynamic covalent bond was embedded in the backbone of polyurethane to endow it with desirable self-healing capacity under mild condition. Moreover, a rational control of the architecture of the networks by adjusting the content of disulfide bond and the degree of cross-linking, a broad glass transition temperature(T_g) was achieved, which enabled the network a versatile shape-memory effect, covering from dual-, triple-so far as to quadrupleshape memory effect. More importantly, the shape recovery and healing process can be realized simultaneously because of the highly matched actuating condition in this system.

A robust self-healing polyurethane elastomer: From H-bonds and stacking interactions to well-defined microphase morphology

Self-healing materials have attracted considerable attention because of their improved safety, lifetime, energy efficiency and environmental impact. Supramolecular interactions have been extensively considered in the field of self-healing materials due to their excellent reversibility and sensitive responsiveness to environmental stimuli. However,development of a polymeric material with good mechanical performance as well as self-healing capacity is very challenging. In this study, we report a robust self-healing polyurethane(PU) elastomer polypropylene glycol-2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol(PPG-mUPy) by integrating ureidopyrimidone(UPy) motifs with a PPG segment with a well-defined architecture and microphase morphology.To balance the self-healing capacity and mechanical performance, a thermal-triggered switch of H-bonding is introduced. The quadruple H-bonded UPy dimeric moieties in the backbone induce phase separation to form a hard domain as well as enable further aggregation into microcrystals by virtue of the stacking interactions, which are stable in ambient temperature. This feature endows the PU with high mechanical strength. Meanwhile, a high healing efficiency can be realized, when the reversibility of the H-bond was unlocked from the stacking at higher temperature. An optimized sample PPG1000-mUPy50%with a good balance of mechanical performance(20.62 MPa of tensile strength) and healing efficiency(93% in tensile strength) was achieved. This strategy will provide a new idea for developing robust self-healing polymers.

A Robust Self-healing Polyurethane Elastomer Enabled by Tuning the Molecular Mobility and Phase Morphology through Disulfide Bonds

Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an asymmetric alicyclic structure adjacent to aromatic disulfide was tactfully introduced into the backbone of polyurethane(PU)elastomer.Specifically,such elastomer(PU-HPS)was fabricated by polycondensing polytetramethylene ether glycol(PTMEG),isophorone diisocyanate(IPDI)and p-hydroxydiphenyl disulfide(HPS)via one-pot method.The molecular mobility and phase morphology of PU-HPS can be tuned by adjusting the HPS content.Consequently,the dynamic exchange of hydrogen and disulfide bonds in the hard segment domains can also be tailored.The optimized sample manifests outstanding tensile strength(46.4 MPa),high toughness(109.1 MJ/m^(3)),high self-healing efficiency after fracture(90.3%),complete scratch recovery(100%)and good puncture resistance.Therefore,this work provides a facile strategy for developing robust self-healing polymers.

Synthesis and Properties of Reversible Disulfide Bond-based Self-healing Polyurethane with Triple Shape Memory Properties

A reversible disulfide bond-based self-healing polyurethane with triple shape memory properties was prepared by chain extending of random copolymer poly(lactide-co-caprolactone)(PCLA), hexamethylene diisocyanate (HDI), polytetrahydrofuran (PTMEG), and 4,4,-aminophenyl disulfide. The chemical structures were characterized using 1H nuclear magnetic resonance (^1H-NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). The thermal properties, selfhealing properties, triple-shape memory effect, and quantitative shape memory response were evaluated by differential scanning calorimetry (DSC), tensile tests, two-step programming process thermal mechanical experiments, and subsequent progressive thermal recovery. The self-healing mechanism and procedures were investigated using polarizing optical microscopy (POM) and an optical profiler. It was concluded that self-healing properties (up to 60%) and triple-shape memory properties around 35 and 50℃(with shape fixation ratios of 94.3% and 98.3%, shape recovery ratios of 76.6% and 85.1%, respectively) were integrated to the shape memory polyurethane. As-prepared polyurethane is expected to have potential applications in multi-shape coatings, films, and step-by-step deploying structures.

A review on room-temperature self-healing polyurethane:synthesis,self-healing mechanism and application

Polyurethanes have been widely used in many fields due to their remarkable features such as excellent mechanical strength, good abrasion resistance, toughness, low temperature flexibility, etc. In recent years, room-temperature self-healing polyurethanes have been attracting broad and growing interest because under mild conditions, room- temperature self-healing polyurethanes can repair damages, thereby extending their lifetimes and reducing maintenance costs. In this paper, the recent advances of room-temperature self-healing polyurethanes based on dynamic covalent bonds, noncovalent bonds and combined dual or triple dynamic bonds are reviewed, focusing on their synthesis methods and self-healing mechanisms, and their mechanical properties, healing efficiency and healing time are also described in detial. In addition, the latest applications of room-temperature self-healing polyurethanes in the fields of leather coatings, photoluminescence materials, flexible electronics and biomaterials are summarized. Finally, the current challenges and future development directions of the room-temprature self-healing polyurethanes are highlighted. Overall, this review is expected to provide a valuable reference for the prosperous development of room- temperature self-healing polyurethanes.

Effect of Molecular Weight of PEG Soft Segments on Photo-stimulated Selfhealing Performance of Coumarin Functionalized Polyurethanes

Polyurethanes consisting of tri-functional homopolymer of hexamethylene diisocyanate （tri-HDI） and polyethylene glycol （PEG） are synthesized, in which photo-reversible coumarin moieties act as pendant groups. Accordingly, the polyurethanes can be repeatedly self-healed under UV lights at room temperature by taking advantages of the photodimerization and photocleavage habits of coumarin. Molecular weight of the soft segment, PEG, is found to be closely related to the healing performance of the polyurethanes. Lower molecular weight PEG that corresponds to higher initial coumarin concentration in the polymer is critical for obtaining higher healing efficiency in the case of the first healing action. Nevertheless, it does not guarantee high reversibility of the photo-remendability during the repeated healing events. In contrast, the polyurethane with moderate molecular weight PEG has achieved balanced performance. Reaction kinetics is less important for the healing effect.

Dynamic Oxime-Urethane Bonds, a Versatile Unit of High Performance Self-healing Polymers for Diverse Applications

Oxime-urethane bond featuring with high reversibility even at room temperature and multiple reactivity is an emerging dynamic covalent bond,and has shown great potential for self-healing polymers,which are one of the most attractive development directions for next generation of polymeric materials.In this review,recent progresses on the oxime-urethane-based self-healing polymers,including their designs and applications in diverse fields such as biomedicine,flexible electronics,soft robots,3D printing,protective materials,and adhesives,are summarized,and outlooks on the future development of this field are discussed.

A fluorine-rich phenolic polyurethane elastomer with excellent selfhealability and reprocessability and its applications for wearable electronics

Polyurethane elastomers with covalent adaptable networks(PU-CANs)based on the dynamic urethane bond have attracted remarkable attention owing to their reprocessability,adaptability,and self-healability.However,it is still a formidable challenge to achieve excellent dynamics at low temperatures since the urethane bond energy is usually high.Herein,a fluorinated phenolic polyurethane(FPPU)elastomer with CANs based on phenol±carbamate bonds was successfully designed and prepared.Subsequently,the effects of fluorine atoms on the mechanical properties,thermal stability,reprocessability,and self-healability,surface free energy,and hydrophobicity of the prepared elastomers were systematically investigated.The FPPU elastomer showed notch-insensitivity,remarkable self-healable efficiency(98%),low dynamic dissociation temperature(60℃),excellent reprocessability,and low surface energy(62 MJ m^(-2))compared with non-fluorinated counterpart phenolic polyurethane elastomer(APPU).Based on the above-mentioned features,FPPU was selected as an elastic substrate to assemble into a triboelectric nanogenerator(TENG)to harvest energy from natural motion.This TENG exhibited an excellent electrical output performance with a peak open-circuit voltage of 103 V,a peak short-circuit current of 4.7μA and a peak short-circuit charge of 43 nC.In addition,the TENG possessed high selfcleaning and reprocessing efficiency.Furthermore,a stretchable and self-healing composite conductor based on FPPU was fabricated for flexible electronic devices.

A leather coating with self-healing characteristics

Genuine leather is often coated before making daily necessities such as shoes,clothing,bags,sofas,car seats,etc.,so as to impart leather products various colours,higher wear resistance and water resistance and so on.However,the coating of these products is often damaged in daily use which will decrease its aesthetic effect and practicability.Therefore,how to improve the scratch resistance of leather coatings has been puzzling people all the time.It is a common knowledge that animals and plants can repair the injured biological tissues by himself.According to this principle,here,we prepared a type of self-healing water-borne polyurethane with disulfide bond in the main chain by using HEDS as chain extender,and the self-healing system was triggered by the disulfide bonds with the help of shape memory function of waterborne Polyurethane,self-healing experiments how that the damaged of leather coating can be repaired fully at 60℃ for 12 h.

面向高性能柔性电子的强韧、可修复和优异抗穿刺的氟化弹性体

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 throughπ-πstacking 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 m J),high tensile strength(27.0 MPa),as well as excellent selfhealing 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.

Cooperative Chemical Coupling and Physical Lubrication Effects Construct Highly Dynamic Ionic Covalent Adaptable Network for High-Performance Wearable Electronics

Covalent adaptable networks(CANs),which combine the benefits of traditional thermosets and thermoplastics,have attracted considerable attention.The dynamics of reversible covalent bonds and mobility of polymer chains in CANs determine the topological rearrangement of the polymeric network,which is critical to their superior features,such as self-healing and reprocessing.Herein,we introduce an ionic liquid to dimethylglyoximeurethane(DOU)-based CANs to regulate both reversible bond dynamics and polymer chain mobility by cooperative chemical coupling and physical lubrication.Small-molecule model experiments demonstrated that ionic liquids can catalyze dynamic DOU bond exchange.Ionic liquid also breaks the hydrogen bonds between polymeric chains,thereby increasing their mobility.As a combined result,the activation energy of the dissociation of the dynamic network decreased from 110 to 85 kJ mol^(−1).Furthermore,as a functional moiety,the ionic liquid imparts new properties to CANs and will greatly expand their applications.For example,the consequent conductivity of resultant ionic CAN(iCAN)has demonstrated a great power to build high-performance multifunctional wearable electronics responsive to multiple stimulations including temperature,strain,and humidity.This study provides a new design principle that simultaneously uses the chemical and physical effects of two structural components to regulate material properties enabling novel applications.