Preparation And Properties Of Self-healing Polyurethane Conductive Materials

As the digital times is coming,intelligent electronic devices have been rapidly developed and widely used,such as electronic conductor,sensors,supercapacitor,lithium ion battery and electronic skin,etc.However,the inherent technical problems of these electronic devices,such as cracks or fractures are formed during the using process.These problems cause low stability,safety and service life,which seriously hinder the expansion and application of these devices in emerging fields such as artificial intelligence and biological medicine.In recent years,the development of self-healing conductive materials has provided a novel idea to solve the above problems,which has a significant meaning in the research and development of a new generation of intelligent electronic devicesIn this thesis,with a simple and feasible way to develop a series of novel polymer structures of self-healing polyurethane material,the molecular structure of the fine design strategy to introduce the healing mechanism of reversible hydrogen bonding into polyurethane system were used.We discussed the polymer structure,healing mechanism and healing performances from the perspective of macro and micro.In the meantime,the self-healing conductive material was prepared by reasonable and simple assembly process,which solves the problems in the application of electronic devices,broadens its application as electronic devices in flexible sensors.The main research contents and conclusions are as follows1.By introducing the quadruple hydrogen bond monomer 2-amino-4-hydroxy-6-methylpyrimidine(UPy)and the photocurable monomer hydroxyethyl methacrylate(HEMA)into the ending group of the polyurethane main chain,the self-healing photocurable waterborne polyurethane(WPU-UxHy)was prepared under the emulsification of hydrophilic monomer dihydroxymethylpropionic acid(DMPA).The effect of the ratio of UPy to HEMA on the properties of WPU-UxHy emulsion was investigated.The molecular structure of the polymer was characterized by transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FT-IR),nuclear magnetic resonance(NMR),thermogravimetric analyzer(TGA)and dynamic thermomechanical analysis(DMA).The kinetics of UV-curing process of WPU-UxHy was studied in situ by real time infrared(real time FT-IR).HEMA gives the system a relatively loose chemical crosslinking network structure,maintaining the overall framework of the cured film,and UPy dimers,urethane groups and urea groups of polyurethane form hydrogen bonds to build a physical crosslinking network.The excellent healing properties of WPU-UxHy were confirmed by scratch healing and tensile properties healing.Dynamic behavior of hydrogen bonds in polymer was analyzed by VT-FTIR,VT-1H NMR and internal friction energy test.In addition,the conductive material was assembled by WPU-UxHy polymer and the conductive filler,which not only has a good mechanical properties and self-healing properties,but also has a good application value in the field of flexible sensors in human motion monitoring experiments2.A self-healing waterborne polyurethane based on "dynamic hard domain" design(WPU-xU)was prepared by introducing the synthesized dihydroxyl monomer(UPy-HDI AMPD)into the side chain of polyurethane through isocyanate reaction.The "dynamic hard domain" formed by the interaction between the assembly structure of the UPy on the side chain and the layered hydrogen bonds(urethane,urea),not only has a positive effect on the mechanical properties,but also contributes to the realization of the good healing ability.At the same time,the soft segment of ether chain can provide enough soft segments in the molecular chain for the polymer.The unique micro-phase separation structure enables the material to exhibit ideal properties such as high mechanical strength,high toughness,resilience and excellent self-healing properties.The effect of the content of UPy-HDI-AMPD on the properties of WPU-xU emulsion was discussed.The structure and composition of the synthesized monomer and the polymer were characterized by TEM,FT-IR,NMR,TGA,DMA,etc.The microstructure and morphology of WPU-xU polymers were analyzed throught X-ray diffraction(XRD)and atomic force microscopy(AFM),and the morphology of phase separation was characterized.The tensile analysis and healing test show that the mechanical strength and self-healing ability of the material are balanced to a certain extent.The healing mechanism of the polymer was characterized by VT-FTIR and VT-1H NMR.The internal friction energy test shows that WPU-xU polymer has excellent impact resistance and resilience.In addition,the conductive material obtained by assembling WPU-xU polymer with conductive filler not only has good mechanical properties and self-healing properties,but also provides a theoretical basis for its monitoring and testing in human motion due to the flexibility and high sensitivity of electrical signal response under different strain tension.The electrical signals of the conductive material when the knuckles and elbows move indicate that it can be used as a wearable device to detect human activities with high sensitivity and reliability.3.The carboxyl group(-COOH)with diethyl amine(-N(CH2CH3)2)can be grfted on the side chain of polyurethane throught isocyanate reaction to form the ion pairs that have a strong electrostatic interaction.These ion pairs interact with weak hydrogen bond of the polyurethane construct an ion hydrogen bonded self-healing polyurethane(PU-ADx)based on a strong/weak hydrogen bond double networks,which has high strength,high tensile and tough.The structure and composition of the synthesized monomer and the polymer were characterized by NMR,FT-IR and elemental analysis(EA),which confirmed the existence of ionic hydrogen bonding.The microstructure and morphology of PU-ADx polymer were analyzed by DMA,XRD and AFM,and the results showed that the structural variation trend of the PU-ADx polymer basically accords with the Eisenberg-Haird-Moore(EHM)ionic structure.According to the results of tensile properties after healing,the material has excellent ambient temperature healing properties,and the polyurethane can be promoted several times by increasing the temperature appropriately.The reversible mechanism of hydrogen bond was characterized by VT-FTIR.According to the internal friction energy test,PU-ADx has a good performance in resilience.Therefore,the conductive material based on PU-ADx polymer not only has good conductivity and healing properties,but also has good stability and repeatability proved by the 2 h tensile test results,which is suitable for practical application.Human motion monitoring results based on the conductive material before and after healing show that the conductive material has excellent healing and stability.