Flexible conductive composite materials based on boronic ester dynamic covalent bonds, their preparation methods and applications

Abstract

This invention relates to the field of flexible sensor technology, and discloses a flexible conductive composite material based on boron ester dynamic covalent bonds, its preparation method, and its application. The preparation method includes: dissolving a macromolecular diol, a boron ester diol, and a diisocyanate in a polar organic solvent; adding a catalyst and stirring; carrying out a polyaddition reaction under an inert atmosphere to obtain a polymer solution; then adding a conductive material and a small molecule polyol; ultrasonically stirring; curing the reaction; and removing the solvent to obtain the flexible conductive composite material based on boron ester dynamic covalent bonds. The flexible conductive composite material provided by this invention exhibits excellent mechanical properties and is completely degradable in a water / organic solvent mixture, solving the problem of incomplete degradation of existing flexible materials. When the flexible conductive composite material is used to fabricate a flexible wearable strain sensor, it exhibits good electrochemical stability and signal response performance.

Description

Technical Field

[0001] This invention relates to the field of flexible sensor technology, and in particular to flexible conductive composite materials based on boron ester dynamic covalent bonds, their preparation methods, and applications. Background Technology

[0002] As human life becomes increasingly intelligent, flexible electronic devices possess enormous market potential, particularly in the biomedical field for wearable physiological monitoring devices, implantable medical electronic devices, and electronic skin. However, the rapid development of the electronics industry has also brought significant challenges to e-waste management. According to the United Nations, tens of millions of tons of e-waste are discarded worldwide each year. Only a small amount of e-waste is recycled, while the majority is sent directly to landfills or incinerators. The heavy metals in this waste pollute soil and groundwater, leading to severe resource waste and environmental pollution. Therefore, there is an urgent need for a biodegradable matrix material suitable for flexible electronic products to alleviate this problem.

[0003] Traditional flexible electronics typically use recyclable materials primarily made of thermoplastic polymers. These polymers have internal molecular chains linked by non-covalent bonds, softening and flowing upon heating, making them easy to repair, reshape, and recycle. Their industrial manufacturing technology is also flexible and convenient, but their stability is relatively poor. Unlike thermoplastic polymers, traditional thermosetting polymers are chemically cross-linked by covalent bonds, possessing excellent mechanical properties, thermal stability, and corrosion resistance, and are widely used in various fields. However, once traditional thermosetting resins have cured, they cannot be reprocessed, making related welding, repair, and recycling extremely difficult, resulting in serious resource waste and environmental pollution problems.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a flexible conductive composite material based on boron ester dynamic covalent bonds, its preparation method and application, aiming to solve the problems of existing flexible materials being unable to completely degrade and polluting the environment and having poor stability.

[0006] To overcome the aforementioned problems of existing flexible materials, the inventors conceived of using glass-like polymers as matrix materials to prepare flexible conductive composite materials. Leveraging the characteristic of introducing dynamic covalent bonds into a thermosetting network, these materials can maintain a constant crosslinking density while initiating exchange reactions through external stimuli. Under normal conditions, glass-like polymers are no different from traditional thermosetting resins, but they can undergo structural adhesion, shape reshaping, and material recycling upon reaction activation. This offers promising prospects for constructing degradable and stable flexible composite materials and their application in the fabrication of flexible wearable sensors.

[0007] The technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a flexible conductive composite material based on boron ester dynamic covalent bonds, comprising the steps of:

[0009] S1. A macromolecular diol, boron ester diol and diisocyanate are dissolved in a polar organic solvent to form a mixed solution. A catalyst is added to the mixed solution and stirred. A polyaddition reaction is carried out under an inert atmosphere to obtain a polymer solution.

[0010] S2. Add conductive material and small molecule polyol to the polymer solution, stir ultrasonically, pour into a mold for curing reaction, remove solvent, and obtain the flexible conductive composite material based on boron ester dynamic covalent bond.

[0011] Optionally, the macromolecular diol includes one or more of polyethylene glycol, polyester polyol, polypropylene glycol, polytetrahydrofuran polyol, polycarbonate polyol, polycaprolactone polyol, and hydroxyl-terminated polydimethylsiloxane.

[0012] Optionally, the borate ester diol has any one of the chemical structural formulas shown in formulas (I) to (XI):

[0013]

[0014] Optionally, the diisocyanate is one or more of aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. Specifically, the diisocyanate may be selected from isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, etc., but is not limited thereto.

[0015] Optionally, the catalyst is selected from one or more of dimethylcyclohexylamine, dibutyltin dilaurate, triazine trimerizing catalyst, stannous octoate, and dibutyltin maleate, but is not limited thereto.

[0016] Optionally, the conductive material includes one or more of polyacetylene, polypyrrole, polyaniline, polythiophene, graphene, metal nanowires, metal nanoparticles, and carbon nanotubes, but is not limited thereto.

[0017] Optionally, the polyol small molecule includes one or more of glycerol, trimethylolpropane, hexanetriol and pentaerythritol, but is not limited thereto.

[0018] Optionally, the molar ratio of the total amount of alcohol hydroxyl groups in the macromolecular diol, borate diol and small molecule polyol to the molar ratio of isocyanate groups in the diisocyanate is 1:(0.9 to 1.4).

[0019] Optionally, the mass of the catalyst accounts for 0.05 to 5% of the theoretical mass of the polymer, and the mass of the conductive material accounts for 1 to 25% of the theoretical mass of the polymer, wherein the theoretical mass of the polymer is equal to the sum of the masses of the macromolecular diol, the borosilicate diol, the diisocyanate, and the polyol small molecules.

[0020] Optionally, in step S1, the step of adding a catalyst to the mixed solution and stirring, and carrying out the polyaddition reaction under an inert atmosphere, includes: adding the catalyst to the mixed solution and stirring until homogeneous, and then carrying out the polyaddition reaction at 60-90°C for 2-12 hours in a nitrogen or argon atmosphere.

[0021] In step S2, optionally, the ultrasonic stirring step includes ultrasonic stirring at room temperature for 1 to 3 hours.

[0022] Optionally, the curing reaction temperature is 60–90°C, and the curing reaction time is 6–24 hours.

[0023] In a second aspect, the present invention provides a flexible conductive composite material based on boron ester dynamic covalent bonds, which is prepared by the method for preparing the flexible conductive composite material based on boron ester dynamic covalent bonds.

[0024] A third aspect of the present invention provides an application of the aforementioned flexible conductive composite material based on boron ester dynamic covalent bonds in the fabrication of flexible wearable sensors.

[0025] Beneficial effects:

[0026] This invention uses a polyurethane-based glass matrix with dynamic covalent bonds of boron esters as the matrix material and prepares a flexible conductive composite material by filling it with conductive materials. This effectively improves the stability between the conductive material and the matrix material, as well as the uniformity of the conductive material distribution. The flexible conductive composite material exhibits strong self-healing ability and mechanical properties. When the material breaks, it self-heals under heating conditions with almost no impact on its original mechanical and sensing properties, making it well-suited for applications requiring frequent stretching. When the material is discarded, it exhibits good degradation rate in a mixed solution of water and polar solvents, allowing for efficient and simple recycling of the polyurethane-based glass matrix and conductive materials under mild conditions, enabling efficient recycling and reuse of the resin matrix and conductive materials. Therefore, the recyclability of the flexible conductive composite material prepared by this invention can significantly reduce electronic waste and its environmental impact, while also lowering manufacturing costs. Furthermore, when the flexible conductive composite material is used to prepare flexible wearable strain sensors, it exhibits good electrochemical stability and signal response performance. Attached Figure Description

[0027] Figure 1This is a macroscopic image of the flexible conductive composite material based on boron ester dynamic covalent bonds prepared in Example 1 of the present invention.

[0028] Figure 2 The relative resistance change of the flexible conductive composite material based on boron ester dynamic covalent bonds prepared in Example 1 of this invention under different strains. Detailed Implementation

[0029] This invention provides a flexible conductive composite material based on boron ester dynamic covalent bonds, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0031] This invention provides a method for preparing a flexible conductive composite material based on boron ester dynamic covalent bonds, comprising the following steps:

[0032] S1. A macromolecular diol, boron ester diol and diisocyanate are dissolved in a polar organic solvent to form a mixed solution. A catalyst is added to the mixed solution and stirred. A polyaddition reaction is carried out under an inert atmosphere to obtain a polymer solution.

[0033] S2. Add conductive material and small molecule polyol to the polymer solution, stir ultrasonically, pour into a mold for curing reaction, remove solvent, and obtain the flexible conductive composite material based on boron ester dynamic covalent bond.

[0034] In some embodiments, the macromolecular diol includes one or more of polyethylene glycol, polyester polyol, polypropylene glycol, polytetrahydrofuran polyol, polycarbonate polyol, polycaprolactone polyol, and hydroxyl-terminated polydimethylsiloxane.

[0035] In some embodiments, the borate ester diol has any one of the chemical structural formulas shown in formulas (I) to (XI):

[0036]

[0037] In some embodiments, the diisocyanate is one or more of aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates. Specifically, the diisocyanate may be selected from isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, etc., but is not limited thereto.

[0038] In some embodiments, the catalyst is selected from one or more of dimethylcyclohexylamine, dibutyltin dilaurate, triazine trimerizing catalyst, stannous octoate, and dibutyltin maleate, but is not limited thereto.

[0039] In some embodiments, the conductive material includes, but is not limited to, one or more of polyacetylene, polypyrrole, polyaniline, polythiophene, graphene, metal nanowires, metal nanoparticles, and carbon nanotubes.

[0040] In some embodiments, the polyol small molecule includes one or more of glycerol, trimethylolpropane, hexanetriol, and pentaerythritol, but is not limited thereto.

[0041] In some embodiments, the molar ratio of the total amount of alcohol hydroxyl groups contained in the macromolecular diol, borate diol and small molecule polyol to the molar ratio of isocyanate groups contained in the diisocyanate is 1:(0.9 to 1.4).

[0042] In some embodiments, the catalyst accounts for 0.05–5% of the theoretical mass of the polymer, and the conductive material accounts for 1–25% of the theoretical mass of the polymer. The theoretical mass of the polymer is equal to the sum of the masses of the macromolecular diol, the borosilicate diol, the diisocyanate, and the small polyol molecules. In the embodiments of this invention, the raw material components and their proportions involved in the preparation of the flexible composite material can be controllably adjusted, making the performance of the prepared flexible conductive composite material controllable.

[0043] In step S1, in some embodiments, the step of adding a catalyst to the mixed solution and stirring, and carrying out the polyaddition reaction under an inert atmosphere, includes: adding the catalyst to the mixed solution and stirring until homogeneous, and then carrying out the polyaddition reaction at 60-90°C for 2-12 hours in a nitrogen or argon atmosphere.

[0044] In step S2, in some embodiments, the ultrasonic stirring step includes ultrasonic stirring at room temperature for 1 to 3 hours.

[0045] In some embodiments, the curing reaction is carried out at a temperature of 60–90°C for 6–24 hours. Typically, the curing reaction is performed in a polytetrafluoroethylene (PTFE) mold.

[0046] This invention provides a flexible conductive composite material based on boron ester dynamic covalent bonds, prepared by the method described above. This flexible conductive composite material exhibits strong self-healing ability and excellent mechanical properties. When the material breaks, it can self-heal under heating conditions with almost no impact on its original mechanical and sensing properties, making it well-suited for applications requiring frequent stretching. When discarded, the flexible conductive composite material shows good degradation rate in a water / polar solvent mixture, allowing for efficient and simple recycling of the polyurethane-based glass matrix and its conductive materials under mild conditions, achieving efficient recycling and reuse of the resin matrix and conductive materials. When used to prepare flexible wearable strain sensors, it exhibits good electrochemical stability and signal response performance. Therefore, the recyclability of the flexible conductive composite material prepared by this invention can significantly reduce electronic waste and its environmental impact, and also lower manufacturing costs.

[0047] This invention provides an application of the flexible conductive composite material based on boron ester dynamic covalent bonds in the fabrication of a flexible wearable sensor. The flexible wearable sensor can be used as a strain or pressure sensor to monitor human respiration, heartbeat, or movement.

[0048] The following detailed description uses specific examples.

[0049] Example 1

[0050] 397 mg of borate diol (as shown in Formula VII), 600 mg of polyethylene glycol (PEG) (Mn = 600) and 1167 g of isophorone diisocyanate were dissolved in 10 ml of N,N-dimethylformamide, 6 mg of dibutyltin dilaurate was added, and the mixture was stirred thoroughly until a homogeneous solution was formed. The mixture was reacted at 70 °C under a nitrogen atmosphere for 6 h to obtain a polyurethane solution.

[0051] 120 mg of carbon nanotubes and 221 mg of trimethylolpropane were added to the polyurethane solution, and the mixture was ultrasonically stirred at room temperature for 2 hours to obtain a homogeneous solution. The homogeneous solution was poured into a polytetrafluoroethylene mold, and the reaction was continued at 80°C for 6 hours. Then, the solvent was removed under vacuum at 90°C for 12 hours to obtain a flexible conductive composite material based on the dynamic covalent bonds of boron esters. Figure 1 As shown, this flexible conductive composite material exhibits excellent mechanical properties under both bending and stretching. The relative resistance change of the flexible conductive composite material under different strains was also tested, and the results are as follows. Figure 2 As shown, it can be concluded that the resistance / original resistance of the flexible conductive composite material increases with increasing strain.

[0052] The prepared flexible conductive composite material was cut open and molded at 130℃ / 2MPa for 40 minutes. It was observed that the damaged conductive composite material re-healed, restoring its complete sensing capability and mechanical integrity. Simultaneously, the relative resistance change of the self-healing conductive composite material under different strains was tested, and the results were consistent with those of the original sample.

[0053] Recycling of flexible conductive composite materials

[0054] Two g of the material was immersed in 10 ml of DMF / H2O (v / v, 5:1) and heated and stirred at 120 °C for 3 h to degrade the polymer matrix into oligomers soluble in the degradation solution, causing the carbon nanotubes to sink to the bottom of the solution. The degraded solution and carbon nanotubes were then mixed and transferred to a mold, and heated in an oven at 100 °C for 3 h to completely remove the solvent, yielding a recovered conductive composite material sample. The relative resistance change of the recovered flexible conductive composite material under different strains was tested, and the results were consistent with those of the original sample.

[0055] Example 2

[0056] 520 mg of borate diol (as shown in Formula IV), 1000 mg of PEG (Mn = 1000) and 882 g of hexamethylene diisocyanate were added to 12 ml of N,N-dimethylformamide, 7 mg of dibutyltin dilaurate was added, and the mixture was stirred thoroughly until a homogeneous solution was formed. The mixture was reacted at 70 °C under a nitrogen atmosphere for 7 h to obtain a polyurethane solution.

[0057] 200 mg of silver nanoparticles and 18.4 mg of glycerol were added to the above polyurethane solution, and the mixture was ultrasonically stirred at room temperature for 2 hours to obtain a homogeneous solution. The homogeneous solution was poured into a polytetrafluoroethylene mold and reacted at 70 °C for 8 hours. Then, the solvent was removed under vacuum at 90 °C for 18 hours to obtain the flexible conductive composite material based on boron ester dynamic covalent bonds. The relative resistance change of the conductive composite material under different strains was tested.

[0058] The aforementioned flexible conductive composite material was cut and molded at 120℃ / 2.55MPa for 60 minutes. The damaged conductive composite material healed itself, restoring its complete sensing capability and mechanical integrity. Simultaneously, the relative resistance change of the self-healing conductive composite material under different strains was tested, and the results were consistent with the original sample.

[0059] Recycling of flexible conductive composite materials

[0060] Two g of flexible conductive composite material was immersed in 15 ml of DMF / H2O (v / v, 2:1) and heated and stirred at 125 °C for 2.5 h. This degraded the polymer matrix into oligomers soluble in the degradation solution, causing the silver nanoparticles to sink to the bottom of the solution. The degraded solution and silver nanoparticles were then mixed and transferred to a mold, and heated in an oven at 110 °C for 3 h. After this process, the solvent was completely removed, yielding a recovered conductive composite material sample. Simultaneously, the relative resistance change of the recovered flexible conductive composite material under different strains was tested, and the results were consistent with those of the original sample.

[0061] Example 3

[0062] 397 mg of borate diol (as shown in Formula VII) and 1000 mg of PEG (M n =1000) and 1167g of isophorone diisocyanate were dissolved in 15ml of N,N-dimethylformamide, 10mg of stannous octoate was added, and the mixture was stirred thoroughly until a homogeneous solution was formed. The reaction was carried out at 80℃ and under a nitrogen atmosphere for 6h to obtain a polyurethane solution.

[0063] 210 mg of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) and 170 mg of pentaerythritol were added to the above polyurethane solution, and the mixture was ultrasonically stirred at room temperature for 2 h to obtain a homogeneous solution. The homogeneous solution was poured into a polytetrafluoroethylene mold, and the reaction was continued at 80 °C for 6 h. Then, the solvent was removed under vacuum at 90 °C for 12 h to obtain the flexible conductive composite material based on boron ester dynamic covalent bonds. The relative resistance change of the flexible conductive composite material under different strains was tested.

[0064] The prepared flexible conductive composite material was cut open and molded at 120℃ / 1.5MPa for 60 min. The damaged conductive composite material re-healed, restoring its complete sensing capability and mechanical integrity. The relative resistance change of the self-healing conductive composite material under different strains was tested, and the results were consistent with those of the original sample.

[0065] Recycling of flexible conductive composite materials

[0066] Two g of the material was immersed in 10 ml of DMF / H2O (v / v, 4:1) and heated and stirred at 120 °C for 2 h to degrade the polymer matrix into oligomers soluble in the degradation solution. The degraded solution was then transferred to a mold and heated to 90 °C in an oven for 5 h until the solvent was completely removed, yielding a recovered conductive composite material sample. The relative resistance change of the recovered conductive composite material under different strains was consistent with that of the original sample.

[0067] The flexible conductive composite material based on boron ester dynamic covalent bonds prepared in Examples 1-3 is cut into rectangular strips, conductive silver paste is coated at both ends of the strips, and they are assembled with copper wires to obtain a wearable sensor. This flexible wearable sensor can be used as a strain or pressure sensor to monitor human respiration, heartbeat, or movement.

[0068] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a flexible conductive composite material based on boron ester dynamic covalent bonds, characterized in that, Including the following steps: S1. A macromolecular diol, borate diol, and diisocyanate are dissolved in a polar organic solvent to form a mixed solution. A catalyst is added to the mixed solution and stirred. A polyaddition reaction is carried out under an inert atmosphere to obtain a polymer solution. S2. Add conductive material and small molecule polyol to the polymer solution, stir ultrasonically, pour into a mold for curing reaction, remove solvent, and obtain the flexible conductive composite material based on boron ester dynamic covalent bond; The macromolecular diols include one or more of polyethylene glycol, polyester polyols, polypropylene glycol, polytetrahydrofuran polyols, polycarbonate polyols, polycaprolactone polyols, and hydroxyl-terminated polydimethylsiloxanes. The borate ester diol has any one of the chemical structural formulas shown in formulas (III) to (XI): The small molecule polyols include one or more of glycerol, trimethylolpropane, hexanetriol, and pentaerythritol.

2. The method for preparing the flexible conductive composite material based on boron ester dynamic covalent bonds according to claim 1, characterized in that, The diisocyanate is one or more of aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates; the catalyst is selected from one or more of dimethylcyclohexylamine, dibutyltin dilaurate, triazine trimerizing catalyst, stannous octoate, and dibutyltin maleate.

3. The method for preparing the flexible conductive composite material based on boron ester dynamic covalent bonds according to claim 1, characterized in that, The conductive material includes one or more of polyacetylene, polypyrrole, polyaniline, polythiophene, graphene, metal nanowires, metal nanoparticles, and carbon nanotubes.

4. The method for preparing the flexible conductive composite material based on boron ester dynamic covalent bonds according to any one of claims 1 to 3, characterized in that, The molar ratio of the total number of alcohol hydroxyl groups in the macromolecular diol, borate diol, and small molecule polyol to the isocyanate groups in the diisocyanate is 1:(0.9-1.4); the mass of the catalyst accounts for 0.05-5% of the theoretical mass of the polymer, and the mass of the conductive material accounts for 1-25% of the theoretical mass of the polymer, wherein the theoretical mass of the polymer is equal to the sum of the masses of the macromolecular diol, the borate diol, the diisocyanate, and the small molecule polyol.

5. The method for preparing the flexible conductive composite material based on boron ester dynamic covalent bonds according to claim 1, characterized in that, In step S1, the step of adding a catalyst to the mixed solution and stirring, and carrying out the polyaddition reaction under an inert atmosphere, includes: adding the catalyst to the mixed solution and stirring until homogeneous, and then carrying out the polyaddition reaction at 60-90°C for 2-12 hours in a nitrogen or argon atmosphere.

6. The method for preparing the flexible conductive composite material based on boron ester dynamic covalent bonds according to claim 1, characterized in that, In step S2, the ultrasonic stirring step includes: ultrasonic stirring at room temperature for 1 to 3 hours; and / or, the curing reaction temperature is 60 to 90°C, and the curing reaction time is 6 to 24 hours.

7. A flexible conductive composite material based on boron ester dynamic covalent bonds, characterized in that, It is prepared by the method for preparing flexible conductive composite material based on boron ester dynamic covalent bonds as described in any one of claims 1 to 6.

8. The application of the flexible conductive composite material based on boron ester dynamic covalent bonds as described in claim 7 in the preparation of flexible wearable sensors.

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