Room temperature self-repairing stretchable transparent electromagnetic shielding material and preparation method thereof

Abstract

The present invention discloses a room temperature self-repairing stretchable transparent electromagnetic shielding material and a preparation method thereof. The method first dissolves aminopropyl-terminated polydimethylsiloxane, hexamethylene diisocyanate, and 4'4-methylenebis(phenyl isocyanate) in a solvent, heats the reaction under a nitrogen atmosphere, and then dries to obtain a polyurea elastomer material with a rapid room temperature self-repairing function. Then, a silver nanowire percolation network is semi-embedded in the polyurea elastomer by a suction filtration transfer method. The stretchable transparent electromagnetic shielding material of the present invention not only has high transparency, high electromagnetic shielding efficiency, and excellent mechanical properties, but also has an excellent room temperature self-repairing function.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials and relates to a room temperature self-repairing stretchable transparent electromagnetic shielding material and a preparation method thereof. Background Art

[0002] Flexible optical electronics (FOEs) have unique advantages, especially their ability to be invisible on exposed areas of the human body (such as the face, neck, and hands), which provides possibilities for many exciting applications. As FOEs develop towards miniaturization and high power density, they will inevitably face the problem of electromagnetic (EM) radiation pollution and interference. Electromagnetic (EM) radiation pollution and interference not only have harmful effects on human health, but also have negative effects on electronic devices. Electromagnetic interference (EMI) shielding materials, as the main components integrated into FOEs, are usually required to work in dynamic application environments with deformation, wear and tear. In addition, ideal EMI shielding materials should also have excellent self-healing ability (Carbon 2020, 166, 56-63), and the healed EMI shielding materials should still have almost fully recovered conductivity and EMI shielding effect (EMI SE) even when stretched again.

[0003] Incorporating conductive fillers into a self-healing stretchable polymer matrix is ​​an effective method for manufacturing self-healing stretchable electromagnetic shielding materials (Matter 2020, 3, 546-557). High electromagnetic shielding efficiency is achieved by loading a large amount of fillers, but the movement of the molecular chain is restricted, resulting in a serious decrease in self-healing efficiency and mechanical compliance, and reducing the transparency of the originally transparent polymer matrix (Compos. B. Eng. 2020, 193, 10815), thereby limiting its application in FOEs. Therefore, it is urgent to develop mechanically flexible, optically transparent, rapidly self-healing and highly efficient electromagnetic shielding materials to protect humans from external stray signals and ensure the operational reliability of FOEs. At present, electromagnetic shielding materials that have the characteristics of self-healing, stretchability, high transparency and high electromagnetic shielding efficiency have not been reported. Summary of the Invention

[0004] The present invention provides a room-temperature self-healing, stretchable, transparent electromagnetic shielding material and its preparation method. This method utilizes a strategy that disrupts crystallization behavior and activates hard-phase hydrogen bonds to produce a colorless, transparent polyurea elastomer with highly dynamic hydrogen bonds. A silver nanowire percolation network is then semi-embedded into the elastomer surface to create the room-temperature self-healing, stretchable, transparent electromagnetic shielding material. The material fully recovers its mechanical and electrical properties within 20 minutes of repair at room temperature, exhibiting an electromagnetic shielding efficiency exceeding 20 dB in both resting and stretched states.

[0005] The room-temperature self-healing, stretchable, transparent electromagnetic shielding material described in this invention is made by semi-embedding a silver nanowire percolation network onto the surface of a polyurea elastomer with highly dynamic hydrogen bonds. The polyurea elastomer, which serves as a matrix, possesses highly dynamic hydrogen bonds, allowing the polymer chains to move rapidly, endowing the matrix with rapid self-healing properties. Broken silver nanowire percolation networks can also rearrange themselves through the dynamic migration of polymer chains during the repair process.

[0006] The structural formula of the polyurea elastomer of the present invention is as follows:

[0007]

[0008] The method for preparing the room temperature self-repairing stretchable transparent electromagnetic shielding material of the present invention comprises the following steps:

[0009] Step 1, under a nitrogen atmosphere, dissolving aminopropyl-terminated polydimethylsiloxane (PDMS) in an organic solvent by stirring to obtain a PDMS solution;

[0010] Step 2: Hexamethylene diisocyanate (HDI) and 4'4-methylenebis(phenyl isocyanate) (MPI) are mixed and dissolved in an organic solvent, and then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture is stirred until uniformly mixed and then reacted to form a polymer solution.

[0011] Step 3: pouring the polymer solution into a mold for molding, and drying to obtain a colorless and transparent polyurea elastomer (PDMS-MPI-HDI) with room temperature self-healing function;

[0012] In step 4, the silver nanowire solution is filtered to form a silver nanowire coating on the filter membrane, the polyurea elastomer is heated, and the filter membrane is covered on the surface of the hot polyurea elastomer and pressed to make the silver nanowire percolation network semi-embedded in the polyurea elastomer, thereby obtaining a room temperature self-healing stretchable transparent electromagnetic shielding material (Ag NWs-m / PDMS-MPI-HDI, where m is the area concentration of silver nanowires).

[0013] Preferably, in step 1, the molecular weight of the PDMS is 3000 to 5000 Da.

[0014] Preferably, in step 2, the total molar amount of hexamethylene diisocyanate and 4'4-methylenebis(phenyl isocyanate) is the same as the molar amount of aminopropyl-terminated PDMS.

[0015] Preferably, in steps 1 and 2, the organic solvent is chloroform, acetone or tetrahydrofuran.

[0016] Preferably, in step 2, the reaction temperature is 55 to -65°C, and the reaction time is 12 to 48 hours.

[0017] Preferably, in step 3, the drying procedure is first drying at room temperature for 6 to 12 hours, and then drying at 60° C. for 12 to 24 hours.

[0018] Preferably, in step 4, the area concentration of the silver nanowires in the silver nanowire coating is 200 to 300 mg / m 2 .

[0019] Preferably, in step 4, the heating temperature is 55-65°C.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) The room temperature self-repairing stretchable transparent electromagnetic shielding material of the present invention has excellent electromagnetic shielding performance and optical properties. The repaired material has an electromagnetic shielding efficiency higher than 20dB in both the resting and stretched states, and the transmittance is higher than 68% at a wavelength of 550nm.

[0022] (2) Compared with general self-repairing elastomeric materials, the room temperature self-repairing stretchable transparent electromagnetic shielding material of the present invention does not require external light, heat or other external stimulation during the repair process, and the repair speed is fast. The mechanical properties can be repaired in 10 minutes at room temperature, and the conductive and electromagnetic shielding properties can be repaired in 20 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Infrared spectra of the room temperature self-healing transparent polyurea elastomer matrix material PDMS-MPI-HDI prepared in Example 1, Example 2, Comparative Example 5 and Comparative Example 6, and the opaque polyurea elastomer material prepared in Comparative Example 1 and Comparative Example 2.

[0024] Figure 2 This is the stress-strain curve of room-temperature self-healing transparent polyurea elastomer matrix material PDMS-MPI-HDI.

[0025] Figure 3 Schematic diagram of the structure of Ag NWs-m / PDMS-MPI-HDI.

[0026] Figure 4 These are scanning electron microscope images of the electromagnetic shielding materials prepared in Example 1 and Comparative Example 6.

[0027] Figure 5 Transparency curves of the electromagnetic shielding materials prepared with the polyurea elastomer matrix material PDMS-MPI-HDI and Example 1, Example 2, Comparative Example 5 and Comparative Example 6.

[0028] Figure 6 These are the electromagnetic shielding curves of the electromagnetic shielding materials prepared with the polyurea elastomer matrix material PDMS-MPI-HDI and Example 1, Example 2, Comparative Example 5 and Comparative Example 6.

[0029] Figure 7 This is a scanning electron microscope image of the cross section of the room temperature self-repairing stretchable transparent electromagnetic shielding material prepared in Example 1.

[0030] Figure 8 These are the electromagnetic shielding curves of the original sample, damaged sample and repaired sample in Example 1 at rest and when stretched 50%.

[0031] Figure 9 Transparency curves of the room temperature self-healing transparent polyurea elastomer matrix material PDMS-MPI-HDI and the opaque polyurea elastomer materials prepared in Comparative Example 1 and Comparative Example 2.

[0032] Figure 10 The differential scanning calorimeter spectra of the room temperature self-healing transparent polyurea elastomer matrix material PDMS-MPI-HDI and the opaque polyurea elastomer materials prepared in Comparative Example 1 and Comparative Example 2.

[0033] Figure 11 Small-angle X-ray scattering spectra of the room-temperature self-healing transparent polyurea elastomer matrix material PDMS-MPI-HDI and the opaque polyurea elastomer materials prepared in Comparative Example 1 and Comparative Example 2.

[0034] Figure 12 Optical photographs and surface and cross-sectional scanning electron microscopy images of Ag NWs-300 / sylgard 184 prepared for Comparative Example 3. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the embodiments and accompanying drawings.

[0036] Example 1

[0037] A method for preparing a room temperature self-repairing stretchable transparent electromagnetic shielding material comprises the following steps:

[0038] Step 1: Under nitrogen atmosphere, 2 mmol of aminopropyl-terminated PDMS with a molecular weight of 3000 Da was dissolved in 15 mL of chloroform by stirring to form a PDMS solution;

[0039] Step 2: 1 mmol of hexamethylene diisocyanate and 1 mmol of 4'4-methylenebis(phenyl isocyanate) were mixed and dissolved in 15 mL of chloroform. The mixture was then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture was stirred until uniformly mixed and reacted at 60°C for 24 hours to generate a polymer PDMS-MPI-HDI solution.

[0040] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60°C for 24 hours to obtain a colorless and transparent polyurea elastomer PDMS-MPI-HDI with room temperature self-healing function;

[0041] Step 4: Dilute 470 μL of the solution with 100 mL of deionized water to a concentration of 0.5 mg / mL. 2 The silver nanowire dispersion was filtered and coated on a polyvinylidene fluoride filter membrane to prepare an area concentration of 200 mg / m 2 Silver nanowire coating;

[0042] Step 5: Heat the polyurea elastomer at 60°C, and cover the filter membrane obtained in step 4 on the polyurea elastomer. After pressing and laminating, tear off the filter membrane to obtain the room temperature self-healing stretchable transparent electromagnetic shielding material Ag NWs-200 / PDMS-MPI-HDI.

[0043] Example 2

[0044] A method for preparing a room temperature self-repairing stretchable transparent electromagnetic shielding material comprises the following steps:

[0045] Step 1: Under nitrogen atmosphere, 2 mmol of aminopropyl-terminated PDMS with a molecular weight of 3000 Da was dissolved in 15 mL of chloroform by stirring to form a PDMS solution;

[0046] Step 2: 1 mmol of hexamethylene diisocyanate and 1 mmol of 4'4-methylenebis(phenyl isocyanate) were mixed and dissolved in 15 mL of chloroform. The mixture was then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture was stirred until uniformly mixed and reacted at 60°C for 24 hours to generate a polymer PDMS-MPI-HDI solution.

[0047] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60°C for 24 hours to obtain a colorless and transparent polyurea elastomer PDMS-MPI-HDI with room temperature self-healing function;

[0048] Step 4: Dilute 705 μL of the solution with 100 mL of deionized water to a concentration of 0.5 mg / mL. 2 The silver nanowire dispersion was filtered and coated on a polyvinylidene fluoride filter membrane to prepare an area concentration of 300 mg / m 2 Silver nanowire coating;

[0049] Step 5: Heat the polyurea elastomer at 60°C, and cover the filter membrane obtained in step 4 on the polyurea elastomer. After pressing and laminating, tear off the filter membrane to obtain the room temperature self-healing stretchable transparent electromagnetic shielding material Ag NWs-300 / PDMS-MPI-HDI.

[0050] like Figure 1 As shown, infrared spectroscopy confirmed that the desired self-healing transparent polyurea elastomer material PDMS-MPI-HDI was successfully prepared.

[0051] like Figure 2 As shown in the figure, PDMS-MPI-HDI can be repaired at room temperature for 10 minutes to basically completely repair the mechanical properties, and has a tensile strength and elongation at break that are basically the same as those of the original sample.

[0052] like Figure 3 As shown, light can pass through the gaps in the silver nanowire network, with only a small amount of light being reflected. The silver nanowire network can still maintain a connected conductive network when the material is stretched.

[0053] like Figure 4 、 Figure 5 and Figure 6 As shown, with the increase of the area concentration of silver nanowires, the silver nanowire network becomes denser, and Examples 1 and 2 have both high transparency and electromagnetic shielding efficiency; Comparative Example 5 has the highest transparency, but the electromagnetic shielding efficiency is too low; Comparative Example 6 has the highest electromagnetic shielding efficiency, but the transparency is too low.

[0054] like Figure 7 and Figure 8 As shown, in Example 1, the silver nanowires are semi-embedded in PDMS-MPI-HDI. This is attributed to the fact that the PDMS-MPI-HDI molecular chains are cross-linked only by hydrogen bonds, which are easily broken and rebuilt, resulting in the silver nanowires being able to easily penetrate and semi-embedded in PDMS-MPI-HDI. During the repair process, the cut silver nanowire network can be reconnected under the drive of the movement of the polymer molecular chains, so that even if the room temperature self-healing stretchable transparent electromagnetic shielding material is damaged, it can still maintain an electromagnetic shielding efficiency of more than 20dB in a 50% stretched state after 20 minutes of repair.

[0055] Comparative Example 1

[0056] Step 1: Under nitrogen atmosphere, 2 mmol of aminopropyl-terminated PDMS with a molecular weight of 3000 Da was dissolved in 15 mL of chloroform by stirring to form a PDMS solution;

[0057] Step 2: Dissolve 2 mmol of hexamethylene diisocyanate in 15 mL of chloroform, then add dropwise to the PDMS solution under a nitrogen atmosphere, stir until the mixture is uniform, and react at 60°C for 24 hours to generate a polymer PDMS-HDI solution;

[0058] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60°C for 24 hours to obtain a partially crystallized white opaque polyurea elastomer material PDMS-HDI.

[0059] Comparative Example 2

[0060] Step 1: Under nitrogen atmosphere, 2 mmol of PDMS was dissolved in 15 mL of chloroform with stirring to form a PDMS solution;

[0061] Step 2: Dissolve 2 mmol of 4'4-methylenebis(phenyl isocyanate) in 15 mL of chloroform and then add the mixture dropwise to the PDMS solution under a nitrogen atmosphere. Stir until the mixture is uniform and react at 60°C for 24 h to generate a polymer PDMS-MPI solution.

[0062] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60° C. for 24 hours to obtain a partially crystallized white opaque polyurea elastomer material PDMS-MPI.

[0063] Comparative Example 3

[0064] Step 1: Mix the basic components of Sylgard 184 and the curing agent in a ratio of 10:1, inject them into a polytetrafluoroethylene mold, and cure them at 60°C for 3 hours to obtain a colorless and transparent chemically cross-linked PDMS elastomer;

[0065] Step 2: Dilute 705 μL of the solution with 100 mL of deionized water to a concentration of 0.5 mg / mL. 2 The silver nanowire dispersion was filtered and coated on a polyvinylidene fluoride filter membrane to prepare an area concentration of 300 mg / m 2 Silver nanowire coating;

[0066] Step 3: Heat the polymer at 60°C and cover the polymer with the filter membrane obtained in step 2. After pressing and fitting, tear off the filter membrane to obtain Ag NWs-300 / sylgard 184 with uneven silver nanowire coating.

[0067] Comparative Example 4

[0068] Step 1: Under nitrogen atmosphere, 2 mmol of aminopropyl-terminated PDMS with a molecular weight of 1000 Da was dissolved in 15 mL of chloroform by stirring to form a PDMS solution;

[0069] Step 2: 1 mmol of hexamethylene diisocyanate and 1 mmol of 4'4-methylenebis(phenyl isocyanate) were mixed and dissolved in 15 mL of chloroform. The mixture was then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture was stirred until uniformly mixed and reacted at 60°C for 24 hours to generate a polymer PDMS-MPI-HDI solution.

[0070] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60°C for 24 hours to obtain a white translucent polyurea elastomer PDMS-MPI-HDI;

[0071] The polyurea elastomer obtained in Comparative Example 4 has low transparency and slow repair speed, and is not suitable for preparing room temperature self-repairing stretchable transparent electromagnetic shielding materials.

[0072] Comparative Example 5

[0073] A method for preparing a room temperature self-repairing stretchable transparent electromagnetic shielding material comprises the following steps:

[0074] Step 1: Under nitrogen atmosphere, 2 mmol of aminopropyl-terminated PDMS with a molecular weight of 3000 Da was dissolved in 15 mL of chloroform by stirring to form a PDMS solution;

[0075] Step 2: 1 mmol of hexamethylene diisocyanate and 1 mmol of 4'4-methylenebis(phenyl isocyanate) were mixed and dissolved in 15 mL of chloroform. The mixture was then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture was stirred until uniformly mixed and reacted at 60°C for 24 hours to generate a polymer PDMS-MPI-HDI solution.

[0076] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60°C for 24 hours to obtain a colorless and transparent polyurea elastomer PDMS-MPI-HDI with room temperature self-healing function;

[0077] Step 4: Dilute 235 μL of the solution with 100 mL of deionized water to a concentration of 0.5 mg / mL. 2 The silver nanowire dispersion was filtered and coated on a polyvinylidene fluoride filter membrane to prepare an area concentration of 100 mg / m 2 Silver nanowire coating;

[0078] Step 5: Heat the polyurea elastomer at 60° C., and cover the polyurea elastomer with the filter membrane obtained in step 4. After laminating and pressing, tear off the filter membrane to obtain the electromagnetic shielding material Ag NWs-100 / PDMS-MPI-HDI.

[0079] Comparative Example 6

[0080] Step 1: Under nitrogen atmosphere, 2 mmol of aminopropyl-terminated PDMS with a molecular weight of 3000 Da was dissolved in 15 mL of chloroform by stirring to form a PDMS solution;

[0081] Step 2: 1 mmol of hexamethylene diisocyanate and 1 mmol of 4'4-methylenebis(phenyl isocyanate) were mixed and dissolved in 15 mL of chloroform. The mixture was then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture was stirred until uniformly mixed and reacted at 60°C for 24 hours to generate a polymer PDMS-MPI-HDI solution.

[0082] Step 3: Pour the polymer solution from step 2 into a mold for molding, first dry it at room temperature for 6 hours, and then dry it at 60°C for 24 hours to obtain a colorless and transparent polyurea elastomer PDMS-MPI-HDI with room temperature self-healing function;

[0083] Step 4: Dilute 940 μL of the solution with 100 mL of deionized water to a concentration of 0.5 mg / mL. 2 The silver nanowire dispersion was filtered and coated on a polyvinylidene fluoride filter membrane to prepare an area concentration of 400 mg / m 2 Silver nanowire coating;

[0084] Step 5: Heat the polyurea elastomer at 60° C., and cover the polyurea elastomer with the filter membrane obtained in step 4. After laminating and pressing, tear off the filter membrane to obtain the electromagnetic shielding material Ag NWs-400 / PDMS-MPI-HDI.

[0085] like Figure 9 As shown, the room temperature self-healing transparent polyurea elastomer matrix material PDMS-MPI-HDI has much higher transparency than the polyurea elastomer matrix materials PDMS-HDI and PDMS-MPI in Comparative Example 1 and Comparative Example 2. The low transparency of Comparative Example 1 and Comparative Example 2 makes them unsuitable for preparing transparent electromagnetic shielding materials.

[0086] like Figure 10 As shown, differential scanning calorimetry analysis shows that PDMS-MPI-HDI has an amorphous structure, while Comparative Examples 1 and 2 exhibit semi-crystalline behavior, so PDMS-MPI-HDI is highly transparent, while PDMS-MPI and PDMS-HDI are basically opaque.

[0087] like Figure 11 As shown, PDMS-MPI-HDI, PDMS-MPI and PDMS-HDI all exhibit isotropic scattering behavior. -1 There is a characteristic peak at , indicating that they are all microphase separation structures, but the peak intensities are different, indicating that the PDMS-MPI and PDMS-HDI hard phases have more obvious crystallization phenomena, indicating that PDMS-MPI and PDMS-HDI are basically opaque.

[0088] like Figure 12As shown, Comparative Example 3 is a chemically cross-linked PDMS elastomer, which has basically no adhesion to silver nanowires. Therefore, the silver nanowires are unevenly distributed on the surface of Comparative Example 3, and some areas even fail to adhere to the silver nanowires. Moreover, the silver nanowire percolation network cannot break the chemical bonds and embed into the chemically cross-linked PDMS elastomer, and only floats on its surface.

Claims

1. Room temperature self-repairing stretchable transparent electromagnetic shielding material, characterized by: The polyurea elastomer is prepared by semi-embedding a silver nanowire percolation network on the surface of the polyurea elastomer with high dynamic hydrogen bonds. The structural formula of the polyurea elastomer is as follows: , prepared by the following steps: Step 1: Under a nitrogen atmosphere, dissolving aminopropyl-terminated PDMS in an organic solvent with stirring to obtain a PDMS solution, wherein the organic solvent is chloroform, acetone or tetrahydrofuran, and the molecular weight of the PDMS is 3000-5000 Da; Step 2: Hexamethylene diisocyanate and 4'4-methylenebis(phenyl isocyanate) are mixed and dissolved in an organic solvent, and then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture is stirred until uniformly mixed and then reacted to form a polymer solution. Step 3: pouring the polymer solution into a mold to form the polymer solution, and drying the mold to obtain a colorless and transparent polyurea elastomer with room temperature self-repairing function; Step 4: Filtering the silver nanowire solution to form a silver nanowire coating on a filter membrane, heating the polyurea elastomer, and covering the filter membrane on the surface of the hot polyurea elastomer and pressing it to make the silver nanowire percolation network semi-embedded in the polyurea elastomer, thereby obtaining a room temperature self-healing stretchable transparent electromagnetic shielding material; In the silver nanowire coating, the area concentration of silver nanowires is 200~300 mg / m 2 .

2. The method for preparing a room temperature self-repairing stretchable transparent electromagnetic shielding material according to claim 1, characterized in that: The following steps are involved: Step 1: Under a nitrogen atmosphere, dissolving aminopropyl-terminated PDMS in an organic solvent with stirring to obtain a PDMS solution, wherein the organic solvent is chloroform, acetone or tetrahydrofuran, and the molecular weight of the PDMS is 3000-5000 Da; Step 2: Hexamethylene diisocyanate and 4'4-methylenebis(phenyl isocyanate) are mixed and dissolved in an organic solvent, and then added dropwise to the PDMS solution under a nitrogen atmosphere. The mixture is stirred until uniformly mixed and then reacted to form a polymer solution. Step 3: pouring the polymer solution into a mold to form the polymer solution, and drying the mold to obtain a colorless and transparent polyurea elastomer with room temperature self-repairing function; Step 4: Filtering the silver nanowire solution to form a silver nanowire coating on a filter membrane, heating the polyurea elastomer, and covering the filter membrane on the surface of the hot polyurea elastomer and pressing it to make the silver nanowire percolation network semi-embedded in the polyurea elastomer, thereby obtaining a room temperature self-healing stretchable transparent electromagnetic shielding material; In the silver nanowire coating, the area concentration of silver nanowires is 200~300 mg / m 2 .

3. The preparation method according to claim 2, characterized in that In steps 1 and 2, the organic solvent is chloroform, acetone or tetrahydrofuran.

4. The preparation method according to claim 2, characterized in that The total molar amount of the hexamethylene diisocyanate and 4'4-methylenebis(phenyl isocyanate) is the same as the molar amount of the aminopropyl-terminated PDMS.

5. The preparation method according to claim 2, wherein In step 2, the reaction temperature is 55~-65°C, and the reaction time is 12~48 h.

6. The preparation method according to claim 2, wherein In step 3, the drying procedure is to first dry at room temperature for 6 to 12 h, and then dry at 60 °C for 12 to 24 h.

7. The preparation method according to claim 2, wherein In step 4, the heating temperature is 55-65°C.

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