A crystalline hyperbranched multi-arm copolymer, a self-supporting graphene film and preparation and application thereof

Abstract

The application discloses a crystalline hyperbranched multi-arm copolymer, a self-supporting graphene film and a preparation and application thereof. The crystalline hyperbranched multi-arm copolymer is prepared by the following method: a hyperbranched macromolecular initiator is obtained by using an alpha-diimine palladium catalyst to catalyze ethylene and a bromine-containing functional monomer in a one-step "chain removal" copolymerization in a water-free grade solvent; and then the hyperbranched macromolecular initiator is used to initiate atom transfer radical polymerization of an acrylate functional monomer to obtain the crystalline hyperbranched multi-arm copolymer. The crystalline hyperbranched multi-arm copolymer, graphite powder and a solvent are mixed in proportion, graphene initial dispersion liquid is obtained through ultrasonic and centrifugal separation, and then the self-supporting graphene film is obtained through filtration, elution and drying in sequence. The application provides an application of the self-supporting graphene film as an electrothermal film, and the self-supporting graphene film has excellent electrothermal performance and mechanical strength.

Description

Technical Field

[0001] The present invention relates to a crystalline hyperbranched multi-arm copolymer, a self-supporting graphene film, and preparation and application thereof. Background Art

[0002] Graphene has a unique two-dimensional nanostructure and excellent electrical, thermal, and mechanical properties. Graphene films made from graphene nanosheets can efficiently and quickly convert electrical energy into thermal energy through the Joule heating effect, demonstrating excellent electric heating capabilities. Compared to traditional electric heating technologies, graphene electric heating films offer advantages such as high electric-to-heat conversion efficiency, fast response, and energy conservation. Furthermore, they are readily available, lightweight, and flexible, offering significant application prospects in a wide range of fields, including de-icing, intelligent driving, healthcare, defense, military, industrial, and civilian applications.

[0003] Existing methods for preparing graphene electrothermal films primarily fall into two categories: First, graphene films are grown on metal substrates using CVD technology, and then transferred to various polymer film surfaces through processes such as etching and transfer printing to obtain polymer-film-based graphene electrothermal films. This method facilitates the production of graphene films with larger lateral dimensions, but the preparation process involves high temperatures, expensive equipment, and complex graphene transfer processes, resulting in high production costs and a disadvantage for large-scale applications. Second, graphene oxide is produced by oxidizing natural graphite, and then subjected to vacuum filtration, dip coating, blade coating, drop coating, spin coating, and high-temperature or chemical reduction to produce self-supporting or polymer-film-based graphene electrothermal films. The graphene oxide used in this method can be stably dispersed in aqueous media, allowing graphene electrothermal films to be produced through a variety of liquid-phase processing methods, facilitating large-scale preparation and application. However, the graphene redox process often involves toxic chemicals, high temperatures, and complex steps, and the resulting graphene has numerous structural defects, which are detrimental to the electrothermal performance of the film. Therefore, how to start from the abundant natural graphite resources, prepare high-performance graphene electric heating films through green, environmentally friendly, simple and feasible processes, and promote their large-scale preparation and application, is still an important key technology that needs to be researched and broken through in this field.

[0004] Furthermore, with the development of advanced information technologies such as 5G, various electronic components are becoming increasingly miniaturized, high-frequency, and multifunctional. Their significantly increased power density makes efficient heat dissipation a common key requirement. To address this need, a series of studies on the preparation and application of high-performance thermally conductive interface materials have been widely reported, primarily including thermally conductive gaskets, thermally conductive gels, thermally conductive adhesives, thermally conductive films, and thermally conductive phase change materials. Among them, graphene thermally conductive films, made with graphene as the primary raw material, have outstanding application advantages in this field for the following reasons: First, graphene materials can be prepared from abundant natural graphite resources; second, graphene has a unique two-dimensional nanostructure, exhibiting excellent anisotropic thermal conductivity; and third, graphene films are lightweight and flexible, better suited to the application needs of electronic components for thinner, lighter, and more flexible applications. Therefore, the development of technologies for the preparation and application of graphene thermally conductive films is of great significance in addressing the heat dissipation needs of electronic components.

[0005] To date, many methods for preparing graphene thermally conductive films have been developed and reported, primarily falling into two categories: The first involves growing a graphene film on various metal substrates via chemical vapor deposition (CVD) and then transferring it to a specific polymer film via transfer or etching, resulting in a polymer-based graphene thermally conductive film. This method involves high temperatures, expensive equipment, and complex graphene transfer processes, resulting in high production costs and hindering large-scale applications. The second method involves oxidizing graphite to produce graphene oxide, which is then processed through vacuum filtration, dip coating, blade coating, drop coating, spin coating, and high-temperature or chemical reduction treatment to produce a graphene thermally conductive film. This method allows for the production of graphene thermally conductive films in a variety of ways via liquid-phase processing. While this method facilitates large-scale applications, the graphene redox process often involves toxic chemicals, high temperatures, and complex steps. Furthermore, the resulting graphene has numerous structural defects, which negatively impacts its thermal conductivity. In addition, with the increasing prevalence and in-depth application of electronic information technology, the interface shapes of electronic components have become more complex and diverse. There is an urgent need to develop graphene flexible thermal conductive films with shape memory function that can adapt to complex interface shapes. However, the research and application of this type of technology are rarely reported. Summary of the Invention

[0006] The first object of the present invention is to provide a crystalline hyperbranched multi-arm copolymer with strong crystallization ability.

[0007] The second object of the present invention is to provide a method for preparing a self-supporting graphene film using the crystalline hyperbranched multi-arm copolymer. This method has significant advantages such as abundant raw material sources, simple preparation process, mild conditions, and controllable and adjustable properties.

[0008] The third object of the present invention is to provide a self-supporting graphene film.

[0009] A fourth object of the present invention is to provide the use of the self-supporting graphene film as an electric heating film, which has both excellent electric heating performance and mechanical strength.

[0010] A fifth object of the present invention is to provide an application of the self-supporting graphene film as a thermally conductive film, which has both shape memory and anisotropic thermal conductivity functions.

[0011] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a crystalline hyperbranched multi-arm copolymer, which is prepared by the following method: using an α-diimine palladium catalyst to catalyze the one-step "chain removal" copolymerization of ethylene and a bromine-containing functional monomer in an anhydrous solvent to obtain a hyperbranched macromolecular initiator; then using the hyperbranched macromolecular initiator to initiate atom transfer radical polymerization of an acrylate functional monomer to obtain a crystalline hyperbranched multi-arm copolymer;

[0013] The structure of the bromine-containing functional monomer is shown below:

[0014]

[0015] The acrylate functional monomer is selected from one of the following compounds: hexadecyl acrylate, tetradecyl acrylate, octadecyl acrylate, and behenyl acrylate;

[0016]

[0017] Preferably, the α-diimine palladium catalyst is selected from α-diimine palladium catalyst 1 or 2 having the following structure:

[0018]

[0019] Both of the above can be synthesized in the laboratory according to the following literature:

[0020] [1] Johnson LK, Killian CM, Brookhart MJAm.Chem.Soc., 1995, 117, 6414; [2] Johnson LK, Mecking S., Brookhart MJAm.Chem.Soc., 1996, 118, 267.

[0021] Preferably, the anhydrous solvent is selected from one of the following: dichloromethane, chlorobenzene, chloroform, preferably anhydrous dichloromethane.

[0022] Preferably, the bromine-containing functional monomer can be synthesized in the laboratory according to the literature (Matyjaszewski K., Gaynor SG, Kulfan A., Podwika M. Macromolecules, 1997, 30, 5192).

[0023] Preferably, in the one-step "chain removal" copolymerization system, the feed concentration of the α-diimine palladium catalyst is 0.5 to 50 g / L, preferably 2 to 20 g / L, based on the total volume of the anhydrous solvent, and the feed concentration of the bromine-containing functional monomer is 0.05 to 10 M, preferably 0.1 to 2 M, based on the total volume of the anhydrous solvent.

[0024] Preferably, the temperature of the one-step "chain removal" copolymerization is 5 to 35° C., preferably 15 to 25° C.; the ethylene pressure is 0.05 to 0.5 MPa, preferably 0.1 MPa; and the copolymerization time is 0.5 to 48 h, preferably 2 to 24 h.

[0025] Preferably, the purification of the hyperbranched macromolecular initiator is carried out according to the following steps:

[0026] (a) After the polymerization reaction is completed, the reaction solution is exposed to air to terminate the reaction;

[0027] (b) removing the solvent by blowing with cold air to obtain a preliminary polymerization product;

[0028] (c) adding an appropriate amount of THF to dissolve the product, then adding a small amount of concentrated HCl and hydrogen peroxide solution, and dissolving the residual palladium particles of catalyst A by stirring or ultrasound;

[0029] (d) removing the solvent by blowing with cold air, adding an appropriate amount of THF to dissolve the product again to form a saturated solution, adding a large amount of methanol to precipitate the product, and removing the upper solution to obtain a polymer product; repeating this step 2 to 4 times;

[0030] (e) The obtained product is vacuum dried at 50-80° C. to a constant weight to obtain a hyperbranched macromolecular initiator.

[0031] Preferably, the atom transfer radical polymerization is specifically as follows: under the protection of an inert gas (nitrogen, argon or other inert gas), a hyperbranched macromolecular initiator, an acrylate functional monomer, anhydrous toluene as a solvent, pentamethyldiethylenetriamine (PMDETA) or 2,2'-bipyridine (bpy) as a ligand, and cuprous bromide (CuBr) as a catalyst are added to a reaction vessel, and after the addition, atom transfer radical polymerization is carried out. After the polymerization is completed, a crystalline hyperbranched multi-arm copolymer is obtained by separation and purification; the feed concentration of the hyperbranched macromolecular initiator in the polymerization system is 0.001 to 0.1 mol / L (preferably 0.001 to 0.01 mol / L) based on the molar concentration of the bromine groups contained therein, and the initial feed molar concentration ratio of the hyperbranched macromolecular initiator, the acrylate functional monomer, the ligand, and the catalyst is 1:200 to 800:0.5 to 4:0.5 to 2, preferably 1:400 to 600:4:2.

[0032] As a further preference, the polymerization temperature of the atom transfer radical polymerization is controlled at 45 to 100° C., more preferably 70 to 80° C.; the reaction time is controlled at 0.5 to 24 h, more preferably 0.5 to 5 h.

[0033] As a further preference, the separation and purification of the crystalline hyperbranched multi-arm copolymer is carried out according to the following steps:

[0034] (a) After the reaction is completed, the reaction solution is exposed to air to terminate the reaction, and a preliminary product is obtained by purging;

[0035] (b) adding an appropriate amount of THF to dissolve the product, then adding a large amount of methanol to precipitate the product, and obtaining a polymer product through separation;

[0036] (c) Repeat step (b) 3 to 5 times, and dry the resulting product at 25 to 80° C. to a constant weight to obtain a final polymer product.

[0037] The crystalline hyperbranched multi-arm copolymer prepared by the invention has a crystallinity of 30 to 80%, preferably 70 to 80%.

[0038] In a second aspect, the present invention provides a method for preparing a self-supporting graphene film, comprising the following steps:

[0039] The crystalline hyperbranched multi-arm copolymer, graphite powder and solvent described in the first aspect are mixed in proportion, and an initial graphene dispersion is obtained by ultrasonic and centrifugal separation, which is then filtered, washed and dried in sequence to obtain a self-supporting graphene film.

[0040] Preferably, the graphite powder is selected from one of the following: natural phosphorus flake graphite or expanded graphite, preferably natural phosphorus flake graphite; the particle size of the graphite powder is controlled in the range of 100 to 1000 mesh, preferably 100 to 500 mesh.

[0041] Preferably, the solvent is one of the following analytically pure or chemically pure solvents: chloroform, THF, acetone, dichloromethane, preferably THF or chloroform.

[0042] Preferably, the initial charge mass of graphite powder is 1 to 200 mg / mL, preferably 2 to 20 mg / mL, based on the total volume of the solvent; the charge mass ratio of the crystalline hyperbranched multi-arm copolymer to the graphite powder is 0.001 to 2, more preferably 0.01 to 2, and further preferably 0.1 to 2.

[0043] Preferably, the ultrasound can be carried out in a container of glass, plastic, metal or other suitable materials; the ultrasound method can be an ultrasound pool or a pulse method, preferably an ultrasound pool method; the ultrasound temperature is controlled at 15-45°C, preferably 25-35°C; the ultrasound power is controlled at 20-100W, preferably 40-80W; and the ultrasound duration is controlled at 12-120h, preferably 24-48h.

[0044] Preferably, the centrifugal separation is carried out at a rotation speed of 500 to 8000 rpm, preferably 2000 to 5000 rpm; the centrifugal time is controlled at 5 to 120 min, preferably 25 to 60 min.

[0045] Preferably, the filtration is performed using a filter membrane with an average pore size of 50 to 300 nm and a material of polytetrafluoroethylene, polyvinylidene fluoride, nylon or polypropylene, preferably a filter membrane with a pore size of 100 to 200 nm and a material of polytetrafluoroethylene or nylon.

[0046] Preferably, in the self-supporting graphene film, the content of the crystalline hyperbranched multi-arm copolymer is controlled to be 5 to 50% by mass, preferably 20 to 40% by mass.

[0047] Preferably, the thickness of the self-supporting graphene film is controlled to be 25 to 500 μm.

[0048] In a third aspect, the present invention provides a self-supporting graphene film prepared according to the preparation method described in the second aspect.

[0049] In a fourth aspect, the present invention provides the use of the self-supporting graphene film described in the third aspect as an electric heating film.

[0050] In a fifth aspect, the present invention provides the use of the self-supporting graphene film described in the third aspect as a thermally conductive film.

[0051] Compared with the prior art, the present invention has the following outstanding advantages and beneficial effects:

[0052] First, the present invention independently designs and synthesizes a crystalline hyperbranched multi-arm copolymer, which is composed of a polyethylene core in the form of a hyperbranched chain and linear polymer side chains. It not only has a hyperbranched chain morphology, but also has strong crystallization ability.

[0053] Secondly, the present invention uses independently designed and synthesized hyperbranched multi-arm copolymers to effectively promote efficient liquid-phase exfoliation of graphite in common low-boiling-point organic solvents through the principle of non-covalent CH-π interaction, thereby obtaining a graphene dispersion. On this basis, a graphene film can be obtained through simple vacuum filtration, avoiding steps such as graphene transfer and oxidation-reduction, and does not involve the use of toxic chemical reagents, high temperatures, and special equipment. It has the advantages of simple process and low preparation cost, and is conducive to large-scale application.

[0054] Third, the synthesis of the hyperbranched multi-arm copolymer described herein primarily uses ethylene as a raw material, with a small amount of functional monomers such as hexadecyl acrylate also being conventional chemical reagents. Subsequent steps utilize natural graphite powder or expanded graphite and conventional organic solvents as primary raw materials. Therefore, the present invention offers the significant advantage of readily available raw materials, which is also beneficial for subsequent applications.

[0055] Fourth, the present invention fully utilizes the multifunctional properties of crystalline hyperbranched multi-arm copolymers, namely, promoting liquid-phase exfoliation of graphene, realizing non-covalent modification of the graphene surface, and promoting the stable assembly of graphene sheets to obtain a self-supporting graphene high-performance multifunctional film with sufficient mechanical strength. This feature makes the preparation process completely controllable, which is conducive to the flexible regulation of film performance.

[0056] Fifth, the graphene described in the present invention is obtained through a liquid phase exfoliation process. Compared with redox graphene, it has fewer structural defects and better performance. At the same time, with the help of the unique structural design of the crystalline hyperbranched multi-arm copolymer, the mechanical strength of the graphene film can be effectively improved through its crystallization assembly. The graphene film has both excellent electrothermal performance and mechanical strength, and can be used as a graphene electrothermal film, which is conducive to its further practical application.

[0057] Sixth, the present invention utilizes the hyperbranched multi-arm copolymer to not only effectively promote liquid-phase exfoliation of natural graphite to obtain low-defect graphene, but also allows the copolymer to be stably adsorbed on the surface of the resulting graphene based on the principle of non-covalent CH-π interaction. Through the crystallization of the polymer side chains in the copolymer structure, the resulting graphene can be stably assembled to obtain a flexible, high-strength, self-supporting graphene film. Furthermore, the copolymer crystallization can impart shape memory to the resulting graphene film. Furthermore, vacuum filtration can achieve the alignment of graphene nanosheets, thereby imparting anisotropic thermal conductivity to the resulting film. Therefore, through the method described in the present invention, the resulting graphene film has excellent flexibility, strength, anisotropic thermal conductivity, and shape memory, and can be used as a thermally conductive film to better meet the interfacial heat dissipation requirements of various electronic components. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 : Schematic diagram of the preparation steps of the self-supporting graphene electric heating film of the present invention.

[0059] Figure 2 :(a) DSC cooling curves of HBPE@PHDA (Example 1) and HBPE@Br (Comparative Example 1); (b) DSC secondary heating curves of HBPE@PHDA (Example 1) and HBPE@Br (Comparative Example 1); (c) Polarizing microscope photos of HBPE@PHDA (Example 1) at 25 and 40°C, respectively.

[0060] Figure 3 :(a) Appearance photo of the sample of Comparative Example 1; (b) Appearance photo of the sample of Example 1; (c) Surface SEM photo of the sample of Example 1; (d) SEM photo of the cross-section of the sample of Example 1; (e) SEM photo of the local cross-section of the sample of Example 1; (f) Stress-strain curve of the sample of Example 1.

[0061] Figure 4 :(a) Electric heating / cooling curves of the sample in Example 1 at different voltages; (b) Infrared thermal images corresponding to various heating times of the sample in Example 1 at a driving voltage of 10V.

[0062] Figure 5 : Electric heating temperature rise / cooling curves of the samples of Example 2 and Comparative Example 2 at a driving voltage of 9V.

[0063] Figure 6 : Electric heating temperature rise / cooling curves of the samples of Example 3 and Comparative Example 2 at a driving voltage of 9V.

[0064] Figure 7 :(a) Comparison of steady-state temperature of samples in Example 4 and Comparative Example 2 at 9V; (b) Comparison of electrothermal heating rate of samples in Example 4 and Comparative Example 2 at 9V.

[0065] Figure 8 :(a) Comparison of steady-state temperature of samples in Example 5 and Comparative Example 2 at 10V; (b) Comparison of electrothermal heating rate of samples in Example 5 and Comparative Example 2 at 10V; (c) Comparison of tensile strength of samples in Example 5 and Comparative Example 2.

[0066] Figure 9 : (a) Appearance of the graphene film obtained in Example 6; (b) Stress-strain curve of the graphene film obtained in Example 6; (c) Appearance of the graphene film obtained in Comparative Example 3; (d) Thermal conductivity results of the graphene film obtained in Example 6; (e) Evaluation of the shape memory performance of the graphene film obtained in Example 6.

[0067] Figure 10 : (a) Thermal conductivity results of the graphene film obtained in Example 7; (b) Method for evaluating the vertical heat transfer performance of the graphene film obtained in Example 7; (c) Trend of surface temperature change of the graphene film obtained in Example 7 with test time (vertical heat transfer); (d) Method for evaluating the in-plane heat transfer performance of the graphene film obtained in Example 7; (eg) Infrared thermal images of the graphene film obtained in Example 7 at different test times (in-plane heat transfer).

[0068] Figure 11 : Evaluation of the application performance of the graphene film obtained in Example 8 in mobile phone heat dissipation.

[0069] Figure 12 : (a) Thermal conductivity of the graphene film obtained in Example 9; (b) Thermal conductivity of the graphene film obtained in Comparative Example 4.

[0070] Figure 13 : (a) Thermal conductivity of the graphene film obtained in Example 10; (b) Thermal conductivity of the graphene film obtained in Comparative Example 4. DETAILED DESCRIPTION

[0071] The present invention will be further described below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0072] Example 1, Comparative Example 1

[0073] 1. Sample preparation

[0074] (1) The sample of Example 1 was prepared according to the following steps:

[0075] Step 1: Under ethylene protection, anhydrous grade solvent (dichloromethane, 20.0 mL) and functional monomer (its structural formula is shown in the attached Figure 1, 1.6 g / 6.0 mmol, feed concentration is 0.30 M) is added to a 100 mL Schlenk flask, stirred for 10 min to form a uniform solution and kept constant at 25° C.; then 0.20 g of catalyst (α-diimine palladium catalyst 1, feed concentration is 10.0 g / L) is added, and the polymerization is continuously stirred for 24 h at an ethylene pressure of 0.1 MPa and 25° C.; after the reaction, the solvent is removed by air purge, and the resulting product is dissolved in a small amount of THF. After adding a few drops of HCl and H2O2 solution, the residual palladium particles are removed by stirring, and the solvent is purged again. The resulting product is dissolved in a small amount of THF and precipitated by methanol. This process is repeated 2 to 3 times. The resulting product is vacuum dried at 60° C. for 24 h to obtain a hyperbranched macromolecular initiator (HBPE@Br, 2.3 g).

[0076] Furthermore, under nitrogen protection, 0.10 g HBPE@Br (containing 0.069 mmol Br), 12.3 g functional monomer (hexadecyl acrylate, HDA, 41.4 mmol) and 12.3 mL of anhydrous grade toluene were sequentially added into a 250 mL Schlenk flask and stirred at room temperature to form a homogeneous solution; then 47.8 mg ligand PMDETA (0.276 mmol) was added, stirred for 0.5 h, and then freeze-thawed three times to remove residual oxygen; then the temperature was raised to 75°C, 19.8 mg catalyst CuBr (0.138 mmol) was added, and the polymerization was continued with stirring for 1 h; after the polymerization was completed, the solvent was removed by air purging, and the resulting product was dissolved in a small amount of THF and precipitated by adding methanol. This process was repeated 2 to 3 times, and the product was dried in vacuum at 60°C for 24 h to obtain a crystalline hyperbranched multi-arm copolymer (HBPE@PHDA, about 0.5 g). ([-Br]:[HDA]:[PMDETA]:[CuBr]=1:600:4:2)

[0077] Step 2: In a 100 mL cylindrical glass bottle, graphite powder (natural flake graphite, 640 mg), HBPE@PHDA (80 mg) and solvent (chloroform, 80 mL) were added in sequence (the initial concentration of graphite powder was 8 mg / mL, and the polymer / graphite mass ratio was 0.125). After sealing, the bottle was placed in an ultrasonic tank (KQ-250V, output power 250 W) and ultrasonicated continuously at room temperature for 48 hours. The obtained product was centrifuged at 4000 rpm for 45 minutes to remove unexfoliated graphite particles. About 70 mL of the supernatant was carefully collected to obtain the graphene initial dispersion. The above process was repeated to obtain a large-volume graphene initial dispersion. An appropriate amount was taken from the sample and vacuum filtered using a 0.20 μm nylon membrane. The sample was then washed with chloroform solvent. The number of washes was controlled to regulate the residual proportion of the polymer in the graphene film. After drying at room temperature, a self-supporting graphene film sample I (thickness of approximately 75.0 μm) with a graphene ratio of 75 wt% was obtained, which was recorded as GH75.

[0078] (2) Comparative Example 1

[0079] HBPE@Br was obtained according to step 1 of Example 1, and a graphene film sample was obtained according to step 2 of Example 1 by replacing HBPE@PHDA with HBPE@Br.

[0080] 2. Characterization and testing

[0081] Differential scanning calorimetry (DSC) analysis was performed using a DSC214 differential scanning calorimeter (Netzsch, Germany) in a nitrogen atmosphere. The sample size was 5–10 mg. The sample was first heated from room temperature to 100°C at a rate of 10°C min-1 and kept constant for 3 min to eliminate the thermal history. The sample was then cooled to -20°C at the same rate, and the cooling curve was recorded. The sample was then heated from room temperature to 100°C at the same rate, and the heating curve was recorded. Polarizing microscope (POM) images were recorded using a BX53M-P hot stage polarizing microscope (Olympus, Japan). The sample was placed on the hot stage surface with a glass slide, first heated from room temperature to 60°C at a constant rate, and then cooled to room temperature at the same rate. The camera shooting interval was 1 s. Scanning electron microscope (SEM) images were taken by Nano Nova The graphene film was obtained using a 450 field emission scanning electron microscope (FEI, USA), and the test sample was obtained by brittle fracture after liquid nitrogen freezing; the stress-strain curve of the graphene film was obtained by testing using an A-7000-SU1 electronic universal material testing machine (Guangzhou High-speed Railway Testing Instrument Co., Ltd.), with a tensile rate of 1 mm / min, a clamp spacing of 10 mm, and a test temperature of room temperature. The sample specifications were: length 30 mm, width 10 mm, and thickness 50 μm; the electrothermal properties of the graphene film were evaluated by using an infrared thermometer to test the change of the film surface temperature with heating time under a DC voltage.

[0082] 3. Comparison and analysis of test results

[0083] like Figure 2 (a) and (b) show that there is an obvious endothermic / exothermic phenomenon on the DSC curve of HBPE@PHDA (Example 1), indicating that the hyperbranched multi-arm copolymer has a strong crystallization ability. Figure 2 The heat of fusion data (126.8 J / g) for the HBPE@PHDA sample (Example 1) measured in (b), combined with that for HAD (166.5 J / g), indicate that the crystallinity of the HBPE@PHDA sample reaches 76.2%. In contrast, the DSC curve for HBPE@Br (Comparative Example 1) shows no endothermic or exothermic behavior, indicating that this hyperbranched macroinitiator lacks crystallization capability. This is due to the incorporation of the crystallizing polyhexadecyl acrylate (PHDA) into the HBPE structure. Figure 2 (c) further provides polarizing microscope photos of the above-mentioned HBPE@PHDA sample at 25 and 40°C, which shows that the sample has an obvious spherulite structure at room temperature, while the crystalline structure disappears due to melting at higher temperatures, which once again confirms that the sample has strong crystallization ability.

[0084] Figure 3 (a) and (b) respectively give the appearance of the graphene films prepared in Comparative Example 1 and Example 1. As shown in the figure, the mechanical strength of the graphene film obtained in Comparative Example 1 is very poor and it cannot exist independently and can only exist under the support of a filter membrane. The graphene film obtained in Example 1 can be peeled off from the surface of the filter membrane and exists as a self-supporting film, showing significantly improved mechanical strength and excellent flexibility. This is because in the film structure obtained in Example 1, the crystalline hyperbranched multi-arm copolymer HBPE@PHDA adsorbed on the graphene surface effectively promotes the close stacking and assembly of the graphene sheets in the system through mutual crystallization and entanglement, thereby forming a macroscopic film of a certain strength. This can be seen from Figure 3 The SEM results of the sample shown in (c)-(e) were confirmed. Figure 3 (f) shows the stress-strain curve of the graphene film prepared in Example 1, which shows that the tensile strength of the film reaches 3.0 MPa and the elongation at break is approximately 2%, which once again confirms that the graphene film obtained in Example 1 has significantly improved mechanical strength.

[0085] Figure 4 (a) shows the electrothermal heating / cooling curves of the film obtained in Example 1 at different drive voltages. The graph shows that the film reaches a steady-state temperature within a relatively short period of time (approximately 30 seconds), reaching steady-state temperatures of 31.6, 43.5, and 58.5°C for drive voltages of 6, 9, and 10 V, respectively. This demonstrates that the graphene film has an excellent electrothermal response rate and adjustable steady-state temperature, demonstrating its superior electrothermal performance. Figure 4 (b) shows infrared thermal images of the film at different heating times at 10V, demonstrating uniform heating performance across different locations. These results demonstrate that, compared to Comparative Example 1, the graphene film prepared in Example 1 significantly improves its mechanical strength by introducing crystallizing PHDA side chains into the HBPE structure, while also exhibiting excellent electrothermal performance.

[0086] Example 2, Comparative Example 2

[0087] 1. Sample preparation

[0088] (1) The sample of Example 2 was prepared according to the following steps:

[0089] Step 1: proceed with reference to Step 1 in Example 1, except that the functional monomer hexadecyl acrylate is replaced by octadecyl acrylate.

[0090] Step 2: proceed as per step 2 in Example 1.

[0091] (2) The sample of Comparative Example 2 was prepared according to the following steps:

[0092] The above-mentioned Example 1 was referred to, and the obtained graphene film sample was used as Comparative Example 2.

[0093] 2. Characterization and testing

[0094] Refer to the method described in Example 1 and Comparative Example 1 above.

[0095] 3. Comparison and analysis of test results

[0096] Figure 5 The electrothermal heating / cooling curves of the samples from Example 2 and Comparative Example 2 were compared at 9V. As shown, the electrothermal performance of the two samples is similar: the steady-state temperature is approximately 45°C, reaching steady-state temperature in approximately 20 seconds. This demonstrates that graphene films with excellent electrothermal performance can be produced using the method of the present invention by substituting octadecyl acrylate for hexadecyl acrylate during the synthesis of the hyperbranched multi-arm copolymer.

[0097] Example 3, Comparative Example 2

[0098] 1. Sample preparation

[0099] (1) The sample of Example 3 was prepared according to the following steps:

[0100] Step 1: proceed as in Step 1 of Example 1, except that the monomer feed ratio ([-Br]:[HDA]:[PMDETA]:[CuBr]) was adjusted from 1:600:4:2 to 1:400:4:2.

[0101] Step 2: proceed as per step 2 in Example 1.

[0102] (2) The sample of Comparative Example 2 was prepared according to the following steps:

[0103] The above-mentioned Example 1 was referred to, and the obtained graphene film sample was used as Comparative Example 2.

[0104] 2. Characterization and testing

[0105] Refer to the method described in Example 1 and Comparative Example 1 above.

[0106] 3. Comparison and analysis of test results

[0107] Figure 6 The electrothermal conversion performance of Example 3 and Comparative Example 2 samples was compared (driving voltage was 9V). As shown in the figure, the sample of Example 3 can reach a steady-state temperature of 42°C in about 30s, and can quickly recover to room temperature within 20s after the voltage is cut off, indicating that it has excellent electrothermal conversion performance. By contrast with Comparative Example 2, it can be found that the electrothermal conversion performance of the sample of Example 3 is substantially close to that of Comparative Example 2. This shows that, in the process of synthesizing hyperbranched multi-arm copolymers, the monomer feed ratio can be adjusted, and a graphene film with excellent electrothermal performance can be obtained by the method described in the present invention within a reasonable ratio range.

[0108] Example 4, Comparative Example 2

[0109] 1. Sample preparation

[0110] (1) The sample of Example 4 was prepared according to the following steps:

[0111] Step 1: proceed as per step 1 in Example 1.

[0112] Step 2: The process was carried out in accordance with Step 2 of Example 1. The differences were that the solvent H used in ultrasonication was replaced by THF instead of chloroform, the initial concentration of graphite powder was changed from 8 mg / mL to 15 mg / mL, and the polymer / graphite mass ratio was changed from 0.125 to 0.20.

[0113] (2) The sample of Comparative Example 2 was prepared according to the following steps:

[0114] The above-mentioned Example 1 was referred to, and the obtained graphene film sample was used as Comparative Example 2.

[0115] 2. Characterization and testing

[0116] Refer to the method described in Example 1 and Comparative Example 1 above.

[0117] 3. Comparison and analysis of test results

[0118] Figure 7 The electrothermal conversion performance of the samples of Example 4 and Comparative Example 2 was compared (driving voltage was 9V). The results in the figure show that the steady-state temperatures of the samples of Example 4 and Comparative Example 2 can reach approximately 50 and 45°C, respectively, and the heating rates are both close to 5.0°C / s. This shows that both samples have rapid electrothermal conversion capabilities despite being at a relatively low driving voltage (only 9V), and can meet the needs of applications such as health therapy. This shows that in the graphene film preparation process described in the present invention, by adjusting the type of graphene liquid-phase exfoliation solvent and the ultrasonic initial feed ratio, within the ratio range provided by the present invention, a graphene electrothermal film with better performance can be obtained.

[0119] Example 5, Comparative Example 2

[0120] 1. Preparation of samples

[0121] (1) Preparation of sample of Example 5 was carried out according to the following steps:

[0122] Step 1: Refer to Step 1 of Example 1.

[0123] Step 2: Refer to Step 2 of Example 1. The difference is that the 0.20 μm nylon membrane used in the suction filtration is replaced by a PTFE membrane with a pore size of 0.10 μm; the mass percentage of the polymer in the obtained graphene film is replaced by 60% from 75%. (2) Preparation of sample of Comparative Example 2 was carried out according to the following steps:

[0124] Refer to the aforementioned Example 1. The obtained graphene film sample is used as Comparative Example 2.

[0125] 2. Characterization and testing

[0126] Refer to the methods described in the aforementioned Example 1 and Comparative Example 1.

[0127] 3. Comparison and analysis of test results

[0128] Figure 8 The electrocaloric conversion performance (driving voltage is 10 V) and mechanical strength of the samples of Example 5 and Comparative Example 2 are compared. The results in the figure show that the steady-state temperature of the samples of Example 5 and Comparative Example 2 can reach approximately 60°C, and the temperature rise rate is close to 5.0°C / s or so, indicating that the two samples have a fast electrocaloric conversion capability at a low driving voltage (only 10 V), which can meet the application requirements of fast and energy-saving environmental temperature regulation. This shows that according to the filter membrane specifications provided by the present application, the graphene film with better mechanical strength and electrocaloric conversion performance can be successfully prepared according to the method.

[0129] Example 6, Comparative Example 3

[0130] 1. Preparation of samples

[0131] (1) The preparation of the graphene film sample of Example 6 is the same as Example 1.

[0132] (2) The preparation of the graphene film sample of Comparative Example 3 is the same as Comparative Example 1.

[0133] 2. Characterization and testing

[0134] The stress-strain curve of the graphene film was obtained by testing with an A-7000-SU1 electronic universal material testing machine (Guangzhou High-speed Railway Testing Instrument Co., Ltd.). The tensile rate was 1 mm / min, the clamp spacing was 10 mm, the test temperature was room temperature, and the sample specifications were: length 30 mm, width 10 mm, and thickness 50 μm. The thermal conductivity (λ) of the graphene film was tested according to formula (1):

[0135] λ=α×ρ×C P (1)

[0136] Wherein, α is the thermal diffusivity, measured by LFA-467 laser thermal conductivity meter (Netzsch, Germany). The test sample is a disc specimen with a diameter of 12.5 mm (vertical test) or 25 mm (horizontal test) and a thickness of about 75-80 μm; ρ is the sample density, measured by ME 204 densitometer (Mettler Toledo, Switzerland). The sample is a 1 cm × 1 cm square sheet; C P The specific heat of the sample was measured by a DSC214 differential scanning calorimeter. 5-10 mg of sample powder was taken and heated at a rate of 10 °C min under N2 protection. -1 The test was conducted by heating the temperature from 0°C to 60°C.

[0137] The shape memory properties of the graphene film were tested by the following steps: the sample was first heat-treated in a 75°C oven for 10 minutes, then bent into a "U" shape, and further maintained in this shape for 15 minutes at room temperature under the action of an external force. The external force was then removed, and the sample was placed on a heating table. The shape of the sample was recorded using an infrared thermograph. At this time, the bending angle of the sample was the initial angle (θ1). The heating table was turned on and heated from 30°C to 50°C at a constant heating rate to restore the shape of the sample. The sample shape was continuously photographed, the recovery angle (θ2) was recorded, and the shape recovery rate (R) of the film was calculated according to formula (2). r ):

[0138]

[0139] 3. Comparison and analysis of test results

[0140] like Figure 9 (a) shows that the graphene film prepared by Example 6 can be directly removed from the surface of the filter membrane and exists as a self-supporting film, showing excellent bendability. Figure 9 As shown in (b), the tensile strength of the film can reach 3.0MPa; in contrast, Figure 9 (c) shows that the graphene thermal conductive film prepared by Comparative Example 3 can only be attached to the surface of the filter membrane and exhibits low mechanical strength, making it difficult to exist independently. Figure 9(d) shows that the in-plane thermal conductivity of the graphene film obtained in Example 6 can reach 37.0 W m -1 K -1 , showing excellent in-plane thermal conductivity, while its vertical thermal conductivity is only 1.0 W m -1 K -1 , showing that the film has outstanding anisotropic thermal conductivity, with an anisotropic thermal conductivity ratio of 37. In addition, Figure 9 (e) shows the shape memory recovery process of the sample from Example 6. This sample can be bent into any shape at 75°C and maintains a stable shape after cooling. Further treatment at 80°C allows for rapid shape recovery within 40 seconds, with a shape recovery rate approaching 100%, demonstrating outstanding shape memory properties. Overall, these results demonstrate that the process described in Example 6 can successfully produce a multifunctional graphene film with excellent flexibility, strength, shape memory, and anisotropic thermal conductivity.

[0141] Example 7, Comparative Example 3

[0142] 1. Sample preparation

[0143] (1) The sample of Example 7 was prepared according to the following steps:

[0144] Step 1: proceed as per Step 1 in Example 6.

[0145] Step 2: proceed as in Step 2 of Example 6. The difference is that the mass percentage of the polymer in the obtained composite film is adjusted from the original 75% to 60% by controlling the number of washing times during the filtration step.

[0146] (2) The sample of Comparative Example 3 was prepared according to the following steps:

[0147] Refer to the above-mentioned Comparative Example 3.

[0148] 2. Characterization and testing

[0149] Refer to the methods described in Example 6 and Comparative Example 3 above.

[0150] 3. Comparison and analysis of test results

[0151] Figure 10 (a) compares the in-plane and perpendicular thermal conductivity data of the sample obtained in Example 7, which are 29.4 and 0.8 W m -1 K -1 , the anisotropy ratio reaches 36.75, indicating that the sample has excellent in-plane thermal conductivity and outstanding anisotropic thermal conductivity characteristics. Figure 10 (b) gives the method for evaluating the vertical heat transfer performance of the sample obtained in Example 7, and the relevant data results are summarized in Figure 10(c); As the test time increases, the surface temperature of the sample gradually increases. For a test time of 55s, the surface temperature of the film can reach nearly 55°C, indicating that it has a certain vertical heat transfer performance. Figure 10 (d) gives the evaluation method of the heat transfer performance of the graphene composite film obtained in Example 7 in the in-plane direction, and the corresponding infrared thermal images of the sample surface at each test time are shown in FIG. Figure 10 (e)-(g); The figure shows that the surface temperature of the obtained graphene thermal conductive film can reach 53.5°C in a test time of only about 4 seconds, indicating that it has excellent in-plane thermal conductivity and also shows that it has significant anisotropic thermal conductivity characteristics. In addition, compared with the sample in Comparative Example 3, the graphene film obtained in Example 7 has better mechanical strength and can exist independently in the form of a self-supporting film; it also exhibits excellent shape memory function. The above results show that a graphene film with both shape memory and anisotropic thermal conductivity can be obtained by the method described in Example 7.

[0152] Example 8, Comparative Example 4

[0153] 1. Sample preparation

[0154] (1) The sample of Example 8 was prepared according to the following steps:

[0155] Step 1: proceed with the same method as Step 1 in Example 6, except that the monomer feed ratio ([-Br]:[HDA]:[PMDETA]:[CuBr]) was adjusted from 1:600:4:2 to 1:400:4:2.

[0156] Step 2: proceed as per Step 2 in Example 6.

[0157] (2) The sample of Comparative Example 4 was prepared according to the following steps:

[0158] Refer to the above-mentioned Example 6.

[0159] 2. Characterization and testing

[0160] Refer to the methods described in Example 6 and Comparative Example 3 above.

[0161] 3. Comparison and analysis of test results

[0162] Figure 11The heat dissipation performance of the graphene film obtained in Example 8 was investigated in a mobile phone. As shown in the figure, without the graphene film, the surface temperature of the back of the phone increased significantly with charging time. After 30 minutes of charging, the temperature reached 43.1°C, a 14.9°C increase from the initial temperature. However, after using the graphene film in Example 8, the corresponding surface temperature was 32.8°C, a 3.5°C increase from the initial temperature, demonstrating the excellent in-plane heat dissipation performance of the graphene film. Furthermore, similar to Examples 6 and 7, the graphene thermally conductive film obtained in Example 8 can also be used as a free-standing film, exhibiting significantly improved mechanical strength compared to Comparative Example 3 while maintaining good flexibility. It also exhibits excellent shape memory, with its shape recovery rate recovering to 100% within 30 seconds when treated above 80°C.

[0163] Example 9, Comparative Example 4

[0164] 1. Sample preparation

[0165] (1) The sample of Example 9 was prepared by referring to the above Example 6, except that the solvent H used for liquid phase stripping in step 2 was replaced by THF instead of chloroform.

[0166] (2) The sample of Comparative Example 4 was prepared by referring to the above Example 6.

[0167] 2. Characterization and testing

[0168] Refer to the methods described in Example 6 and Comparative Example 3 above.

[0169] 3. Comparison and analysis of test results

[0170] Figure 12 The thermal conductivity of the graphene film obtained in Example 9 and Comparative Example 4 was compared. Figure 12 (a) corresponds to the result of the film obtained in Example 9. This sample was prepared by liquid phase exfoliation in THF and its in-plane thermal conductivity was as high as 29.0 W m -1 K -1 , and the vertical thermal conductivity is 0.85W m -1 K -1 , the anisotropy ratio is 34.11, indicating that the sample also has excellent anisotropic thermal conductivity. Figure 12 (b) corresponds to the graphene film obtained in Comparative Example 4, which was prepared by liquid phase exfoliation in chloroform. The in-plane and out-of-plane thermal conductivities of this sample were 37 and 1.0 W m -1 K -1The anisotropy ratio was 37, generally close to the results of Example 9. Furthermore, both Example 9 and Comparative Example 4 exhibited shape memory, excellent flexibility, and mechanical strength. These results demonstrate that a variety of solvents can be used for liquid-phase exfoliation during the preparation of graphene films, with THF being an effective solvent.

[0171] Example 10, Comparative Example 4

[0172] 1. Sample preparation

[0173] (1) The sample of Example 10 was prepared according to the following steps:

[0174] Step 1: Refer to the sample preparation step (1) in Example 6.

[0175] Step 2: The sample preparation step (2) in Example 6 was referred to. The difference was that the 0.20 μm nylon membrane used for filtration was replaced with a PTFE membrane with a pore size of 0.10 μm.

[0176] (2) The sample of Comparative Example 4 was prepared according to the following steps:

[0177] The above-mentioned Example 6 was referred to, and the obtained graphene film sample was used as Comparative Example 4.

[0178] 2. Characterization and testing

[0179] Refer to the methods described in Example 6 and Comparative Example 3 above.

[0180] 3. Comparison and analysis of test results

[0181] Figure 13 The thermal conductivity of the graphene thermal conductive films obtained in Example 10 and Comparative Example 4 was compared. The preparation steps and processes of the two samples were the same, except that the specifications of the filter membranes used in the preparation of the graphene membranes were different. Example 10 used a 0.1 μm PTFE membrane, while Comparative Example 4 used a 0.2 μm nylon membrane. Figure 13 (a) shows the in-plane and perpendicular thermal conductivities of the graphene thermally conductive film obtained in Example 10, which are 32.4 and 1.05 W m -1 K -1 , with an anisotropy ratio of 30.9, demonstrating excellent anisotropic thermal conductivity; this result is generally similar to that of the sample obtained in Comparative Example 4. Furthermore, the membranes obtained in Example 10 and Comparative Example 4 can both function as self-supporting membranes and exhibit stable shape memory properties. These results demonstrate that the methods described herein can be used to prepare graphene thermally conductive membranes exhibiting both anisotropic thermal conductivity and shape memory properties using both types of membranes.

Claims

1. A crystalline hyperbranched multi-arm copolymer, characterized in that: The crystalline hyperbranched multi-arm copolymer is prepared by the following method: using an α-diimine palladium catalyst to catalyze the "chain removal" copolymerization of ethylene and a bromine-containing functional monomer in an anhydrous solvent in a one-step process to obtain a hyperbranched macromolecular initiator; then using the hyperbranched macromolecular initiator to initiate atom transfer radical polymerization of an acrylate functional monomer, wherein the feed concentration of the hyperbranched macromolecular initiator in the polymerization system is 0.001 to 0.1 mol / L based on the molar concentration of the bromine groups contained therein, and the initial feed molar concentration ratio of the hyperbranched macromolecular initiator to the acrylate functional monomer is 1:200 to 800, thereby obtaining a crystalline hyperbranched multi-arm copolymer; The structure of the bromine-containing functional monomer is shown below: The acrylate functional monomer is selected from one of the following compounds: hexadecyl acrylate, tetradecyl acrylate, octadecyl acrylate, and behenyl acrylate.

2. The crystalline hyperbranched multi-arm copolymer according to claim 1, wherein: The α-diimine palladium catalyst is selected from the α-diimine palladium catalyst 1 or 2 whose structure is shown below: ； The anhydrous solvent is selected from one of the following: dichloromethane, chlorobenzene, and chloroform.

3. The crystalline hyperbranched multi-arm copolymer according to claim 1 or 2, wherein: In the one-step "chain removal" copolymerization system, the feed concentration of the α-diimine palladium catalyst is 0.5-50 g / L based on the total volume of the anhydrous solvent, and the feed concentration of the bromine-containing functional monomer is 0.05-10 M based on the total volume of the anhydrous solvent.

4. The crystalline hyperbranched multi-arm copolymer according to claim 3, wherein: In the one-step "chain removal" copolymerization system, the feed concentration of the α-diimine palladium catalyst is 2-20 g / L based on the total volume of the anhydrous grade solvent.

5. The crystalline hyperbranched multi-arm copolymer according to claim 3, wherein: In the one-step "chain removal" copolymerization system, the feed concentration of the bromine-containing functional monomer is 0.1-2 M based on the total volume of the anhydrous grade solvent.

6. The crystalline hyperbranched multi-arm copolymer according to claim 1, wherein: The temperature of the one-step "chain removal" copolymerization is 5-35°C; the ethylene pressure is 0.05-0.5 MPa; and the copolymerization time is 0.5-48 h.

7. The crystalline hyperbranched multi-arm copolymer according to claim 6, wherein: The temperature of the one-step "chain removal" copolymerization is 15-25°C; the ethylene pressure is 0.1 MPa; and the copolymerization time is 2-24 h.

8. The crystalline hyperbranched multi-arm copolymer according to claim 1, wherein: The atom transfer radical polymerization specifically comprises the following steps: under the protection of an inert gas, adding a hyperbranched macromolecular initiator, an acrylate functional monomer, anhydrous toluene as a solvent, pentamethyldiethylenetriamine or 2,2'-bipyridine as a ligand, and cuprous bromide as a catalyst into a reaction vessel; performing atom transfer radical polymerization after the addition is completed; the polymerization temperature of the atom transfer radical polymerization is controlled at 45-100° C., the reaction time is controlled at 0.5-24 h, and after the polymerization is completed, a crystalline hyperbranched multi-arm copolymer is obtained through separation and purification; in the polymerization system, the initial molar concentration ratio of the hyperbranched macromolecular initiator, the acrylate functional monomer, the ligand, and the catalyst is 1:200-800:0.5-4:0.5-2.

9. The crystalline hyperbranched multi-arm copolymer according to claim 1, wherein: The crystallinity of the crystalline hyperbranched multi-arm copolymer is 30-80%.

10. The crystalline hyperbranched multi-arm copolymer according to claim 9, wherein: The crystallinity of the crystalline hyperbranched multi-arm copolymer is 70-80%.

11. A method for preparing a self-supporting graphene film, characterized in that: The preparation method comprises the following steps: The crystalline hyperbranched multi-arm copolymer according to any one of claims 1 to 10, graphite powder and solvent are mixed in proportion, subjected to ultrasonication and centrifugal separation to obtain an initial graphene dispersion, and then filtered, washed and dried in sequence to obtain a self-supporting graphene film.

12. The preparation method according to claim 11, wherein: In the self-supporting graphene film, the content of the crystalline hyperbranched multi-arm copolymer is controlled to be 5-50% by mass.

13. The preparation method according to claim 12, wherein: In the self-supporting graphene film, the content of the crystalline hyperbranched multi-arm copolymer is controlled to be 20-40% by mass.

14. A self-supporting graphene film prepared according to the preparation method according to any one of claims 11 to 13.

15. Use of the self-supporting graphene film according to claim 14 as an electric heating film.

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