A macromolecular silane surface-modified thermally conductive powder, its preparation method and application

Abstract

This invention discloses a macromolecular silane surface-modified thermally conductive powder, its preparation method, and its application. The preparation method of the macromolecular silane surface-modified thermally conductive powder includes the following steps: S1. Dissolving a macromolecular silane coupling agent in an alcohol-water mixed solvent, adjusting the pH to 3.5-5.5, and stirring to hydrolyze, obtaining a hydrolysate; S2. After drying and pre-treating the thermally conductive powder, adding it to the hydrolysate from step S1, and stirring the reaction at 50℃-90℃; after the reaction, separating the solid, washing, and drying to obtain the macromolecular silane surface-modified thermally conductive powder. The macromolecular silane surface-modified thermally conductive powder of this invention, through multi-site Si-O-Al chemical bond anchoring, forms a stable flexible polysiloxane coating layer on the powder surface, which can significantly reduce the processing viscosity of high-filler systems and improve interfacial thermal conductivity, meeting the requirements for high thermal conductivity materials in the field of electronic component heat dissipation packaging.

Description

Technical Field

[0001] This invention belongs to the field of thermal interface materials technology, specifically relating to a macromolecular silane surface-modified thermally conductive powder, its preparation method, and its application. Background Technology

[0002] Composites of thermally conductive powders (such as alumina, aluminum nitride, boron nitride, and zinc oxide) with polymer matrices are the mainstream technical approach for preparing high thermal conductivity interface materials. However, poor interfacial compatibility between inorganic thermally conductive powders and organic polymer matrices, easy powder agglomeration, and high interfacial thermal resistance have always been key bottlenecks restricting the improvement of the performance of thermally conductive composite materials. Currently, surface modification of powders using surface treatment agents is one of the core methods to solve these problems.

[0003] Traditional small-molecule silane coupling agents (such as KH-550, KH-560, and KH-570) have been widely used in the field of thermally conductive powder surface modification. However, with the continuous increase in the power density of electronic components, higher requirements are placed on the thermal conductivity of thermal interface materials. Although small-molecule silane coupling agents can reduce the polarity of powder surfaces to a certain extent, the coating layer they form is extremely thin (usually only 1-3 nanometers), which cannot effectively shield phonon scattering between the powder surface and the matrix, resulting in high interfacial thermal resistance in the composite material. In addition, small-molecule silanes are usually only anchored to the powder surface at a single point. Under high temperature and humidity environments or during long-term use, the treated layer is prone to hydrolysis and detachment, leading to secondary agglomeration of the powder, which in turn affects the long-term reliability of the composite material.

[0004] To overcome the aforementioned shortcomings, research on macromolecular silane coupling agents for surface modification of thermally conductive powders has received increasing attention in recent years. Chinese patent CN116082641A discloses a macromolecular alkoxysilane treatment agent with a T-shaped symmetric structure. Utilizing its unique T-shaped symmetric structure and reactive alkoxy groups in the middle of the polymer chain, it can form an "umbrella-like" coating on the filler surface, improving the hydrophobicity of the thermally conductive filler and enhancing the interfacial compatibility between the filler and the polymer matrix. However, the synthesis route of this type of macromolecular treatment agent with a specific structure is complex, and its molecular chain segments are relatively rigid. In high-filling systems with a filler content >85 wt%, steric hindrance can easily lead to a decrease in the flowability of the polymer matrix, resulting in a high processing viscosity of the composite material, which is unfavorable for continuous production in compression molding or extrusion processes.

[0005] Therefore, the present invention aims to develop a macromolecular silane surface-modified thermally conductive powder with reasonable structural design, controllable processing technology, and excellent comprehensive performance, so as to meet the demand for high thermal conductivity interface materials under the development of high power and high integration of electronic components. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, the present invention aims to provide a method for preparing a macromolecular silane surface-modified thermally conductive powder.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a macromolecular silane surface-modified thermally conductive powder, comprising the following steps: S1. Dissolve the macromolecular silane coupling agent in an alcohol-water mixed solvent, adjust the pH to 3.5-5.5, stir and hydrolyze to obtain a hydrolysate; S2. After drying and pretreating the thermally conductive powder, add it to the hydrolysate of step S1 and stir the reaction at 50℃-90℃. After the reaction is completed, separate the solid, wash and dry it to prepare macromolecular silane surface-modified thermally conductive powder.

[0008] The macromolecular silane coupling agent has a polysiloxane chain as its main chain, and the molecular chain contains at least two active anchoring groups that can react with the hydroxyl groups on the surface of the thermally conductive powder. Preferably, the active anchoring groups are selected from any one or more of alkoxy and silanol groups.

[0009] The alkoxy group is preferably one or more of methoxy and ethoxy groups.

[0010] Preferably, the active anchoring group is located at the end of the molecular chain. More preferably, the macromolecular silane coupling agent has a dual-terminal multi-active-group structure. Macromolecular silanes with dual-terminal multi-active-group structures can be bonded to the powder surface in a "bridging" manner. Even if one end is partially hydrolyzed, the other end remains firmly connected, effectively inhibiting the attack of water molecules on the anchoring bond under high temperature and high humidity, and exhibiting higher stability.

[0011] Furthermore, the number average molecular weight of the macromolecular silane coupling agent is 1500-8000, preferably 2000-6000.

[0012] Furthermore, the molecular chain ends or side chains of the macromolecular silane coupling agent contain functional groups that are compatible with or react with the polymer matrix. These functional groups are selected from one or more of long-chain alkyl, phenyl, vinyl, amino, epoxy, and methacryloxy groups. Preferably, the functional groups are selected from one or more of long-chain alkyl, phenyl, vinyl, and amino groups. Macromolecular silane coupling agents with side-linked long-chain alkyl groups form a dense, hydrophobic brush structure, which can significantly reduce the surface polarity of the powder, allowing the highly filled system to maintain a low processing viscosity. Vinyl-terminated macromolecular silane coupling agents can not only participate in matrix vulcanization to form a chemically bonded interface, but also react efficiently with the Si-H groups of addition-type silicone oils, making the powder substantially part of a cross-linked network, greatly improving the filler-matrix load transfer efficiency. Macromolecular silane coupling agents with phenyl (-C6H5) side-linked branches can improve the rigidity of the molecular chain and the thermal stability of the thermally conductive composite material. Furthermore, they can effectively promote the formation of an efficient arrangement of powder particles within the matrix, improving phonon scattering and thus achieving a higher thermal conductivity with the same amount of powder added. Amino-modified macromolecular silane coupling agents can chemically crosslink with the polymer matrix, preventing the formation of "island" effects of thermally conductive powder particles within the matrix system and effectively reducing the interfacial thermal resistance between the powder and the polymer matrix.

[0013] Preferably, the long-chain alkyl group is selected from straight-chain alkyl groups having 8-20 carbon atoms.

[0014] Preferably, the thermally conductive powder is selected from alumina powder.

[0015] Furthermore, the alumina powder is spherical, near-spherical, or flake-shaped alumina, preferably spherical alumina.

[0016] Furthermore, the alumina powder is α-Al2O3 with a purity ≥99.5%.

[0017] Furthermore, the particle size D50 of the alumina powder is 0.5-50 μm, preferably 1-30 μm. This invention can utilize powders with a single particle size or a mixture of different particle sizes.

[0018] Further, in step S1, the mass ratio of the macromolecular silane coupling agent to the alcohol-water mixed solvent is 1:(5-22).

[0019] Furthermore, in step S1, the stirring hydrolysis time is 10-40 min; the stirring speed is 300-800 rpm.

[0020] Further, in step S1, the alcohol-water mixed solvent is an aqueous ethanol solution. Preferably, the volume ratio of ethanol to water in the aqueous ethanol solution is (5.5-9):1.

[0021] Furthermore, in step S2, the drying pretreatment temperature of the thermally conductive powder is 100-130℃, and the drying pretreatment time is 2-4h.

[0022] As a preferred embodiment, the thermally conductive powder is placed in a vacuum drying oven for drying pretreatment.

[0023] Furthermore, in step S2, the mass ratio of thermally conductive powder to hydrolysate is 1:(1.5-4); the stirring reaction time is 1-4 hours; and the stirring speed is 500-1500 rpm.

[0024] In a preferred embodiment, 30%-50% of the hydrolysate is first pre-reacted with the dried and pretreated thermally conductive powder for 20-40 minutes, and then the remaining hydrolysate is added and the reaction is continued with stirring for 1-3 hours; preferably, the temperature of the pre-reaction is 50-90°C.

[0025] Furthermore, in step S2, the stirring reaction is carried out under ultrasonic conditions, with an ultrasonic power of 100-500W and an ultrasonic frequency of 20-40kHz.

[0026] Further, in step S2, after the reaction is completed, the solid can be obtained by filtration or centrifugation. The solid is washed with anhydrous ethanol to remove unreacted free silane and byproducts. Then, the washed solid is vacuum dried at 80-120℃ for 2-6 hours to prepare macromolecular silane surface-modified thermally conductive powder.

[0027] In a second aspect, the present invention provides a macromolecular silane surface-modified thermally conductive powder, which is prepared by the preparation method described in the first aspect.

[0028] The macromolecular silane surface-modified thermally conductive powder is formed by chemical bonding to create a flexible coating layer of macromolecular silane coupling agent with a thickness of 5-20 nm on the surface of the thermally conductive powder.

[0029] Thirdly, the present invention also provides the application of the macromolecular silane surface-modified thermally conductive powder in the preparation of thermally conductive composite materials.

[0030] Fourthly, the present invention provides a high thermal conductivity composite material comprising a matrix polymer and the macromolecular silane surface-modified thermally conductive powder described in the second aspect.

[0031] Furthermore, the matrix polymer is selected from any one or more of addition-type liquid silicone rubber, condensation-type silicone rubber, epoxy resin, and polyurethane resin.

[0032] Furthermore, the mass content of the macromolecular silane surface-modified thermally conductive powder in the high thermal conductivity composite material is 70wt%-98wt%.

[0033] Fifthly, the present invention also provides the application of the aforementioned high thermal conductivity composite material in the preparation of thermally conductive pads, thermally conductive gels, thermally conductive potting compounds, or thermally conductive phase change materials. It is applicable to the field of heat dissipation packaging for electronic components.

[0034] Compared with the prior art, the present invention has the following beneficial effects: First, this invention modifies the surface of thermally conductive alumina using a macromolecular silane coupling agent containing specific active groups. This utilizes multi-site chemical bonds to strongly anchor the surface of the thermally conductive powder, forming a flexible coating layer of macromolecular silane coupling agent. This significantly improves its chemical stability under high temperature / high humidity conditions, making it less prone to hydrolysis and preventing secondary agglomeration of the powder. Furthermore, the chain length of this coating layer has good entanglement matching with commonly used matrix polymers, enabling the construction of a gradient interface layer between the thermally conductive powder and the polymer. This effectively reduces the high interfacial thermal resistance caused by phonon scattering, resulting in materials with higher thermal conductivity. Simultaneously, the long-chain polysiloxane structure of the macromolecular silane can more thoroughly shield the polar hydroxyl groups on the surface of the thermally conductive powder, reducing the friction coefficient between powders and the shear resistance between the powder and the matrix, allowing the system to maintain a low processing viscosity even with high filling amounts. Secondly, this invention uses an alcohol-water hydrolysis condensation method to prepare macromolecular silane surface-modified thermally conductive powder. By specifically optimizing the process conditions, it effectively avoids the problem of abnormal thixotropic behavior of the system caused by excessive cross-linking or excessively high local concentration when using macromolecular silane coupling agents to modify the surface of thermally conductive powder. This ensures that the obtained thermally conductive composite material has ideal shear thinning characteristics, which is convenient for coating and molding. Detailed Implementation

[0035] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0036] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0037] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±1°C.

[0038] The materials used in the embodiments and comparative examples of this invention are described below, but are not limited to these materials. Example 1

[0039] This embodiment provides a macromolecular silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Take 100 g of alumina powder (spherical α-Al2O3, purity ≥99.5%) with D50=5 μm, place it in a vacuum drying oven, and dry it at 120℃ for 3 h for later use; (2) Add 1.5 g of macromolecular silane coupling agent (terminated methoxy polydimethylsiloxane, molecular formula: (CH3O)3SiO[Si(CH3)2O]). n Si(CH3)3, where n=30-32; molecular weight Mn=2500) was dissolved in 20 g of ethanol / water mixed solvent (volume ratio, ethanol:water=9:1), the pH was adjusted to 4.5 with glacial acetic acid, and the mixture was stirred at 400 rpm for 20 min at room temperature to obtain the hydrolysate. (3) Take some of the dried alumina powder and add it to the hydrolysate. The mass ratio of alumina powder to hydrolysate is 1:2.5. Stir the reaction at 1000 rpm in a constant temperature water bath at 70℃ for 2.5 h. After the reaction is completed, filter the mixture and wash it three times with anhydrous ethanol. Place the filter cake in a vacuum drying oven and dry it at 100℃ for 4 h to obtain macromolecular silane surface modified thermal conductive powder. Example 2

[0040] This embodiment provides a macromolecular silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Take 100 g of alumina powder (spherical α-Al2O3, purity ≥99.5%) with D50=20 μm, place it in a vacuum drying oven, and dry it at 120℃ for 3 h for later use; (2) Add 1.0 g of macromolecular silane coupling agent (amino-modified polydimethylsiloxane, molecular formula: (CH3O)3SiO[Si(CH3)2O]). m [Si(CH3)(CH2CH2NH2)O] n Si(CH3)3, wherein m+n=50-53, amino content=0.6 mmol / g, molecular weight Mn=4500) was dissolved in 15 g of ethanol / water mixed solvent (volume ratio, ethanol:water=8.5:1.5), the pH was adjusted to 5.0 with glacial acetic acid, and the mixture was hydrolyzed at room temperature by stirring at 400 rpm for 30 min to obtain the hydrolysate; (3) Take some of the dried alumina powder and add it to the hydrolysate. The mass ratio of alumina powder to hydrolysate is 1:4. Stir the reaction at 1200 rpm in a constant temperature water bath at 80℃ for 2 hours. After the reaction is completed, filter the powder, wash it three times with anhydrous ethanol, and dry it under vacuum at 110℃ for 3 hours to obtain macromolecular silane surface modified thermal conductive powder. Example 3

[0041] This embodiment provides a macromolecular silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Alumina powders with mixed D50=2 μm and D50=30 μm (spherical α-Al2O3, mass ratio d2:d2) 30 =4:6 (purity ≥99.5%), a total of 100 g, placed in a vacuum drying oven and dried at 120℃ for 3 hours, for later use; (2) Add 1.2 g of macromolecular silane coupling agent (vinyl-terminated polymethylphenylsiloxane, molecular formula: (CH3O)3SiO[Si(CH3)(C6H5)O] m [Si(CH3)2O] n Si(CH3)2CH=CH2, where m+n=40-45, molecular weight Mn=3500) was dissolved in 25 g of ethanol / water mixed solvent (volume ratio, ethanol:water=9:1), the pH was adjusted to 4.2 with glacial acetic acid, and the mixture was hydrolyzed at 600 rpm for 15 min at room temperature to obtain the hydrolysate. (3) According to the mass ratio of alumina powder to hydrolysate of 1:3, a segmented feeding process is adopted. First, 30% of the hydrolysate and alumina powder are stirred at 800 rpm for 40 min under ultrasonic conditions at 50℃. Then, the remaining hydrolysate is added, the temperature is raised to 65℃, and the reaction is continued under ultrasonic conditions for 3 h with ultrasonic power of 400 W and ultrasonic frequency of 30 kHz. After the reaction is completed, the mixture is filtered and washed 3 times with anhydrous ethanol. The filter cake is placed in a vacuum drying oven and dried at 90℃ for 5 h to obtain macromolecular silane surface modified thermally conductive powder. Example 4

[0042] This embodiment provides a macromolecular silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Take 100 g of alumina powder (spherical α-Al2O3, purity ≥99.5%) with D50=10 μm, place it in a vacuum drying oven, and dry it at 120℃ for 3 h for later use; (2) Add 0.8 g of macromolecular silane coupling agent (long-chain alkyl-modified polysiloxane, molecular formula: (CH3O)3SiO[Si(CH3)(C 12 H 25 )O] m [Si(CH3)2O] n Si(OCH3)3, wherein m=8, n=50, alkyl grafting rate 15%, molecular weight Mn=6000) was dissolved in 15 g of ethanol / water mixed solvent (volume ratio, ethanol:water=9:1), the pH was adjusted to 4.8 with glacial acetic acid, and the mixture was hydrolyzed at room temperature by stirring at 400 rpm for 25 min to obtain the hydrolysate. (3) According to the mass ratio of alumina powder to hydrolysate of 1:3, a segmented feeding process is adopted. First, 40% of the hydrolysate and alumina powder are stirred at 60℃ and 1000rpm for 30min for pre-reaction. Then, the remaining hydrolysate is added, the temperature is raised to 75℃ and the stirring reaction is continued for 2h. After the reaction is completed, the mixture is filtered and washed 3 times with anhydrous ethanol. The filter cake is placed in a vacuum drying oven and dried at 100℃ for 4h to obtain macromolecular silane surface modified thermally conductive powder. Example 5

[0043] This embodiment provides a macromolecular silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Take 100 g of alumina powder (spherical α-Al2O3, purity ≥99.5%) with D50=10 μm, place it in a vacuum drying oven, and dry it at 120℃ for 3 h for later use; (2) Add 0.8 g of macromolecular silane coupling agent (long-chain alkyl-modified polysiloxane, molecular formula: (CH3O)3SiO[Si(CH3)(C 12 H 25 )O] m [Si(CH3)2O] n Si(OCH3)3, wherein m=8, n=50, alkyl grafting rate 15%, molecular weight Mn=6000) was dissolved in 15 g of ethanol / water mixed solvent (volume ratio, ethanol:water = 9:1), the pH was adjusted to 4.8 with glacial acetic acid, and hydrolyzed at room temperature for 25 min to obtain hydrolysate; (3) According to the mass ratio of alumina powder to hydrolysate of 1:3, a segmented feeding process is adopted. First, 40% of the hydrolysate and alumina powder are stirred at 1000 rpm for 30 min under ultrasonic conditions at 60℃. Then, the remaining hydrolysate is added, the temperature is raised to 75℃, and the reaction is continued under ultrasonic conditions for 2 h with ultrasonic power of 400W and ultrasonic frequency of 30kHz. After the reaction is completed, the mixture is filtered and washed 3 times with anhydrous ethanol. The filter cake is placed in a vacuum drying oven and dried at 100℃ for 4 h to obtain macromolecular silane surface modified thermally conductive powder. Example 6

[0044] This embodiment provides a macromolecular silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Take 100 g of alumina powder (spherical α-Al2O3, purity ≥99.5%) with D50=10 μm, place it in a vacuum drying oven, and dry it at 120℃ for 3 h for later use; (2) Add 0.8 g of macromolecular silane coupling agent (long-chain alkyl-modified polysiloxane, molecular formula: (CH3O)3SiO[Si(CH3)(C 12 H 25)O] m [Si(CH3)2O] n Si(OCH3)3, wherein m=8, n=50, alkyl grafting rate 15%, molecular weight Mn=6000) was dissolved in 15 g of ethanol / water mixed solvent (volume ratio, ethanol:water = 9:1), the pH was adjusted to 4.8 with glacial acetic acid, and hydrolyzed at room temperature for 25 min to obtain hydrolysate; (3) Take a portion of the dried alumina powder and add it to the hydrolysate. The mass ratio of alumina powder to hydrolysate is 1:3. Stir the mixture at 1000 rpm in a constant temperature water bath at 75℃ for 2.5 h. After the reaction is completed, filter the mixture and wash it three times with anhydrous ethanol. Place the filter cake in a vacuum drying oven and dry it at 100℃ for 4 h to obtain macromolecular silane surface modified thermally conductive powder.

[0045] Comparative Example 1 Take 100 g of the same spherical α-Al2O3 powder (D50=5 μm) as in Example 1, and perform vacuum drying (120°C, 3h) without any silane surface treatment.

[0046] Comparative Example 2 This comparative example provides a small molecule silane surface-modified thermally conductive powder, the preparation method of which is as follows: (1) Take 100 g of the same alumina powder (spherical α-Al2O3, purity ≥99.5%, D50=5 μm) as in Example 1, place it in a vacuum drying oven, and dry it at 120℃ for 3 h for later use; (2) Dissolve 1.5 g of silane coupling agent KH-570 (γ-methacryloxypropyltrimethoxysilane) in 20 g of ethanol / water mixed solvent (volume ratio, ethanol:water = 9:1), adjust the pH to 4.5 with glacial acetic acid, and hydrolyze for 20 min at room temperature to obtain hydrolysate; (3) Take a portion of the dried alumina powder and add it to the hydrolysate. The mass ratio of alumina powder to hydrolysate is 1:2.5. Stir the mixture at 1000 rpm in a constant temperature water bath at 70℃ for 2.5 h. After the reaction is completed, filter the mixture and wash it three times with anhydrous ethanol. Place the filter cake in a vacuum drying oven and dry it at 100℃ for 4 h to obtain small molecule silane surface modified thermal conductive powder.

[0047] Comparative Example 3 This comparative example provides a macromolecular silane surface-modified thermally conductive powder. The only difference between this powder and Example 1 is that it uses terminal methoxy polydimethylsiloxane with a number average molecular weight Mn=10000. The rest is the same as Example 1.

[0048] The modified alumina obtained in Examples 1-6 and Comparative Examples 1-3 were mixed with vinyl silicone oil (viscosity 500 mPa·s, vinyl content 0.5 mmol / g) at a mass ratio of 9:1 (powder:silicone oil = 9:1). A platinum catalyst was added, and after vacuum degassing, 2 mm thick thermal pads were prepared and cured at 120°C for 30 min. Performance tests were then conducted.

[0049] Relevant performance testing methods: Thermal conductivity: The thermal conductivity of the sample was characterized by laser flash analysis (LFA 467, Netzsch, standard: ASTM E1461). Interfacial thermal resistance: The interfacial thermal resistance of the sample was determined by steady-state heat flow method (standard: ASTM D5470), with a test pressure of 40 psi, a hot surface temperature of 60°C, and a cold surface temperature of 30°C. Mixed viscosity: measured by rotational rheometer at 25°C and a shear rate of 10 s⁻¹ -1 The determination was made under the specified conditions.

[0050] Aging resistance test: Aging conditions are 85°C, 85% R / H, and aging time is 200h; the thermal conductivity of the sample before and after aging is tested, and the thermal conductivity retention rate is calculated. Thermal conductivity retention rate = thermal conductivity after aging / thermal conductivity before aging * 100%.

[0051] Table 1 Performance test results of Examples 1-6 and Comparative Examples 1-3

[0052] The results above show that the macromolecular silane surface-modified thermally conductive powder prepared by the method of the present invention modifies the surface of thermally conductive alumina by using a macromolecular silane coupling agent containing specific active groups. It utilizes the strong anchoring of multi-site Si-O-Al chemical bonds to form a flexible coating layer of macromolecular silane coupling agent on the surface of the thermally conductive powder, which effectively improves the interfacial compatibility between the thermally conductive powder and the matrix polymer. It can significantly reduce the processing viscosity of the high-filler system and improve the interfacial thermal conductivity, and has excellent chemical stability.

[0053] The above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a macromolecular silane surface-modified thermally conductive powder, characterized in that, Includes the following steps: S1. Dissolve the macromolecular silane coupling agent in an alcohol-water mixed solvent, adjust the pH to 3.5-5.5, stir and hydrolyze to obtain a hydrolysate; S2. After drying and pretreating the thermally conductive powder, add it to the hydrolysate of step S1 and stir the reaction at 50℃-90℃. After the reaction is completed, separate the solid, wash and dry it to prepare macromolecular silane surface-modified thermally conductive powder. The main chain of the macromolecular silane coupling agent is a polysiloxane chain, and the molecular chain contains at least two active anchoring groups that can react with the hydroxyl groups on the surface of the thermally conductive powder. The number average molecular weight of the macromolecular silane coupling agent is 1500-8000.

2. The method for preparing macromolecular silane surface-modified thermally conductive powder according to claim 1, characterized in that: The active anchoring group is selected from any one or more of alkoxy and silanol groups; preferably, the alkoxy group is selected from any one or more of methoxy and ethoxy groups.

3. The method for preparing macromolecular silane surface-modified thermally conductive powder according to claim 1, characterized in that: The macromolecular silane coupling agent has functional groups at the molecular chain ends or side chains that are compatible with or react with the polymer matrix. The functional groups are selected from any one or more of long-chain alkyl, phenyl, vinyl, amino, epoxy, and methacryloxy groups. The thermally conductive powder is selected from thermally conductive alumina powder. The thermally conductive alumina powder is α-Al2O3 with a particle size D50 of 0.5-50 μm.

4. The method for preparing macromolecular silane surface-modified thermally conductive powder according to claim 1, characterized in that, In step S1, the mass ratio of the macromolecular silane coupling agent to the alcohol-water mixed solvent is 1:(5-22); the stirring and hydrolysis time is 10-40 min; the alcohol-water mixed solvent is an aqueous ethanol solution; the volume ratio of ethanol to water in the aqueous ethanol solution is (5.5-9):

1.

5. The method for preparing the macromolecular silane surface-modified thermally conductive powder according to claim 1, characterized in that, In step S2, the drying pretreatment temperature of the thermally conductive powder is 100-130℃, and the drying pretreatment time is 2-4h; the mass ratio of the thermally conductive powder to the hydrolysate is 1:(1.5-4); and the stirring reaction time is 1-4h.

6. The method for preparing the macromolecular silane surface-modified thermally conductive powder according to claim 1, characterized in that, In step S2, the stirring reaction is carried out under ultrasonic conditions, with an ultrasonic power of 100-500W and an ultrasonic frequency of 20-40kHz.

7. The method for preparing the macromolecular silane surface-modified thermally conductive powder according to claim 1, characterized in that, In step S2, 30%-50% of the hydrolysate is first pre-reacted with the dried and pretreated thermally conductive powder for 20-40 minutes, and then the remaining hydrolysate is added and the reaction is continued with stirring for 1-3 hours.

8. A macromolecular silane surface-modified thermally conductive powder, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The application of the macromolecular silane surface-modified thermally conductive powder according to claim 8 in the preparation of thermally conductive composite materials.

10. A high thermal conductivity composite material, characterized in that: It comprises a matrix polymer and the macromolecular silane surface-modified thermally conductive powder according to any one of claims 1-7; Preferably, the matrix polymer is selected from any one or more of addition-type liquid silicone rubber, condensation-type silicone rubber, epoxy resin, and polyurethane resin; Preferably, the mass content of macromolecular silane surface-modified thermally conductive powder in the high thermal conductivity composite material is 70%-98%.

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