High-purity polydimethylsilane and preparation method thereof

Abstract

The invention provides high-purity polydimethylsilane and a preparation method thereof, and the preparation method comprises the following steps: adding dimethyldichlorosilane and alkali metal into a benzene solvent under the protection of inert gas, and reacting at high temperature to obtain a product; adding alcohol into the product, neutralizing unreacted raw materials, and then filtering to obtain crude polydimethylsilane; providing a cleaning container provided with two layers of filter screen assemblies, and adding the crude polydimethylsilane between the two layers of filter screen assemblies; a cleaning solvent is added into the cleaning container to be higher than the upper-layer filter screen assembly, and cleaning is conducted; a part of liquid in the cleaning container is discharged from the upper part of the upper-layer filter screen assembly, and then the residual liquid is discharged from the lower part of the lower-layer filter screen assembly; and repeating for multiple times, and finally evaporating to obtain the high-purity polydimethylsilane. According to the method, the content of oxygen-containing silane, chloride ions and alkali metal ions in the polydimethylsilane can be reduced, and the high-purity polydimethylsilane with the oxygen content lower than 0.5%, the chloride ion content lower than 20 ppm and the alkali metal ion content lower than 20 ppm is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polydimethylsilane preparation, and particularly relates to high-purity polydimethylsilane and a preparation method thereof. BACKGROUND

[0002] Polycarbosilane is a high polymer material with a main chain composed of silicon and carbon atoms, which has important uses in many fields such as organic semiconductor devices, functional materials, and medical fields, and is an important precursor material for preparing silicon carbide material. Silicon carbide material has excellent high-temperature oxidation resistance and chemical corrosion resistance, and is widely used in aerospace and extreme environments, and is a kind of cutting-edge material. The less the oxygen content and impurity content of the silicon carbide material, the better the high-temperature oxidation resistance and mechanical properties, especially in the application of silicon carbide fibers. Polydimethylsilane is a precursor material for preparing polycarbosilane, and the oxygen content and impurity content of polydimethylsilane determine the purity of polycarbosilane, which directly affects the preparation of high-quality silicon carbide fibers.

[0003] At present, the preparation of polydimethylsilane mainly adopts the method of Wurtz reaction of chlorosilane with alkali metal, and there are still a lot of reaction raw materials in the system after the reaction. Therefore, alcohol is usually added for neutralization, but a lot of oxygen-containing silane by-products will be produced after neutralization. In addition, there are impurities such as chloride ions and alkali metal ions in the reaction product. In order to remove the impurities, filtration and washing are usually used. Polydimethylsilane is an insoluble and infusible powder that cannot pass through the filter screen, while the impurities such as oxygen-containing silane, chloride ions and alkali metal ions can be dissolved in the cleaning solvent and pass through the filter screen, which can be separated by filtration. The Chinese patent document with the publication number CN114130345A discloses a preparation method of polydimethylsilane. After the product is prepared, the product mixture is first subjected to suction filtration to obtain a first material; the first material is washed; and then dried to obtain finished polydimethylsilane. However, a small amount of impurity oxygen-containing silane is usually wrapped in the crude polydimethylsilane. When the crude polydimethylsilane is cleaned with pure water or benzene, since the densities of polydimethylsilane and part of the oxygen-containing silane are both smaller than that of water, they float on the liquid surface. After stirring, the water is filtered from the bottom, and the polydimethylsilane is intercepted by the filter screen, while part of the oxygen-containing silane, chloride ions and sodium ions adhere to the surface of the polydimethylsilane and float above the water. This part of impurities will be intercepted together with the polydimethylsilane by the filter screen and is difficult to be effectively removed. In order to obtain high-purity polydimethylsilane, it is necessary to repeatedly use alcohol as a surfactant and clean with pure water and benzene for multiple times, which is a complicated process. SUMMARY

[0004] The technical problem solved by this invention is to provide a high-purity polydimethylsilane and its preparation method, which can effectively reduce the oxygen content, chloride ion and alkali metal ion content of polydimethylsilane, to obtain high-purity polydimethylsilane with an oxygen content of less than 0.5%, a chloride ion content of less than 20 ppm and an alkali metal ion content of less than 20 ppm.

[0005] To address the above problems, one aspect of the present invention provides a method for preparing high-purity polydimethylsilane, comprising the following steps:

[0006] S1. Under the protection of an inert gas, dimethyldichlorosilane and an alkali metal are added to a benzene solvent and reacted at high temperature to obtain the product;

[0007] S2. Add alcohols to the product to neutralize unreacted raw materials, then filter to obtain crude polydimethylsilane;

[0008] S3. A cleaning container is provided, wherein the cleaning container is provided with two layers of filter screen assemblies, and the crude polydimethylsilane is added between the two layers of filter screen assemblies;

[0009] S4. Add cleaning solvent to the cleaning container to clean the crude polydimethylsilane. The height of the added cleaning solvent exceeds the upper filter screen assembly.

[0010] S5. After cleaning, drain a portion of the liquid in the cleaning container from the top of the upper filter assembly, and then drain the remaining liquid from the bottom of the lower filter assembly.

[0011] S6. Repeat steps S4 and S5 multiple times, then evaporate the washed product to remove the washing solvent, and obtain high-purity polydimethylsilane.

[0012] Preferably, in step S3, the filter assembly is one or more of a polymer filter assembly, a metal filter assembly, or a non-woven fabric assembly.

[0013] Preferably, in step S4, the cleaning solvent is an inorganic solvent or an organic solvent; the inorganic solvent is pure water; the organic solvent is one or a mixture of alcohols, benzenes, and tetrahydrofurans.

[0014] Preferably, in the repeated steps S4 and S5, at least one cleaning process uses an inorganic solvent.

[0015] Preferably, in step S4, when using pure water to clean the crude polydimethylsilane, the mass ratio of pure water to dimethyldichlorosilane in the first cleaning is 1:(0.2-0.5).

[0016] Preferably, when the cleaning solvent is pure water, pure water at a temperature of 60–80°C is used.

[0017] Preferably, in step S1, the molar ratio of dimethyldichlorosilane to the alkali metal is 1:(1.9 to 2.1).

[0018] Preferably, the alkali metal is one or a mixture of two of sodium and potassium; the benzene solvent is one or a mixture of two of toluene and xylene; and the alcohol is one or a mixture of two of methanol and ethanol.

[0019] Preferably, in step S6, the evaporation temperature is 60–100°C, and the evaporation pressure is atmospheric pressure or vacuum.

[0020] Another aspect of the present invention provides a high-purity polydimethylsilane prepared by the above-described preparation method.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The method for preparing high-purity polydimethylsilane of the present invention involves placing crude polydimethylsilane between two filter screen assemblies in a cleaning container, adding a large amount of solvent for cleaning, and ensuring the solvent submerges and extends beyond the upper filter screen assembly. During cleaning, the polydimethylsilane and liquid oxygen-containing silane are trapped together by the upper filter screen assembly, and the polydimethylsilane and oxygen-containing silane are separated by stirring. When using inorganic solvents for cleaning, alkali metal chlorides and alkali metal alkoxides dissolve in the inorganic solvent. Polydimethylsilane is a very low-density powder insoluble in any solvent, while oxysilane is a liquid insoluble in inorganic solvents. The liquid oxysilane, less dense than the cleaning solvent, floats on the surface of the inorganic solvent under buoyancy and lies above it. The liquid oxysilane, denser than the inorganic solvent, lies below it and lies below the lower filter assembly. Polydimethylsilane is trapped between the two filter assemblies, thus separating it from impurities. When using organic solvents, polydimethylsilane is trapped between the two filter assemblies, while oxysilane, soluble in organic solvents, can pass through both filter assemblies and be carried away by the organic solvent, thereby separating polydimethylsilane from impurities. Using a cleaning container with upper and lower filter assemblies, the upper filter assembly presses the polydimethylsilane below the liquid surface, allowing the solvent to better wet the coarse polydimethylsilane and separate and remove impurities.

[0023] The method for preparing high-purity polydimethylsilane of the present invention can effectively reduce the content of oxygen-containing silanes, chloride ions and alkali metal ions in polydimethylsilane, and obtain high-purity polydimethylsilane with an oxygen content of less than 0.5%, a chloride ion content of less than 20 ppm and an alkali metal ion content of less than 20 ppm. Detailed Implementation

[0024] The technical solutions of the present application will be described clearly and completely below in connection with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present application.

[0025] One aspect of the embodiments of the present application provides a preparation method of high-purity polydimethylsilane, comprising the following steps:

[0026] S1. Under the protection of inert gas, dimethyldichlorosilane and alkali metal are added into a benzene solvent to react at high temperature to obtain a product;

[0027] S2. Alcohol is added into the product to neutralize unreacted raw materials, and then the crude polydimethylsilane is obtained by filtration;

[0028] S3. A cleaning container is provided, and two layers of filter screen assemblies are arranged in the cleaning container, and the crude polydimethylsilane is added between the two layers of filter screen assemblies;

[0029] S4. A cleaning solvent is added into the cleaning container to clean the crude polydimethylsilane, and the height of the added cleaning solvent exceeds the upper filter screen assembly;

[0030] S5. After cleaning, the liquid in the cleaning container is first discharged from above the upper filter screen assembly, and then the remaining liquid is discharged from below the lower filter screen assembly;

[0031] S6. Steps S4 and S5 are repeated for multiple times, and then the cleaned product is evaporated to remove the cleaning solvent to obtain high-purity polydimethylsilane.

[0032] The principle of separating polydimethylsilane, alkali metal chloride, alkali metal alcoholate and oxygen-containing silane is that polydimethylsilane is insoluble powder and cannot pass through the upper and lower filter screen assemblies, while oxygen-containing silane, alkali metal chloride and alkali metal alcoholate are dissolved in the cleaning solvent or are in liquid state and can pass through the upper and lower filter screen assemblies. Specifically, the method for preparing high-purity polydimethylsilane according to the embodiment of the present application obtains polydimethylsilane, alkali metal chloride, unreacted dimethyldichlorosilane and alkali metal after step S1. After neutralizing dimethyldichlorosilane in step S2, the product polydimethylsilane, alkali metal chloride, alkali metal alcoholate, oxygen-containing silane and the mixture of residual alcohol are obtained. The oxygen-containing silane is dimethyldimethoxysilane or dimethyldiethoxysilane. The mixture is filtered to obtain crude polydimethylsilane containing alkali metal chloride, alkali metal alcoholate and a small amount of oxygen-containing silane. The crude polydimethylsilane is placed between the two filter screen assemblies in the cleaning container, a large amount of solvent is added for cleaning, the solvent submerges the upper filter screen assembly and exceeds the upper filter screen assembly, and during the cleaning, polydimethylsilane and liquid impurities oxygen-containing silane are wrapped together and are intercepted by the upper filter screen assembly. Stirring is performed to separate polydimethylsilane and oxygen-containing silane. When inorganic solvent is used, alkali metal chloride and alkali metal alcoholate are dissolved in the inorganic solvent, polydimethylsilane is insoluble in any solvent and is powder with very small density, and the oxygen-containing silane byproduct is liquid insoluble in the inorganic solvent and has smaller density than the cleaning solvent. The liquid oxygen-containing silane is separated by the buoyancy of the inorganic solvent, passes through the upper filter screen assembly, is layered on the liquid surface of the inorganic solvent and is located above the upper filter screen assembly. The liquid oxygen-containing silane with larger density than the inorganic solvent is layered below the inorganic solvent and is located below the lower filter screen assembly. Polydimethylsilane is blocked between the two filter screen assemblies and is separated from impurities. When organic solvent is used, polydimethylsilane is intercepted between the two filter screen assemblies, while oxygen-containing silane is dissolved in the organic solvent and can pass through the upper and lower filter screen assemblies and be taken away by the organic solvent, so that polydimethylsilane is separated from impurities. The upper filter screen assembly is used to press polydimethylsilane below the liquid surface, so that the solvent can better wet the crude polydimethylsilane and various impurities can be more easily separated.

[0033] The method for preparing high-purity polydimethylsilane according to the embodiment of the present application can effectively reduce the content of oxygen-containing silane, chlorine ions and alkali metal ions in polydimethylsilane.

[0034] In some embodiments, the filter screen assembly is used for solid-liquid separation, and specifically, components that can separate solid from liquid components can be used. Preferably, in step S3, the filter screen is one or a combination of high-molecular filter screen assembly, metal filter screen assembly or non-woven fabric assembly.

[0035] In some embodiments, the cleaning solvent in step S4 is an inorganic solvent or an organic solvent. Preferably, the inorganic solvent is pure water; the organic solvent is one or a mixture of several of alcohol, benzene and tetrahydrofuran.

[0036] In some embodiments, the number of repetitions of steps S4 and S5 can be adjusted, preferably, at least 3 times.

[0037] In some embodiments, the cleaning solvent used in each cleaning can be the same or different. For example, pure water can be used in each cleaning, or inorganic and organic solvents can be used alternately. Preferably, in the repeated steps S4 and S5, at least one cleaning uses an inorganic solvent, and at least one cleaning uses an organic solvent, so that various types of impurities in the crude polydimethylsilane can be dissolved and washed out. Further preferably, inorganic and organic solvents are used alternately in repeated cleanings, which can result in higher product purity.

[0038] In some embodiments, in step S4, when pure water is used to clean the crude polydimethylsilane, the mass ratio of pure water to dimethyldichlorosilane in the first cleaning is 1:(0.2-0.5). Since the crude polydimethylsilane contains a large amount of sodium chloride, and the solubility of sodium chloride in water is about 36g, in order to ensure that sodium chloride is fully dissolved and separated, the mass ratio of pure water to reaction raw material is further limited.

[0039] In some embodiments, when the cleaning solvent is pure water, the temperature of the pure water is RT-100℃. The higher the temperature of the pure water, the better the wettability, which can better wet the surface of the crude polydimethylsilane and achieve better cleaning effect. Preferably, the temperature of the pure water is 60-80℃.

[0040] In some embodiments, in step S4, the crude polydimethylsilane is cleaned by stirring, so as to facilitate the separation of polydimethylsilane and various impurities.

[0041] In some embodiments, the cleaning container is provided with two or more sets of filter screen assemblies, and the crude polydimethylsilane is placed between any two sets of filter screen assemblies. Each set of filter screen assemblies can include multiple layers of filter screens, and the multiple layers of filter screens are stacked, with the filter screen having smaller filter holes being arranged in the uppermost layer or in the middle layer to play a filtering role, and the filter screen having larger filter holes being arranged in the lower filter screen to play a supporting role of the upper filter screen. In some embodiments, each layer of filter screen can be a filter screen having a mesh size of 50-2000.

[0042] In some embodiments, in step S1, the molar ratio of dimethyldichlorosilane to the alkali metal is 1:(1.9-2.1). This can make the conversion rate of the reaction higher, the yield of the product polydimethylsilane higher, and the remaining amount of dimethyldichlorosilane and alkali metal less.

[0043] In some embodiments, the alkali metal is one or a mixture of both of sodium and potassium.

[0044] In some embodiments, the benzene solvent is one or a mixture of both of toluene and xylene.

[0045] In some embodiments, the alcohol is one or a mixture of both of methanol and ethanol.

[0046] In some embodiments, in step S6, the evaporation temperature is 60-100°C, and the evaporation pressure is normal pressure or vacuum.

[0047] Another aspect of the embodiments of the present application provides high-purity polydimethylsilane prepared by the above preparation method.

[0048] Embodiment 1

[0049] The preparation method of the high-purity polydimethylsilane of the present embodiment includes the following steps:

[0050] S1. Under the protection of N2, 36 kg of metallic sodium was melted in 200 L of toluene at 110°C, 100 kg of dimethyldichlorosilane was added, and the reaction was carried out for 36 h to obtain a product;

[0051] S2. 100 kg of ethanol was added to the product to neutralize the unreacted raw material, and then filtered to obtain crude polydimethylsilane;

[0052] S3. A washing container is provided, which is equipped with two layers of filter screen assemblies. The crude polydimethylsilane is added between the two layers of filter screen assemblies. Each layer of filter screen assembly includes three layers of metal filter screens with 500 mesh, 200 mesh and 50 mesh from top to bottom.

[0053] S4. 300 kg of pure water at room temperature is added to the washing container to wash the crude polydimethylsilane. The height of the pure water exceeds the upper layer of filter screen assembly.

[0054] S5. After washing, the liquid in the washing container is stratified. The liquid silane with small density above the upper layer of filter screen assembly is discharged first. Then the solution (pure water, sodium chloride, sodium ethoxide) and the liquid silane with large density are discharged from below the lower layer of filter screen assembly. The polydimethylsilane powder is intercepted above the lower layer of filter screen assembly.

[0055] S6. Steps S4 and S5 are repeated for three times. Then the washed product is evaporated at 80°C to remove residual water to obtain high-purity polydimethylsilane.

[0056] Example 2

[0057] The preparation method of high-purity polydimethylsilane in this example includes the following steps:

[0058] S1. 36 kg of metallic sodium is melted in 200 L of xylene at 110°C under N2 protection. 100 kg of dimethyldichlorosilane is added. The reaction is carried out for 36 h to obtain a product.

[0059] S2. 100 kg of ethanol is added to the product to neutralize the unreacted raw material. Then the product is filtered to obtain crude polydimethylsilane.

[0060] S3. A washing container is provided, which is equipped with two layers of filter screen assemblies. The crude polydimethylsilane is added between the two layers of filter screen assemblies. Each layer of filter screen assembly includes three layers of metal filter screens with 500 mesh, 200 mesh and 50 mesh from top to bottom.

[0061] S4. 300 kg of pure water at 80°C is added to the washing container to wash the crude polydimethylsilane. The height of the pure water exceeds the upper layer of filter screen assembly.

[0062] S5. After washing, the liquid in the washing container is stratified. The liquid silane with small density above the upper layer of filter screen assembly is discharged first. Then the solution (pure water, sodium chloride, sodium ethoxide) and the liquid silane with large density are discharged from below the lower layer of filter screen assembly. The polydimethylsilane powder is intercepted above the lower layer of filter screen assembly.

[0063] S6. Repeat steps S4, S5 3 times, then evaporate the residual moisture from the washed product at 80°C to obtain high-purity polydimethylsilane.

[0064] Example 3

[0065] The method for preparing high-purity polydimethylsilane in this example includes the following steps:

[0066] S1. Under N2protection, melt 36 kg of metallic sodium in 200 L of xylene at 110°C, add 100 kg of dimethyldichlorosilane, and react for 36 h to obtain a product;

[0067] S2. Add 100 kg of methanol to the product to neutralize the unreacted raw material, then filter to obtain crude polydimethylsilane;

[0068] S3. Provide a washing container, which is equipped with two layers of filter screen assemblies, and add the crude polydimethylsilane between the two layers of filter screen assemblies in the washing container; each layer of filter screen assembly includes three layers of metal filter screens from top to bottom, i.e., 500 mesh, 200 mesh, and 50 mesh;

[0069] S4. Add 300 kg of normal-temperature pure water to the washing container to wash the crude polydimethylsilane, and the height of the pure water exceeds the upper layer of filter screen assembly;

[0070] S5. After washing, wait for the liquid in the washing container to stratify, first discharge the liquid-state oxygen-containing silane with smaller density above the upper layer of filter screen assembly, then discharge the solution (pure water, sodium chloride, sodium ethoxide) and the liquid-state oxygen-containing silane with larger density from below the lower layer of filter screen assembly, and the polydimethylsilane powder is intercepted above the lower layer of filter screen assembly;

[0071] S6. Repeat steps S4, S5 3 times, then evaporate the residual moisture from the washed product at 80°C under a vacuum of -0.1 MPa to obtain high-purity polydimethylsilane.

[0072] Example 4

[0073] The method for preparing high-purity polydimethylsilane in this example includes the following steps:

[0074] S1. Under N2protection, melt 36 kg of metallic sodium in 200 L of xylene at 120°C, add 100 kg of dimethyldichlorosilane, and react for 36 h to obtain a product;

[0075] S2. Add 100 kg of ethanol to the product to neutralize the unreacted raw material, then filter to obtain crude polydimethylsilane;

[0076] S3. A cleaning container is provided with two layers of filter screen assemblies, and the crude polydimethylsilane is added between the two layers of filter screen assemblies in the cleaning container; each layer of filter screen assembly includes three layers of metal filter screens from top to bottom, with a 500-mesh, 200-mesh, and 50-mesh filter screen;

[0077] S4. 300 kg of normal temperature pure water is added to the cleaning container to clean the crude polydimethylsilane, and the height of the pure water exceeds the upper layer of filter screen assembly;

[0078] S5. After cleaning, the liquid in the cleaning container is stratified, the liquid oxygen-containing silane with smaller density above the upper layer of filter screen assembly is discharged first, and then the solution (pure water, sodium chloride, sodium ethoxide) and the liquid oxygen-containing silane with larger density are discharged from below the lowermost layer of filter screen assembly, and the polydimethylsilane powder is intercepted above the lower layer of filter screen assembly;

[0079] S6. Steps S4 and S5 are repeated 3 times, the second time is cleaned with 250 kg of tetrahydrofuran, and the third time is cleaned with 300 kg of pure water, and then the cleaned product is evaporated at 80°C to remove residual moisture to obtain high-purity polydimethylsilane.

[0080] Example 5

[0081] The difference between the preparation method of high-purity polydimethylsilane in this embodiment and that in Example 4 is that the crude polydimethylsilane is cleaned with 300 kg of pure water at a temperature of 90°C, 250 kg of tetrahydrofuran, and 300 kg of pure water at a temperature of 90°C, respectively, in the three cleaning processes.

[0082] Example 6

[0083] The difference between the preparation method of high-purity polydimethylsilane in this embodiment and that in Example 7 is that the crude polydimethylsilane is cleaned with 200 kg of pure water at a temperature of 80°C, 250 kg of tetrahydrofuran, and 200 kg of pure water at a temperature of 80°C, respectively, in the three cleaning processes.

[0084] Example 7

[0085] The difference between the preparation method of high-purity polydimethylsilane in this embodiment and that in Example 7 is that the crude polydimethylsilane is cleaned with 500 kg of pure water at a temperature of 80°C, 250 kg of tetrahydrofuran, and 500 kg of pure water at a temperature of 80°C, respectively, in the three cleaning processes.

[0086] Example 8

[0087] The preparation method of high purity polydimethylsilane in this embodiment is different from that in embodiment 4 in that the crude polydimethylsilane is washed with 300 kg of pure water at 80 ℃, 250 kg of tetrahydrofuran, 250 kg of dimethylbenzene, 300 kg, 300 kg, and 300 kg of pure water at 80 ℃, respectively, in 6 times of washing.

[0088] The oxygen content, chloride ion content, and alkali metal content of the polydimethylsilane obtained in each of the above embodiments are detected, and the results are shown in Table 1. As can be seen from Table 1, under the same conditions, the higher the water temperature, the lower the oxygen content, chloride ion content, and sodium ion content of the polydimethylsilane. The oxygen content of the oligomeric polydimethylsilane is lower when washed with organic solvents and inorganic solvents alternately. The number of times of washing and the amount of pure water have a more obvious effect on the chloride ion and sodium ion content, and the effect of organic solvent washing on the oxygen content is more obvious.

[0089] Table 1

[0090] Item Oxygen content % Chloride ion content ppm Alkali metal content ppm Example 1 0.5 9 11 Example 2 0.4 6 5 Example 3 0.5 19 20 Example 4 0.3 19 20 Example 5 0.2 12 15 Example 6 0.6 32 35 Example 7 0.2 9 10 Example 8 0.1 2 3

[0091] Obviously, the above embodiments are merely examples for clarity and are not limiting of the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. All embodiments do not need to be exhausted here, and obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for producing high-purity polydimethylsilane, characterized by, The method comprises the following steps: S1. Under the protection of inert gas, dimethyldichlorosilane and alkali metal are added into a benzene solvent to react at high temperature to obtain a product; S2. Alcohol is added into the product to neutralize unreacted raw materials, and then the product is filtered to obtain crude polydimethylsilane; S3. A cleaning container is provided, which is provided with two layers of filter screen assemblies, and the crude polydimethylsilane is added between the two layers of filter screen assemblies; S4. A cleaning solvent is added into the cleaning container to clean the crude polydimethylsilane, and the height of the cleaning solvent added exceeds the upper filter screen assembly; S5. After cleaning, a part of the liquid in the cleaning container is discharged from above the upper filter screen assembly, and then the remaining liquid is discharged from below the lower filter screen assembly; S6. Steps S4 and S5 are repeated multiple times, and then the cleaned product is evaporated to remove the cleaning solvent to obtain high-purity polydimethylsilane.

2. The preparation method according to claim 1, wherein: In step S3, the filter screen assembly is one or more of a high-molecular filter screen assembly, a metal filter screen assembly or a non-woven fabric assembly.

3. The preparation method according to claim 1, wherein: In step S4, the cleaning solvent is an inorganic solvent or an organic solvent; the inorganic solvent is pure water; and the organic solvent is a mixture of one or more of alcohol, benzene and tetrahydrofuran.

4. The preparation method according to claim 3, wherein: In the multiple times of repeating steps S4 and S5, at least one time of cleaning uses an inorganic solvent as the cleaning solvent.

5. The preparation method according to claim 3, wherein: In step S4, when pure water is used to clean the crude polydimethylsilane, in the first time of cleaning, the mass ratio of pure water to dimethyldichlorosilane is 1:(0.2-0.5).

6. The preparation method according to claim 3, wherein: When the cleaning solvent is pure water, the temperature is RT ～ 100°C.

7. The preparation method according to claim 1, wherein: In step S1, the molar ratio of dimethyldichlorosilane to the alkali metal is 1:(1.9-2.1).

8. The preparation method according to claim 1, wherein: The alkali metal is one or a mixture of both of sodium and potassium; the benzene solvent is one or a mixture of both of toluene and xylene; and the alcohol is one or a mixture of both of methanol and ethanol.

9. The preparation method according to claim 1, wherein: In step S6, the evaporation temperature is 60-100℃, and the evaporation pressure is normal pressure or vacuum.

10. High-purity polydimethylsilane prepared by the preparation method according to any one of claims 1-9.