Polymethylsilane with adjustable C / Si atomic ratio as well as preparation method and application of polymethylsilane

Abstract

The invention discloses polymethylsilane capable of regulating and controlling the C / Si atomic ratio and a preparation method and application thereof.The preparation method comprises the steps that metal sodium is cut and crushed, and metal sodium fragments are obtained; adding the metal sodium fragments into an organic solvent, and heating until the metal sodium is in a molten state to obtain a mixture; stirring and cooling the mixture to obtain a sodium sand mixture; mixing methyl dichlorosilane, allyl methyl dichlorosilane, tetrahydrofuran and 15-crown ether-5, and then dropwise adding the mixture into the sodium sand mixture to react; the sodium sand in the preparation method has the characteristics of uniform particle size, high activity and clean surface; tetrahydrofuran and 15-crown ether-5 are added into dichloromethylsilane and allyl methyldichlorosilane, so that the single electron transfer rate of metallic sodium to dichloromethylsilane can be increased, the reaction activation energy can be reduced, the reaction efficiency can be improved, the molecular structure can be optimized, the loss of carbon elements can be made up, and the problem that PMS is rich in silicon after pyrolysis can be solved.

Description

Technical Field

[0001] This invention relates to the field of polymethylsilane technology, specifically to a polymethylsilane with an adjustable C / Si atomic ratio, its preparation method, and its applications. Background Technology

[0002] Polymethylsilanes are key intermediates in the preparation of important precursors such as SiC ceramic fibers and silicon-carbon-nitrogen ceramics. Their synthesis mainly relies on the sodium condensation method, specifically the dechlorination polycondensation reaction between metallic sodium and chloromethylsilane in an inert solvent (such as xylene or tetrahydrofuran). The core step of this reaction is the attack of sodium on the Si-Cl bond, and the reaction rate and conversion are highly dependent on the specific surface area and fresh active surface of metallic sodium. Therefore, improving the activity of metallic sodium plays a crucial role in the subsequent synthesis of polymethylsilanes.

[0003] The traditional method involves mechanically cutting / crushing sodium blocks into thin slices or fragments in an inert glove box. This is the most primitive method, resulting in sodium fragments with limited surface area, easily re-adhesive edges, and rapid oxidation and subsequent NaCl coating of the active surface. It is extremely inefficient and highly dangerous.

[0004] Furthermore, polymethylsilane (PMS), like other polysilanes, exhibits high-temperature pyrolysis properties, enabling it to be inorganicated at high temperatures to generate SiC ceramics. Since the Si to C molar ratio in the PMS molecule is 1, ideally, it should produce stoichiometric SiC. However, in reality, the pyrolysis of PMS releases small-molecule CH4, resulting in carbon loss. Therefore, the SiC generated from PMS pyrolysis is generally silicon-rich, with a Si / C molar ratio of 1.2–1.3. Excess silicon may react with C / C composites, damaging the carbon fibers and creating a strongly bonded interface, which is detrimental to the preparation of high-performance C / C-SiC composites. Due to the volatilization of low-molecular-weight small molecules and the gas (H2) generated by dehydrogenation, PMS experiences severe volume expansion and significant mass loss during crosslinking, resulting in low pyrolysis ceramic yields and poor structural continuity. These drawbacks make unmodified PMS difficult to use directly as a high-performance SiC precursor, but they also leave considerable room for exploration in its practical applications in matrix-modified C / C composites.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a polymethylsilane with an adjustable C / Si atomic ratio, its preparation method, and its applications. The preparation method involves high-temperature dispersion of metallic sodium in a specific organic solvent system, followed by rapid cooling to obtain sodium sand products with uniform particle size, high activity, clean surface, and suitability for polymethylsilane synthesis. Furthermore, by adding tetrahydrofuran and 15-crown ether-5 to dichloromethylsilane and allylmethyldichlorosilane, the single-electron transfer rate from metallic sodium to dichloromethylsilane can be increased, the activation energy of the reaction can be reduced, and the reaction efficiency can be improved. The addition of allylmethyldichlorosilane optimizes the molecular structure, compensates for carbon loss, and solves the problem of silicon enrichment after PMS pyrolysis. In addition, polymethylsilanes containing allylmethyldichlorosilane monomers can undergo thermal polymerization at lower temperatures, achieving self-crosslinking of the precursor and solving the problem of volume expansion in ceramic products.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] The first aspect of this invention provides a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0009] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain metallic sodium fragments;

[0010] (b) Under stirring conditions, sodium metal fragments are added to an organic solvent and heated until the sodium metal is molten to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane;

[0011] (c) Stir the mixture at a stirring speed of 400~600 rpm for a period of time, and then cool the mixture at a stirring speed of 800~1000 rpm and a cooling rate of 15~25℃ / min to obtain a sodium sand mixture.

[0012] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran and 15-crown ether-5 are mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution is then cooled, separated into solid and liquid, and distilled to obtain the polymethylsilane with adjustable C / Si atomic ratio.

[0013] Preferably, in step (b), the solid-liquid ratio of the sodium metal fragments and the organic solvent is 1:(10~15).

[0014] Preferably, in step (b), the stirring speed is 100~250 rpm; the volume ratio of xylene to cyclohexane is (8~10):1; and the temperature is heated to 99~110℃.

[0015] Preferably, in step (c), the stirring time is 30-60 minutes; and the temperature is lowered to below 70°C.

[0016] Preferably, in step (a), the sodium metal fragments are cubes with a side length of 3-5 cm.

[0017] Preferably, in step (c), the cooling method is solvent quenching and jacketed cold bath.

[0018] Preferably, in step (d), the volume ratio of dichloromethylsilane, allylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 is 1:(0.08~0.2):(0.8~1.2):(0.02~0.3); the molar ratio of the sum of the molar numbers of dichloromethylsilane and allylmethyldichlorosilane to that of sodium sand is 1:(2~2.2).

[0019] Preferably, in step (d), the dropping conditions are: temperature 65~75℃, dropping rate 0.5~1L / h, and stirring speed 200~500rpm;

[0020] The Wurtz coupled polymerization reaction conditions are: temperature 65~110℃, stirring speed 300~800rpm, reaction time 10~15h, and nitrogen flow rate 0.5~1L / min.

[0021] A second aspect of the present invention provides a polymethylsilane with an adjustable C / Si atomic ratio prepared by the above-described preparation method.

[0022] The third aspect of this invention provides the application of polymethylsilane with an adjustable C / Si atomic ratio prepared by the above-described method in the pyrolysis preparation of SiC ceramics.

[0023] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0024] This invention obtains sodium sand with uniform particle size, high activity, and clean surface, suitable for the synthesis of polymethylsilane, by dispersing metallic sodium at high temperature in a specific organic solvent system followed by rapid cooling. This process results in a more stable reaction and higher conversion efficiency during subsequent polymethylsilane synthesis, improving the yield and quality of the final product. Furthermore, the sodium sand preparation method of this invention is simple, allowing for one-step production in a reaction vessel, eliminating the need for complex molten sodium tanks, closed pipelines, and specialized mechanical grinding equipment. This simplifies the process and reduces equipment investment, maintenance difficulty, and failure rate, while also lowering experimental risks. Additionally, this invention does not introduce foreign substances, ensuring the chemical purity of the sodium sand from the source. This not only directly improves the quality of the synthesized polymethylsilane but also eliminates the complex process of separating impurities and waste, reducing environmental pressure and treatment costs.

[0025] The preparation method of this invention improves the single-electron transfer rate of metallic sodium to dichloromethylsilane by adding tetrahydrofuran and 15-crown ether-5 to dichloromethylsilane and allylmethyldichlorosilane, thereby reducing the activation energy and improving the reaction efficiency. Furthermore, the addition of allylmethyldichlorosilane optimizes the molecular structure, compensates for the loss of carbon, and solves the problem of silicon enrichment after PMS pyrolysis. In addition, polymethylsilane containing allylmethyldichlorosilane monomers can undergo thermal polymerization at a lower temperature, achieving self-crosslinking of the precursor and solving the problem of volume expansion of ceramic products. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0027] Figure 1 This is a photograph of the sodium sand prepared for the synthesis of polymethylsilane in Example 3 of the present invention.

[0028] Figure 2 This is a photograph of the sodium sand prepared for the synthesis of polymethylsilanes in Comparative Example 1 of this invention.

[0029] Figure 3 This is a photograph of the sodium sand prepared for the synthesis of polymethylsilanes in Comparative Example 2 of this invention.

[0030] Figure 4 This is a photograph of the sodium sand prepared for the synthesis of polymethylsilanes in Comparative Example 3 of this invention.

[0031] Figure 5 This is a photograph of the sodium sand prepared for the synthesis of polymethylsilanes in Comparative Example 4 of this invention.

[0032] Figure 6 This is a pyrolysis optical photograph of the polymethylsilane prepared in Example 3 of the present invention.

[0033] Figure 7 This is a pyrolysis electron microscope image of the polymethylsilane prepared in Example 3 of the present invention. Detailed Implementation

[0034] The embodiments of the technical solution of the present invention will be described in detail below with reference to the examples. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore only examples, and should not be used to limit the scope of protection of the present invention.

[0035] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0036] This invention provides a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0037] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain metallic sodium fragments;

[0038] (b) Under stirring conditions, sodium metal fragments are added to an organic solvent and heated until the sodium metal is molten to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane;

[0039] (c) Stir the mixture at a stirring speed of 400~600 rpm for a period of time, and then cool the mixture at a stirring speed of 800~1000 rpm and a cooling rate of 15~25℃ / min to obtain a sodium sand mixture.

[0040] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran and 15-crown ether-5 are mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution is then cooled, separated into solid and liquid, and distilled to obtain the polymethylsilane with adjustable C / Si atomic ratio.

[0041] In one embodiment, in step (b), the solid-liquid ratio of the sodium metal fragments and the organic solvent is 1:(10~15).

[0042] In one embodiment, in step (b), the stirring speed is 100~250 rpm; the volume ratio of xylene to cyclohexane is (8~10):1.

[0043] In one embodiment, in step (b), the temperature is raised to 99-110°C.

[0044] In one embodiment, in step (c), the stirring time is 30-60 minutes.

[0045] In one embodiment, in step (c), the temperature is lowered to below 70°C.

[0046] In one embodiment, in step (a), the sodium metal fragments are cubes with a side length of 3 to 5 cm.

[0047] In one embodiment, in step (c), the cooling method is solvent quenching and jacketed cold bath.

[0048] In one embodiment, in step (d), the volume ratio of dichloromethylsilane, allylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 is 1:(0.08~0.2):(0.8~1.2):(0.02~0.3); the molar ratio of the sum of the molar numbers of dichloromethylsilane and allylmethyldichlorosilane to that of sodium sand is 1:(2~2.2).

[0049] In one embodiment, in step (d), the dropping conditions are: temperature 65~75℃, dropping rate 0.5~1L / h, and stirring speed 200~500rpm;

[0050] The Wurtz coupled polymerization reaction conditions are: temperature 65~110℃, stirring speed 300~800rpm, reaction time 10~15h, and nitrogen flow rate 0.5~1L / min.

[0051] Another embodiment of the present invention provides a polymethylsilane with an adjustable C / Si atomic ratio prepared by the above preparation method.

[0052] Another embodiment of the present invention provides the application of polymethylsilane with an adjustable C / Si atomic ratio prepared by the above preparation method in the pyrolysis preparation of SiC ceramics.

[0053] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0054] Example 1

[0055] This embodiment describes a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0056] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0057] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:10, sodium metal fragments are added to organic solvent under stirring at 100 rpm and heated to 99°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 10:1.

[0058] (c) Stir the mixture at 400 rpm for 60 min, and then cool the mixture to below 70°C at a cooling rate of 15°C / min while stirring at 800 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0059] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated into solid and liquid phases, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.08:0.8:0.02; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2; the dropping conditions were: temperature 65℃, dropping rate 1L / h, and stirring speed 500rpm; the Wurtz coupled polymerization reaction conditions were: temperature 65℃, stirring speed 800rpm, reaction time 15h, and nitrogen flow rate 0.5L / min.

[0060] Example 2

[0061] This embodiment describes a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0062] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0063] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:15, sodium metal fragments are added to organic solvent under stirring at 250 rpm and heated to 110°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 8:1.

[0064] (c) Stir the mixture at 600 rpm for 30 min, and then cool the mixture to below 70°C at a cooling rate of 25°C / min while stirring at 1000 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0065] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated into solid and liquid phases, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.2:1.2:0.3; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.2; the dropping conditions were: temperature 75℃, dropping rate 0.5 L / h, and stirring speed 200 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 110℃, stirring speed 300 rpm, reaction time 10 h, and nitrogen flow rate 1 L / min.

[0066] Example 3

[0067] This embodiment describes a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0068] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0069] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 9:1.

[0070] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 20°C / min while stirring at 900 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0071] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated from the solid, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.1:1:0.2; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring speed 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0072] Comparative Example 1

[0073] This comparative example illustrates a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0074] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0075] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is xylene.

[0076] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 20°C / min while stirring at 900 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0077] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated from the solid, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.1:1:0.2; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring speed 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0078] Comparative Example 2

[0079] This comparative example illustrates a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0080] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0081] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and n-hexane in a volume ratio of 9:1.

[0082] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 20°C / min while stirring at 900 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0083] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated from the solid, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.1:1:0.2; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring speed 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0084] Comparative Example 3

[0085] This comparative example illustrates a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0086] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0087] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 9:1.

[0088] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 10°C / min while stirring at 900 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0089] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated from the solid, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.1:1:0.2; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring speed 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0090] Comparative Example 4

[0091] This comparative example illustrates a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0092] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0093] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 9:1.

[0094] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 20°C / min while stirring at 500 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0095] (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated from the solid, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 was 1:0.1:1:0.2; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring speed 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0096] Comparative Example 5

[0097] This comparative example illustrates a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0098] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0099] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 9:1.

[0100] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 20°C / min while stirring at 900 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0101] (d) Dichloromethylsilane, propenylmethyldichlorosilane, and tetrahydrofuran were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated from the solid, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, propenylmethyldichlorosilane, and tetrahydrofuran was 1:0.1:1.2; the molar ratio of the sum of the molar numbers of dichloromethylsilane and propenylmethyldichlorosilane to that of sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring speed 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0102] Comparative Example 6

[0103] This comparative example illustrates a method for preparing polymethylsilane with an adjustable C / Si atomic ratio, the method comprising the following steps:

[0104] (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain square fragments of metallic sodium with a side length of 3~5cm;

[0105] (b) With a solid-liquid ratio of sodium metal fragments to organic solvent of 1:12, sodium metal fragments are added to organic solvent under stirring at 200 rpm and heated to 105°C and kept at that temperature until the sodium metal is in a molten state to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane in a volume ratio of 9:1.

[0106] (c) Stir the mixture at 500 rpm for 40 min, and then cool the mixture to below 70°C at a cooling rate of 20°C / min while stirring at 900 rpm (cooling method is solvent quenching and jacketed cold bath, solvent is the same as the organic solvent in step (b)) to obtain sodium sand mixture.

[0107] (d) Dichloromethylsilane, tetrahydrofuran, and 15-crown ether-5 were mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution was then cooled, separated into solid and liquid phases, and distilled to obtain the polymethylsilane. The volume ratio of dichloromethylsilane, tetrahydrofuran, and 15-crown ether-5 was 1.1:1:0.2; the molar ratio of dichloromethylsilane to sodium sand was 1:2.1; the dropping conditions were: temperature 70℃, dropping rate 0.8 L / h, and stirring speed 400 rpm; the Wurtz coupled polymerization reaction conditions were: temperature 100℃, stirring rate 800 rpm, reaction time 12 h, and nitrogen flow rate 0.8 L / min.

[0108] Experimental Example

[0109] Sodium sand mixtures from Example 3 and Comparative Examples 1-4 were obtained, and after settling and filtration, sodium sand was obtained.

[0110] Sodium sand prepared in Example 3, such as Figure 1 As shown, the sodium sand prepared in Comparative Examples 1-4 are respectively shown in the diagrams. Figures 2-5 ;

[0111] Polymethylsilanes with adjustable C / Si atomic ratios were prepared according to the preparation methods of Examples 3 and Comparative Examples 1-6, respectively.

[0112] The yield of the above preparation method was calculated, and the calculation formula is shown in Equation 1. The calculation results are shown in Table 1.

[0113] Formula 1

[0114] In the formula, γ is the yield of synthesized polymethylsilane, %; m is the actual yield, kg; and M is the theoretical yield, kg.

[0115] The weight loss rate, molecular weight, and yield of ceramic products after pyrolysis at 1200℃ of polymethylsilane with adjustable C / Si atomic ratio were calculated. Optical photographs and electron microscope images of the polymethylsilane after pyrolysis in Example 3 are shown below. Figures 6-7 As shown, the calculation results are shown in Table 1;

[0116] Molecular weight (Mn): determined by gel permeation chromatography (GPC).

[0117] Thermogravimetric temperature: The decomposition temperature was tested using a Q-50 thermogravimetric analyzer from TA Instruments (USA). Nitrogen was used as the test atmosphere, with a nitrogen flow rate of 40 ml / min. The sample mass was approximately 10 mg. The test temperature was increased from room temperature to 800 °C at a heating rate of 5 °C / min.

[0118] Table 1

[0119] Group Yield (%) Weight loss rate (%) Molecular weight (Mw) Pyrolysis product yield (%) Example 3 84.55 44.23 989 55.77 Comparative Example 1 70.42 49.37 745 50.63 Comparative Example 2 72.69 47.23 821 52.77 Comparative Example 3 72.01 45.89 795 54.11 Comparative Example 4 71.28 46.68 810 53.32 Comparative Example 5 79.52 47.97 869 52.03 Comparative Example 6 80.53 48.99 952 47.65

[0120] As shown in Table 1:

[0121] Compared to the comparative examples, the polymethylsilane prepared in the embodiments of this application has better yield and pyrolysis product yield.

[0122] The chemical composition of the products after pyrolysis at 1200 °C of polymethylsilane with adjustable C / Si atomic ratio prepared according to the preparation methods of Example 3 and Comparative Examples 1-6 were analyzed, and the results are shown in Table 2.

[0123] Table 2

[0124] Group C (wt%) O (wt%) N (wt%) Si (wt%) Example 3 31.45 3.24 0.20 65.11 Comparative Example 1 30.15 3.92 0.28 65.65 Comparative Example 2 30.42 2.68 0.14 66.76 Comparative Example 3 28.89 3.25 0.37 67.49 Comparative Example 4 30.23 2.62 0.23 66.92 Comparative Example 5 29.84 3.05 0.22 66.89 Comparative Example 6 23.87 2.26 0.09 73.78

[0125] As shown in Table 2:

[0126] Compared to the comparative example, the polymethylsilane prepared in this application retains more carbon elements after pyrolysis.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing polymethylsilane with an adjustable C / Si atomic ratio, characterized in that, The preparation method includes the following steps: (a) Under an inert gas atmosphere, metallic sodium is cut and crushed to obtain metallic sodium fragments; (b) Under stirring conditions, sodium metal fragments are added to an organic solvent and heated until the sodium metal is molten to obtain a mixture; the organic solvent is a mixture of xylene and cyclohexane; (c) Stir the mixture at a stirring speed of 400~600 rpm for a period of time, and then cool the mixture at a stirring speed of 800~1000 rpm and a cooling rate of 15~25℃ / min to obtain a sodium sand mixture. (d) Dichloromethylsilane, propenylmethyldichlorosilane, tetrahydrofuran and 15-crown ether-5 are mixed and then added dropwise to a sodium sand mixture to carry out a Wurtz coupled polymerization reaction. The reaction solution is then cooled, separated into solid and liquid, and distilled to obtain the polymethylsilane with adjustable C / Si atomic ratio.

2. The preparation method according to claim 1, characterized in that, In step (b), the solid-liquid ratio of the sodium metal fragments and the organic solvent is 1:(10~15).

3. The preparation method according to claim 1, characterized in that, In step (b), the stirring speed is 100~250 rpm; the volume ratio of xylene to cyclohexane is (8~10):1; and the temperature is heated to 99~110℃.

4. The preparation method according to claim 1, characterized in that, In step (c), the stirring is carried out for 30 to 60 minutes; the temperature is then lowered to below 70°C.

5. The preparation method according to claim 1, characterized in that, In step (a), the sodium metal fragments are cubes with a side length of 3-5 cm.

6. The preparation method according to claim 1, characterized in that, In step (c), the cooling method is solvent quenching and jacketed cold bath.

7. The preparation method according to claim 1, characterized in that, In step (d), the volume ratio of dichloromethylsilane, allylmethyldichlorosilane, tetrahydrofuran, and 15-crown ether-5 is 1:(0.08~0.2):(0.8~1.2):(0.02~0.3); the molar ratio of the sum of the molar numbers of dichloromethylsilane and allylmethyldichlorosilane to that of sodium sand is 1:(2~2.2).

8. The preparation method according to claim 1, characterized in that, In step (d), the dropping conditions are: temperature 65~75℃, dropping rate 0.5~1L / h, and stirring speed 200~500rpm; The Wurtz coupled polymerization reaction conditions are: temperature 65~110℃, stirring speed 300~800rpm, reaction time 10~15h, and nitrogen flow rate 0.5~1L / min.

9. The polymethylsilane with adjustable C / Si atomic ratio prepared by any one of claims 1 to 8.

10. The application of the polymethylsilane with adjustable C / Si atomic ratio prepared by the preparation method according to any one of claims 1 to 8 in the pyrolysis preparation of SiC ceramics.

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