New method for electrochemically preparing liquid polycarbosilane with high alkenyl content and silicon hydrogen content

Abstract

The invention relates to a novel method for electrochemically preparing liquid polycarbosilane with high alkenyl and silicon hydrogen content, and belongs to the technical field of high-performance ceramic material synthesis, the method comprises the following steps: in an inert atmosphere, putting first substituted silane into a reaction tank containing electrolyte and an organic solvent, and carrying out prepolymerization reaction under an electrified condition to obtain a prepolymer; mixing the prepolymer with second substituted silane and third substituted silane, carrying out a copolymerization reaction under a power-on condition, adding chloropropene to terminate the reaction, and carrying out separation and purification to obtain liquid polycarbosilane with high alkenyl and silicon hydrogen content; according to the method, the conditions of high temperature, high pressure and the like are not needed, the polymerization of halogen-containing substituted silane can be realized at normal temperature and normal pressure, and the liquid polycarbosilane with proper viscosity and higher ceramic yield can be obtained without using a reducing agent such as LiAlH4 and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance ceramic material synthesis, and particularly to a new method for electrochemically preparing liquid polycarbosilane with high vinyl and silicon hydride contents. Background Art

[0002] High-performance ceramic materials have extremely high temperature resistance, oxidation resistance, corrosion resistance, etc., and are a high-tech new material that is difficult to match with general metal materials and polymer materials. Therefore, they have great application potential in the fields of aviation, aerospace industry and energy-related fields. Silicon carbide ceramics have the advantages of corrosion resistance, wear resistance, good high-temperature stability, light weight, high strength, etc., and can be used to manufacture hot-end components of aero-engine, support structures of space remote sensing systems, thermal protection materials of space launch vehicles, etc. As a precursor of silicon carbide ceramics, increasing the ceramic yield of polycarbosilane can better meet the harsh requirements of these high-end applications for material properties, enabling related components to have a longer service life and higher reliability in extreme environments.

[0003] As a key raw material for preparing C / SiC ceramic matrix composites by the PIP method, the key performance indicators of polycarbosilane (PCS) mainly include the following aspects: (1) Moderate molecular weight (600-1000) and narrow molecular weight distribution (PDI < 2.5); (2) The viscosity is generally 20-100 mPa·s. If the viscosity is too high, impregnation is difficult and it is difficult to fill the tiny pores in the preform; if the viscosity is too low, although the fluidity is good, it may be difficult to form a stable coating; (3) The ceramic yield is directly related to the content of the SiC matrix in the final C / SiC composite material. A high ceramic yield means that more PCS can be converted into SiC, thereby improving the density and mechanical properties of the composite material. Generally, the higher the better.

[0004] Currently reported synthesis methods include ring-opening polymerization method, Grignard coupling polymerization method, Wurtz coupling polymerization method, hydrosilylation method, etc., and these methods all have some disadvantages. For example, the raw materials used in the ring-opening polymerization method are difficult to obtain and the synthesis cost is relatively high, resulting in the inability to synthesize a large amount of liquid hyperbranched polycarbosilane; a large amount of lithium aluminum hydride used in the Grignard coupling polymerization method will bring unforeseeable safety hazards, and a large amount of wastewater will be generated during the post-treatment of the product, which also greatly limits its application.

[0005] Electrochemical reduction is a method for synthesizing polysilanes that has emerged in recent years. This method involves preparing polysilanes by cathodic reduction of silane monomers in an electrolytic cell. In 1993, Nonaka et al. used (chloromethyl)dimethylsilane as the raw material, aluminum as the anode, Ni as the cathode, and ethylene glycol dimethyl ether and tetrahydrofuran as solvents to synthesize Si-C oligomers without active groups, with a low ceramic yield. In 2008, Wang et al. synthesized polymers containing a large number of Si-Cl groups by an electrochemical method using (chloromethyl)dichlorosilane as the raw material, and still used LiAlH4 for reduction, resulting in too high a cost. Summary of the Invention

[0006] In view of one or more technical problems existing in the prior art, the present invention provides a new method for electrochemically preparing liquid polycarbosilane with high alkenyl and silicon hydride contents. This method does not require conditions such as high temperature and high pressure, realizes the polymerization of halogen-substituted silanes at normal temperature and pressure, and obtains liquid polycarbosilane with suitable viscosity and high ceramic yield without using reducing agents such as LiAlH4.

[0007] In a first aspect, the present invention provides a new method for electrochemically preparing liquid polycarbosilane with high alkenyl and silicon hydride contents, the method comprising:

[0008] Under an inert atmosphere, placing a first substituted silane in a reaction cell containing an electrolyte and an organic solvent, and carrying out a prepolymerization reaction under the condition of energization to obtain a prepolymer;

[0009] Mixing the prepolymer with a second substituted silane and a third substituted silane, and carrying out a copolymerization reaction under the condition of energization, adding allyl chloride to terminate the reaction, and obtaining liquid polycarbosilane with high alkenyl and silicon hydride contents through separation and purification;

[0010] The molecular formula of the first substituted silane is R1R2R3SiCH2X, the molecular formula of the second substituted silane is R4R5XSiCH=CH2, and the molecular formula of the third substituted silane is R6R7XSi-H; wherein, R1, R2, R3, R4, R5, R6, R7 are selected from one of saturated hydrocarbon groups, unsaturated hydrocarbon groups with ≤5 carbon atoms, aromatic groups, and halogens; X is a halogen.

[0011] Preferably, at least one of the first substituted silanes is a substituted silane containing two or more halogen atoms in the molecule.

[0012] Preferably, the electrolyte includes one or more of ammonium tetrabutylborate (NBu4BF4), tetrabutylphosphonium tetrafluoroborate (NBu4PF4), ammonium tetrabutyl iodide (NBu4I4), ammonium tetrabutyl bromide (NBu4Br4), sodium tetrafluoroborate (NaBF4), sodium tetrafluorophosphate (NaPF4), sodium iodide (NaI), sodium bromide (NaBr), lithium iodide (LiI), lithium bromide (LiBr), lithium tetrafluoroborate (LiBF4), lithium tetrafluorophosphate (LiPF4), tetrabutylammonium perchlorate (TBAP), sodium perchlorate (NaClO4), lithium perchlorate (LiClO4), and ammonium tetrabutyl perchlorate (NBu4ClO4).

[0013] Preferably, the organic solvent is one or more of tetrahydrofuran (THF), N,N-dimethylformamide (DMF), acetonitrile (MeCN), dichloromethane (DCM), dimethyl sulfoxide (DMSO), acetone, methanol, ethylene carbonate (EC), tris(3,6-dioxaheptyl)amine (TDA-1), ethylene glycol dimethyl ether (DME), and dimethylacetamide (DMA).

[0014] Preferably, the electrode pair used in the reaction cell is one of Al-Fe, Mg-Fe, Ni-Fe, Cu-Fe, Mg-Fe, Zn-Fe, Mg-Mg, Mg-C, C-C, Pt-C, and Pt-Pt.

[0015] Preferably, the inert gas is one of nitrogen and helium.

[0016] Preferably, the number of moles of allyl chloride is greater than the number of moles of remaining Si-Cl in the reaction system after the copolymerization reaction.

[0017] Preferably, the separation and purification include filtering, concentrating, extracting, washing, and drying the mixed system after the reaction ends.

[0018] In a second aspect, the present invention provides a liquid polycarbosilane with high alkenyl and silicon hydrogen content, which is synthesized by the method described in the first aspect.

[0019] In a third aspect, the present invention provides an application of the liquid polycarbosilane with high alkenyl and silicon hydrogen content described in the second aspect, which is applied to the preparation of silicon carbide ceramics.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] The present invention first conducts an electrochemical prepolymerization reaction on a first substituted silane containing a -CH2Cl substituent to form a prepolymer with a main chain having an alternating arrangement of silicon and carbon atoms. Then, the prepolymer is electrochemically copolymerized with a second substituted silane containing a -CH2=CH and a halogen substituent and a third substituted silane containing a Si-H group to form a hyperbranched polycarbosilane while introducing a large number of carbon-carbon double bonds and Si-H active groups into the polymer. Finally, the reaction is terminated by reacting allyl chloride with the remaining Si-Cl, and the Si-Cl can be removed without using reducing agents such as LiAlH4. At the same time, carbon-carbon double bonds can also be introduced to obtain a hyperbranched polycarbosilane without Si-Cl and with high vinyl and high Si-H contents, thereby improving the ceramic yield of the polycarbosilane.

[0022] The synthesis method of the polycarbosilane of the present invention does not require conditions such as high temperature and high pressure, realizes the polymerization of halogen-substituted silanes at normal temperature and pressure, and obtains a hyperbranched polycarbosilane with high vinyl and high Si-H contents without using reducing agents such as LiAlH4. The preparation method is simple, the conditions are easy to control, and energy is saved, effectively solving the problem of too high preparation cost. Its high performance and low cost are the keys to promoting from "usable" to "affordable". The polycarbosilane prepared by this method has a suitable viscosity, can effectively improve the impregnation efficiency in the preparation process of ceramic materials, and has a low crosslinking temperature, which can effectively improve the ceramic yield of ceramic materials, thereby enhancing the high-temperature oxidation resistance and mechanical properties of ceramic materials. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 1H-NMR spectrum of the liquid polycarbosilane with high vinyl and Si-H contents synthesized in Example 1 of the present invention;

[0025] Figure 2 13C-NMR spectrum of the liquid polycarbosilane with high vinyl and Si-H contents synthesized in Example 1 of the present invention;

[0026] Figure 3 FTIR spectrum of the liquid polycarbosilane with high vinyl and Si-H contents synthesized in Example 1 of the present invention;

[0027] Figure 4 Gel permeation chromatography (GPC) of the liquid polycarbosilane with high vinyl and Si-H contents synthesized in Example 1 of the present invention;

[0028] Figure 5 This is the thermogravimetric curve (TG) of the liquid polycarbosilane with high vinyl and silicon hydride contents synthesized in Example 1 of the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] In the first aspect, the present invention provides a new method for electrochemically preparing a liquid polycarbosilane with high vinyl and silicon hydride contents. The method includes:

[0031] Under an inert atmosphere, a first substituted silane is placed in a reaction cell containing an electrolyte and an organic solvent, and a prepolymerization reaction is carried out under the condition of energization to obtain a prepolymer;

[0032] The prepolymer is mixed with a second substituted silane and a third substituted silane, and a copolymerization reaction is carried out under the condition of energization. Chloropropene is added to terminate the reaction, and after separation and purification, a liquid polycarbosilane with high vinyl and silicon hydride contents is obtained; the molecular formula of the first substituted silane is R1R2R3SiCH2X, the molecular formula of the second substituted silane is R4R5XSiCH=CH2, and the molecular formula of the third substituted silane is R6R7XSi-H; wherein, R1, R2, R3, R4, R5, R6, R7 are selected from one of saturated hydrocarbon groups, unsaturated hydrocarbon groups, aromatic groups, and halogens with ≤5 carbon atoms; X is a halogen.

[0033] The present invention first carries out an electrochemical prepolymerization reaction on the first substituted silane containing a -CH2Cl substituent to form a prepolymer with a main chain having an alternating arrangement of silicon and carbon atoms, and then electrochemically copolymerizes the prepolymer with the second substituted silane containing -CH2=CH and halogen substituents and the third substituted silane containing a Si-H group to introduce a large number of carbon-carbon double bonds and silicon hydride active groups in the polymer while forming a hyperbranched polycarbosilane. Finally, chloropropene is used to react with the remaining Si-Cl to terminate the reaction, and Si-Cl can be removed without using a reducing agent such as LiAlH4, and at the same time, carbon-carbon double bonds can be introduced to obtain a hyperbranched polycarbosilane without Si-Cl and with high vinyl and high silicon hydride contents, improving the ceramic yield of the polycarbosilane.

[0034] The synthesis method of the polycarbosilane of the present invention does not require conditions such as high temperature and high pressure, polymerizes halogen-substituted silanes at normal temperature and pressure, and obtains hyperbranched polycarbosilane with high vinyl and high silicon-hydrogen content without using reducing agents such as LiAlH4. The preparation method is simple, the conditions are easy to control, and energy is saved, effectively solving the problem of too high preparation cost. Its high performance and low cost are the key to promoting from "being available" to "being affordable". The polycarbosilane prepared by this method has a suitable viscosity, can effectively improve the impregnation efficiency in the preparation process of ceramic materials, and has a low cross-linking temperature, can effectively improve the ceramic yield of ceramic materials, and further improve the high-temperature oxidation resistance and mechanical properties of ceramic materials.

[0035] In the present invention, the time of the prepolymerization reaction and the copolymerization reaction is determined by the magnitude of the energized current.

[0036] According to some preferred embodiments, the first substituted silane includes at least one substituted silane containing two or more halogen atoms in the molecule. The first substituted silane of the present invention can include a variety of monomers, at least one of which has two or more halogen atoms, that is, at least one of R1, R2, and R3 in the monomer is a halogen.

[0037] According to some preferred embodiments, the electrolyte includes one or more of tetrabutylammonium tetrafluoroborate (NBu4BF4), tetrabutylphosphonium tetrafluoroborate (NBu4PF4), tetrabutylammonium iodide (NBu4I4), tetrabutylammonium bromide (NBu4Br4), sodium tetrafluoroborate (NaBF4), sodium tetrafluorophosphate (NaPF4), sodium iodide (NaI), sodium bromide (NaBr), lithium iodide (LiI), lithium bromide (LiBr), lithium tetrafluoroborate (LiBF4), lithium tetrafluorophosphate (LiPF4), tetrabutylammonium perchlorate (TBAP), sodium perchlorate (NaClO4), lithium perchlorate (LiClO4), tetrabutylammonium perchlorate (NBu4ClO4).

[0038] According to some preferred embodiments, the organic solvent is one or more of tetrahydrofuran (THF), N,N-dimethylformamide (DMF), acetonitrile (MeCN), dichloromethane (DCM), dimethyl sulfoxide (DMSO), acetone, methanol, ethylene carbonate (EC), tris(3,6-dioxaheptyl)amine (TDA-1), ethylene glycol dimethyl ether (DME), dimethylacetamide (DMA).

[0039] According to some preferred embodiments, the electrode pair used in the reaction cell is one of Al-Fe, Mg-Fe, Ni-Fe, Cu-Fe, Mg-Fe, Zn-Fe, Mg-Mg, Mg-C, C-C, Pt-C, Pt-Pt.

[0040] According to some preferred embodiments, the inert gas is one of nitrogen and helium.

[0041] According to some preferred embodiments, the number of moles of allyl chloride is greater than the number of moles of remaining Si-Cl in the reaction system after the copolymerization reaction. In the present invention, the amount of Si-Cl participating in the reaction is calculated by the amount of charge transferred during the reaction, and the reaction is terminated by adding an excessive amount of allyl chloride (the number of moles of allyl chloride is preferably 1.5 times the number of moles of remaining Si-Cl in the reaction system after the copolymerization reaction) to react with the remaining Si-Cl in the polymer, while consuming the Si-Cl in the polymer to obtain a polycarbosilane without Si-Cl.

[0042] According to some preferred embodiments, the separation and purification includes filtering, concentrating, extracting, washing, and drying the mixed system after the reaction ends.

[0043] According to some specific embodiments, the solvent used for extraction is at least one of n-hexane, ether, and petroleum ether, and the desiccant used for drying is anhydrous sodium sulfate.

[0044] In the second aspect, the present invention provides a liquid polycarbosilane with high vinyl and silicon hydride content, which is synthesized by the method described in the first aspect.

[0045] The liquid polycarbosilane of the present invention has a hyperbranched structure, moderate viscosity, can effectively improve the impregnation efficiency in the preparation process of ceramic materials, and has a low crosslinking temperature, can effectively improve the ceramic yield of ceramic materials, and further improve the high-temperature oxidation resistance and mechanical properties of ceramic materials, and can be used for the preparation of high-performance silicon carbide ceramics.

[0046] In the third aspect, the present invention provides an application of the liquid polycarbosilane with high vinyl and silicon hydride content described in the second aspect, which is applied to the preparation of silicon carbide ceramics.

[0047] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention will be further described below with reference to examples. The present invention does not specifically limit the sources of each reagent used in the examples and comparative examples, and they can be directly purchased or synthesized by oneself.

[0048] Example 1

[0049] (1) Add 66 g of electrolyte NBu4BF4 (0.2 M) into the reaction cell. The reaction electrode is Mg-C. Vacuum the reaction system, and then displace the gas in the reaction system with an inert gas to atmospheric pressure, and repeat at least 3 times to maintain an inert atmosphere in the reaction system. Add 100 mL of ultra-dry solvent (the volume ratio of DMF to THF is 1:1). After starting stirring and dissolution, add 26 mL of Si(CH2Cl)Cl2CH3 (0.2 M), 27 mL of Si(CH2Cl)Cl(CH3)2 (0.2 M), and 25 mL of Si(CH2Cl)(CH3)3 (0.2 M). Set the current to 50 mA. After stirring for 24 h, a polymerization reaction occurs to obtain a prepolymer.

[0050] (2) Maintain an inert atmosphere. Add 13 mL of (CH2=CH)SiCl3 (0.1 M), 12 mL of (CH2=CH)SiCl2CH3 (0.1 M), and 15 mL of Cl(CH3)2SiH (0.15 M) to the prepolymer. Continue to energize and stir for the reaction. After the reaction is completed, add 30 mL of allyl chloride to react with the remaining Si-Cl to terminate the reaction. Then filter the reaction mixture system and concentrate the filtrate. Add 20 mL of n-hexane and 80 mL of water for extraction and washing 3 times. Collect the upper layer liquid, add anhydrous sodium sulfate for drying, and concentrate to obtain 57.2 g of liquid polycarbosilane with high vinyl and silicon hydride content.

[0051] The liquid polycarbosilane synthesized in this example has a hyperbranched structure, excellent comprehensive properties, a ceramic yield of 53%, a number-average molecular weight of 677, and a viscosity of 98 mPa·s.

[0052] The 1H NMR spectrum of the liquid polycarbosilane with high vinyl and silicon hydride content synthesized in this example in deuterated chloroform is as Figure 1 shown. The sharp peak at the chemical shift δ = 7.26 ppm is the intrinsic hydrogen NMR peak of deuterated chloroform. The sharp peaks at the chemical shift δ = 5.5 - 6.1 ppm are the hydrogens on CH2=CH, and the broad peak at δ = 4.5 ppm belongs to the hydrogens on Si-H. The results of this figure indicate the successful introduction of CH2=CH and Si-H bonds.

[0053] The 13C NMR spectrum of the liquid polycarbosilane with high vinyl and silicon hydride content synthesized in this example in deuterated chloroform is as Figure 2 shown. The sharp peaks at the chemical shift δ = 120 - 140 ppm are the carbons on CH2=CH, and the peak at 0 ppm belongs to the carbons on Si-C-Si.

[0054] The infrared spectrum of the liquid polycarbosilane with high vinyl and silicon hydride content prepared in Example 1 of the present invention is as Figure 3 shown. The wavelength is 1000 - 1050 cm -1The peak at [location] is the out-of-plane vibration peak of the Si-O-Si bond, 2100 cm -1 The peak at [location] is the stretching vibration peak of the Si-H bond, 950 - 800 cm -1 The peak at [location] is the deformation vibration peak of the Si-H bond, 3000 cm -1 The peak at [location] is the stretching vibration peak of the saturated C-H bond on the methyl group, 770 cm -1 The peak at [location] is the stretching vibration peak of the Si-C bond, 920 cm -1 The peak at [location] is the stretching vibration peak of Si-C=C.

[0055] The GPC spectrum of the high-vinyl and silicon-hydrogen-containing liquid polycarbosilane prepared in Example 1 of the present invention is as Figure 4 shown. The number-average molecular weight (Mn) of the liquid polysilane is 535, the weight-average molecular weight (Mw) is 1209, and the molecular weight distribution coefficient PDI (Mw / Mn) is 2.26, indicating that the liquid polysilane has a good branched structure.

[0056] The TG curve of the high-vinyl and silicon-hydrogen-containing liquid polycarbosilane synthesized in this example is as Figure 5 shown. The ceramic yield of the polysilane is 53% at 1200 °C in a nitrogen atmosphere.

[0057] As can be seen from the above, hyperbranched liquid polycarbosilanes with high ceramic yields, relatively large molecular weights, and relatively low viscosities can be obtained by introducing vinyl groups and silicon-hydrogen into polycarbosilane through an electrochemical method.

[0058] Example 2

[0059] (1) Add 66 g of electrolyte NBu4BF4 (0.2 M) to the reaction cell. The reaction electrode is Al-Fe. Evacuate the reaction system, and then replace the gas in the reaction system with an inert gas to atmospheric pressure, and repeat at least 3 times to maintain an inert atmosphere in the reaction system. Add 100 mL of ultra-dry solvent MeCN. After starting stirring and dissolving, add 26 mL of Si(CH2Cl)Cl2CH3 (0.2 M), 29 mL of Si(CH2Cl)Cl(Ph)2 (0.2 M), and 25 mL of Si(CH2Cl)(Ph)3 (0.2 M). Set the applied current to 50 mA. After stirring for 24 h, a polymerization reaction occurs to obtain a prepolymer.

[0060] (2) Maintain an inert atmosphere, add 13 mL of (CH2=CH)SiCl3 (0.1 M) and 15 mL of Cl(CH3)2SiH (0.15 M), continue to conduct electricity and stir for the reaction. After the reaction is completed, add 30 mL of allyl chloride to react with the remaining Si-Cl to terminate the reaction. Subsequently, filter the reaction mixture system and concentrate the filtrate. Add 20 mL of n-hexane and 80 mL of water for extraction and washing three times. Collect the upper layer liquid, add anhydrous sodium sulfate for drying, and concentrate to obtain 46.1 g of liquid polycarbosilane with high vinyl and silicon hydride content.

[0061] The liquid polycarbosilane synthesized in this example has a hyperbranched structure, excellent comprehensive properties, a ceramic yield of 42%, a number average molecular weight of 563, and a viscosity of 72 mPa·s.

[0062] Example 3

[0063] (1) Add 66 g of electrolyte NBu4BF4 (0.2 M) into the reaction cell, and the reaction electrode is Al-Fe. Evacuate the reaction system, and then displace the gas in the reaction system with an inert gas to atmospheric pressure, and repeat at least 3 times. Maintain an inert atmosphere in the reaction system, add 100 mL of ultra-dry solvent DMF, start stirring to dissolve, add 13 mL of Si(CH2Cl)Cl2CH3 (0.1 M) and 27 mL of Si(CH2Cl)Cl(CH3)2 (0.2 M), set the applied current to 50 mA, and stir for 24 h to carry out a polymerization reaction to obtain a prepolymer.

[0064] (2) Maintain an inert atmosphere, add 26 mL of (CH2=CH)SiCl3 (0.2 M) and 40 mL of Cl(CH3)2SiH (0.4 M) to the prepolymer, continue to conduct electricity and stir for the reaction. After the reaction is completed, add 30 mL of allyl chloride to react with the remaining Si-Cl to terminate the reaction. Subsequently, filter the reaction mixture system and concentrate the filtrate. Add 20 mL of n-hexane and 80 mL of water for extraction and washing three times. Collect the upper layer liquid, add anhydrous sodium sulfate for drying, and concentrate to obtain 47.6 g of liquid polycarbosilane with high vinyl and silicon hydride content.

[0065] The liquid polycarbosilane synthesized in this example has a hyperbranched structure, excellent comprehensive properties, a ceramic yield of 41%, a number average molecular weight of 577, and a viscosity of 102 mPa·s.

[0066] Example 4

[0067] (1) Add 68 g of electrolyte TBAClO4 (0.2 M) into the reaction cell. The reaction electrode is Al-Fe. Evacuate the reaction system, then displace the gas in the reaction system with an inert gas to atmospheric pressure, and repeat at least 3 times to maintain an inert atmosphere in the reaction system. Add 100 mL of ultra-dry solvent (a 1:1 volume ratio mixture of DMF and THF). After starting stirring for dissolution, add 26 mL of Si(CH2Cl)Cl2CH3 (0.2 M), 13 mL of Si(CH2Cl)Cl(CH3)2 (0.1 M), and 12 mL of Si(CH2Cl)(CH3)3 (0.1 M). Set the applied current to 50 mA. After stirring for 24 h, a polymerization reaction occurs to obtain a prepolymer.

[0068] (2) Maintain the inert atmosphere. Add 13 mL of (CH2=CH)SiCl3 (0.1 M) and 15 mL of Cl(CH3)2SiH (0.15 M) to the prepolymer, and continue the reaction with stirring under applied current. After the reaction ends, add 30 mL of allyl chloride to react with the remaining Si-Cl to terminate the reaction. Subsequently, filter the reaction mixture and concentrate the filtrate. Add 20 mL of n-hexane and 80 mL of water for extraction and washing 3 times. Collect the upper layer liquid, add anhydrous sodium sulfate for drying, and concentrate to obtain 59.2 g of a liquid polycarbosilane with high vinyl and silicon hydride contents.

[0069] The liquid polycarbosilane synthesized in this example has a hyperbranched structure, excellent comprehensive properties, a ceramic yield of 29%, a number average molecular weight of 467, and a viscosity of 44 mPa·s.

[0070] Example 5

[0071] (1) Add 66 g of electrolyte NBu4BF4 (0.2 M) into the reaction cell. The reaction electrode is Al-Fe. Evacuate the reaction system, then displace the gas in the reaction system with an inert gas to atmospheric pressure, and repeat at least 3 times to maintain an inert atmosphere in the reaction system. Add 100 mL of ultra-dry DMF. After starting stirring for dissolution, add 27 mL of Si(CH2Cl)Cl(CH3)2 (0.2 M) and 25 mL of Si(CH2Cl)(CH3)3 (0.2 M). Set the applied current to 50 mA. After stirring for 24 h, a polymerization reaction occurs to obtain a prepolymer.

[0072] (2) Maintain an inert atmosphere, add 26 mL of (CH2=CH)SiCl3 (0.2 M) and 40 mL of Cl(CH3)2SiH (0.4 M) to the prepolymer, continue to stir under electricity for reaction. After the reaction, add 30 mL of allyl chloride to react with the remaining Si-Cl to terminate the reaction. Subsequently, filter the reaction mixture and concentrate the filtrate, extract and wash with 20 mL of n-hexane and 80 mL of water for 3 times, collect the upper layer liquid, add anhydrous sodium sulfate for drying, and concentrate to obtain 34.6 g of liquid polycarbosilane with high vinyl and silicon hydride content.

[0073] The liquid polycarbosilane synthesized in this example has a hyperbranched structure, excellent comprehensive properties, a ceramic yield of 32%, a number-average molecular weight of 594, and a viscosity of 87 mPa·s.

[0074] Comparative Example 1

[0075] (1) Add 66 g of electrolyte NBu4BF4 (0.2 M) into the reaction cell, and the reaction electrode is Mg-C. Evacuate the reaction system, and then replace the gas in the reaction system with inert gas to normal pressure, repeat ≥3 times to maintain an inert atmosphere in the reaction system. Add 100 mL of ultra-dry solvent (the volume ratio of DMF to THF is 1:1), start stirring to dissolve, add Si(CH2Cl)Cl(CH3)2, set the electric current to 50 mA, and stir for 24 h to initiate a polymerization reaction.

[0076] (2) After the reaction, add allyl chloride to react with the remaining Si-Cl to terminate the reaction. Subsequently, filter and concentrate the filtrate, extract and wash with 20 mL of n-hexane and 80 mL of water for 3 times, collect the upper layer liquid, add anhydrous sodium sulfate for drying, and concentrate to obtain 36.5 g of linear liquid polycarbosilane with a small amount of double bonds.

[0077] The liquid polycarbosilane synthesized in this comparative example has a linear structure and a small vinyl content, with poor product performance, a ceramic yield of only 13%, a number-average molecular weight of 306, and a viscosity of 40 mPa·s.

[0078] Comparative Example 2

[0079] (1) Add 66 g of electrolyte NBu4BF4 (0.2 M) into the reaction cell, and the reaction electrode is Mg-C. Evacuate the reaction system, and then replace the gas in the reaction system with inert gas to normal pressure, repeat ≥3 times to maintain an inert atmosphere in the reaction system. Add 100 mL of ultra-dry solvent (the volume ratio of DMF to THF is 1:1), start stirring to dissolve, add Si(CH2Cl)Cl2CH3, set the electric current to 50 mA, and stir for 24 h to initiate a polymerization reaction.

[0080] (2) After the reaction is completed, allyl chloride is added to react with the remaining Si-Cl to terminate the reaction. Subsequently, the filtrate is filtered and concentrated, and 20 mL of n-hexane and 80 mL of water are added for extraction and washing three times. The upper layer liquid is collected, anhydrous sodium sulfate is added for drying, and after concentration, 41.1 g of liquid polycarbosilane containing a small amount of double bonds is obtained.

[0081] Although the liquid polycarbosilane synthesized in this comparative example changes from a linear structure to a branched structure, the content of alkenyl groups is small, and the comprehensive properties of its products are still not good. The ceramic yield is only 18%, the number average molecular weight is 377, and the viscosity is 32 mPa·s.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A new method for electrochemically preparing liquid polycarbosilane with high vinyl and silicon hydride contents, characterized in that, The method includes: Under an inert atmosphere, placing a first substituted silane in a reaction cell containing an electrolyte and an organic solvent, and carrying out a prepolymerization reaction under the condition of energization to obtain a prepolymer; Mixing the prepolymer with a second substituted silane and a third substituted silane, and carrying out a copolymerization reaction under the condition of energization, adding allyl chloride to terminate the reaction, and through separation and purification, obtaining a liquid polycarbosilane with high vinyl and silicon hydride contents; The molecular formula of the first substituted silane is R1R2R3SiCH2X, the molecular formula of the second substituted silane is R4R5XSiCH=CH2, and the molecular formula of the third substituted silane is R6R7XSi-H; wherein, R1, R2, R3, R4, R5, R6, R7 are selected from one of saturated hydrocarbon groups, unsaturated hydrocarbon groups with ≤5 carbon atoms, aromatic groups, and halogens; X is a halogen.

2. The method according to claim 1, wherein The first substituted silane includes at least one substituted silane containing two or more halogen atoms in the molecule.

3. The method according to claim 1, characterized in that The electrolyte includes one or more of ammonium tetrafluoroborate, tetrabutylphosphonium tetrafluoroborate, tetrabutylammonium iodide, tetrabutylammonium bromide, sodium tetrafluoroborate, sodium tetrafluorophosphate, sodium iodide, sodium bromide, lithium iodide, lithium bromide, lithium tetrafluoroborate, lithium tetrafluorophosphate, tetrabutylammonium perchlorate, sodium perchlorate, lithium perchlorate, and tetrabutylammonium perchlorate.

4. The method according to claim 1, wherein The organic solvent is one or more of tetrahydrofuran, N,N-dimethylformamide, acetonitrile, dichloromethane, dimethyl sulfoxide, acetone, methanol, ethylene carbonate, tris(3,6-dioxaheptyl)amine, ethylene glycol dimethyl ether, and dimethylacetamide.

5. The method according to claim 1, wherein The electrode pair used in the reaction cell is one of Al-Fe, Mg-Fe, Ni-Fe, Cu-Fe, Mg-Fe, Zn-Fe, Mg-Mg, Mg-C, C-C, Pt-C, and Pt-Pt.

6. The method according to claim 1, characterized in that The inert gas is one of nitrogen and helium.

7. The method according to claim 1, characterized in that The molar amount of the allyl chloride is greater than the molar amount of the remaining Si-Cl in the reaction system after the copolymerization reaction.

8. The method according to claim 1, wherein The separation and purification includes filtering, concentrating, extracting, washing, and drying the mixed system after the reaction ends.

9. A liquid polycarbosilane with a high vinyl group and silicon hydride content, characterized in that, Synthesized by using the method according to any one of claims 1-8.

10. Use of the liquid polycarbosilane with a high vinyl group and silicon hydride content according to claim 9, characterized in that, Applied to the preparation of silicon carbide ceramics.

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