A silicon carbide fiber precursor, polycarbosilane, and its preparation method

Abstract

This invention discloses a silicon carbide fiber precursor polycarbosilane and its preparation method, belonging to the field of polycarbosilane preparation technology. The preparation method of the silicon carbide fiber precursor polycarbosilane includes the following steps: Step 1: Preparing a Grignard reagent; Step 2: Adding an organic alkane to tetrahydrofuran, stirring and mixing, then slowly adding it to the Grignard reagent, stirring and reacting; after the reaction is complete, heating to room temperature, adding a composite organic auxiliary agent, stirring and reacting; after the reaction is complete, quenching the reaction, separating the liquids, washing, and drying to obtain a prepolymer; Step 3: After vacuum distillation of the prepolymer, transferring it to a reaction vessel, heating and polymerizing it under argon atmosphere; after the reaction is complete, adding it to toluene, dissolving, filtering, precipitating, and drying to obtain the silicon carbide fiber precursor polycarbosilane. The polycarbosilane prepared by the above method has excellent thermal stability and high-temperature mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of polycarbosilane preparation technology, specifically relating to a silicon carbide fiber precursor polycarbosilane and its preparation method. Background Technology

[0002] Polycarbosilanes, as key precursors for the preparation of high-performance silicon carbide fibers, originated from the urgent need for high-temperature resistant ceramic materials in the 20th century. Early research used chlorosilanes such as dichlorodimethylsilane as raw materials, synthesizing them through processes such as sodium condensation or pyrolysis rearrangement. However, the resulting products contained oxygen or metallic impurities, leading to insufficient high-temperature oxidation resistance in the final fibers. With advancements in materials science, researchers have significantly improved the purity and molecular structure regularity of precursors by optimizing polymerization pathways, such as using electron beam irradiation and chemical vapor crosslinking, thereby improving the temperature resistance and mechanical properties of the fibers. Simultaneously, breakthroughs in forming technologies such as dry spinning and melt spinning have enabled the preparation of continuous and uniform fiber precursors from polycarbosilanes, laying the foundation for subsequent non-melting treatment and high-temperature pyrolysis. In recent years, with the increasing demand for lightweight, high-strength ceramic matrix composites in the aerospace field, polycarbosilanes, due to their strong designability and good process compatibility, have become a core raw material for the industrialization of silicon carbide fibers, driving the evolution of high-temperature structural materials towards higher performance.

[0003] Patent CN106987924B discloses a method for preparing polycarbosilane infusible fibers, comprising the following steps: 1) blending polycarbosilane with vinylsilazane to obtain spinning polycarbosilane; 2) melt spinning the spinning polycarbosilane and introducing an initiator to obtain polycarbosilane fibers; 3) crosslinking the polycarbosilane fibers under ultraviolet light and heat to obtain pre-cured polycarbosilane fibers; 4) heat-treating the pre-cured polycarbosilane fibers in an inert atmosphere to obtain infusible polycarbosilane fibers. This invention can achieve low-oxygen infusibility (≤2wt%) of polycarbosilane fibers, uses simple equipment, has low cost, and causes little environmental pollution, making it suitable for continuous industrial production and showing great application prospects in the preparation of high-performance SiC fibers. Although the above-mentioned patented method shows many advantages in the preparation of infusible polycarbosilane fibers, the polycarbosilane prepared by this method still has significant defects when further preparing fibers, mainly in that the mechanical properties of the fibers are difficult to reach the ideal level, and the strength and toughness need to be improved. The reason for this defect is that the synergy between the steps in the blending reaction, melt spinning, crosslinking and heat treatment is insufficient, resulting in an uneven and dense internal structure of the fiber and unstable interaction between molecular chains, which in turn affects the overall mechanical properties of the fiber. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon carbide fiber precursor, polycarbosilane, and its preparation method, to solve the technical problems of poor ceramic yield, thermal stability, and spinnability of polycarbosilane used as a silicon carbide fiber precursor in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing polycarbosilane, a silicon carbide fiber precursor, comprising the following steps:

[0007] Step 1: Under argon atmosphere, vinyl chloride and magnesium shavings are added to tetrahydrofuran, heated and stirred to react. After the reaction is complete, Grignard reagent is obtained.

[0008] Step 2: Add the organic alkane to tetrahydrofuran, stir and mix, then slowly add it to the Grignard reagent, stir and react. After the reaction is complete, heat to room temperature, add the composite organic auxiliaries, stir and react. After the reaction is complete, quench the reaction, separate the liquids, wash, and dry to obtain the prepolymer.

[0009] Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it for polymerization under argon atmosphere. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

[0010] Preferably, the method for preparing the organic alkane includes the following steps:

[0011] Q1: In an argon glove box, 1,5-cyclooctadiene nickel, triphenylphosphine, zinc powder, 1-phenylbutadiene and diphenyldichlorosilane are added sequentially to a container containing tetrahydrofuran. After the addition is complete, the container is sealed and the reaction is carried out by magnetic stirring.

[0012] Q2: Add ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash, and dry to obtain an organic alkane.

[0013] In the above process, the synthesis reaction formula for organic alkanes is as follows:

[0014]

[0015] The mass spectrometry analysis results of the organic alkanes were as follows: m / z: 312.13 (100.0%), 313.14 (24.0%), 313.13 (5.1%), 314.14 (4.0%), 314.13 (3.3%).

[0016] Preferably, in Q1, the ratio of 1,5-cyclooctadiene nickel, triphenylphosphine, zinc powder 1-phenylbutadiene, diphenyldichlorosilane, and tetrahydrofuran is (0.33-0.38) g : (0.41-0.53) g : (0.02-0.06) g : (1.12-1.64) g : (2.02-2.35) g : (6-9) mL, the magnetic stirring reaction temperature is 25-30℃, and the time is 20-24 h.

[0017] Preferably, in Q2, the volume of ethyl acetate added is 5-8 mL, and the mixture is washed successively with deionized water and saturated sodium chloride aqueous solution, and then dried with anhydrous sodium sulfate.

[0018] Preferably, the preparation method of the composite organic additive includes the following steps:

[0019] S1: Under nitrogen atmosphere, decaborane was added to a container containing acetonitrile, and the mixture was heated under reflux. After the reaction was completed, the mixture was cooled, filtered, washed, and dried to obtain organic compound 1.

[0020] S2: 4,4',4''-triiodotriphenylamine, bis(triphenylphosphine)palladium chloride and cuprous iodide were added to a container. After evacuation, tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature, triethylamine was added and the reaction was continued at room temperature. Then, tetrahydrofuran containing 1-(4-alkynylphenyl)-1,2,2-tristyrene was added and the reaction was stirred at room temperature. After the reaction was completed, the mixture was rotary evaporated and purified to obtain organic compound 2.

[0021] S3: Add organic compound 2 and organic compound 1 to a container, inject toluene under nitrogen atmosphere, reflux the reaction, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

[0022] In the above process, under heating conditions, acetonitrile, as a Lewis base, attacks the boron atom in decaborane with its lone pair of electrons, causing the BHB bridge bond to break. The acetonitrile molecule replaces two bridged hydrogen atoms, yielding organic compound 1. 4,4',4''-triiodotriphenylamine and 1-(4-alkynylphenyl)-1,2,2-triphenylene undergo a Sonogashira cross-coupling reaction in the presence of bis(triphenylphosphine)palladium chloride, cuprous iodide, and triethylamine to prepare organic compound 2. Subsequently, organic compound 2 undergoes an addition reaction with organic compound 1 to prepare a composite organic auxiliary agent.

[0023] Preferably, in S1, the ratio of decborane to acetonitrile is (8.85-9.32) g: (125-158) mL, and the mixture is heated to 90-110℃ and refluxed for 12-18 h.

[0024] Preferably, in S2, the ratio of 4,4',4''-triiodotriphenylamine, bis(triphenylphosphine)palladium chloride, cuprous iodide, and 1-(4-alkynylphenyl)-1,2,2-tristyrene is (0.21-0.33) g : (0.01-0.05) g : (0.004-0.012) g : (0.32-0.48) g. The mixture is stirred at room temperature for 10-20 min, then stirred for another 30-35 min, and finally stirred at room temperature for 20-24 h.

[0025] Preferably, in S3, the ratio of organic compound 2, organic compound 1 and toluene is (0.17-0.23) g: (0.21-0.36) g: (45-55) mL, and the reflux reaction time is 24-48 h.

[0026] Preferably, in step one, the ratio of vinyl chloride, magnesium shavings, and tetrahydrofuran is (0.72-0.92) g : (1.26-1.48) g : (20-25) mL, and the mixture is heated to 40-70℃ and stirred for 18-24 h; in step two, the ratio of organic alkane, tetrahydrofuran, Grignard reagent, and composite organic auxiliaries is (0.82-0.97) g : (18-22) mL : (0.22-0.28) g : (0.68-0.78) g, the stirring temperature is 0-5℃, the stirring time is 1-2 h, the stirring time is 4-8 h, and saturated ammonium chloride aqueous solution is added for quenching; in step three, the temperature is increased to 250-350℃ at a heating rate of 1-5℃ / min, and the polymerization reaction time is 12-20 h.

[0027] A silicon carbide fiber precursor, polycarbosilane, is prepared using the preparation method described above.

[0028] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0029] 1. The present invention applies the prepared organic alkane and composite organic additives to the preparation process of polycarbosilane, which can effectively improve its ceramic yield, spinnability, thermal stability, high-temperature mechanical properties and antioxidant properties.

[0030] 2. The organic alkane obtained in this invention is applied to the preparation process of polycarbosilane, which can effectively improve its ceramic yield, spinnability and thermal stability. The benzene ring contained in the organic alkane is introduced into the polymer backbone. The large steric hindrance effect of the benzene ring can effectively inhibit the premature crosslinking of the prepolymer, thereby improving the rheological properties and facilitating spinning. The high carbon content phenyl can be used as a carbon source in the subsequent thermal polymerization and ceramicization process to inhibit the premature cracking and removal of organic groups around silicon atoms, reducing the quality loss of the ceramicization process. At the same time, the phenyl combines with the boron carbon produced by the decomposition of the composite organic additive, which can form a more uniform Si-BC solid solution in the silicon carbide lattice, enhancing the high-temperature oxidation resistance and crystallization inhibition ability of the material.

[0031] 3. This invention applies the prepared composite organic additive to the preparation process of polycarbosilane, which can effectively improve the ceramic yield, high-temperature mechanical properties and antioxidant properties of polycarbosilane. The composite organic additive can be directly embedded in the polymer chain as a rigid thermally stable unit. The large number of benzene ring structures contained therein can be retained as molecular skeletons and transformed into high-melting-point boron carbide nanophases during subsequent prepolymerization and high-temperature ceramicization, and then dispersed into the silicon carbide matrix. Through the pinning effect, it effectively inhibits the abnormal growth of SiC grains, thereby maintaining the high strength and high modulus of the fiber. At the same time, the introduction of boron element promotes the formation of a dense borosilicate glass protective layer on the material surface under high-temperature oxidation environment, which significantly delays the diffusion of oxygen into the matrix and extends the service life of polycarbosilane. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: This example discloses a method for preparing an organic alkane, comprising the following steps:

[0034] Q1: In an argon glove box, 0.35g of 1,5-cyclooctadiene nickel, 0.47g of triphenylphosphine, 0.04g of zinc powder, 1.38g of 1-phenylbutadiene and 2.18g of diphenyldichlorosilane were added sequentially to a container containing 7.5mL of tetrahydrofuran. After the addition was complete, the container was sealed and the mixture was magnetically stirred at 25°C for 24 hours.

[0035] Q2: Add 5 mL of ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash with deionized water and saturated sodium chloride solution in sequence, and dry with anhydrous sodium sulfate to obtain an organic alkane.

[0036] This embodiment discloses a method for preparing a composite organic additive, including the following steps:

[0037] S1: Under nitrogen atmosphere, 9.08 g of decborane was added to a container containing 137 mL of acetonitrile, heated to 100 °C and refluxed for 18 h. After the reaction was completed, the mixture was cooled, filtered, washed and dried to obtain organic compound 1.

[0038] S2: 0.27 g of 4,4',4''-triiodotriphenylamine, 0.03 g of bis(triphenylphosphine)palladium chloride and 0.008 g of cuprous iodide were added to a container. After evacuation, 5 mL of tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature for 15 min, 0.2 g of triethylamine was added, and the reaction was continued to be stirred at room temperature for 30 min. Then, 4 mL of tetrahydrofuran containing 0.4 g of 1-(4-ynylphenyl)-1,2,2-tristyrene was added, and the reaction was stirred at room temperature for 24 h. After the reaction was completed, the mixture was purified by rotary evaporation to obtain organic compound 2.

[0039] S3: Add 0.2g of organic compound 2 and 0.29g of organic compound 1 to a container, inject 50mL of toluene under nitrogen atmosphere, reflux for 48h, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

[0040] This embodiment discloses a method for preparing polycarbosilane, a silicon carbide fiber precursor, including the following steps:

[0041] Step 1: Under argon atmosphere, add 0.82g vinyl chloride and 1.37g magnesium shavings to 22.5mL tetrahydrofuran, heat to 60℃ and stir for 24h. After the reaction is complete, Grignard reagent is obtained.

[0042] Step 2: Add 0.88g of organic alkane to 20mL of tetrahydrofuran, stir and mix, then slowly add to 0.25g of Grignard reagent, stir and react at 0℃ for 2h. After the reaction is complete, heat to room temperature, add 0.73g of composite organic auxiliaries, stir and react for 6h. After the reaction is complete, add saturated ammonium chloride aqueous solution for quenching, separate the liquid, wash, and dry to obtain the prepolymer.

[0043] Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it to 250°C at a rate of 4°C / min under argon atmosphere for 18 hours for polymerization. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

[0044] Example 2: This example discloses a method for preparing an organic alkane, comprising the following steps:

[0045] Q1: In an argon glove box, 0.33g of 1,5-cyclooctadiene nickel, 0.41g of triphenylphosphine, 0.02g of zinc powder, 1.12g of 1-phenylbutadiene and 2.02g of diphenyldichlorosilane were added sequentially to a container containing 9mL of tetrahydrofuran. After the addition was complete, the container was sealed and the mixture was magnetically stirred at 25°C for 24 hours.

[0046] Q2: Add 5 mL of ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash with deionized water and saturated sodium chloride solution in sequence, and dry with anhydrous sodium sulfate to obtain an organic alkane.

[0047] This embodiment discloses a method for preparing a composite organic additive, including the following steps:

[0048] S1: Under nitrogen atmosphere, 8.85 g of decborane was added to a container containing 125 mL of acetonitrile, heated to 100 °C and refluxed for 18 h. After the reaction was completed, the mixture was cooled, filtered, washed and dried to obtain organic compound 1.

[0049] S2: 0.21 g of 4,4',4''-triiodotriphenylamine, 0.05 g of bis(triphenylphosphine)palladium chloride and 0.004 g of cuprous iodide were added to a container. After evacuation, 5 mL of tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature for 15 min, 0.2 g of triethylamine was added, and the reaction was continued to be stirred at room temperature for 30 min. Then, 4 mL of tetrahydrofuran containing 0.32 g of 1-(4-ynylphenyl)-1,2,2-triphenylene was added, and the reaction was stirred at room temperature for 24 h. After the reaction was completed, the mixture was purified by rotary evaporation to obtain organic compound 2.

[0050] S3: Add 0.17g of organic compound 2 and 0.21g of organic compound 1 to a container, inject 45mL of toluene under nitrogen atmosphere, reflux for 48h, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

[0051] This embodiment discloses a method for preparing polycarbosilane, a silicon carbide fiber precursor, including the following steps:

[0052] Step 1: Under argon atmosphere, add 0.72g vinyl chloride and 1.26g magnesium shavings to 20mL tetrahydrofuran, heat to 60℃ and stir for 24h. After the reaction is complete, Grignard reagent is obtained.

[0053] Step 2: Add 0.82g of organic alkane to 18mL of tetrahydrofuran, stir and mix, then slowly add to 0.28g of Grignard reagent, stir and react at 0℃ for 2h. After the reaction is complete, heat to room temperature, add 0.68g of composite organic auxiliaries, stir and react for 6h. After the reaction is complete, add saturated ammonium chloride aqueous solution for quenching, separate the contents, wash, and dry to obtain the prepolymer.

[0054] Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it to 250°C at a rate of 3°C / min under argon atmosphere for 18 hours for polymerization. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

[0055] Example 3: This example discloses a method for preparing an organic alkane, comprising the following steps:

[0056] Q1: In an argon glove box, 0.38g of 1,5-cyclooctadiene nickel, 0.53g of triphenylphosphine, 0.06g of zinc powder, 1.64g of 1-phenylbutadiene and 2.35g of diphenyldichlorosilane were added sequentially to a container containing 6mL of tetrahydrofuran. After the addition was complete, the container was sealed and the mixture was magnetically stirred at 25°C for 24 hours.

[0057] Q2: Add 5 mL of ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash with deionized water and saturated sodium chloride solution in sequence, and dry with anhydrous sodium sulfate to obtain an organic alkane.

[0058] This embodiment discloses a method for preparing a composite organic additive, including the following steps:

[0059] S1: Under nitrogen atmosphere, 9.32 g of decborane was added to a container containing 158 mL of acetonitrile, heated to 100 °C and refluxed for 18 h. After the reaction was completed, the mixture was cooled, filtered, washed, and dried to obtain organic compound 1.

[0060] S2: 0.33 g of 4,4',4''-triiodotriphenylamine, 0.01 g of bis(triphenylphosphine)palladium chloride and 0.012 g of cuprous iodide were added to a container. After evacuation, 5 mL of tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature for 15 min, 0.2 g of triethylamine was added, and the reaction was continued to be stirred at room temperature for 30 min. Then, 4 mL of tetrahydrofuran containing 0.48 g of 1-(4-ynylphenyl)-1,2,2-triphenylene was added, and the reaction was stirred at room temperature for 24 h. After the reaction was completed, the mixture was purified by rotary evaporation to obtain organic compound 2.

[0061] S3: Add 0.23g of organic compound 2 and 0.36g of organic compound 1 to a container, inject 55mL of toluene under nitrogen atmosphere, reflux for 48h, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

[0062] This embodiment discloses a method for preparing polycarbosilane, a silicon carbide fiber precursor, including the following steps:

[0063] Step 1: Under argon atmosphere, add 0.92g vinyl chloride and 1.48g magnesium shavings to 25mL tetrahydrofuran, heat to 60℃ and stir for 24h. After the reaction is complete, Grignard reagent is obtained.

[0064] Step 2: Add 0.97g of organic alkane to 22mL of tetrahydrofuran, stir and mix, then slowly add to 0.22g of Grignard reagent, stir and react at 0℃ for 2h. After the reaction is complete, heat to room temperature, add 0.78g of composite organic auxiliaries, stir and react for 6h. After the reaction is complete, add saturated ammonium chloride aqueous solution for quenching, separate the contents, wash, and dry to obtain the prepolymer.

[0065] Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it to 250°C at a rate of 1-5°C / min under argon atmosphere for 18 hours for polymerization. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

[0066] Example 4: This example discloses a method for preparing an organic alkane, comprising the following steps:

[0067] Q1: In an argon glove box, 0.34g of 1,5-cyclooctadiene nickel, 0.44g of triphenylphosphine, 0.03g of zinc powder, 1.21g of 1-phenylbutadiene and 2.11g of diphenyldichlorosilane were added sequentially to a container containing 7mL of tetrahydrofuran. After the addition was complete, the container was sealed and the mixture was magnetically stirred at 25°C for 24 hours.

[0068] Q2: Add 5 mL of ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash with deionized water and saturated sodium chloride solution in sequence, and dry with anhydrous sodium sulfate to obtain an organic alkane.

[0069] This embodiment discloses a method for preparing a composite organic additive, including the following steps:

[0070] S1: Under nitrogen atmosphere, 8.91 g of decborane was added to a container containing 132 mL of acetonitrile, heated to 100 °C and refluxed for 18 h. After the reaction was completed, the mixture was cooled, filtered, washed, and dried to obtain organic compound 1.

[0071] S2: 0.24 g of 4,4',4''-triiodotriphenylamine, 0.02 g of bis(triphenylphosphine)palladium chloride and 0.006 g of cuprous iodide were added to a container. After evacuation, 5 mL of tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature for 15 min, 0.2 g of triethylamine was added, and the reaction was continued to be stirred at room temperature for 30 min. Then, 4 mL of tetrahydrofuran containing 0.36 g of 1-(4-ynylphenyl)-1,2,2-triphenylene was added, and the reaction was stirred at room temperature for 24 h. After the reaction was completed, the mixture was purified by rotary evaporation to obtain organic compound 2.

[0072] S3: Add 0.18g of organic compound 2 and 0.25g of organic compound 1 to a container, inject 48mL of toluene under nitrogen atmosphere, reflux for 48h, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

[0073] This embodiment discloses a method for preparing polycarbosilane, a silicon carbide fiber precursor, including the following steps:

[0074] Step 1: Under argon atmosphere, add 0.77g vinyl chloride and 1.32g magnesium shavings to 21mL tetrahydrofuran, heat to 60℃ and stir for 24h. After the reaction is complete, Grignard reagent is obtained.

[0075] Step 2: Add 0.85g of organic alkane to 19mL of tetrahydrofuran, stir and mix, then slowly add to 0.23g of Grignard reagent, stir and react at 0℃ for 2h. After the reaction is complete, heat to room temperature, add 0.71g of composite organic auxiliaries, stir and react for 6h. After the reaction is complete, add saturated ammonium chloride aqueous solution for quenching, separate the liquid, wash, and dry to obtain the prepolymer.

[0076] Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it to 250°C at a rate of 3°C / min under argon atmosphere for 18 hours for polymerization. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

[0077] Example 5: This example discloses a method for preparing an organic alkane, comprising the following steps:

[0078] Q1: In an argon glove box, 0.36g of 1,5-cyclooctadiene nickel, 0.49g of triphenylphosphine, 0.05g of zinc powder, 1.51g of 1-phenylbutadiene and 2.27g of diphenyldichlorosilane were added sequentially to a container containing 8mL of tetrahydrofuran. After the addition was complete, the container was sealed and the mixture was magnetically stirred at 25°C for 24 hours.

[0079] Q2: Add 5 mL of ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash with deionized water and saturated sodium chloride solution in sequence, and dry with anhydrous sodium sulfate to obtain an organic alkane.

[0080] This embodiment discloses a method for preparing a composite organic additive, including the following steps:

[0081] S1: Under nitrogen atmosphere, 9.21 g of decborane was added to a container containing 146 mL of acetonitrile, heated to 100 °C and refluxed for 18 h. After the reaction was completed, the mixture was cooled, filtered, washed and dried to obtain organic compound 1.

[0082] S2: 0.31 g of 4,4',4''-triiodotriphenylamine, 0.04 g of bis(triphenylphosphine)palladium chloride and 0.01 g of cuprous iodide were added to a container. After evacuation, 5 mL of tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature for 15 min, 0.2 g of triethylamine was added, and the reaction was continued to be stirred at room temperature for 30 min. Then, 4 mL of tetrahydrofuran containing 0.44 g of 1-(4-ynylphenyl)-1,2,2-triphenylene was added, and the reaction was stirred at room temperature for 24 h. After the reaction was completed, the mixture was purified by rotary evaporation to obtain organic compound 2.

[0083] S3: Add 0.22g of organic compound 2 and 0.32g of organic compound 1 to a container, inject 52mL of toluene under nitrogen atmosphere, reflux for 48h, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

[0084] This embodiment discloses a method for preparing polycarbosilane, a silicon carbide fiber precursor, including the following steps:

[0085] Step 1: Under argon atmosphere, add 0.87g vinyl chloride and 1.42g magnesium shavings to 24mL tetrahydrofuran, heat to 60℃ and stir for 24h. After the reaction is complete, Grignard reagent is obtained.

[0086] Step 2: Add 0.93g of organic alkane to 21mL of tetrahydrofuran, stir and mix, then slowly add to 0.27g of Grignard reagent, stir and react at 0℃ for 2h. After the reaction is complete, heat to room temperature, add 0.75g of composite organic auxiliaries, stir and react for 6h. After the reaction is complete, add saturated ammonium chloride aqueous solution for quenching, separate the liquid, wash, and dry to obtain the prepolymer.

[0087] Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it to 250°C at a rate of 5°C / min under argon atmosphere for 18 hours for polymerization. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

[0088] Comparative Example 1: Compared with Example 1, Comparative Example 1 used chlorosilane instead of organic alkane in the process of preparing polycarbosilane, the precursor of silicon carbide fiber, while keeping other conditions unchanged.

[0089] Comparative Example 2: Compared with Example 1, Comparative Example 2 did not add composite organic additives in the process of preparing polycarbosilane, the precursor of silicon carbide fiber, while other conditions remained unchanged.

[0090] Performance testing:

[0091] I. Ceramic Yield and Pyrolysis Behavior Testing:

[0092] 10 mg of samples prepared according to Examples 1-5 and Comparative Examples 1-2 were accurately weighed and placed in an alumina crucible. Under nitrogen atmosphere (flow rate 50 mL / min), the temperature was increased from room temperature to 1000℃ at a heating rate of 10℃ / min. The mass change during the heating process was recorded, and the 5% weight loss temperature and the maximum weight loss rate temperature were obtained. Simultaneously, 2 g (m1) of samples prepared according to Examples 1-5 and Comparative Examples 1-2 were accurately weighed and placed in a vacuum furnace. Under vacuum conditions <10 Pa, the temperature was increased to 1000℃ at a heating rate of 2℃ / min and held at that temperature for 60 min. After naturally cooling to room temperature, the mass m2 of the residue was accurately weighed. According to the formula ceramic yield (%) = (m2 / m1) × 100%, the results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As shown in Table 1, the test results indicate that polycarbosilanes with excellent ceramic yield and thermal stability can be prepared using the methods described in Examples 1-5. A comparison between Comparative Example 1 and Examples 1-5 reveals that the use of organic alkanes can effectively improve the ceramic yield and thermal stability of polycarbosilanes; a comparison between Comparative Example 2 and Examples 1-5 shows that the use of composite organic additives can effectively improve the ceramic yield of polycarbosilanes.

[0096] II. Spinability testing:

[0097] The samples prepared according to Examples 1-5 and Comparative Examples 1-2 were heated and melted, and after being kept at this temperature for 1 hour, they were allowed to form a uniform melt. Under nitrogen pressure, the melt was extruded from the spinneret to form filaments. The average breakage-free time during the spinning process was recorded, and the results are shown in Table 2.

[0098] Table 2

[0099]

[0100] A shorter average breakage-free time indicates poorer spinnability. Table 2 shows that polycarbosilanes with excellent spinning properties can be prepared using the methods described in Examples 1-5. A comparison between Comparative Example 1 and Examples 1-5 reveals that the use of organic alkanes can effectively improve the spinning performance of polycarbosilanes.

[0101] III. High-Temperature Mechanical Property Testing:

[0102] The samples prepared according to Examples 1-5 and Comparative Examples 1-2 were oxidized in air at 200°C, and then sintered in a vacuum environment at 1200°C to obtain ceramic fibers. The flexural strength and modulus were then measured using the three-point bending method, and the hardness was measured using a Vickers hardness tester. The results are shown in Table 3.

[0103] Table 3

[0104]

[0105] As shown in Table 3, the test results indicate that polycarbosilanes with excellent high-temperature mechanical properties can be prepared using the methods described in Examples 1-5. A comparison between Comparative Example 2 and Examples 1-5 reveals that the use of composite organic additives can effectively improve the high-temperature mechanical properties of polycarbosilanes.

[0106] IV. Antioxidant performance test:

[0107] The samples prepared according to Examples 1-5 and Comparative Examples 1-2 were oxidized in air at 200°C, and then sintered in a vacuum environment at 1200°C to obtain ceramic fibers. These fibers were then placed in a muffle furnace and subjected to long-term isothermal oxidation treatment at 1200°C in air atmosphere. The mass changes at different times were recorded, and the results are shown in Table 4.

[0108] Table 4

[0109]

[0110] As shown in Table 4, the test results indicate that polycarbosilanes with excellent antioxidant properties can be prepared using the methods described in Examples 1-5. A comparison between Comparative Example 1 and Examples 1-5 reveals that the use of organic alkanes can effectively improve the antioxidant properties of polycarbosilanes.

[0111] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0112] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing polycarbosilane, a silicon carbide fiber precursor, characterized in that, Includes the following steps: Step 1: Under argon atmosphere, vinyl chloride and magnesium shavings are added to tetrahydrofuran, heated and stirred to react. After the reaction is complete, Grignard reagent is obtained. Step 2: Add the organic alkane to tetrahydrofuran, stir and mix, then slowly add it to the Grignard reagent, stir and react. After the reaction is complete, heat to room temperature, add the composite organic auxiliaries, stir and react. After the reaction is complete, quench the reaction, separate the liquids, wash, and dry to obtain the prepolymer. Step 3: After vacuum distillation of the prepolymer, transfer it to a reaction vessel and heat it for polymerization under argon atmosphere. After the reaction is complete, add it to toluene, dissolve, filter, precipitate, and dry to obtain polycarbosilane, the precursor of silicon carbide fiber.

2. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 1, is characterized in that, The method for preparing the organic alkane includes the following steps: Q1: In an argon glove box, 1,5-cyclooctadiene nickel, triphenylphosphine, zinc powder, 1-phenylbutadiene and diphenyldichlorosilane are added sequentially to a container containing tetrahydrofuran. After the addition is complete, the container is sealed and the reaction is carried out by magnetic stirring. Q2: Add ethyl acetate to the container where the reaction has ended, stir to dissolve, transfer to a separatory funnel, wash, and dry to obtain an organic alkane.

3. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 2, is characterized in that, In Q1, the ratio of 1,5-cyclooctadiene nickel, triphenylphosphine, zinc powder, 1-phenylbutadiene, diphenyldichlorosilane and tetrahydrofuran is (0.33-0.38) g : (0.41-0.53) g : (0.02-0.06) g : (1.12-1.64) g : (2.02-2.35) g : (6-9) mL.

4. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 2, is characterized in that, In Q2, the volume of ethyl acetate added is 5-8 mL.

5. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 1, is characterized in that, The preparation method of the composite organic additive includes the following steps: S1: Under nitrogen atmosphere, decaborane was added to a container containing acetonitrile, and the mixture was heated under reflux. After the reaction was completed, the mixture was cooled, filtered, washed, and dried to obtain organic compound 1. S2: 4,4',4''-triiodotriphenylamine, bis(triphenylphosphine)palladium chloride and cuprous iodide were added to a container. After evacuation, tetrahydrofuran was injected under nitrogen atmosphere. After stirring at room temperature, triethylamine was added and the reaction was continued at room temperature. Then, tetrahydrofuran containing 1-(4-alkynylphenyl)-1,2,2-tristyrene was added and the reaction was stirred at room temperature. After the reaction was completed, the mixture was rotary evaporated and purified to obtain organic compound 2. S3: Add organic compound 2 and organic compound 1 to a container, inject toluene under nitrogen atmosphere, reflux the reaction, cool, quench the reaction, rotary evaporate, and purify to obtain the composite organic auxiliary agent.

6. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 5, is characterized in that, In S1, the ratio of decborane to acetonitrile is (8.85-9.32) g : (125-158) mL.

7. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 5, is characterized in that, In S2, the ratio of 4,4',4''-triiodotriphenylamine, bis(triphenylphosphine)palladium chloride, cuprous iodide, and 1-(4-alkynylphenyl)-1,2,2-tristyrene is (0.21-0.33) g : (0.01-0.05) g : (0.004-0.012) g : (0.32-0.48) g.

8. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 5, is characterized in that, In S3, the ratio of organic compound 2, organic compound 1 and toluene is (0.17-0.23) g : (0.21-0.36) g : (45-55) mL.

9. The method for preparing polycarbosilane, a silicon carbide fiber precursor, according to claim 1, is characterized in that, In step one, the ratio of vinyl chloride, magnesium shavings, and tetrahydrofuran is (0.72-0.92) g : (1.26-1.48) g : (20-25) mL; in step two, the ratio of organic alkane, tetrahydrofuran, Grignard reagent, and composite organic auxiliaries is (0.82-0.97) g : (18-22) mL : (0.22-0.28) g : (0.68-0.78) g; in step three, the temperature is increased to 250-350℃ at a heating rate of 1-5℃ / min, and the polymerization reaction time is 12-20 h.

10. A silicon carbide fiber precursor polycarbosilane, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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