A method for synthesizing an aluminum-containing high molecular weight polycarbosilane

Abstract

The application discloses a synthesis method of an aluminum-containing high-molecular-weight polycarbosilane, and comprises the following steps: S1, preparing a homogeneous solution of liquid polycarbosilane and trichlorosilane; S2, under the protection of an inert atmosphere, adding anhydrous aluminum chloride into the homogeneous solution, and condensing and refluxing under certain conditions until the anhydrous aluminum chloride is completely dissolved; and S3, removing unreacted small molecules through vacuum distillation to obtain a target product. The application has the following advantages: the preparation temperature is low, the process is environment-friendly and efficient, the process can be scaled up by equal proportion, and the prepared product has good stability at room temperature.

Description

Technical Field

[0001] This application relates to the field of ceramic precursor preparation technology, and in particular to a method for synthesizing aluminum-containing high molecular weight polycarbosilanes. Background Technology

[0002] Silicon carbide (SiC) ceramics are considered to be the most promising high-temperature structural ceramics due to their excellent high-temperature stability, oxidation resistance, low activity under irradiation conditions, high hardness, high modulus, and low density. However, the relatively high brittleness of SiC ceramics limits their application in the field of structural materials. Introducing the heteroelement Al into SiC ceramics can effectively improve the brittleness of the ceramics and enhance their fracture toughness. At the same time, the introduction of heteroelement can also improve the dielectric properties, high-temperature mechanical properties, and affinity of SiC ceramics to the surface of the metal matrix when used as a metal-based reinforcing agent.

[0003] Existing methods for synthesizing Al-containing polycarbosilanes can be divided into two categories based on the raw materials: (1) using organosilicon polymers containing Si-Si bonds (mostly PDMS) and [Al(acac)3] as raw materials, reacting them in a high-pressure reactor at 450°C to obtain the product; (2) using polycarbosilanes containing a Si-C framework as raw materials, co-dissolving [Al(acac)3] in xylene, and reacting them at 300°C to 350°C under normal pressure to obtain the product. It can be seen that both types of reactions require high temperatures, and the introduction of acetylacetone groups leads to the precursor's hygroscopicity, severely affecting its storage, transport, and subsequent applications. Therefore, developing environmentally friendly, efficient, and energy-saving methods for preparing PACS is of paramount importance. Summary of the Invention

[0004] This invention provides a method for synthesizing aluminum-containing high molecular weight polycarbosilanes, which addresses the shortcomings of existing technologies in the synthesis of PACS precursors, such as high cost and difficulty in storage.

[0005] To achieve the above objectives, this invention proposes a method for synthesizing aluminum-containing high molecular weight polycarbosilanes, comprising the following steps:

[0006] S1. Prepare a homogeneous solution of liquid polycarbosilane and trichlorosilane;

[0007] S2. Under the protection of an inert atmosphere, anhydrous aluminum chloride is added to the homogeneous solution, and the solution is refluxed under certain conditions until the anhydrous aluminum chloride is completely dissolved.

[0008] S3. Reduced pressure distillation is used to remove unreacted small molecules to obtain the target product.

[0009] This invention has the following advantages;

[0010] 1. The preparation temperature is low, the process is environmentally friendly and efficient, and it can be scaled up in equal proportions;

[0011] 2. The obtained product has good stability at room temperature. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0013] Figure 1 A schematic diagram of a condensation reflux device;

[0014] Figure 2 The image shows an infrared comparison of the products under different ingredient conditions in Example 1.

[0015] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0018] This invention proposes a method for synthesizing aluminum-containing high molecular weight polycarbosilanes, comprising the following steps:

[0019] S1. Prepare a homogeneous solution of liquid polycarbosilane and trichlorosilane;

[0020] S2. Under the protection of an inert atmosphere, anhydrous aluminum chloride is added to the homogeneous solution, and the solution is refluxed under certain conditions until the anhydrous aluminum chloride is completely dissolved.

[0021] S3. Reduced pressure distillation is used to remove unreacted small molecules to obtain the target product.

[0022] This invention addresses the problem that liquid polycarbosilane (LPCS), a byproduct of polymethylsilane (PDMS) cracking, is difficult to use directly for preparing ceramic materials due to its small molecular weight (Mn≈300g / mol) and low ceramic yield (≤1wt.%). Starting from LPCS, trichlorosilane and anhydrous aluminum trichloride at the target content are added. Under an inert atmosphere, the mixture is refluxed until the aluminum trichloride is completely dissolved, and then naturally cooled to room temperature to obtain a novel aluminum-containing polycarbosilane precursor (PACS). The obtained PACS has the advantages of high molecular weight (Mn≥25000) and can be used as a precursor for preparing SiC ceramic matrix composites.

[0023] Further, in step S1, the general formula of trichlorosilane is R-Si-Cl3, where R is H, a saturated alkane, or an unsaturated alkane. The feed can be one or more of these.

[0024] Furthermore, in step S1, the volume ratio of liquid polycarbosilane to trichlorosilane is (1:3) to (1:1).

[0025] Furthermore, in step S2, the upper limit of the mass-volume concentration of anhydrous aluminum chloride for liquid polycarbosilane is 0.1 g / mL.

[0026] Furthermore, in step S2, the specific process of the condensation reflux reaction is as follows:

[0027] Add the reactants to a three-necked flask at room temperature, turn on reflux, introduce inert gas for protection, turn on heating, raise the temperature from room temperature to the reaction temperature, and stop the reaction after holding the temperature at the reaction temperature for a period of time; the reaction temperature is 110-200℃.

[0028] Furthermore, in step S2, the temperature of the reflux condensation does not exceed 0°C. For example... Figure 1 The diagram shows a device for providing condensation reflux.

[0029] Furthermore, in step S2, the inert atmosphere is nitrogen or argon.

[0030] Furthermore, in step S3, the pressure of vacuum distillation is -0.1 MPa to -0.09 MPa.

[0031] To further understand the present invention, the method and effects of the present invention will be further described below with reference to specific embodiments.

[0032] Example 1:

[0033] 1) Prepare a homogeneous solution of 50 ml LPCS and 50 ml MeSiCl3 at room temperature, and add 5 g of anhydrous aluminum chloride under nitrogen protection.

[0034] 2) Heating to 110℃ under -20℃ reflux conditions and reacting for 1 hour, at which point aluminum chloride completely disappears;

[0035] 3) Unreacted small molecules were removed at room temperature and -0.1 MPa to obtain the target product PACS, with a number-average molecular weight Mn = 28540 g / mol.

[0036] The precursor ceramic yield was 53.75%. After being stored at room temperature for one month, the precursor viscosity increased by only 12.3 mPa·s, demonstrating good stability.

[0037] like Figure 2 As shown, infrared comparison images of products under different ingredient conditions are provided. When LPCS+AlCl3 and LPCS+MeSiCl3 are present in pairs at 110℃ / 1h, the Si-H signal in the resulting products is strong, and aluminum-containing polymeric polycarbosilane precursors cannot be obtained. In the LPCS+AlCl3+MeSiCl3 (Example 1) system, the Si-H signal disappears, and a high molecular weight aluminum-containing precursor is obtained.

[0038] Example 2:

[0039] 1) Prepare a homogeneous solution of 50 ml LPCS and 50 ml CH2=CH-CH2-SiCl3 at room temperature, and add 5 g of anhydrous aluminum chloride under nitrogen protection;

[0040] 2) Heating to 110℃ under -20℃ reflux conditions and reacting for 1 hour, at which point aluminum chloride completely disappears;

[0041] 3) Unreacted small molecules were removed at room temperature and -0.1 MPa to obtain the target product PACS, with a number-average molecular weight Mn = 31620 g / mol.

[0042] The precursor ceramic yield was 55.71%. After being stored at room temperature for one month, the precursor viscosity increased by only 15.4 mPa·s, demonstrating good stability.

[0043] Example 3:

[0044] 1) Prepare a homogeneous solution of 50 ml LPCS and 50 ml MeSiCl3 at room temperature, and add 5 g of anhydrous aluminum chloride under nitrogen protection.

[0045] 2) Heating to 200℃ under reflux conditions at -20℃, reacting until aluminum chloride is completely eliminated;

[0046] 3) Unreacted small molecules were removed at room temperature and -0.1 MPa to obtain the target product PACS, with a number-average molecular weight Mn = 56840 g / mol.

[0047] The precursor ceramic yield was 68.21%. After being stored at room temperature for one month, the precursor viscosity increased by only 34.6 mPa·s, demonstrating good stability.

[0048] Example 4:

[0049] 1) Prepare a homogeneous solution of 50 ml LPCS and 50 ml CH2=CH-SiCl3 at room temperature, and add 5 g of anhydrous aluminum chloride under nitrogen protection;

[0050] 2) Heating to 110℃ under reflux conditions at -20℃, reacting until aluminum chloride is completely eliminated;

[0051] 3) Unreacted small molecules were removed at room temperature and -0.1 MPa to obtain the target product PACS, with a number-average molecular weight Mn = 33410 g / mol.

[0052] The precursor ceramic yield was 56.12%. After being stored at room temperature for one month, the precursor viscosity increased by only 18.2 mPa·s, demonstrating good stability.

[0053] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for synthesizing aluminum-containing high molecular weight polycarbosilane, characterized in that, Includes the following steps: S1. Prepare a homogeneous solution of liquid polycarbosilane and trichlorosilane; S2. Under the protection of an inert atmosphere, anhydrous aluminum chloride is added to the homogeneous solution, and the solution is refluxed under certain conditions until the anhydrous aluminum chloride is completely dissolved. S3. Reduced pressure distillation is used to remove unreacted small molecules to obtain the target product.

2. The synthesis method according to claim 1, characterized in that, In step S1, the general formula of the trichlorosilane is R-Si-Cl3, where R is H, a saturated alkane, or an unsaturated alkane.

3. The synthesis method according to claim 1, characterized in that, In step S1, the volume ratio of liquid polycarbosilane to trichlorosilane is (1:3) to (1:1).

4. The synthesis method according to claim 1, characterized in that, In step S1, the temperature for preparing the homogenized solution is room temperature.

5. The synthesis method according to claim 1, characterized in that, In step S2, the upper limit of the mass-volume concentration of anhydrous aluminum chloride for liquid polycarbosilane is 0.1 g / mL.

6. The synthesis method according to claim 1, characterized in that, In step S2, the specific process of the condensation reflux reaction is as follows: Add the reactants to a three-necked flask at room temperature, turn on reflux, introduce inert gas for protection, turn on heating, raise the temperature from room temperature to the reaction temperature, and stop the reaction after holding the temperature at the reaction temperature for a period of time; the reaction temperature is 110-200℃.

7. The synthesis method according to claim 1, characterized in that, In step S2, the temperature of the condensation reflux does not exceed 0°C.

8. The synthesis method according to claim 1, characterized in that, In step S2, the inert atmosphere is nitrogen or argon.

9. The synthesis method according to claim 1, characterized in that, In step S3, the pressure of vacuum distillation is -0.1 MPa to -0.09 MPa.

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