Synthesis method of polydimethylsilane and application of polydimethylsilane in preparation of polycarbosilane

Abstract

The invention belongs to the technical field of polycarbosilane, and particularly relates to a synthesis method of polydimethylsilane and application of the polydimethylsilane in preparation of polycarbosilane. In the Wurtz polymerization reaction of polydimethylsilane, polar solvents such as crown ether, diethylene glycol dimethyl ether, hexamethylphosphoric triamide and polyether are added into a reaction system, and the polar solvents have a complexing effect on sodium ions, so that tight ion pairs can be promoted to become loose ion pairs, the concentration of active anions is greatly increased, and the reaction time is shortened; therefore, the initiation period of the reaction is shortened, the polymerization reaction speed is accelerated, the molecular weight of polydimethylsilane is improved, and the yield is improved; the molecular weight of the polydimethylsilane is increased, the pyrolysis activation energy of the polydimethylsilane is gradually reduced, and the prepared polycarbosilane has higher Si-H bonds, and is high in A-grade conversion rate and good in spinning performance; according to the method, original reaction equipment does not need to be changed, reaction process parameters are also in original design, and the method has practical application value.

Description

Technical Field

[0001] The present invention relates to the technical field of polycarbosilane, and in particular to a method for synthesizing polydimethylsilane and application thereof in preparing polycarbosilane. Background Art

[0002] With the rapid development of science and technology, more and more new silicone materials are widely used in various fields of society. Polydimethylsilane, whose main chain is composed of silicon atoms, has the physical and chemical properties unique to carbon-based and silicon-oxygen-based polymers, and has become a new type of compound in silicone materials, especially in the application of SiC precursors, showing good development prospects.

[0003] The preparation of continuous silicon carbide fibers by ceramic precursor method is one of the successful industrialized technology routes today. Polycarbosilane (PCS) obtained by high-temperature pyrolysis and rearrangement reaction of polydimethylsilane (PDMS) is a precursor for the production of silicon carbide ceramics and silicon carbide fibers. The molecular weight and chemical structure of polydimethylsilane are the fundamental factors affecting whether polydimethylsilane that can be continuously spun can be prepared, and have an important influence on the production process and final performance of silicon carbide fibers. The polydimethylsilane suitable for the synthesis of polycarbosilane is HO[SiMe2] n OH structure, with high crystallinity and insoluble and infusible properties. With the increase of molecular weight, the thermal decomposition activation energy of polydimethylsilane gradually decreases, so the prepared polycarbosilane has better spinning performance.

[0004] Polydimethylsilane is usually prepared by the Wurtz reaction of dimethyldichlorosilane and alkali metals, but the molecular weight is low and the reaction yield is also low, which limits the further application of polycarbosilane in organosilicon materials. The synthesis method of polydimethylsilane is still an important issue for the further development of polycarbosilane.

[0005] The Wurtz reaction to synthesize polydimethylsilane is essentially a dechlorination condensation reaction between the chlorine atoms of dimethyldichlorosilane and the alkali metal atoms in the alkali metal suspension. Its molecular weight and reaction yield are affected by the solvent effect in the reaction system and the steric hindrance effect of the reaction monomer. Therefore, if a suitable additive can be selected to increase the solvent effect, the polymerization reaction of polydimethylsilane can be promoted, the molecular weight can be rapidly increased, the reaction time can be greatly shortened, and the yield can be improved.

[0006] At present, the synthesis of polydimethylsilane (PDMS) mainly uses dimethyldichlorosilane as a reaction monomer and sodium metal to carry out Wurtz synthesis reaction in a benzene solvent. Wurtz reaction belongs to anionic polymerization mechanism and is a heterogeneous reaction. The generated polydimethylsilane (PDMS) cannot be dissolved in non-polar benzene solvents. In benzene solvents, active intermediates mainly appear in the form of tight ion pairs, the concentration of active anions is low, and the polymerization reaction rate is slow, resulting in a small molecular weight of polydimethylsilane (PDMS) and a low yield. Summary of the invention

[0007] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art. The present invention provides a method for synthesizing polydimethylsilane and its application in preparing polycarbosilane.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for synthesizing polydimethylsilane, the steps of which are:

[0009] (1) evacuating the reactor and introducing an inert gas to a slightly positive pressure, then introducing an inert gas for circulation, and finally heating and keeping the reactor warm to dry the reactor and remove moisture;

[0010] (2) under the protection of inert gas, adding a first solvent and a second solvent into a reaction kettle, and then adding a sodium sand mixed solution, stirring and heating the mixture to obtain a reaction solution; wherein the first solvent is a hydrocarbon or aromatic hydrocarbon solvent, and the second solvent is a polar solvent;

[0011] (3) When the reaction temperature is reached, dimethyldichlorosilane is added dropwise to the reaction solution, and the reaction temperature is maintained for a certain period of time;

[0012] (4) adding a third solvent to the reaction solution to neutralize the incompletely reacted metallic sodium; wherein the third solvent is an alcohol solvent;

[0013] (5) washing the product obtained in step (4) with a fourth solvent to remove unreacted raw materials, by-products and solvent, and performing solid-liquid separation; wherein the fourth solvent is an alcohol solvent and water;

[0014] (6) Drying the solid phase product after solid-liquid separation at high temperature to remove the fourth solvent and obtain polydimethylsilane.

[0015] Furthermore, in step (2), the hydrocarbon and aromatic hydrocarbon solvents are one or more of benzene, toluene, xylene, n-hexane, and petroleum ether; and the polar solvent is one or more of crown ether, diethylene glycol dimethyl ether, hexamethylphosphoric acid triamide, and polyether.

[0016] Furthermore, in step (4), the alcohol solvent is one or more of methanol and ethanol.

[0017] Furthermore, in step (5), the alcohol solvent is ethanol; the washing step is specifically as follows: firstly, the raw materials, by-products and solvents that have not been completely reacted are extracted and removed with ethanol, and finally the ethanol and by-products are removed with water, and the washing step is repeated for more than 3 times to ensure thorough washing.

[0018] Furthermore, in step (2), the preparation process of the sodium sand mixed solution is specifically as follows: metallic sodium and the first solvent are mixed and reacted at a mass ratio of 1:1 to 1:2, and heated to 98° C. to 120° C., and stirred to form a sodium sand mixed solution.

[0019] Furthermore, the amount of the second solvent used is 5% to 20% of the total amount of the first solvent used; the mass ratio of the total amount of the first solvent used to dimethyldichlorosilane is 5:1 to 2:1; the molar mass ratio of dimethyldichlorosilane to metallic sodium is 1:2 to 1:2.1; the amount of the third solvent used is a molar mass ratio of metallic sodium of 0.1:1 to 0.5:1; the volume ratio of the fourth solvent used to the solid phase product is 1:1 to 3:1.

[0020] Furthermore, in step (3), the reaction temperature of the dimethylsilane is 80° C. to 120° C., and after the addition of dimethyldichlorosilane is completed, the reaction temperature is maintained for 12 h to 72 h.

[0021] Furthermore, in step (6), the solid phase product is dried at a high temperature of 100°C to 120°C.

[0022] The present invention also provides the use of the prepared polydimethylsilane in the preparation of polycarbosilane. The obtained polydimethylsilane is added into a synthesis kettle to carry out a high-temperature cracking and rearrangement reaction, and finally the polycarbosilane is obtained.

[0023] Furthermore, the preparation process of the high-temperature cracking and rearrangement of polydimethylsilane is specifically as follows: firstly, polydimethylsilane is heated to 350°C to 450°C for cracking, and then rearrangement reaction is carried out at 430°C to 480°C, and finally light yellow transparent polycarbosilane is obtained.

[0024] From the above description of the structure of the present invention, it can be seen that compared with the prior art, the present invention has the following advantages:

[0025] The invention mainly adopts crown ether, diethylene glycol dimethyl ether, hexamethylphosphoric triamide, polyether and other polar solvents to be added into the reaction system in the Wurtz polymerization reaction of polydimethylsilane. These polar solvents have a complexing effect on sodium ions, can promote tight ion pairs to become loose ion pairs, greatly increase the concentration of active anions, thereby shortening the initiation period of the reaction, accelerating the polymerization reaction speed, increasing the molecular weight of polydimethylsilane and improving the yield; the molecular weight of polydimethylsilane is increased, the thermal decomposition activation energy thereof is gradually reduced, the prepared polycarbosilane has higher Si-H bonds, high A-level conversion rate and good spinning performance; the method does not need to change the original reaction equipment, and the reaction process parameters thereof are also within the original design, and has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0027] Figure 1 is the infrared spectrum of the polydimethylsilane of the present invention;

[0028] Figure 2 This is the infrared spectrum of organic matter after the pyrolysis of polydimethylsilane of the present invention;

[0029] Figure 3 This is the infrared spectrum of polydimethylsilane of Example 1 of the present invention;

[0030] Figure 4 This is the infrared spectrum of polycarbosilane of Example 1 of the present invention;

[0031] Figure 5 This is the infrared spectrum of polydimethylsilane according to Example 2 of the present invention;

[0032] Figure 6 This is the infrared spectrum of polycarbosilane of Example 2 of the present invention;

[0033] Figure 7 This is the infrared spectrum of polydimethylsilane of Example 3 of the present invention;

[0034] Figure 8 This is the infrared spectrum of polycarbosilane according to Example 3 of the present invention. DETAILED DESCRIPTION

[0035] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0036] A method for synthesizing polydimethylsilane, comprising the following steps:

[0037] (1) evacuating the reactor and introducing an inert gas to a slightly positive pressure, then introducing an inert gas for circulation, and finally heating and keeping the reactor warm to dry the reactor and remove moisture;

[0038] (2) under the protection of inert gas, adding a first solvent and a second solvent to a reaction kettle, and then adding a sodium sand mixed solution, stirring and heating the mixture to obtain a reaction solution; wherein the first solvent is a hydrocarbon or aromatic hydrocarbon solvent, and the second solvent is a polar solvent; the hydrocarbon or aromatic hydrocarbon solvent is one or more of benzene, toluene, xylene, n-hexane, and petroleum ether; the polar solvent is one or more of crown ether, diethylene glycol dimethyl ether, hexamethylphosphoric acid triamide, and polyether; the preparation process of the sodium sand mixed solution is specifically as follows: mixing metallic sodium and the first solvent at a mass ratio of 1:1 to 1:2 for reaction, and heating the mixture to 98° C. to 120° C. to form a sodium sand mixed solution;

[0039] (3) When the reaction temperature is reached, dimethyldichlorosilane is added dropwise to the reaction solution, and the reaction temperature is maintained for a certain period of time; the reaction temperature of the dimethylsilane is 80° C. to 120° C., and after the addition of dimethyldichlorosilane is completed, the reaction temperature is maintained for 12 h to 72 h;

[0040] (4) adding a third solvent to the reaction solution to neutralize the incompletely reacted metallic sodium; wherein the third solvent is an alcohol solvent; and the alcohol solvent is one or more of methanol and ethanol;

[0041] (5) washing the product obtained in step (4) with a fourth solvent to remove incompletely reacted raw materials, by-products and solvent, and performing solid-liquid separation; wherein the fourth solvent is an alcohol solvent and water; the alcohol solvent is ethanol; the washing step specifically comprises: firstly extracting and removing the incompletely reacted raw materials, by-products and solvent with ethanol, and finally removing the ethanol and by-products with water, and the washing step is repeated for more than 3 times to ensure that the washing is thorough;

[0042] (6) Drying the solid phase product after solid-liquid separation at high temperature to remove the fourth solvent and obtain polydimethylsilane; the solid phase product is dried at high temperature at 100° C. to 120° C.

[0043] The amount of the second solvent used is 5% to 20% of the total amount of the first solvent used; the mass ratio of the total amount of the first solvent used to dimethyldichlorosilane is 5:1 to 2:1; the molar mass ratio of dimethyldichlorosilane to metallic sodium is 1:2 to 1:2.1; the amount of the third solvent used is a molar mass ratio of metallic sodium of 0.1:1 to 0.5:1; the volume ratio of the fourth solvent used to the solid phase product is 1:1 to 3:1.

[0044] The present invention also provides the use of the prepared polydimethylsilane in the preparation of polycarbosilane. The obtained polydimethylsilane is first heated to 350°C to 450°C for cracking, and then rearranged at 430°C to 480°C to finally obtain light yellow transparent polycarbosilane.

[0045] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0046] Example 1

[0047] The reactor was evacuated to 0.09 MPa, and then an inert gas was introduced to a slight positive pressure, and the operation was repeated three times. Then, an inert gas was introduced for circulation, and the reactor was heated to 110°C and kept warm for 5 hours to dry the reactor and remove moisture. Under the protection of the inert gas, xylene and diethylene glycol dimethyl ether were added to the dry and clean reactor, and then a xylene-sodium mixed solution was added, and the mixture was fully stirred and heated to 100°C, wherein the mass ratio of metallic sodium to xylene was 1:2, and the amount of diethylene glycol dimethyl ether used was 15% of that of xylene. Dimethyldichlorosilane is added dropwise to the reaction solution, and the reaction temperature is maintained at 110°C ± 5°C, and the molar mass ratio of dimethyldichlorosilane to metallic sodium is 1:2; after the reaction is completed, ethanol is added to the reactor to neutralize the metallic sodium that has not reacted completely; then the material is washed with ethanol and water, and the solid phase product is separated and dried at a high temperature of 120°C to obtain polydimethylsilane; the polydimethylsilane is cracked at 400°C and rearranged at 450°C to obtain light yellow transparent polycarbosilane; the polycarbosilane is used for spinning, and the A-level conversion rate can reach 45%.

[0048] Since polydimethylsilane is infusible and insoluble, the infrared spectrum of polydimethylsilane after the addition of dimethyldichlorosilane is completed and the reaction is kept warm is tested to test the Si-Cl bond content to characterize its relative molecular weight. The higher the relative value of Si-CH3 and Si-Cl bonds in polydimethylsilane, the higher the relative molecular weight of polydimethylsilane. The infrared spectrum of polydimethylsilane is shown in Figure 3 Polycarbosilane can be used to test the Si-H bond content. The higher the Si-H bond content, the higher the activity and the better the spinning effect. Its infrared spectrum is shown in Figure 4 .

[0049] Example 2

[0050] The reactor was evacuated to 0.09 MPa, and then an inert gas was introduced to a slight positive pressure, and the operation was repeated three times, and then an inert gas was introduced for circulation, and then the reactor was heated to 100°C and kept warm for 7 hours to dry the reactor and remove moisture; under the protection of the inert gas, toluene and hexamethylphosphoric acid triamide were added to the dry and clean reactor, and then a toluene-sodium mixed solution was added, and the mixture was fully stirred and heated to 100°C, wherein the mass ratio of metallic sodium to toluene was 1:2, and the amount of hexamethylphosphoric acid triamide used was 5% of toluene; dichloromethane was added dropwise to the reaction solution at a certain speed; Methyldichlorosilane, and the reaction temperature is maintained at 100℃±5℃, the molar mass ratio of dimethyldichlorosilane to metallic sodium is 1:2; after the reaction is completed, ethanol is added to the reactor to neutralize the metallic sodium that has not reacted completely; then the material is washed with ethanol and water, and the solid phase product is separated and dried at high temperature at 120℃ to obtain polydimethylsilane; the polydimethylsilane is cracked at 400℃ and rearranged at 450℃ to obtain light yellow transparent polycarbosilane; the polycarbosilane is used for spinning, and the A-level conversion rate can reach 47%; the infrared spectrum of polydimethylsilane is shown in Figure 5 , infrared spectrum of polycarbosilane is shown in Figure 6 .

[0051] Example 3

[0052] The reactor was evacuated to 0.09 MPa, and then an inert gas was introduced to a slight positive pressure, and the operation was repeated three times. Then, an inert gas was introduced for circulation, and the reactor was heated to 115°C and kept warm for 6 hours to dry the reactor and remove moisture. Under the protection of the inert gas, xylene and polyether were added to the dry and clean reactor, and then a xylene-sodium mixed solution was added, which was fully stirred and heated to 115°C, wherein the mass ratio of metallic sodium to xylene was 1:2, and the amount of polyether used was 10% of toluene. Dimethyl dimethacrylate was added dropwise to the reaction solution at a certain speed. Chlorosilane, and the reaction temperature is maintained at 115℃±5℃, the molar mass ratio of dimethyldichlorosilane to metallic sodium is 1:2; after the reaction is completed, ethanol is added to the reactor to neutralize the metallic sodium that has not reacted completely; then the material is washed with ethanol and water, and the solid phase product is separated and dried at high temperature at 120℃ to obtain polydimethylsilane; the polydimethylsilane is cracked at 400℃ and rearranged at 450℃ to obtain light yellow transparent polycarbosilane; the polycarbosilane is used for spinning, and the A-level conversion rate can reach 43%; the infrared spectrum of polydimethylsilane is shown in Figure 7 , infrared spectrum of polycarbosilane is shown in Figure 8 .

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing polydimethylsilane, characterized in that: The steps are: (1) evacuating the reactor and introducing an inert gas to a slightly positive pressure, then introducing the inert gas for circulation, and finally heating and keeping the reactor warm; (2) under the protection of inert gas, adding a first solvent and a second solvent into a reaction kettle, and then adding a sodium sand mixed solution, stirring and heating the mixture to obtain a reaction solution; wherein the first solvent is a hydrocarbon or aromatic hydrocarbon solvent, and the second solvent is a polar solvent; (3) When the reaction temperature is reached, dimethyldichlorosilane is added dropwise to the reaction solution, and the reaction temperature is maintained for a certain period of time; (4) adding a third solvent to the reaction solution to neutralize the incompletely reacted metallic sodium; wherein the third solvent is an alcohol solvent; (5) washing the product obtained in step (4) with a fourth solvent to remove unreacted raw materials, by-products and solvent, and performing solid-liquid separation; wherein the fourth solvent is an alcohol solvent and water; (6) Drying the solid phase product after solid-liquid separation at high temperature to remove the fourth solvent and obtain polydimethylsilane.

2. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: In step (2), the hydrocarbon and aromatic hydrocarbon solvents are one or more of benzene, toluene, xylene, n-hexane, and petroleum ether; and the polar solvent is one or more of crown ether, diethylene glycol dimethyl ether, hexamethylphosphoric acid triamide, and polyether.

3. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: In step (4), the alcohol solvent is one or more of methanol and ethanol.

4. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: In step (5), the alcohol solvent is ethanol; the washing step is specifically as follows: firstly, the raw materials, by-products and solvents that have not been completely reacted are extracted and removed with ethanol, and finally the ethanol and by-products are removed with water, and the washing step is repeated for more than 3 times.

5. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: In step (2), the preparation process of the sodium sand mixed solution is specifically as follows: metallic sodium and the first solvent are mixed and reacted in a mass ratio of 1:1 to 1:2, and heated to 98° C. to 120° C. to form a sodium sand mixed solution.

6. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: The amount of the second solvent used is 5% to 20% of the total amount of the first solvent used; the mass ratio of the total amount of the first solvent used to dimethyldichlorosilane is 5:1 to 2:1; the molar mass ratio of dimethyldichlorosilane to metallic sodium is 1:2 to 1:2.1; the amount of the third solvent used is a molar mass ratio of metallic sodium of 0.1:1 to 0.5:1; the volume ratio of the fourth solvent used to the solid phase product is 1:1 to 3:

1.

7. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: In step (3), the reaction temperature of the dimethylsilane is 80° C. to 120° C., and after the addition of dimethyldichlorosilane is completed, the reaction temperature is maintained for 12 h to 72 h.

8. A method for synthesizing polydimethylsilane according to claim 1, characterized in that: In step (6), the solid phase product is dried at a high temperature of 100°C to 120°C.

9. Use of polydimethylsilane synthesized by the synthesis method according to any one of claims 1 to 8 in the preparation of polycarbosilane, characterized in that: The obtained polydimethylsilane is added into a synthesis kettle for high temperature cracking and rearrangement reaction to finally obtain polycarbosilane.

10. The use according to claim 9, characterized in that: The preparation process of high-temperature cracking and rearrangement of polydimethylsilane is specifically as follows: firstly, polydimethylsilane is heated to 350° C. to 450° C. for cracking, and then rearrangement reaction is carried out at 430° C. to 480° C., and finally light yellow transparent polycarbosilane is obtained.

Images