Silicon-containing ring and method for producing same, modified polysiloxane and method for producing same, and thermal protection material

Abstract

This invention relates to the field of thermal protection materials technology, specifically to silicon-containing cyclic bodies and their preparation methods, modified polysiloxanes and their preparation methods, and thermal protection materials. The silicon-containing cyclic body has the structural formula shown in Formula I: where A is O or N; a is any value between 1 and 3; b is 1 or 2; and R is the structure of the Si-H silane excluding the H atom. The silicon-containing cyclic body can react with vinyl silicone oils, etc., to form a ring-linear structure, avoiding excessive cross-linking during the reaction. Simultaneously, this results in modified polysiloxanes possessing high tensile strength and elongation at break, as well as high residual weight at high temperatures and excellent ablation resistance. This modified polysiloxane provides a new material option for developing high-performance flexible polymer ablation-resistant materials suitable for ultra-high temperature environments, showing promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of thermal protection materials technology, and more specifically, to silicon-containing cyclic compounds and their preparation methods, modified polysiloxanes and their preparation methods, and thermal protection materials. Background Technology

[0002] With the rapid development of the aerospace industry, the harsh ultra-high temperature environment has placed higher demands on thermal protection materials (TPMs) to protect spacecraft structural units from extreme temperatures and severe erosion. Polymer ablation materials (PAMs), due to their low density, low thermal conductivity, and excellent processability, have become an important branch of thermal protection materials. Rigid polymer ablation materials (including phenolic resin and silicone resin-based ablation materials) are widely used in reentry capsules, rocket nozzle throats, and reentry missions. In recent years, the rapid development of the aerospace industry has placed demands on large and complex deformations in spacecraft maneuvering components, which traditional rigid PAMs can no longer meet. In contrast, flexible matrix materials, such as nitrile rubber (NBR), ethylene propylene rubber (EPDM), polyphosphazene, and silicone rubber (SR), possess good deformability and are suitable choices for protecting such maneuvering components. Among them, silicone rubber, with its inherent Si-O-Si main chain structure, exhibits excellent heat oxidation resistance and a wide application temperature range, making it a highly promising flexible PAM. However, pure silicone rubber is difficult to form a dense protective layer under the action of heat flow, so it cannot meet the needs of practical applications.

[0003] To improve the heat flux resistance of silicone rubber, numerous studies have focused on introducing ceramic filler modifiers into the SR matrix. These fillers ensure the integrity and robustness of the carbon layer under high heat flux conditions, thereby reducing the ablation rate of the material. However, direct incorporation into the SR matrix leads to decreased flexibility and increased density in SR-based PAMs due to low compatibility between the filler and the matrix. To avoid these problems, multifunctional organic molecules with good designability and reactivity are typically used as modifying components. Introducing multifunctional organic molecules into the SR matrix via covalent bonds allows for the in-situ formation of a ceramic structure under high-temperature heat flux, resulting in molecularly modified SR materials exhibiting superior thermal insulation performance and effectively blocking heat and oxygen. Liu et al. vulcanized a coating of hydroxyl-terminated polydimethylsiloxane (HPDMS) and polyethoxylated polysilsesquioxane (EOPS) (EOPS@HPDMS) at room temperature. The linear ablation rate and mass ablation rate of EOPS@HPDMS were 0.3796 mm·s, respectively. -1 and 0.1284 g·s -1Compared to pure SR, the degradation rates were reduced by 22.4% and 32.39%, respectively. Ma et al. designed and introduced tetravinyl polysilsesquioxane (TV-DDSQ) into SR, forming a three-dimensional network structure with moderate density and introducing a high-temperature resistant cage structure. Compared with SR, 1 phr TV-DDSQ / SR exhibits good high-temperature oxidative combustion resistance (reaching UL-94V0 level in vertical combustion tests) and excellent ablation performance (linear ablation reduced by 21.2%). In existing studies, due to the excessively large molecular volume and the difficulty in controlling the number of organic groups, the modified SR materials of multifunctional organic molecules cannot balance mechanical properties, thermal oxidation performance, and ablation resistance.

[0004] Therefore, a silicon-containing cyclic structure for use in thermal protection materials is constructed to modify polysiloxanes to form a ring-line topology, which is then vulcanized to obtain a modified silicone rubber elastomer, thus preparing a flexible PAM with high strength, high toughness, high heat resistance and ablation resistance.

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

[0006] The purpose of this invention is to provide silicon-containing cyclic compounds and their preparation methods, modified polysiloxanes and their preparation methods, and thermal protection materials. An embodiment of this invention provides a silicon-containing cyclic compound containing a quantitative amount of reactive groups, which can react with vinyl silicone oils, etc., to form a ring-linear structure. The resulting modified silicone rubber elastomer exhibits high tensile strength and elongation at break, as well as high residual weight at heat and excellent ablation resistance.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a silicon-containing ring having the structural formula shown in Formula I: Where A is O or N; a is any value between 1 and 3; b is 1 or 2; and R is the structure of the Si-H silane excluding the H atom. In an optional embodiment, R is any one of trimethylsilyl, triethylsilyl, ethyldimethylsilyl, trihexylsilyl, triphenylsilyl, phenylmethylsilyl, diphenylmethylsilyl, pentamethyldisiloxy, and heptamethyltrisiloxy.

[0008] In a second aspect, the present invention provides a method for preparing the silicon-containing cyclic body described in the foregoing embodiments, comprising: mixing a polyvinyl silicon-containing cyclic raw material, a Si-H silane, and a platinum catalyst and reacting them.

[0009] In an optional implementation, the reaction satisfies at least one of the following conditions: (1) For every 100 parts of the polyvinylsilane-containing cyclic raw material, 20-80 parts of the Si-H silane and 0.001-20 parts of the platinum catalyst are added accordingly; (2) The polyvinylsilane-containing cyclic raw material is selected from at least one of trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, pentamethylpentavinylcyclopentasiloxane, trimethyltrivinylcyclotrisilazane and tetramethyltetravinylcyclotetrasilazane; (3) The Si-H silane is selected from at least one of trimethylsilane, triethylsilane, ethyldimethylsilane, trihexylsilane, triphenylsilane, phenylmethylsilane, diphenylmethylsilane, pentamethyldisiloxane and heptamethyltrisiloxane; (4) The platinum catalyst is selected from at least one of chloroplatinic acid, platinum(0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane and octanol-modified chloroplatinic acid; (5) Reaction conditions include: temperature of 60-100℃; time of 5-30h.

[0010] In an optional embodiment, the method further includes: after the reaction is completed, the reaction system is rotary evaporated at 80-120°C under a vacuum of 0.09 MPa for 45-90 minutes to obtain a crude intermediate; the crude intermediate is heated to 100-250°C, evacuated to a vacuum degree of 0.09-0.1 MPa and allowed to stand, and argon gas is introduced every 1-3 minutes to distill off some of the product with a relatively high boiling point that has not been discharged, and this process is repeated several times before being cooled under pressure.

[0011] Thirdly, the present invention provides a modified polysiloxane, which is prepared by the silicon-containing cyclic body described in the foregoing embodiments.

[0012] In an optional implementation, it has the structural formula shown in Formula II: , Where A is O or N; a is any value between 1 and 3; c is 0 or 1; and R is the structure in Si-H silanes other than H atoms.

[0013] Fourthly, the present invention provides a method for preparing modified polysiloxane, comprising: mixing vinyl silicone oil, a polysiloxane compound containing silane-hydrogen bonds, a catalyst, and the aforementioned silicon-containing cyclic compound for reaction.

[0014] In an optional implementation, the reaction satisfies at least one of the following conditions: (1) 50-200 parts vinyl silicone oil, 1-50 parts silicon-containing cyclic compound, 1-25 parts polysiloxane compound and 0.001-20 parts catalyst; (2) The catalyst is a platinum catalyst; (3) The kinematic viscosity of the vinyl silicone oil is 5000-30000 cst, and the number average molecular weight M nThe concentration is 5000-100000 g / mol, and the vinyl content is 0.001-0.3 mol Vi / 100g; (4) The polysiloxane compound is selected from polymethylhydrosiloxane or polymethylphenylhydrosiloxane; (5) The polysiloxane compound contains 0.035~1.2 mol / 100g of Si-H and 0.035~1.2 mol / 100g of phenyl. n The concentration ranges from 300 to 10000 g / mol. (6) The reaction conditions include: pressure of 5-20 MPa; temperature of 80-110 °C; and time of 0.5-5 h.

[0015] Fifthly, the present invention provides a thermal protection material, which is prepared by the modified polysiloxane described in the foregoing embodiments.

[0016] The present invention has the following beneficial effects: (1) The present invention provides a silicon-containing cyclic body, which reduces its functionality as a crosslinking point, and then forms a ring-line topology during the subsequent reaction and curing process with vinyl silicone oil and polysiloxane compounds containing silane bonds, thus avoiding excessive crosslinking during the reaction and curing process.

[0017] (2) The modified polysiloxane provided by this invention possesses high tensile strength and elongation at break; it also exhibits high residual weight under nitrogen atmosphere; furthermore, the modified polysiloxane demonstrates excellent ablation resistance, capable of increasing residual carbon content through its numerous carbon-containing groups, and transforming in situ into SiC under high heat flux, thus providing an anchoring effect within the carbon layer and converting into SiO2 on the carbon layer surface to block external oxidizing gas erosion, effectively strengthening the carbon layer. The modified polysiloxane provided by this invention offers a new material option for developing high-performance flexible PAMs suitable for ultra-high temperature environments, with promising application prospects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A roadmap for the modified polysiloxane provided by this invention; Figure 2 Tensile curves of modified polysiloxanes provided for comparative examples and embodiments of the present invention; Figure 3 The experimental results of the thermal properties of the modified polysiloxanes in the comparative examples and embodiments provided by this invention are shown in the figure. Figure 3 In Figure a, TGA curve is shown under a nitrogen atmosphere, and DTG curve is shown under a nitrogen atmosphere. Figure 4 The present invention provides FTIR spectra of pyrolysis products in nitrogen at different temperatures, wherein... Figure 4 In Figure a, the FTIR spectrum of the pyrolysis products of the pure sample in nitrogen is shown. Figure 4 In Figure b, the FTIR spectrum of the pyrolysis product of triethylcyclic modified silicone rubber in nitrogen is shown. Figure 4 c represents the FTIR spectrum of the pyrolysis product of phenyl cyclic modified silicone rubber in nitrogen. Figure 5 The graph shows the results of different peak intensities varying with temperature, as provided by this invention. Figure 5 In the middle, 'a' represents 1030 cm under a nitrogen atmosphere. -1 The graph showing the peak intensity as a function of temperature. Figure 5 In the middle, b represents 3015 cm under a nitrogen atmosphere. -1 Graph showing the peak intensity as a function of temperature; Figure 6 The optical morphology of different samples after ablation in a 2MW / m² oxyacetylene flame for 30 seconds is provided by the present invention. Figure 6 The af values ​​are: SR, SR-Ph, 1 / 16-Et-D4Vi-SR, 1 / 8-Et-D4Vi-SR, 1 / 16-Ph-D4Vi-SR and 1 / 8-Ph-D4Vi-SR; Figure 7 The ablation performance results of the modified polysiloxanes provided in the comparative examples and embodiments of the present invention are shown in the figure. Figure 7 In the middle, 'a' represents the MAR results. Figure 7 Image b in the middle is the CR result image. Figure 7 In the middle, c represents the compressive strength curve of the carbon layer. Figure 7 In the diagram, d represents the compressive strength result of the carbon layer; Figure 8 Surface morphology of the carbon layer of the modified polysiloxane provided for comparative examples and embodiments of the present invention; Figure 9 Mercury intrusion porosimetry (MIRP) curves of the modified polysiloxanes provided in the comparative examples and embodiments of this invention. Detailed Implementation

[0020] 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 clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] In a first aspect, embodiments of the present invention provide a silicon-containing ring having the structural formula shown in Formula I: Where A is O or N; a is any value between 1 and 3; b is 1 or 2; and R is a structure in a Si-H silane other than the H atom. For example, R is any one of trimethylsilyl, triethylsilyl, ethyldimethylsilyl, trihexylsilyl, triphenylsilyl, phenylmethylsilyl, diphenylmethylsilyl, pentamethyldisiloxy, and heptamethyltrisiloxy.

[0022] It should be noted that "cyclic" refers to a compound with a ring structure composed of multiple silicon-containing units. For example, cyclotetrasiloxane refers to a compound with three or more units. Its side groups can be alkanes, alkenes, or other groups.

[0023] "Si-H silanes" refer to compounds with silicon atoms as the central atom, containing at least one silicon-hydrogen bond, and whose remaining groups are all hydrocarbon groups.

[0024] "Polysiloxane compounds containing silane bonds" refers to organosilicon compounds that contain silane bonds in their polysiloxane molecular chains.

[0025] Specifically, the silicon-containing cyclic body is selected from any one of the compounds shown in the following structural formulas: trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, pentamethylpentavinylcyclopentasiloxane, trimethyltrivinylcyclotrisilazane, and tetramethyltetravinylcyclotetrasilazane.

[0026] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned silicon-containing cyclic body, comprising: mixing a polyvinyl silicon-containing cyclic raw material, a Si-H silane and a platinum catalyst and reacting them, and performing post-treatment on the reaction system after the reaction is completed.

[0027] Furthermore, the aforementioned polyvinylsilane-containing cyclic raw material is selected from at least one of trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, pentamethylpentavinylcyclopentasiloxane, trimethyltrivinylcyclotrisilazane, and tetramethyltetravinylcyclotetrasilazane.

[0028] And / or, the Si-H silane is selected from at least one of trimethylsilane, triethylsilane, ethyldimethylsilane, trihexylsilane, triphenylsilane, phenylmethylsilane, diphenylmethylsilane, pentamethyldisiloxane, and heptamethyltrisiloxane.

[0029] And / or, the platinum catalyst is selected from at least one of chloroplatinic acid, platinum(0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane and octanol-modified chloroplatinic acid.

[0030] And / or, for every 100 parts of the aforementioned polyvinylsilane-containing cyclic raw material, 20-80 parts of the aforementioned Si-H silane and 0.001-20 parts of the aforementioned platinum catalyst are added. Specifically, for every 100 parts of the aforementioned polyvinylsilane-containing cyclic raw material, the amount of Si-H silane added is any value between 20 and 80 parts, such as 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts, or 80 parts. The amount of platinum catalyst added is any value between 1 and 20 parts, such as 1 part, 5 parts, 10 parts, 15 parts, or 20 parts.

[0031] Furthermore, the reaction temperature is any value between 60-100℃, such as 60℃, 70℃, 80℃, 90℃, or 100℃. The reaction time is any value between 5-30h, such as 5h, 10h, 15h, 20h, 25h, or 30h.

[0032] Furthermore, the post-processing includes: after the reaction is completed, the reaction system is rotary evaporated at 80-120℃ under a vacuum of 0.09 MPa for 45-90 minutes to obtain a crude intermediate; the crude intermediate is heated to 100-250℃, evacuated to a vacuum degree of 0.09-0.1 MPa and allowed to stand, and argon gas is introduced every 1-3 minutes to evaporate some of the product with a relatively high boiling point that has not been discharged. After repeating this process several times, the product is cooled under pressure to obtain the desired silicon-containing cyclic product.

[0033] Thirdly, embodiments of the present invention provide a modified polysiloxane, which is prepared by the aforementioned silicon-containing cyclic compound. Specifically, vinyl silicone oil, a polysiloxane compound containing silicon-hydrogen bonds, a catalyst, and a silicon-containing cyclic compound are mixed and reacted. That is, under the action of a catalyst, the vinyl silicone oil, the silicon-containing cyclic compound, and the polysiloxane compound are mixed, reacted, and cured. See [link to previous section]. Figure 1 .

[0034] Further, by weight, 50-200 parts vinyl silicone oil, 1-50 parts silicon-containing cyclic compound, 1-25 parts polysiloxane compound, and 0.001-20 parts catalyst. For example, 100 parts vinyl silicone oil, 12.5 parts silicon-containing cyclic compound, 9 parts polysiloxane compound, and 0.5 parts catalyst; Among them, the kinematic viscosity of vinyl silicone oil is 5000-30000 cst, and the number average molecular weight M n The concentration is 5000-100000 g / mol, and the vinyl content is 0.001-0.3 mol Vi / 100g. Polysiloxane compounds are selected from polymethylhydrosiloxanes; the Si-H content in polysiloxane compounds is 0.035-1.2 mol / 100g, M nThe concentration is 300-10000 g / mol. The catalyst is a platinum catalyst; for example, at least one of chloroplatinic acid, platinum(0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane or octanol-modified chloroplatinic acid.

[0035] Furthermore, the material is cured at 80-110 °C for 0.5-4 hours under conditions of 5-20 MPa. These conditions are conducive to the curing reaction and the formation of modified polysiloxane.

[0036] It should be noted that "polysiloxane compounds containing silane bonds" refers to organosilicon compounds that contain silane bonds in their polysiloxane molecular chains.

[0037] The modified polysiloxane has the structural formula shown in Formula II: , Where A is O or N; a is any value between 1 and 3; c is 0 or 1; and R is the structure in Si-H silanes other than H atoms.

[0038] The modified polysiloxane provided in this invention has high tensile strength and elongation at break; it also has high residual weight under nitrogen atmosphere; in addition, the modified polysiloxane has excellent ablation resistance, can increase the residual carbon content through its own multiple carbon-containing groups, and can be converted in situ into a SiC-reinforced carbon layer under high heat flux.

[0039] Fifthly, the present invention provides a thermal protection material, which is prepared by the modified polysiloxane described in the foregoing embodiments.

[0040] The raw materials and their sources provided in the embodiments of the present invention are as follows: 2,4,6,8-Tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane (D4-4Vi), triethylsilane, dimethylphenylsilane, and Karstedt's catalyst were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (China). Toluene (≥99.8%) was purchased from Chengdu Kelon Chemical Co., Ltd., China. Vinyl silicone oil (VSO, 8000 cst, M n = 58000, vinyl content 0.01 mol Vi / 100g) was provided by Zhonglan Chenguang Research Institute (China). Polymethylhydrosiloxane (PMHS, Si-H content 0.8 mol / 100g) was purchased from Guangzhou Tianling Co., Ltd., China, and polymethylphenylhydrosiloxane (PMPhHS, Si-H content 0.5 mol / 100g, phenyl content 0.5 mol / 100g) was purchased from Shandong Dayi Chemical Co., Ltd., China.

[0041] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0042] Example 1 This embodiment provides a method for synthesizing triethylsilane cyclic compounds, including: 1. Synthesis process Weigh 21.032g of D4-4Vi and 14.188g of triethylsilane, respectively, and dissolve them in 63.096g and 42.564g of toluene at 95℃.

[0043] Mix 2.6g of Karstedt's catalyst, D4-4Vi solution and triethylsilane solution, and stir at 80°C for 18h.

[0044] 2. Post-processing The reaction system was rotary evaporated at 110°C under a vacuum of 0.09 MPa for 1 hour to obtain a crude intermediate. The crude intermediate was heated to 190°C, evacuated to a vacuum of 0.09~0.1 MPa and allowed to stand. Argon gas was introduced every 2 minutes to distill off some of the product with a relatively high boiling point that had not been discharged. This process was repeated 10 times before the product was cooled under pressure.

[0045] This embodiment also provides a method for preparing triethylsilane cyclic modified silicone rubber (Et-D4Vi-SR), comprising: The above-mentioned triethylsilane cyclic compound, VSO, PMHS, and platinum catalyst were mixed, and bubbles were removed under a vacuum of 0.09 MPa. The mass ratio of VSO to triethylsilane cyclic compound in the mixture was 8:1, and the amounts of each raw material are shown in Table 1. The reaction system was cured at 100 °C for 3 h under 10 MPa to prepare triethylsilane cyclic modified silicone rubber, designated as D4-2Vi-SR. The vinyl silicone oil had a kinematic viscosity of 8000 cst and a molecular weight of 1000 mM. n The value is 58000, the vinyl content is 0.01 mol Vi / 100g, the Si-H content in the polysiloxane compound is 0.8 mol Si-H / 100g, and M n It is 6000.

[0046] Example 2 This embodiment provides a method for synthesizing phenylsilane rings, including: 1. Synthesis process 21.032 g of D4-4Vi and 16.6 g of phenyldimethylsilane were weighed and dissolved in 63.096 g and 49.8 g of toluene, respectively, at 95 °C. A mixture containing 2.6 g of Karstedt's catalyst was added to the D4-4Vi and phenyldimethylsilane solutions and stirred at 80 °C for 18 h. The reaction mixture was then rotary evaporated at 110 °C under a vacuum of 0.09 MPa for 1 h to obtain the crude intermediate.

[0047] 2. Post-processing The crude intermediate was heated to 190°C, evacuated to a vacuum of 0.09~0.1MPa and left to stand. Argon gas was introduced every 2 minutes to distill off the remaining product with a relatively high boiling point. This process was repeated 10 times before the product was cooled under pressure.

[0048] This embodiment also provides a method for preparing phenylsilane cyclic modified silicone rubber (Ph-D4Vi-SR), comprising: The above-mentioned phenylsilane cyclic compound, VSO, PMHS, and platinum catalyst were mixed, and bubbles were removed under a vacuum of 0.09 MPa. The mass ratio of VSO to triethylsilane cyclic compound in the mixture was 8:1, and the amounts of each raw material are shown in Table 1. The reaction system was cured at 100 °C for 3 h under 10 MPa to prepare triethylsilane cyclic modified silicone rubber, designated as D4-Ph-2Vi-SR. The vinyl silicone oil had a kinematic viscosity of 8000 cst and a molecular weight of 1000 mM. n The value is 58000, the vinyl content is 0.01 mol Vi / 100g, the Si-H content in the polysiloxane compound is 0.8 mol Si-H / 100g, and M n It is 6000.

[0049] Table 1. Amounts of each raw material used in the examples and comparative examples.

[0050] Comparative Example 1 This comparative example provides a method for preparing silicone rubber, comprising: VSO, PMHS, and platinum catalyst were mixed, and bubbles were removed under a vacuum of 0.09 MPa. The amounts of each raw material in the mixture are shown in Table 1. The mixture was cured at 100 °C for 3 h under 10 MPa to prepare silicone rubber, denoted as SR.

[0051] Comparative Example 2 This comparative example provides a method for preparing silicone rubber, comprising: VSO, PMPhHS, and platinum catalyst were mixed and degassed under a vacuum of 0.09 MPa. The amounts of each raw material in the mixture are shown in Table 1. The mixture was cured at 100 °C for 3 h under 10 MPa to prepare silicone rubber, denoted as SR-Ph.

[0052] Test Example 1: Mechanical Property Testing The mechanical properties of Et-D4Vi-SR, Ph-D4Vi-SR prepared in Examples 3-6 and SR prepared in Comparative Examples 1 and 2 were measured respectively.

[0053] Tensile strength and elongation at break of different specimens were tested using an Instron 5567 tensile testing machine (USA) according to GB / T528-2009 standard. All results for each sample are the average of four valid data points. Strength and toughness are key factors in evaluating the adaptability of elastomers under heavy load deformation, and tensile strength and elongation at break can assess these properties.

[0054] See results Figure 2 . Figure 2 The tensile properties of SR and silicon-cyclic modified SR samples were demonstrated. Compared to SR, the tensile strength and elongation at break of the silicon-cyclic modified SR were significantly improved. Among them, the 1 / 8-Et-D4Vi-SR sample exhibited the highest tensile strength (1.1192 MPa) and elongation at break (326.44%), which were 326.69% and 120.44% higher than those of pure silicone rubber, respectively. The stress-strain curves of different SR samples indicate that their tensile fracture behavior can be classified as brittle fracture. The introduction of silicon-cyclic molecules allows the cyclic molecules to act as rigid units to withstand stress, thereby increasing the energy required for chain slippage and breakage under high stress. Simultaneously, the expansion of the interchain spacing increases the spacing between crosslinking points, creating a larger free volume for chain movement. The resulting novel network structure promotes the movement and rearrangement of polysiloxane chains under stress, reducing stress concentration and hindering crack propagation, thus significantly improving the strength and toughness of the material.

[0055] Test Example 2: Thermal Performance Test The thermal properties of Et-D4Vi-SR, Ph-D4Vi-SR prepared in Examples 3-6 and SR prepared in Comparative Examples 1 and 2 were measured respectively.

[0056] The thermal properties of various samples were characterized by thermogravimetric analysis (TGA) under a nitrogen atmosphere. Specifically, TGA was performed using a thermogravimetric analyzer (NETZSCH, Germany) under a nitrogen atmosphere with a gas flow rate of 60 mL / min. The temperature range was 30℃ to 800℃, and the heating rate was 10℃ / min. Thermogravimetric-infrared spectroscopy (TG-IR) was performed using an IS50 infrared spectrometer (Thermo Fisher, USA). The test conditions were as follows: heating rate 10℃ / min, nitrogen atmosphere, temperature range 30–800℃.

[0057] See results Figure 3 .like Figure 3As shown in Figures a and b, the early decomposition of the SR matrix before 350 °C was significantly suppressed after the introduction of the silicon-containing cyclic compound, and the residual weights of Et-D4Vi-SR and Ph-D4Vi-SR were significantly increased. In particular, the residual weight of Ph-D4Vi-SR increased to 74.18% compared to SR (63.57%). Figure 3 The DTG thermogravimetric curves of C show that the addition of the ring effectively inhibits the decomposition of the SR matrix at temperatures above 500℃.

[0058] To analyze the differences in the pyrolysis processes of three samples—SR, Et-D4Vi-SR, and Ph-D4Vi-SR—TG-FTIR technology was used for real-time analysis of degradation products. Results are shown below. Figure 4 and Figure 5 , Figure 4 Three-dimensional FTIR spectra at different temperatures were shown. Figure 5 The FTIR absorbance results of the main pyrolysis products at various temperatures are presented.

[0059] Under a nitrogen atmosphere, zippering, random cleavage, and side-group cleavage are the main degradation pathways. Through zipper-like decomposition or random cleavage of the polysiloxane chains, the main degradation products D3 and D4 of polysiloxanes are generated. Characteristic signal peaks attributable to the Si-O-Si structure are particularly evident at 1030 and 1080 cm⁻¹. - ¹ Location. Simultaneously, 3015 cm - The peak at ¹ is attributed to methane, which is produced by the cleavage of methyl groups on the side of different polysiloxane chains.

[0060] like Figure 4 As shown in Figures 5ac, 5a, and 5b, under a nitrogen atmosphere, the release of siloxanes is suppressed after the introduction of the silicon-containing cyclic structure compared to SR, because the signal peaks associated with the cyclic oligomers are significantly reduced. Since D3 and D4 are difficult to form near the cyclic structure in Et-D4Vi-SR and Ph-D4Vi-SR, the random cleavage of polysiloxane chains is partially suppressed. Furthermore, because the cyclic structure increases the intermolecular distance, the methyl cleavage between two different polysiloxane chains is suppressed, and the release of methane is also inhibited.

[0061] Test Example 3: Test of Ablation Performance The ablation properties of Et-D4Vi-SR, Ph-D4Vi-SR prepared in Examples 1 and 2, and SR prepared in Comparative Examples 1 and 2 were measured respectively.

[0062] Experimental methods: (1) Determination of ablation performance The ablation performance of samples with different dimensions of Φ30 mm × 10 mm was tested for 30 seconds using an oxyacetylene ablation machine (ZR-323A, Qinhe Co., Ltd., China) at a heat flux density of 4 MW / m², referring to GJB 323A-1996. The mass ablation rate (MAR, g / s) and char rate (CR, mm / s) were calculated using the following equations:

[0063] Where m1 and m2 are the mass (g) of the sample before and after the ablation test, l1 is the original thickness of the sample, l2 is the thickness before and after the ablation test, and t is the test time (s). The final data is the average of four tests for each sample.

[0064] (2) Determination of the mechanical properties of the carbon layer The compressive strength of the carbon layer was determined using a universal testing machine (Instron 5567, Instron, USA). All results for each sample are the average of four valid data points. The test bar diameter was 2 mm, and the loading rate was 2 mm / min. The composition of the carbon layer was analyzed by scanning electron microscopy (SEM), mercury intrusion testing, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The microstructure was observed using a JSM-5900 (S-4800, Hitachi, Japan) scanning electron microscope at an accelerating voltage of 10 kV. The pore size distribution of the carbon layer was characterized using an automated mercury permeameter (AutoPore IV 9500, Micromeritics Co., USA). XRD patterns of the carbon layers were obtained using an X-ray diffractometer (Ultima IV, Rigaku Corporation, Japan) with Cu-Kα radiation (λ = 0.1540 nm), an accelerating voltage of 40 kV, an emission current of 40 mA, a 2θ range of 5–80º, and a scan rate of 10° / min.

[0065] (3) Characterization of the microstructure of carbon layers Microstructure images were observed using a scanning electron microscope (SEM) instrument (Helios G4 UC, Thermal Fisher Scientific, USA) at an accelerating voltage of 10 kV.

[0066] (4) Characterization of carbon layer pore structure The pore size distribution of the carbon layer was characterized using an automated mercury permeameter (AutoPore IV 9500, Micromeritics, USA).

[0067] Experimental results: (1) To study the anti-peeling properties of SR and divinyl modified SR, an oxyacetylene ablation test was used to simulate actual application conditions. Figure 6 The image shows the optical morphology of SR, Et-D4Vi-SR, and Ph-D4Vi-SR samples after exfoliation. Unlike the pure SR sample and the SR-Ph sample (where the carbon layer is completely destroyed), Et-D4Vi-SR and Ph-D4Vi-SR can form a carbon layer on the substrate surface.

[0068] (2) MAR and CR values ​​were calculated to characterize the ablation performance of SR-based PAMs. The results are as follows: Figure 7 Figures a and b show the mass loss rate (MAR) during ablation, which is related to the decomposition products released by polysiloxanes and the mechanical erosion of the char layer. CR represents the damaged area of ​​the PAMs; the char layer recession is determined by thermomechanical erosion, heat transfer, and thermal decomposition. Compared to SR, Et-D4Vi-SR and Ph-D4Vi-SR showed maximum reductions in MAR of 46.67% and 47.22%, respectively, and maximum reductions in CR values ​​of 36.48% and 59.10%, respectively.

[0069] The above ablation experiment results show that the addition of high doses of cyclic siloxanes helps to inhibit oxidative flame erosion, especially under high heat flux density conditions, which is conducive to the formation of a complete carbon layer.

[0070] (3) The mechanical properties of the carbon layer are a key factor in evaluating the erosion resistance of PAMs under thermal flow, particularly reflecting their resistance to thermomechanical erosion. Compression performance tests and compressive strength tests were conducted on the carbon layer to characterize its resistance to thermomechanical erosion. The results of the compressive strength test on the carbon layer are as follows: Figure 7 As shown in Figures c and d. The SR, SR-Ph, and SR carbon layers with a small amount of added cyclic siloxanes could not be tested due to their excessive brittleness. The Ph-D4Vi-SR carbon layer exhibited the highest compressive stress of 1.9787 MPa, which is 52.96% higher than the highest value of Et-D4Vi-SR. Compared to Et-D4Vi-SR, Ph-D4Vi-SR enables the carbon layer to resist high-speed heat flow more effectively, thereby protecting more substrate areas from flame damage.

[0071] (4) The microstructure of the carbon layer of different modified SR samples was studied by scanning electron microscopy (SEM) to reveal the relationship between the carbon layer structure and ablation performance. Figure 8 Figures a and b show the surface morphology of the carbon layer in the eroded samples. The surfaces of the Et-D4Vi-SR and Ph-D4Vi-SR samples are dense, indicating that the protective effect of the carbon layer is improved. Especially in the Ph-D4Vi-SR sample, the melt fills the defects on the surface of the carbon layer, and the dense surface layer effectively blocks external oxidizing gases.

[0072] (5) To reveal the densifying effect of Et-D4Vi-SR and Ph-D4Vi-SR on the carbon layer, the pore structure of the carbon layer was characterized by mercury intrusion experiments, and the results are as follows: Figure 9 As shown, both SR and SR-Ph exhibit large pores larger than 10,000 nm, corresponding to areas of severe carbon layer erosion. After the introduction of the ring, the number of large pores decreased, and the size of these pores also decreased, corresponding to a reduction in the erosion of the carbon layer by the Owen heat flux. With increasing amounts of Et-D4Vi-SR and Ph-D4Vi-SR, the degree of carbon layer erosion was further reduced, especially with high addition amounts of Ph-D4Vi-SR, which exhibited the fewest and smallest large pores, corresponding to a tightly packed carbon mass in the electron microscopy image.

[0073] In summary, introducing divinylcyclic siloxanes into the SR matrix to form a cyclic-linear siloxane structure simultaneously improves the mechanical properties, thermal properties, and ablation resistance of the material. Based on ¹H NMR and mass spectrometry analysis, the chemical structures of Et-D4Vi-SR and Ph-D4Vi-SR were confirmed. The introduction of the cyclic linear siloxane structure also positively impacts the thermal properties of the SR matrix. Tensile tests verified the significant improvement in the mechanical properties of the modified SR matrix: the modified SR material with the cyclic-linear siloxane structure exhibited increases in tensile strength and elongation at break of 326.69% and 120.44%, respectively. The introduction of the cyclic linear siloxane structure reduces stress concentration, and the cyclic structure can act as a rigid unit to withstand stress, thereby simultaneously improving strength and toughness. Compared to the pure SR sample (63.57%), the residual rates of Et-D4Vi-SR and Ph-D4Vi-SR were increased to a maximum of 72.56% and 74.18% under nitrogen atmosphere. In the cyclic-linear siloxane structure, the decomposition products of cyclic polysiloxanes are difficult to form near the sterically hindered cyclic structure, thereby suppressing the random breakage of polysiloxane chains. Most importantly, compared with pure SR, Et-D4Vi-SR and Ph-D4Vi-SR form a coherent carbon layer, thereby improving ablation resistance. In particular, the mass ablation rate and carbonization rate of Ph-D4Vi-SR are reduced by 47.22% and 59.10%, respectively. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon-containing ring, characterized in that, It has the following structural formula as shown in Equation I: Where A is O or N; a is any value between 1 and 3; b is 1 or 2; and R is the structure of Si-H silane excluding H atoms.

2. The silicon-containing ring according to claim 1, characterized in that, R is any one of trimethylsilyl, triethylsilyl, ethyldimethylsilyl, trihexylsilyl, triphenylsilyl, phenylmethylsilyl, diphenylmethylsilyl, pentamethyldisiloxy, and heptamethyltrisiloxy.

3. A method for preparing the silicon-containing ring according to claim 1, characterized in that, include: The polyvinyl silicone raw material, Si-H silane, and platinum catalyst are mixed and reacted.

4. The preparation method according to claim 3, characterized in that, The reaction satisfies at least one of the following conditions: (1) For every 100 parts of the polyvinylsilane-containing cyclic raw material, 20-80 parts of the Si-H silane and 0.001-20 parts of the platinum catalyst are added accordingly; (2) The polyvinylsilane-containing cyclic raw material is selected from at least one of trimethyltrivinylcyclotrisiloxane, tetramethyltetravinylcyclotetrasiloxane, pentamethylpentavinylcyclopentasiloxane, trimethyltrivinylcyclotrisilazane and tetramethyltetravinylcyclotetrasilazane; (3) The Si-H silane is selected from at least one of trimethylsilane, triethylsilane, ethyldimethylsilane, trihexylsilane, triphenylsilane, phenylmethylsilane, diphenylmethylsilane, pentamethyldisiloxane and heptamethyltrisiloxane; (4) The platinum catalyst is selected from at least one of chloroplatinic acid, platinum(0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane and octanol-modified chloroplatinic acid; (5) Reaction conditions include: temperature of 60-100℃; time of 5-30h.

5. The preparation method according to claim 3, characterized in that, It also includes: after the reaction is completed, the reaction system is rotary evaporated at 80-120℃ under a vacuum of 0.09 MPa for 45-90 minutes to obtain a crude intermediate; the crude intermediate is heated to 100-250℃, evacuated to a vacuum degree of 0.09-0.1 MPa and left to stand, and argon gas is introduced every 1-3 minutes to distill off some of the products with relatively high boiling points that have not been discharged. This process is repeated several times and then cooled under pressure.

6. A modified polysiloxane, characterized in that, It is prepared by the silicon-containing cyclic body described in claim 1.

7. The modified polysiloxane according to claim 6, characterized in that, It has the structural formula shown in Equation II below. , Where A is O or N; a is any value between 1 and 3; c is 0 or 1; and R is the structure of Si-H silane excluding H atoms.

8. A method for preparing the modified polysiloxane according to claim 6, characterized in that, include: The reaction involves mixing vinyl silicone oil, polysiloxane compounds containing silane bonds, a catalyst, and a silicon-containing cyclic compound.

9. The preparation method according to claim 8, characterized in that, The reaction satisfies at least one of the following conditions: (1) 50-200 parts vinyl silicone oil, 1-50 parts silicon-containing cyclic compound, 1-25 parts polysiloxane compound and 0.001-20 parts catalyst; (2) The catalyst is a platinum catalyst; (3) The kinematic viscosity of the vinyl silicone oil is 5000-30000 cst, and the number average molecular weight M n The concentration is 5000-100000 g / mol, and the vinyl content is 0.001-0.3 mol Vi / 100g; (4) The polysiloxane compound is selected from polymethylhydrosiloxane or polymethylphenylhydrosiloxane; (5) The polysiloxane compound contains 0.035~1.2 mol / 100g of Si-H and 0.035~1.2 mol / 100g of phenyl. n The concentration ranges from 300 to 10000 g / mol. (6) The reaction conditions include: pressure of 5-20 MPa; temperature of 80-110 °C; and time of 0.5-5 h.

10. A thermal protection material, characterized in that, It is prepared by the modified polysiloxane described in claim 6.

Images