Preparation methods, curing methods and applications of block copolymer benzoxazine resins containing carborane and siloxane structures

Abstract

A disclosed method for preparing block copolymer benzoxazine resins containing carborane and siloxane structures: S1. Aromatic diamine, carborane bisphenol, and paraformaldehyde are mixed in a solvent in a certain proportion and reacted under an inert atmosphere; when the molecular weight of the product reaches (0.9~1.1) M... n1 Time-quenching reaction, M n1 The product is the number-average molecular weight at which it reaches the theoretical degree of polymerization; the reaction solution is poured into methanol to collect the precipitate; S2: Bisphenol, diamino-terminated polysiloxane, and paraformaldehyde are mixed in proportion and reacted in a solvent under an inert atmosphere; when the product molecular weight reaches (0.9~1.1) M n2 Time-quenching reaction, M n2 The product is the number-average molecular weight at which it reaches the theoretical degree of polymerization. The reaction solution is poured into methanol to collect the precipitate. In step S3, the products from S1 and S2 are mixed in a solvent and reacted under an inert atmosphere. After the reaction, the mixture is poured into ethanol to collect the precipitate and wash it. This resin product is manufactured using a multi-stage stepped thermosetting process. The cured product exhibits excellent heat resistance and good toughness, making it suitable for application as an aerospace thermal protection material.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and relates to a specially synthesized resin, specifically to a method for preparing, curing, and applying a block copolymer benzoxazine resin containing carborane and siloxane structures. Technical Background

[0002] With the rapid development of aerospace technology and commercial spaceflight, the demand for lightweight thermal protection materials in the aerospace field continues to grow.

[0003] Currently, ablation-type thermal protection remains the most mature technology for spacecraft to cope with extreme high temperatures (above 1500℃). Phenolic resin can be used as the matrix component of ablation-type thermal protection materials, achieving an ablation char residue rate of over 50% in an air / oxygen atmosphere. Benzoxazine resin is a special type of phenolic resin that, in addition to inheriting the excellent heat resistance of phenolic resin, also possesses properties such as no byproduct release during curing and low curing shrinkage. However, cured benzoxazine resins suffer from insufficient toughness. Materials lacking toughness are prone to developing through-cracks or even complete fragmentation under external impact, seriously threatening the safety of thermal protection structures. Insufficient toughness severely restricts the application of benzoxazine resin-based thermal protection materials in the aerospace field.

[0004] Generally, the heat resistance and toughness of thermosetting polymers are two mutually restrictive indicators. Studies have shown that introducing a carborane structure into the polymer backbone significantly improves the material's heat resistance because carborane can generate a boron oxide (B2O3) passivation layer in situ under high-temperature, oxygen-rich conditions to isolate oxygen. However, the carborane structure has high rigidity and steric hindrance; simply introducing the carborane structure will further increase the material's brittleness and reduce its toughness. Polysiloxanes are a class of polymers with a Si-O-Si structure in their main chain. Due to the high bond energy of the Si-O bonds, the materials possess good thermal stability; simultaneously, the Si-O bonds have a low rotational energy barrier and a long bond length, thus imparting good toughness. Simultaneously introducing carborane and polysiloxane structures into the main chain molecule of the material is a promising approach to simultaneously improve heat resistance and toughness; however, this technical approach has not yet been reported. Summary of the Invention

[0005] To further improve the heat resistance and toughness of cured benzoxazine resins, this invention provides a method for preparing block copolymerized benzoxazine resins containing carborane and siloxane structures, comprising the following steps:

[0006] S1 Preparation of carborane benzoxazine oligomers: Aromatic diamine, carborane bisphenol, and paraformaldehyde (calculated as repeating unit CH2O) are mixed in a molar ratio of 1:1.5~2:4.2 in 3~5 times the volume of solvent and reacted at 70~90℃ under an inert gas atmosphere.

[0007] During the reaction, samples were taken and the molecular weight of the reaction products was determined in real time using GPC chromatography to judge the progress of the reaction (chromatographic test conditions: PS-DVB gel column, toluene as mobile phase, column temperature 40℃, flow rate 1.0 mL / min, standard PS as standard sample, RI detector).

[0008] When the molecular weight of the reaction product reaches (0.9~1.1) M n1 Within the specified range, the reaction is quenched by rapidly cooling to below 0°C within 10 minutes, wherein M... n1 For the product of step S1 to reach the theoretical degree of polymerization (X) n1 The number-average molecular weight at that time was determined; finally, the reaction solution was poured into methanol, and the precipitate was collected; the yield of this step was approximately 50-70%.

[0009] S2 Preparation of polysiloxane benzoxazine oligomers: Bisphenol, diamino-terminated polysiloxane, and paraformaldehyde are mixed in a molar ratio of 1:2~3:4.2 and then reacted in 3~5 times the volume of solvent under an inert gas atmosphere at 90~110℃.

[0010] Similarly, the progress of the reaction is judged by taking samples and measuring the molecular weight of the reaction products during the reaction process;

[0011] When the molecular weight of the reaction product reaches (0.9~1.1) M n2 Within the specified range, the reaction is quenched by rapidly cooling to below 0°C within 10 minutes, wherein M... n2 For the product of step S2 to reach the theoretical degree of polymerization (X) n2 The number-average molecular weight at that time was determined; finally, the reaction solution was poured into methanol, and the precipitate was collected; the yield of this step was approximately 50-60%.

[0012] Preparation of block polymer in S3: The products of S1 and S2 are mixed in 3 to 5 times the volume of solvent and reacted at 100 to 120°C for 10 to 15 hours under an inert gas atmosphere. After the reaction is completed, the reaction solution is poured into ethanol, the precipitate is collected, and the product is washed with saturated sodium carbonate solution and deionized water to obtain the target resin product. The yield of this step is about 90 to 95%.

[0013] Furthermore, in step S1:

[0014] The theoretical degree of aggregation (X) n1 The value of is calculated by the following formula:

[0015] ,

[0016] n in the above formula A and n B These are the amounts of aromatic diamine and carborane bisphenol, respectively.

[0017] The M n1 Calculated by the following formula:

[0018]

[0019] In the above formula, Mr A and Mr B These are the relative molecular masses of the aromatic diamine and the carborane bisphenol, respectively.

[0020] Furthermore, in step S2:

[0021] The theoretical degree of aggregation (X) n2 The value of is calculated by the following formula:

[0022] ,

[0023] n in the above formula C and n D These are the amounts of bisphenol and diamino-terminated polysiloxane, respectively.

[0024] The M n2 Calculated by the following formula:

[0025]

[0026] In the above formula, Mr C and Mr D These are the relative molecular masses of bisphenol and diamino-terminated polysiloxane, respectively.

[0027] Preferably, in step S1, the aromatic diamine is one or a mixture of 1,3-phenylenediamine, 1,4-phenylenediamine, 1,2-phenylenediamine, 4,4-diaminodiphenylmethane, 3,3-diaminodiphenylmethane, 4,4-diaminodiphenyl sulfone, 3,3-diaminodiphenyl sulfone, 2,4-diaminotoluene, 2,6-diaminotoluene, 4,4-diaminobiphenyl, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene.

[0028] Preferably, in step S1, the carborane bisphenol is one or more of 1,2-bis(4-hydroxyphenyl)-o-carborane, 1,7-bis(4-hydroxyphenyl)-m-carborane, 1,12-bis(4-hydroxyphenyl)-p-carborane, 1,2-bis(3-hydroxyphenyl)-o-carborane, 1,7-bis(3-hydroxyphenyl)-m-carborane, and 1,12-bis(3-hydroxyphenyl)-p-carborane.

[0029] Preferably, in step S2, the bisphenol is one or more of bisphenol A, bisphenol F, bisphenol B, bisphenol S, bisphenol Z, tetramethylbisphenol F, bisphenol M, and bisphenol fluorene.

[0030] Preferably, in step S2: the dual-amino-terminated polysiloxane is an amino-terminated polydimethylsiloxane, M w It ranges from 1000 to 1500.

[0031] Preferably, the solvent is one or a mixture of toluene, 1,4-dioxane, and tetrahydrofuran.

[0032] A block copolymer benzoxazine resin containing carborane and siloxane structures is prepared by the above method.

[0033] A method for curing a block copolymer benzoxazine resin containing carborane and siloxane structures is disclosed: multi-stage stepped thermosetting molding is employed, with the first stage cured at 120-150℃ for 1-2 hours, the second stage cured at 140-180℃ for 2-4 hours, and the third stage cured at 180-250℃ for 3-5 hours. This gradient thermosetting molding method is suitable for this resin and can control the separation of soft and hard microphases to achieve better mechanical properties.

[0034] The application of the aforementioned block copolymer benzoxazine resin containing carborane and siloxane structures in aerospace thermal protection materials is disclosed.

[0035] The principle of this application is as follows:

[0036] The block copolymer benzoxazine resin containing carborane and siloxane structures prepared by the method of this application exhibits excellent heat resistance and ablation resistance in its cured form. This is attributed to the icosahedral rigid cage structure of the carborane. Furthermore, the synergistic effect of boron and silicon elements in the cured resin strengthens the residual carbon skeleton of the ablation products. Under high-temperature oxidative ablation conditions, the boron and silicon elements on the main chain undergo a co-oxidation reaction, generating a dense and continuous borosilicate (B2O3-SiO2) mixed glassy passivation layer in situ on the material surface. This passivation layer exhibits good thermal stability and strengthens the residual carbon structure skeleton, thereby improving the thermal protection effect of the heat insulation barrier and enhancing the heat resistance of the cured product under high-temperature ablation conditions. The cured product exhibits a residual carbon content as high as 59.6% at 800℃ in air, a limiting oxygen index (LOI) greater than 40, and a glass transition temperature (Tg). g It can reach temperatures above 350℃.

[0037] Regarding toughness, this invention prepares a benzoxazine random copolymer with both carborane and polysiloxane unit structures in the main chain via a stepwise polymerization reaction. Specifically, it enables the benzoxazine resin to acquire a block copolymer structure of carborane cages and polysiloxane segments. After thermosetting, this resin structure can form a microphase-separated structure with a 30-80 nm scale of "carborane-rich rigid framework" and "siloxane-rich flexible microregions." The soft and hard segments can be more uniformly and finely distributed to achieve a better phase separation structure, thereby significantly improving the brittleness caused by the carborane and benzoxazine structures. This submicron-level phase-separated network structure achieves a toughening effect. The elongation at break of the cured product can reach 3.2%, and the fracture toughness K0 is [not specified]. IC Values ​​can reach up to 1.4 MPa·m 1 / 2 .

[0038] Through the above technical solutions, the present invention has at least the following beneficial effects:

[0039] The block copolymer benzoxazine resin containing carborane and siloxane structures prepared by stepwise polymerization in this application has excellent heat resistance and good toughness in its cured product. At the same time, the resin softening point can be lower than 145°C, and it has good processability, making it suitable for use as a thermal protection material in high-end fields such as aerospace. Attached Figure Description

[0040] Figure 1 Thermogravimetric curves (in air) of the cured resin products of Examples 1-3 and Comparative Example 1.

[0041] Figure 2 The infrared spectrum of the product in Example 1;

[0042] Figure 3 The image shows the DMA (Dynamic Thermomechanical Analysis) loss tangent curves of the resin cured products of Example 1 and Comparative Example 3. Detailed Implementation

[0043] The present invention will be further illustrated by the following embodiments, but the application of the present invention is not limited to the embodiments described.

[0044] Example 1

[0045] The preparation method of the block copolymer benzoxazine resin containing carborane and siloxane structures in this example includes the following steps:

[0046] Step 1 (Preparation of carborane benzoxazine oligomers): 4,4-diaminodiphenylmethane (Mr=198.26), 1,12-bis(3-hydroxyphenyl)-p-carborane (Mr=328.42), and paraformaldehyde (calculated as repeating unit CH2O) were mixed in a molar ratio of 1:1.5:4.2 in 4 times the volume of 1,4-dioxane solvent. The reaction was carried out at 80°C under an inert gas atmosphere. During the reaction, samples were taken and the molecular weight M was determined by GPC chromatography. n (Chromatographic test conditions: PS-DVB gel column, toluene as mobile phase, column temperature 40℃, flow rate 1.0 mL / min, standard PS as standard sample, RI detector) When the molecular weight of the product reaches 2500 (in the range of 2400~3000), the reaction is quenched by rapidly cooling to below 0℃ within 10 minutes. The reaction solution is poured into methanol to collect the precipitated product, and the yield is about 62%.

[0047] Step 2 (Preparation of polysiloxane benzoxazine oligomers): Bisphenol A, diamino-terminated polysiloxane (M... w =1500), paraformaldehyde was mixed in a molar ratio of 1:2:4.2 and then reacted in 5 times its volume of 1,4-dioxane solvent at 90°C under an inert gas atmosphere. During the reaction, samples were taken and the molecular weight M was determined by GPC chromatography. n When the molecular weight reaches 5100 (within the range of 4700~5800), the reaction is quenched by rapidly cooling to below 0°C within 10 minutes. The reaction solution is then poured into methanol to collect the precipitated product, with a yield of approximately 58%.

[0048] Step 3 (Preparation of block polymer): The products from Step 1 and Step 2 are mixed in 3 times the volume of 1,4-dioxane solvent and reacted at 110°C for 12 hours under an inert gas atmosphere. After the reaction is completed, the reaction solution is poured into ethanol, the precipitate is collected, and the product is washed with saturated sodium carbonate solution and deionized water to obtain the target resin product.

[0049] The above-mentioned resin product is formed by multi-stage stepped thermosetting molding. The first stage is thermoset at 120℃ for 1 hour, the second stage is thermoset at 180℃ for 2 hours, and the third stage is thermoset at 240℃ for 4 hours.

[0050] Example 2

[0051] The preparation method of the block copolymer benzoxazine resin containing carborane and siloxane structures in this example includes the following steps:

[0052] Step 1 (Preparation of carborane benzoxazine oligomers): 4,4-diaminodiphenylmethane, 1,12-bis(3-hydroxyphenyl)-p-carborane, and paraformaldehyde (calculated as repeating unit CH2O) were mixed in a molar ratio of 1:2:4.2 in 4 times the volume of 1,4-dioxane solvent. The reaction was carried out at 70°C under an inert gas atmosphere. During the reaction, samples were taken and the molecular weight M was determined by GPC chromatography. n (Chromatographic test conditions: PS-DVB gel column, toluene as mobile phase, column temperature 40℃, flow rate 1.0 mL / min, standard PS as standard sample, RI detector) When the molecular weight of the product reaches 1620 (in the range of 1500~1800), the reaction is quenched by rapidly cooling to below 0℃ within 10 minutes. The reaction solution is poured into methanol to collect the precipitated product, and the yield is about 54%.

[0053] Step 2 (Preparation of polysiloxane benzoxazine oligomers): Bisphenol A, diamino-terminated polysiloxane (M... w =1500), paraformaldehyde was mixed in a molar ratio of 1:3:4.2 and then reacted in 5 times its volume of tetrahydrofuran solvent at 100°C under an inert gas atmosphere. During the reaction, samples were taken and the molecular weight M was determined by GPC chromatography. n When the molecular weight reaches 3340 (within the range of 3100~3900), the reaction is quenched by rapidly cooling to below 0°C within 10 minutes. The reaction solution is then poured into methanol to collect the precipitated product, with a yield of approximately 51%.

[0054] Step 3 (Preparation of block polymer): The products from Step 1 and Step 2 are mixed in 3 times the volume of tetrahydrofuran solvent and reacted at 100°C for 15 hours under an inert gas atmosphere. After the reaction is completed, the reaction solution is poured into ethanol, the precipitate is collected, and the product is washed with saturated sodium carbonate solution and deionized water to obtain the target resin product.

[0055] The above-mentioned resin product is formed by multi-stage stepped thermosetting molding. The first stage is thermoset at 130℃ for 2 hours, the second stage is thermoset at 140℃ for 4 hours, and the third stage is thermoset at 180℃ for 5 hours.

[0056] Example 3

[0057] The preparation method of the block copolymer benzoxazine resin containing carborane and siloxane structures in this example includes the following steps:

[0058] Step 1 (Preparation of carborane benzoxazine oligomers): 1,4-phenylenediamine, 1,7-bis(4-hydroxyphenyl)-m-carborane, and paraformaldehyde (calculated as repeating unit CH2O) were mixed in a molar ratio of 1:1.7:4.2 in 4 times the volume of 1,4-dioxane solvent. The reaction was carried out at 90°C under an inert gas atmosphere. During the reaction, samples were taken and the molecular weight M was determined by GPC chromatography. n (Chromatographic test conditions: PS-DVB gel column, toluene as mobile phase, column temperature 40℃, flow rate 1.0 mL / min, standard PS as standard sample, RI detector) When the molecular weight of the product reaches 1600 (in the range of 1450~1800), the reaction is quenched by rapidly cooling to below 0℃ within 10 minutes. Finally, the reaction solution is poured into methanol, and the precipitated product is collected. The yield is about 58%.

[0059] Step 2 (Preparation of polysiloxane benzoxazine oligomers): Bisphenol F, diamino-terminated polysiloxane (M... w =1000), paraformaldehyde was mixed in a molar ratio of 1:2.5:4.2 and then reacted in 5 times its volume of 1,4-dioxane solvent at 110°C under an inert gas atmosphere. During the reaction, samples were taken and the molecular weight M was determined by GPC chromatography. n When the molecular weight reaches 2750 (within the range of 2550~3150), the reaction is quenched by rapidly cooling to below 0°C within 10 minutes. Finally, the reaction solution is poured into methanol, and the precipitated product is collected. The yield is about 54%.

[0060] Step 3 (Preparation of block polymer): The products from Step 1 and Step 2 are mixed in 3 times the volume of tetrahydrofuran solvent and reacted at 120°C for 10 hours under an inert gas atmosphere. After the reaction is completed, the reaction solution is poured into ethanol, the precipitate is collected, and the product is washed with saturated sodium carbonate solution and deionized water to obtain the target resin product.

[0061] The above-mentioned resin product is formed by multi-stage stepped thermosetting molding. The first stage is thermoset at 150℃ for 1 hour, the second stage is thermoset at 170℃ for 3 hours, and the third stage is thermoset at 250℃ for 3 hours.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Based on the present invention, and through the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0063] The principles of the above embodiments are as follows:

[0064] The block copolymer benzoxazine resin containing carborane and siloxane structures prepared by the method of this application exhibits excellent heat resistance and ablation resistance in its cured form. This is attributed to the icosahedral rigid cage structure of the carborane. Furthermore, the synergistic effect of boron and silicon elements in the cured resin strengthens the residual carbon skeleton of the ablation products. Under high-temperature oxidative ablation conditions, the boron and silicon elements on the main chain undergo a co-oxidation reaction, generating a dense and continuous borosilicate (B2O3-SiO2) mixed glassy passivation layer in situ on the material surface. This passivation layer exhibits good thermal stability and strengthens the residual carbon structure skeleton, thereby improving the thermal protection effect of the heat insulation barrier and enhancing the heat resistance of the cured product under high-temperature ablation conditions. The cured product exhibits a residual carbon content as high as 59.6% at 800℃ in air, a limiting oxygen index (LOI) greater than 40, and a glass transition temperature (Tg). g It can reach temperatures above 350℃.

[0065] Regarding toughness, this invention prepares a benzoxazine random copolymer with both carborane and polysiloxane unit structures in the main chain via a stepwise polymerization reaction. Specifically, it enables the benzoxazine resin to acquire a block copolymer structure of carborane cages and polysiloxane segments. After thermosetting, this resin structure can form a microphase-separated structure with a 30-80 nm scale of "carborane-rich rigid framework" and "siloxane-rich flexible microregions." The soft and hard segments can be more uniformly and finely distributed to achieve a better phase separation structure, thereby significantly improving the brittleness caused by the carborane and benzoxazine structures. This submicron-level phase-separated network structure achieves a toughening effect. The elongation at break of the cured product can reach 3.2%, and the fracture toughness K0 is [not specified]. IC Values ​​can reach up to 1.4 MPa·m 1 / 2 .

[0066] Comparative Example 1 (without carborane bisphenol)

[0067] The preparation method of the hybrid benzoxazine resin in this example includes the following steps:

[0068] Step 1: Replace 1,12-bis(3-hydroxyphenyl)-p-carborane in Step 1 of Example 1 with bisphenol A. Stop the reaction when the molecular weight of the product reaches 2100 (2000~2450) and collect the product. The remaining conditions are the same as in Step 1 of Example 1.

[0069] Step 2: Same as Step 2 in Example 1.

[0070] Step 3: Same as Step 3 in Example 1

[0071] The thermosetting conditions for the resin product are the same as in Example 1.

[0072] Comparative Example 2 (without polysiloxane)

[0073] The preparation method of the hybrid benzoxazine resin in this example includes the following steps:

[0074] Step 1: Same as Step 1 in Example 1.

[0075] Step 2: The double-terminated amino polysiloxane (M) from Step 2 of Example 1... w =1500) was replaced with 4,4-diaminodiphenylmethane, and the reaction was stopped when the molecular weight of the reactants was 1300 (1200~1500), and the products were collected.

[0076] Step 3: Same as Step 3 in Example 1

[0077] The thermosetting conditions for the resin product are the same as in Example 1.

[0078] Comparative Example 3 (Synthesized using a one-step method)

[0079] The preparation method of the hybrid benzoxazine resin in this example includes the following steps:

[0080] 1,12-bis(3-hydroxyphenyl)-p-carborane, bisphenol A, 4,4-diaminodiphenylmethane, and diamino-terminated polysiloxane (molecular weight M) w =1500), paraformaldehyde was mixed in dioxane at a molar ratio of 1.5:1:1:2:8.4, and reacted at 100°C for 15 hours under an inert gas atmosphere. The reaction solution was then naturally cooled to room temperature, poured into ethanol, and the precipitate was collected. The product was washed with saturated sodium carbonate solution and deionized water to obtain the final product.

[0081] The thermosetting conditions for the resin product are the same as in Example 1.

[0082] The following technical indicators were measured for the cured resins of the above embodiments and comparative examples, and the results are shown in Table 1 below:

[0083] According to GB / T 46838-2025 "Plastics - Fracture toughness (K) under high loading rate (1m / s)" IC The determination of )

[0084] According to GB / T 12007.6-1989 "Determination of softening point of epoxy resin - Ring and ball method";

[0085] Limiting Oxygen Index (LOI) determined according to ASTM D2863.

[0086] The glass transition temperature (T) was determined by dynamic thermomechanical analysis (DMA). g );

[0087] The char yield was determined by thermogravimetric analysis (TGA) (air atmosphere, 800°C).

[0088] Table 1:

[0089]

[0090] As can be seen from the data in Table 1 above, the block copolymer benzoxazine resins (Examples 1-3) containing carborane and siloxane structures proposed in this invention simultaneously leverage the advantages of both carborane bisphenol and polysiloxane structures, resulting in cured products with excellent heat resistance and toughness. In Comparative Example 1, due to the absence of a carborane structure, the heat resistance and flame retardant properties of the material are significantly lower than those obtained in this invention. In Comparative Example 2, although the material obtained does not contain a polysiloxane soft segment structure, it exhibits good heat resistance but is noticeably brittle. In Comparative Example 3, although the product contains both carborane and polysiloxane structures, a block copolymer structure is not formed; therefore, the brittleness problem remains significant, and the heat resistance is also inferior to that of the materials in Examples 1-3.

[0091] Depend on Figure 1 The comparison shows that, due to the absence of carborane segments in the product of Comparative Example 1, the heat resistance of the cured material is significantly lower than that of the products in the three sets of examples. This comparison demonstrates that introducing a carborane icosahedral rigid structure into the benzoxazine resin in this invention can substantially improve the heat resistance of the cured product.

[0092] like Figure 2 The image shown is the infrared spectrum of the product from Example 1, at 3140 cm⁻¹. -1 The peak is the CH signal peak of a carborane icosahedral cage, at 2608 cm⁻¹. -1 The peak is the BH signal peak of a carborane icosahedral cage; 1047 cm⁻¹ -1 and 1119 cm -1 The peak is attributed to the Si-O-Si structure signal. Therefore, it can be proven that the product contains both carborane and siloxane chain segments.

[0093] Depend on Figure 3 The comparison clearly shows that the material in Example 1 exhibits two peaks in its glass transition curve, indicating two distinct glass transition temperatures. The lower glass transition temperature (122°C) belongs to the soft segment region of the polysiloxane, while the peak at 402°C belongs to the hard segment region—a typical characteristic of block polymers. In Comparative Example 3, although both carborane and polysiloxane were used in the raw materials, the one-step synthesis resulted in a random and uniform distribution of hard and soft segments, unlike a block polymer structure; therefore, only one glass transition peak was observed. Based on the fracture toughness test results, it can be inferred that the material prepared in this invention possesses block polymer characteristics, enabling the formation of an appropriate phase-separated microstructure, thereby significantly improving the material's brittleness.

Claims

1. A method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures, characterized in that, Includes the following steps: S1 Preparation of carborane benzoxazine oligomers: Aromatic diamine, carborane bisphenol, and paraformaldehyde are mixed in a solvent at a molar ratio of 1:1.5 to 2:4.2 and reacted at 70 to 90°C under an inert gas atmosphere. When the molecular weight of the reaction product reaches (0.9~1.1) M n1 Within the specified range, the reaction is quenched by rapidly cooling to below 0°C within 10 minutes, wherein M... n1 For the product of step S1 to reach the theoretical degree of polymerization (X) n1 The number-average molecular weight at that time was calculated; finally, the reaction solution was poured into methanol, and the precipitate was collected. S2 Preparation of polysiloxane benzoxazine oligomers: Bisphenol, diamino-terminated polysiloxane, and paraformaldehyde are mixed in a molar ratio of 1:2~3:4.2 and reacted in a solvent at 90~110℃ under an inert gas atmosphere. When the molecular weight of the reaction product reaches (0.9~1.1) M n2 Within the specified range, the reaction is quenched by rapidly cooling to below 0°C within 10 minutes, wherein M... n2 For the product of step S2 to reach the theoretical degree of polymerization (X) n2 The number-average molecular weight at that time was calculated; finally, the reaction solution was poured into methanol, and the precipitate was collected. Preparation of block polymer by S3: The products of S1 and S2 are mixed in a solvent and reacted at 100-120℃ for 10-15 hours under an inert gas atmosphere. After the reaction is completed, the reaction solution is poured into ethanol, the precipitate is collected, and the product is washed with saturated sodium carbonate solution and deionized water to obtain the target resin product.

2. The method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures according to claim 1, characterized in that, In step S1: The theoretical degree of aggregation (X) n1 The value of is calculated by the following formula: ， ； n in the above formula A and n B These are the amounts of aromatic diamine and carborane bisphenol, respectively. The M n1 Calculated by the following formula: ； In the above formula, Mr A and Mr B These are the relative molecular masses of the aromatic diamine and the carborane bisphenol, respectively.

3. The method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures according to claim 1, characterized in that, In step S2: The theoretical degree of aggregation (X) n2 The value of is calculated by the following formula: ， ； n in the above formula C and n D These are the amounts of bisphenol and diamino-terminated polysiloxane, respectively. The M n2 Calculated by the following formula: ； In the above formula, Mr C and Mr D These are the relative molecular masses of bisphenol and diamino-terminated polysiloxane, respectively.

4. The method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures according to claim 1, characterized in that: In step S1, the aromatic diamine is one or a mixture of 1,3-phenylenediamine, 1,4-phenylenediamine, 1,2-phenylenediamine, 4,4-diaminodiphenylmethane, 3,3-diaminodiphenylmethane, 4,4-diaminodiphenyl sulfone, 3,3-diaminodiphenyl sulfone, 2,4-diaminotoluene, 2,6-diaminotoluene, 4,4-diaminobiphenyl, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene.

5. The method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures according to claim 1, characterized in that: In step S1, the carborane bisphenol is one or a mixture of 1,2-bis(4-hydroxyphenyl)-o-carborane, 1,7-bis(4-hydroxyphenyl)-m-carborane, 1,12-bis(4-hydroxyphenyl)-p-carborane, 1,2-bis(3-hydroxyphenyl)-o-carborane, 1,7-bis(3-hydroxyphenyl)-m-carborane, and 1,12-bis(3-hydroxyphenyl)-p-carborane.

6. The method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures according to claim 1, characterized in that: In step S2, the bisphenol is one or more of bisphenol A, bisphenol F, bisphenol B, bisphenol S, bisphenol Z, tetramethylbisphenol F, bisphenol M, and bisphenol fluorene.

7. The method for preparing a block copolymer benzoxazine resin containing carborane and siloxane structures according to claim 1, characterized in that, In step S2: the dual-amino-terminated polysiloxane is an amino-terminated polydimethylsiloxane, M w The range is 1000~1500.

8. A block copolymer benzoxazine resin containing carborane and siloxane structures, characterized in that: It is prepared by any one of the methods of claims 1-7.

9. A curing method for a block copolymer benzoxazine resin containing carborane and siloxane structures as described in claim 8, characterized in that: It adopts a multi-stage stepped thermosetting molding process. The first stage is thermoset at 120~150℃ for 1-2 hours, the second stage is thermoset at 140~180℃ for 2-4 hours, and the third stage is thermoset at 180~250℃ for 3-5 hours.

10. The application of a block copolymer benzoxazine resin containing a carborane and siloxane structure as described in claim 8 in aerospace thermal protection materials.

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