A nanometer bicontinuous phase poly (siloxane imide) phenolic ablation-resistant resin and its preparation method and use

Abstract

The present invention provides a controllable nano-bicontinuous phase organosilicon / phenolic ablation-resistant resin and its preparation method and use, which belong to the field of advanced materials. The present invention first reacts a polymer modifier containing a Si-O-Si main chain, an acid anhydride, and an alkoxy-containing end-capping agent to form an alkoxy-terminated poly(siloxane amic acid), and then solidifies and imidizes it with a phenolic resin to prepare a new nano-bicontinuous phase organosilicon / phenolic ablation-resistant resin. The polymer modifier containing a Si-O-Si main chain has a structure of formula (I), wherein n is 1 to 50, R1 is hydroxyl, carboxyl, aminopropyl, methyl, alkoxy, acetoxy, and R2 is hydroxyl, carboxyl, aminopropyl, methyl, alkoxy, acetoxy. Compared with the island phase organosilicon / phenolic resin, the nano-bicontinuous phase organosilicon / phenolic ablation-resistant resin of the present invention has better long-term high-temperature antioxidant ability and ablation resistance, and has broad application prospects in the fields of fireproof materials, high-temperature resistant resin coatings, high-temperature resistant adhesives, ablation-resistant insulation materials, etc. #imgabs0#

Description

Technical Field

[0001] The invention belongs to the field of heat protection materials, and in particular relates to a nanometer bicontinuous phase poly (siloxane imide) phenolic ablation-resistant resin, and a preparation method and application thereof. Background Art

[0002] When carrying out missions such as space exploration, round-trip travel, and re-entry, spacecraft experience extremely harsh environments such as ultra-high temperatures. To protect spacecraft from the effects of ultra-high heat loads, a suitable thermal protection system (TPS) is required. Phenolic resin (PR) is widely used as a TPS material due to its high carbonization rate, excellent thermal stability, and good thermal insulation properties. However, with the rapid development of spacecraft, traditional PR can no longer meet the increasingly stringent requirements. Therefore, there is an urgent need to modify PR to prepare a new type of PR that can withstand the erosion of ultra-high temperature oxygen-containing hot air flows for a long time.

[0003] Nanomaterials, due to their small size and large specific surface area, offer superior performance compared to traditional materials. Therefore, nanomaterials such as nano-SiO2, carbon nanotubes (CNTs), and graphene are often introduced into polyurethane (PR) to improve its thermal performance. Zhong (H. Zhong, H. Hu, B. Ni, Y. Guo, Z. Luo, T. Zhao, B.-x JP Zhang, Silica sol nanoparticles hybridized allyl phenolic resins for improving mechanical and thermal performance, Polymer 254 (2022) 125052) introduced non-polar silica sol nanoparticles into polyurethane to prepare a silica / phenolic hybrid resin, which exhibited improved mechanical properties and ablation resistance. Yum (SHYum, SHKim, WILee, HJCSKim, Technology, Improvement of ablation resistance of phenolic composites reinforced with low concentrations of carbon nanotubes, Compos. Sci. Technol. 121 (2015) 16-24) introduced CNT into PR to prepare CNT / PR composite resin. Since CNT can serve as crystal growth nuclei for resin graphitization, the ablation resistance of CNT / PR composite materials is increased by 30% and 34% respectively compared with pure PR. However, it is worth noting that although the introduction of nanomaterials into PR can effectively improve thermal stability, the phenomenon of nanomaterials being difficult to disperse or agglomerate in the matrix always occurs during the introduction process. This phenomenon is fatal to the improvement of the thermal protection performance of the material.

[0004] To avoid this phenomenon, researchers have attempted to introduce non-metallic elements such as B and Si into the PR system through chemical bonds through inorganic-organic hybridization. Although the introduction of B can improve the thermal properties of PR, the melting and boiling points of B2O3, B4C, etc. formed during the ablation process are low, and their resistance to ultra-high temperature hot air flow is poor. There are a large number of high-bond energy Si-O-Si in silicone molecules. At the same time, it is also an excellent ceramic precursor. At high temperatures, it will decompose into ceramics such as SiO2 and SiC with high melting and high boiling points. It has unparalleled advantages in thermal stability and flame retardancy. Therefore, silicone-modified PR has attracted increasing interest. However, the compatibility between silicone and PR is poor, and phase separation is easy to occur in the resin matrix, forming an "island phase" structure, which is not conducive to further improving the ablation resistance of the hybrid resin.

[0005] Qin Zheng etc. (Plastics Industry, December 2014 the 42nd volume the 12th phase) reported a kind of epoxy-terminated polysiloxane modified phenolic resin, it is by the copolymerization reaction of oligomeric epoxy-terminated polysiloxane (E-PDMS) and formaldehyde and phenol, prepared toughening modified phenolic resin, result shows, the impact strength, tensile strength and the thermotolerance of this modified phenolic resin are better than unmodified phenolic resin.But in this epoxy-terminated polysiloxane modified phenolic resin, the compatibility of epoxy-terminated polysiloxane and phenolic resin is relatively poor, can form " island phase " structure, the ablation resistance of modified phenolic resin is exerted on.Previous research has shown, compared to the relatively poor island phase structure of interface compatibility, the organosilicon in the nanometer bicontinuous phase structure with good interface compatibility can form close-packed SiO at high temperature protective layer, has isolated oxygen, and protects carbon layer from oxidation. However, these studies all involved compounding and polycondensing small siloxane molecules with phenolic resins, resulting in polysiloxanes with relatively low molecular weights. During the ceramicization process, a significant amount of small cyclic siloxane volatilization occurs, adversely affecting the formation of ceramics such as SiO2 and SiC, hindering the maximization of the hybrid resin's ablation resistance.

[0006] In order to overcome the above problems, it is urgent to develop a method that can regulate the phase structure of silicone / phenolic hybrid resin, so as to improve the ablation resistance of phenolic resin and maximize the thermal protection ability of hybrid resin. Summary of the Invention

[0007] The purpose of the present invention is to provide a nanometer bicontinuous phase organosilicon / phenolic ablation-resistant resin and a preparation method and use thereof.

[0008] The invention provides a composite resin, which is prepared by using a polymer modifier containing a Si-O-Si main chain, an acid anhydride, an alkoxy-containing end-capping agent and a phenolic resin as raw materials, wherein the mass ratio of the polymer modifier containing a Si-O-Si main chain to the acid anhydride is 1:(0.1-1.5), the molar ratio of the polymer modifier containing a Si-O-Si main chain to the alkoxy-containing end-capping agent is 100:(1-50), and the mass ratio of the polymer modifier containing a Si-O-Si main chain to the phenolic resin is 1:(1-10).

[0009] Furthermore, the mass ratio of the polymer modifier containing Si-O-Si main chain of the structure of formula (I) to the acid anhydride is 1: (0.1-1.5);

[0010] and / or, the molar ratio of the polymer modifier containing a Si-O-Si main chain of the structure of formula (I) to the end-capping agent containing an alkoxy group is 100:(1-50);

[0011] And / or, the mass ratio of the polymer modifier containing Si-O-Si main chain of the structure of formula (I) to the phenolic resin is 1: (1-10).

[0012] Furthermore, the polymer modifier containing a Si-O-Si main chain has a structure of formula (I).

[0013] Furthermore, in the polymer modifier of the structure of formula (I), R1 is hydroxyl, carboxyl, aminopropyl, methyl, alkoxy, or acetoxy, and R2 is hydroxyl, carboxyl, aminopropyl, methyl, alkoxy, or acetoxy.

[0014] Furthermore, in the polymer modifier of the structure of formula (I), n is 1-50.

[0015] Furthermore, the acid anhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0016] Furthermore, the alkoxy-containing end-capping agent is 3-aminopropyltriethoxysilane.

[0017] The present invention also provides a method for preparing the composite resin, the method comprising the following steps:

[0018] (1) adding an acid anhydride to an organic solution of a Si-O-Si main chain polymer modifier having a structure of formula (I), reacting the solution, then adding an alkoxy-containing end-capping agent, and continuing the reaction to obtain an alkoxy-terminated prepolymer;

[0019] (2) reacting the alkoxy-terminated prepolymer with phenolic resin in a solvent, removing the solvent, and performing compression molding to obtain a composite resin.

[0020] Furthermore, in step (1), the organic solvent in the organic solution of the polymer modifier containing the Si-O-Si main chain of the structure of formula (I) is tetrahydrofuran, acetone, anhydrous ethanol, or dimethylformamide; the reaction temperature is 0-80°C, and the reaction time is 0.5-10 hours; the temperature of the continued reaction is 0-80°C, and the continued reaction time is 0.5-8 hours;

[0021] In step (2), the solvent is tetrahydrofuran, acetone, anhydrous ethanol, and dimethylformamide, the reaction temperature is 50-100°C, and the reaction time is 0.5-3 hours; the molding conditions are: 0.5h at 120°C, 1h at 160°C, 1h at 180°C, and 2h at 200°C.

[0022] The present invention also provides use of the composite resin in preparing heat protection materials.

[0023] The invention designs and synthesizes a novel organosilicon / phenolic ablation-resistant resin by reacting a polymer modifier containing a Si-O-Si main chain, an acid anhydride and an alkoxy-containing end-capping agent to form an ethoxy-terminated prepolymer, which is then cured with a phenolic resin.

[0024] The present invention further explores the effects of different structures of Si-O-Si main chain polymer modifiers and different amounts of alkoxy-containing end-capping agents on the phase morphology and thermal protection performance of organosilicon / phenolic ablation resistant resin. It is found that the PR-PIS prepared in Example 1 860-10％ and PR-PIS prepared in Example 2 860-5％ The compatibility of the silicone resin and phenolic resin in the present invention is improved, showing a nanometer double continuous phase structure; while the PR-PIS prepared in Comparative Example 1 4400-10％ The cross section of the phenolic resin matrix showed an "island" morphology, with the silicone segments presenting spherical particles of 4 μm in size, and obvious phase separation occurred. 4400-10％ Compared with the PR-PIS of nano-bicontinuous phase 860-10％ PR-PIS 860-5％ The nano-bicontinuous phase structured organosilicon / phenolic ablation-resistant resin provided by the present invention has broad application prospects in the field of thermal protection systems.

[0025] Obviously, based on the above contents of the present invention, according to common technical knowledge and customary means in this field, without departing from the above basic technical ideas of the present invention, other various forms of modifications, replacements or changes can be made.

[0026] The following further describes the above content of the present invention in detail through specific embodiments in the form of examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above content of the present invention fall within the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 .FTIR characterization results of (a) PSA, (b) PR and PR-PIS.

[0028] Figure 2 .SEM images of the cross-section of PR and PR-PIS resin. (a) PR; (b) PR-PIS 860-10％ (c)PR-PIS 860-5％ (d) PR-PIS 4400-10％ .

[0029] Figure 3 .AFM images. (a) PR-PIS 860-10％Height map; (b) PR-PIS 860-10％ Phase diagram; (c) PR-PIS 860-5％ Height map; (d) PR-PIS 860-5％ Phase diagram.

[0030] Figure 4 .(a) TG and DTG of PR and PR-PIS under nitrogen; (b) TG and DTG of PR and PR-PIS under air; (c) Residual weight of resin after treatment at 1000℃ / 1h; (d) XRD of PR and PR-PIS after high-temperature heat treatment in a tube furnace.

[0031] Figure 5 Optical and SEM images of PR and PR-PIS after high-temperature heat treatment in a tube furnace. (a)(e)(i) PR; (b)(f)(j) PR-PIS 860-10％ ;(c)(g)(k)PR-PIS 860-5％ ;(d)(h)(l)PR-PIS 4400-10％ . Figure 6 (a) Schematic diagram of oxyacetylene; (b) mass ablation rate; (c) line ablation rate; (d) to (g) optical images after resin ablation: (d) PR, (e) PR-PIS 860-10％ , (f) PR-PIS 860-5％ , (g) PR-PIS 4400-10％ (h) to (k) 3D contours after resin ablation: (h) PR, (i) PR-PIS 860-10％ , (j) PR-PIS 860-5％ , (k)PR-PIS 4400-10％ . DETAILED DESCRIPTION

[0032] The raw materials and equipment used in the present invention are all known products and are obtained by purchasing commercially available products.

[0033] Phenolic resin (PR) was purchased from Henan Zhongfan Dongsheng Co., Ltd., with brands A103, PF-2021, A901, and A902. The polymer modifier with a Si-O-Si backbone structure of formula (1) was purchased from Shin-Etsu Co., Ltd., Japan. 3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA) was provided by Beijing Fusman Technology Co., Ltd. 3-Aminopropyltriethoxysilane (APTES) was purchased from Aladdin. Tetrahydrofuran, acetone, anhydrous ethanol, and dimethylformamide were from Shanghai Titan Technology Co., Ltd.

[0034] Example 1: Preparation of silicone / phenolic ablation-resistant resin PR-PIS 860-10％

[0035] 1. Preparation of ethoxy-terminated prepolymer: PSA 860-10％

[0036] Under nitrogen atmosphere, first, 20-50 g of a polymer modifier containing a Si-O-Si main chain of formula (I) was added dropwise to a three-necked flask containing 10-15 g of BPDA and 40-52.5 g of an organic solution, and the mixture was reacted at 25-50°C for 1-10 hours. Then, 0.1-2 mL of a capping agent, APTES, was added, and the reaction was continued at 25-50°C for 1-5 hours to obtain a transparent, viscous, ethoxy-terminated prepolymer, named PSA. 860-10％ .

[0037] 2. Preparation of silicone / phenolic ablation-resistant resin: PR-PIS 860-10％

[0038] First, 40-70g of PR was dissolved in 60g of organic solution in a three-necked flask. Then, all the PSA prepared in step 1 was added. 860-10％ Add to the organic solution of PR and react at 25-90°C for 1-4 hours. Finally, vacuum and remove the solvent to obtain a yellow powder resin. The resin is cured and molded by molding to obtain a silicone / phenolic ablation-resistant resin named PR-PIS. 860-10％ The molding program was set to 120°C / 0.5h+160°C / 1h+180°C / 1h+200°C / 2h.

[0039] Example 2: Preparation of silicone / phenolic ablation-resistant resin PR-PIS 860-5％

[0040] 1. Preparation of ethoxy-terminated prepolymer: PSA 860-5％

[0041] The method of step 1 of Example 1 was referred to, except that the amount of the end-capping agent APTES was changed from 0.1 to 2 mL to 0.05 to 1 mL. The obtained ethoxy-terminated prepolymer was named PSA. 860-5％ .

[0042] 2. Preparation of silicone / phenolic ablation-resistant resin: PR-PIS 860-5％

[0043] Refer to the method of step 2 of Example 1, except that PSA 860-10％ Replaced by PSA 860-5％ , a silicone / phenolic ablation-resistant resin was prepared and named PR-PIS 860-5％ .

[0044] The following is the preparation method of the control sample.

[0045] Comparative Example 1: Preparation of silicone / phenolic ablation-resistant resin PR-PIS 4400-10％

[0046] 1. Preparation of ethoxy-terminated prepolymer: PSA 4400-10％

[0047] Referring to the method of step 1 of Example 1, the only difference is that n=5 is replaced by n=15 of the polymer modifier containing Si-O-Si main chain of formula (I) to prepare an ethoxy-terminated prepolymer, named PSA 4400-10％ .

[0048] 2. Preparation of silicone / phenolic ablation-resistant resin: PR-PIS 4400-10％

[0049] Refer to the method of step 2 of Example 1, except that PSA 860-10％ Replaced by PSA 4400-10％ , a silicone / phenolic ablation-resistant resin was prepared and named PR-PIS 4400-10％ .

[0050] The beneficial effects of the present invention are demonstrated by experimental examples below.

[0051] Experimental Example 1: Molecular Structure Characterization

[0052] 1. Experimental methods

[0053] Fourier transform infrared spectroscopy (FTIR) measurements were performed on a Nicolet is50.

[0054] 2. Experimental results

[0055] Figure 1 (a) shows the FTIR spectrum of nano-co-continuous phase organosilicon / phenolic ablation-resistant resin (PSA resin). 1100-1020 cm -1 The broad peak at 1574 cm is the stretching vibration of the Si-O-Si skeleton in the PSA main chain. -1 This is the "ring breathing" mode in aromatic amines, corresponding to the NH angle vibration in the amide group, and is the amide II band (37). -1 The peak at 3090 cm belongs to the C=O stretching vibration of the amide group and is called the amide I band (38). -1 The broad peak at represents the NH stretching vibration bound by hydrogen bonds, which indicates that the amide group has been successfully introduced into the polysiloxane main chain.

[0056] The FTIR spectrum of silicone / phenolic ablation-resistant resin (PR-PIS resin) is as follows: Figure 1 Compared with PR, after adding PIS, PR-PIS resin has a -1 and 1716cm -1Two absorption peaks appeared near 1387cm, which correspond to the asymmetric stretching and symmetric stretching of C=O in the imide group. -1 The peak at 1026 cm represents the C=N stretching vibration of the imide group. -1 The absorption peak at 970 cm represents the Si-O-Si stretching vibration in the PIS molecular skeleton. These indicate that PIS has been successfully introduced into PR. -1 The peaks nearby represent the Si-O-ph structure formed by the reaction between the ends of the PIS molecular chain and the hydroxyl groups in PR. However, the peak intensities of these peaks are relatively weak, even in the PR-PIS 4400-10％ There is no peak at all in the sample, which is mainly because there are fewer ethoxy groups in PIS.

[0057] Experimental Example 2: Microstructure Characterization

[0058] 1. Experimental methods

[0059] The micromorphology of the hybrid resin and the cross-section of the ablated carbon layer was characterized using a scanning electron microscope (SEM, S-4800, Hitachi Co., Japan) at an accelerating voltage of 15 kV.

[0060] Atomic force microscopy (AFM): The resin was trimmed using an ultrathin microtome to obtain smooth resin sections. The resin sections were observed using a Bruker Dimension ICON, and images were acquired in tapping mode.

[0061] 2. Experimental results

[0062] The microstructure of the PR-PIS resin cross section was characterized using SEM. Figure 2 As shown. Figure 2 It can be seen from (b) and (c) that PR-PIS 860-10％ and PR-PIS 860-5％ There is almost no phase separation in the PR-PIS, which is mainly attributed to the fact that the imide ring in the silicone resin increases its polarity and improves its compatibility with the phenolic resin. 4400-10％ The cross section of the PR matrix showed an "island" morphology, with the silicone segments presenting spherical particles of 4 μm in size, and obvious phase separation occurred. This may be due to the PR-PIS 4400-10％ The silicone chain between the two imide rings is long, and the polarity increase brought about by the introduction of the imide ring cannot offset the polarity difference between the silicone chain segment itself and the phenolic resin.

[0063] To more accurately characterize PR-PIS 860-10％ and PR-PIS 860-5％The microstructure of the samples was tested by AFM. Figure 3 As shown. According to the difference in the phase angle of the actual vibration between the probe and PIS and PR, the PR-PIS is obtained. 860-10％ and PR-PIS 860-5％ The bright area is PR, and the dark area is PIS. Figure 3 It can be found that with PR-PIS 860-5％ In comparison, PR-PIS has more Si-O-ph bonds. 860-10％ In the quartz crystal, the silicone chain segments are more continuous and longer in length, presenting a bicontinuous structure with a periodic length of 200 nm.

[0064] The above experimental results show that the PR-PIS prepared in Example 1 860-10％ and PR-PIS prepared in Example 2 860-5％ The compatibility of the silicone resin and phenolic resin in the comparative example 1 was improved, showing a nanometer double continuous phase structure; however, the PR-PIS 4400-10％ The cross section shows an "island" morphology, and the silicone chain segments appear as spherical particles of 4μm in size in the phenolic resin matrix, with obvious phase separation occurring.

[0065] Experimental Example 3: Characterization of long-term high-temperature oxidation resistance

[0066] 1. Experimental methods

[0067] The samples were subjected to TG test using a German NETZSCH STA 449F3. The carbon layer was subjected to XRD test using a US ThermoFischer ESCALAB 250Xi with an analysis chamber vacuum of 8×10-10 Pa and Al ka rays as the excitation source (hv=1486.6 eV).

[0068] 2. Experimental results

[0069] The TGA curves of PR and PR-PIS in nitrogen and air atmospheres are shown in Figure 2. Figure 4 (a) and (b) show that PR-PIS 860-10％ PR-PIS 860-5％ and PR-PIS 4400-10％ The residual weight at 800℃ is not much different, but both are smaller than PR. This may be because the ethoxy group at the end of PIS reacts with the hydroxymethyl group of PR, destroying the cross-linked network structure of PR, resulting in a low degree of curing of the hybrid resin. In air atmosphere, the residual weight of PR-PIS resin at 800℃ is significantly higher than that of PR, indicating that the addition of PIS can improve the thermal stability of PR in an aerobic environment. At the same time, compared with the PR-PIS of the island phase 4400-10％, PR-PIS of nano-bicontinuous phase 860-10％ PR-PIS 860-5％ The thermal residual weight is improved, which may be because the dual-continuous phase hybrid resin is more conducive to forming a dense protective layer in a high-temperature oxygen atmosphere.

[0070] PR and PR-PIS resins were subjected to high temperature heat treatment in a muffle furnace at 1000℃ / 1h. The residual weight of the resins was Figure 4 (c) PR has been basically pyrolyzed after being treated at 1000℃ / 1h, while PR-PIS 860-10％ The residual weight of the resin is the highest, reaching 7.5%, which indicates that the fine nano-bicontinuous structure has better high-temperature oxidation resistance than the island phase structure. Figure 4 (d) XRD results show that the peak at 22° for the sample after high temperature treatment represents SiO2, while the small peak at 26° represents residual carbon.

[0071] Figure 5 Optical photographs and SEM images of the resin before and after treatment at 1000°C for 1 hour in a muffle furnace are shown. While the PR is essentially burned after treatment at 1000°C for 1 hour, the PR-PIS retains a relatively intact shape, with a white surface coating and excellent long-term high-temperature oxidation resistance. Figure 5 (i) to (l) show that there are many micron-sized holes in the residual PR, which is caused by the gas produced by the high-temperature thermal decomposition of PR. 4400-10％ , PR-PIS 860-10％ PR-PIS 860-5％ The surface of the resin is covered with a dense SiO2 liquid film, which can effectively protect the resin from oxygen corrosion, which is consistent with the above conclusion.

[0072] The above experimental results show that compared with pure phenolic resin, PR-PIS resin has better long-term high-temperature antioxidant ability; and compared with the island phase PR-PIS 4400-10％ Compared with the PR-PIS of nano-bicontinuous phase 860-10％ PR-PIS 860-5％ It has better long-term high-temperature antioxidant capacity and high-temperature resistance, among which PR-PIS 860-10％ The best performance.

[0073] Experimental Example 4: Ablation Resistance Test

[0074] 1. Experimental methods

[0075] The samples were tested using an oxyacetylene ablation machine (ZR-323A, Zhirui Co., China) at 4 MW / m 2Ablation performance under heat flow, with an ablation time of 30 seconds for each sample. Optical images of the ablated samples were taken using a KEYENCE 3D profilometer.

[0076] 2. Experimental results

[0077] The ablation performance of PR-PIS resin was tested, and the ablation rate and ablation morphology were Figure 6 shown. Figure 6 (b) and (c) show the line ablation rate and mass ablation rate of PR-PIS and PR. 860-10％ PR-PIS 860-5％ and PR-PIS 4400-10％ The line ablation rate of PR-PIS has shown a significant decrease. 4400-10％ Compared with pure PR, PR-PIS 860-10％ PR-PIS 860-5％ There was a slight decline. Among them, PR-PIS 860-10％ The mass ablation rate and linear ablation rate of the PR were reduced by 11% and 59% respectively compared with those of PR (0.058 g / s and 0.086 mm / s).

[0078] Figure 6 (d) to (k) are the optical photos and surface 3D profiles of PR and PR-PIS after ablation. 2 After the oxyacetylene flame, the sample is about to be burned through. 860-10％ PR-PIS 860-5％ and PR-PIS 4400-10％ It can better resist the erosion of oxyacetylene flame.

[0079] The above experimental results show that the PR-PIS 4400-10％ Compared with the PR-PIS of nano-bicontinuous phase 860-10％ PR-PIS 860-5％ Possesses better ablation resistance.

Claims

1. A composite resin, characterized in that: The invention is prepared from a polymer modifier containing a Si-O-Si main chain of the formula (I), an acid anhydride, an alkoxy-containing end-capping agent and a phenolic resin as raw materials, wherein the mass ratio of the polymer modifier containing a Si-O-Si main chain of the formula (I) to the acid anhydride is 1:(0.1-1.5), the molar ratio of the polymer modifier containing a Si-O-Si main chain of the formula (I) to the alkoxy-containing end-capping agent is 100:(1-50), and the mass ratio of the polymer modifier containing a Si-O-Si main chain of the formula (I) to the phenolic resin is 1:(1-10). The acid anhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride, and the alkoxy-containing end-capping agent is 3-aminopropyltriethoxysilane; In the structure of formula (I), R1 is hydroxyl, carboxyl, aminopropyl, methyl, alkoxy, or acetoxy, R2 is hydroxyl, carboxyl, aminopropyl, methyl, alkoxy, or acetoxy, and n is 5.

2. A method for preparing the composite resin according to claim 1, characterized in that: The method comprises the following steps: (1) adding an acid anhydride to an organic solution of a Si-O-Si main chain polymer modifier having a structure of formula (I), reacting the solution, then adding an alkoxy-containing end-capping agent, and continuing the reaction to obtain an alkoxy-terminated prepolymer; (2) reacting the alkoxy-terminated prepolymer with phenolic resin in a solvent, removing the solvent, and performing compression molding to obtain a composite resin.

3. The method according to claim 2, wherein: In step (1), the organic solvent in the organic solution of the polymer modifier containing the Si-O-Si main chain of the structure of formula (I) is tetrahydrofuran, acetone, anhydrous ethanol, and DMF; the reaction temperature is 0-80°C, and the reaction time is 0.5-10 hours; the temperature of the continued reaction is 0-80°C, and the continued reaction time is 0.5-8 hours; In step (2), the solvent is tetrahydrofuran, acetone, anhydrous ethanol, and DMF, the reaction temperature is 50-100°C, and the reaction time is 0.5-3 hours; the molding conditions are: 0.5h at 120°C, 1h at 160°C, 1h at 180°C, and 2h at 200°C.

4. Use of the composite resin according to claim 1 in preparing heat protection materials.

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