Preparation method of nano-silica modified polyurethane thermal insulation material

Abstract

The application relates to the technical field of polyurethane thermal insulation materials, and discloses a preparation method of a nano-silicon dioxide modified polyurethane thermal insulation material. 4-chloro-1-butylamine, formaldehyde and diphenylol are used as raw materials, a Mannich reaction is carried out, an intermediate 1 is obtained, the intermediate 1 and PEPA are used to carry out a substitution reaction under the catalysis of pyridine, and a benzoxazine-based bis-PEPA is obtained. N,N-diethyl-aminopropyl methyl dimethoxysilane is used as a bridge to carry out a quaternary ammonium salt reaction with the intermediate 1, and then a condensation reaction with nano-silicon dioxide is carried out, so that a benzoxazine-based bis-nano-silicon dioxide is obtained. Finally, polyether polyol, the benzoxazine-based bis-nano-silicon dioxide, the benzoxazine-based bis-PEPA and a curing agent are used as raw materials, are uniformly stirred and mixed, and are foamed and formed, so that the nano-silicon dioxide modified polyurethane thermal insulation material is obtained. The nano-silicon dioxide modified polyurethane thermal insulation material prepared by the application has good flame-retardant effect, antibacterial effect, mechanical property and thermal stability.

Description

[0001] The present application claims priority to the Chinese patent application No. 202510135926.X filed on February 7, 2025 to the Chinese Patent Office and entitled "Preparation method of nano-silica modified polyurethane thermal insulation material", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of polyurethane thermal insulation materials, in particular to a preparation method of nano-silica modified polyurethane thermal insulation material. BACKGROUND

[0003] Polyurethane thermal insulation material is an important thermal insulation material, which is widely used in the field of building engineering, etc. However, polyurethane thermal insulation material is highly flammable and has poor fireproof performance, which limits its application in many fields. Therefore, it is one of the important research directions to prepare a polyurethane thermal insulation material with flame retardation effect to expand its application field.

[0004] Nano-silica is an important inorganic material, commonly known as white carbon black. Because it is super-fine nanometer-based, it has many excellent and unique properties, such as improving the aging resistance, strength and chemical resistance of the material, and has a wide range of applications in catalysis, light filtering, light absorption, medicine, new materials and other fields. 1-oxyl phosphorus-4-hydroxymethyl-2,6,7-trioxa-bicyclo[2,2,2]octane (PEPA) has a highly symmetrical cage structure, good carbon formation, excellent thermal stability, and rich carbon and acid sources, so it is favored by researchers.

[0005] For example, the patent with the authorized announcement No. CN114106683B discloses a waterproof thermal insulation integrated material and its production process. The material prepared from polyurethane material, nano-silica and the like has good flame retardation effect and mechanical properties, but does not improve the antibacterial property and thermal stability of the material. SUMMARY

[0006] (I) Technical problems to be solved

[0007] In view of the deficiencies of the prior art, the present application provides a preparation method of nano-silica modified polyurethane thermal insulation material. The prepared thermal insulation material has good antibacterial property, flame retardation, mechanical property and thermal stability.

[0008] (II) Technical solutions

[0009] A preparation method of nano-silica modified polyurethane thermal insulation material, the preparation method is:

[0010] Polyether polyol, foam stabilizer, catalyst, blowing agent, deionized water stirring 5-10min mixed evenly, then add benzoxazine-based double nano silica, benzoxazine-based double PEPA stirring mixed evenly, then add curing agent, stirring speed of 3000rmp 10-20s, quickly pour into 300mm*300mm*150mm mold, foaming molding, mold temperature control at 50 DEG C, get nano silica modified polyurethane insulation materials.

[0011] Preferably, the mass ratio of polyether polyol, foam stabilizer, catalyst, blowing agent, deionized water, benzoxazine-based double nano silica, benzoxazine-based double PEPA, curing agent is 80-100:1-2:1-2:20-25:1-2:5-20:1-10:100.

[0012] Preferably, the catalyst is one of N,N-dimethylcyclohexylamine, dibutyltin dilaurate.

[0013] Preferably, the preparation method of benzoxazine-based double PEPA is:

[0014] (1) 4-chloro-1-butylamine, formaldehyde is added to dioxane solvent, stirring at room temperature for 30-40min, then add diphenylol, heating to 80-90 DEG C, reaction 8-12h, after the reaction, cool to room temperature, rotary evaporation, drying, to get intermediate 1;

[0015] (2) PEPA is added to acetonitrile solvent, stirring and dispersing, heating to 55-65 DEG C, add intermediate 1 to it, stirring and mixing evenly, heating to 85-90 DEG C, add pyridine to it, reflux reaction 22-26h, after the reaction, hot filtration, ethanol washing, drying, to get benzoxazine-based double PEPA.

[0016] Further preferably, in the (1), the molar ratio of 4-chloro-1-butylamine, formaldehyde, diphenylol is 2-2.5:6-7:1.

[0017] Further preferably, in the (2), the molar ratio of PEPA, intermediate 1, pyridine is 2-2.5:1:0.4-0.6.

[0018] Further, the preparation method of benzoxazine-based double nano silica is:

[0019] S1, under nitrogen protection, N,N-diethyl-aminopropyl methyl dimethoxy silane is added to ethanol solvent, stirring and dispersing, heating to 50-55 DEG C, add intermediate 1 to it, reaction 8-12h, after the reaction, cool to room temperature, rotary evaporation, diethyl ether washing, drying, to get intermediate 2;

[0020] S2, intermediate 2 is added to toluene solvent, stirred and dispersed, then nano-silica is added, stirring is continued for 20-40 min, 75% mass fraction of ethanol aqueous solution is added, heating is refluxed for 2-3 h, after the end, cooling to room temperature, suction filtration, washing with toluene and diethyl ether in sequence, drying, to obtain benzoxazine-based double nano-silica.

[0021] Further preferably, in S1, the molar ratio of N,N-diethyl-aminopropyl methyl dimethoxysilane and intermediate 1 is 2-2.4:1.

[0022] Further preferably, in S2, the mass ratio of intermediate 2 and nano-silica is 4-6:1.

[0023] (Three) beneficial technical effects

[0024] The benzoxazine-based double nano-silica and benzoxazine-based double PEPA obtained through a series of reactions of the application have simple preparation method and novel structure, and when they are added to polyurethane insulation material, the heat stability of the polyurethane insulation material is improved by the synergistic effect of the benzoxazine structure, nano-silica and benzene ring structure in the polyurethane insulation material, the antibacterial performance of the material is improved by the antibacterial effect of the double quaternary ammonium salt structure, and the flame retardant performance of the material is improved by the formation of an organic-inorganic flame retardant system of the inorganic nano-silica and the strong dehydrating polyphosphoric acid generated by the phosphorus-containing group in the combustion process. In addition, the benzoxazine-based double nano-silica and benzoxazine-based double PEPA obtained by the application not only contain nano-silica as stress concentration points and have good dispersity, but also have more long-chain structures which can intertwine with each other to form more crosslinking sites, thereby improving the mechanical properties of the material. The polyurethane insulation material prepared by the application has good antibacterial performance, flame retardant performance, mechanical properties and thermal stability. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the reaction route of intermediate 1;

[0026] Figure 2 is the reaction route of intermediate 2;

[0027] Figure 3 is the reaction route of benzoxazine-based double PEPA. DETAILED DESCRIPTION

[0028] In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0029] Embodiment 1

[0030] (1) 0.2 mol of 4-chloro-1-butylamine and 0.65 mol of formaldehyde were added into a dioxane solvent, stirred for 40 min at room temperature, 0.1 mol of diphenylol was added into the mixture, the temperature was increased to 85 °C, and the mixture was reacted for 10 h. After the reaction was completed, the mixture was cooled to room temperature, rotary evaporated, and dried to obtain an intermediate 1.

[0031] (2) 1 mol of PEPA was added into an acetonitrile solvent, stirred and dispersed, the temperature was increased to 60 °C, 0.5 mol of the intermediate 1 was added into the mixture, the mixture was stirred and mixed uniformly, the temperature was increased to 90 °C, 0.25 mol of pyridine was added into the mixture, and the mixture was refluxed for 25 h. After the reaction was completed, the mixture was filtered while hot, washed with ethanol, and dried to obtain a benzoxazinyl bis-PEPA.

[0032] (3) 1 mol of N,N-diethyl-aminopropyl methyl dimethoxysilane was added into an ethanol solvent under nitrogen protection, stirred and dispersed, 0.5 mol of the intermediate 1 was added into the mixture at 55 °C, and the mixture was reacted for 10 h. After the reaction was completed, the mixture was cooled to room temperature, rotary evaporated, washed with diethyl ether, and dried to obtain an intermediate 2.

[0033] (4) 40 g of the intermediate 2 was added into a toluene solvent, stirred and dispersed, 10 g of nano-silica was added into the mixture, the mixture was continuously stirred for 30 min, 75% by mass of an ethanol aqueous solution was added into the mixture, the mixture was heated and refluxed for 2 h, and after the reaction was completed, the mixture was cooled to room temperature, suction filtered, sequentially washed with toluene and diethyl ether, and dried to obtain a benzoxazinyl bis-nano-silica.

[0034] (5) 80 g of polyether polyol (LY-4110), 2 g of foam stabilizer (AK8814), 1 g of N,N-dimethylcyclohexylamine catalyst, 25 g of hydrofluorocarbon blowing agent (HFC-365mfc), 1 g of deionized water were stirred for 8 min to mix uniformly, 5 g of benzoxazine-based bis-nano-silica, 1 g of benzoxazine-based bis-PEPA were stirred and mixed uniformly, 100 g of polyphenyl polymethylene polyisocyanate (PM-200) curing agent was added, stirred at a speed of 3000 rpm for 20 s, and then quickly poured into a 300 mm x 300 mm x 150 mm mold, foamed and molded, the mold temperature was controlled at 50°C, and a nano-silica modified polyurethane thermal insulation material was obtained.

[0035] Example 2

[0036] (1) 0.25 mol of 4-chloro-1-butylamine and 0.6 mol of formaldehyde were added to a dioxane solvent, stirred at room temperature for 40 min, 0.1 mol of diphenylol was added, heated to 90°C, and reacted for 8 h. After the reaction was completed, it was cooled to room temperature, rotary evaporated, and dried to obtain intermediate 1.

[0037] (2) 1.2 mol of PEPA was added to an acetonitrile solvent and stirred and dispersed, heated to 65°C, 0.5 mol of intermediate 1 was added and stirred and mixed uniformly, heated to 90°C, 0.25 mol of pyridine was added, and refluxed for 24 h. After the reaction was completed, it was filtered while hot, washed with ethanol, and dried to obtain benzoxazine-based bis-PEPA.

[0038] (3) Under nitrogen protection, 1.2 mol of N,N-diethyl-aminopropyl methyl dimethoxy silane was added to an ethanol solvent and stirred and dispersed, 0.5 mol of intermediate 1 was added at 55°C, and reacted for 8 h. After the reaction was completed, it was cooled to room temperature, rotary evaporated, washed with diethyl ether, and dried to obtain intermediate 2.

[0039] (4) 45 g of intermediate 2 was added to a toluene solvent and stirred and dispersed, 10 g of nano-silica was added and stirred for 20 min, and 75% mass fraction of an ethanol aqueous solution was added and refluxed for 2 h. After the reaction was completed, it was cooled to room temperature, suction filtered, washed with toluene and diethyl ether in sequence, and dried to obtain benzoxazine-based bis-nano-silica.

[0040] (5) 90 g of polyether polyol (LY-4110), 2 g of foam stabilizer (AK8814), 1 g of dibutyltin dilaurate catalyst, 20 g of hydrofluorocarbon blowing agent (HFC-365mfc), 2 g of deionized water were stirred for 5 min and mixed uniformly, 10 g of benzoxazine-based bis-nano-silica and 3 g of benzoxazine-based bis-PEPA were added and stirred and mixed uniformly, 100 g of polyphenyl polymethylene polyisocyanate (PM-200) curing agent was added, stirred at a speed of 3000 rpm for 15 s, and then quickly poured into a 300 mm x 300 mm x 150 mm mold, foamed and molded, the mold temperature was controlled at 50°C, and a nano-silica modified polyurethane thermal insulation material was obtained.

[0041] Example 3

[0042] (1) 0.24 mol of 4-chloro-1-butylamine and 0.7 mol of formaldehyde were added to a dioxane solvent, stirred at room temperature for 30 min, 0.1 mol of diphenylol was added, heated to 80°C, and reacted for 12 h. After the reaction was completed, it was cooled to room temperature, rotary evaporated, and dried to obtain intermediate 1.

[0043] (2) 1 mol of PEPA was added to an acetonitrile solvent and stirred and dispersed, heated to 60°C, 0.5 mol of intermediate 1 was added and stirred and mixed uniformly, heated to 90°C, 0.2 mol of pyridine was added, and refluxed for 22 h. After the reaction was completed, it was filtered while hot, washed with ethanol, and dried to obtain benzoxazine-based bis-PEPA.

[0044] (3) Under nitrogen protection, 1.2 mol of N,N-diethyl-aminopropyl methyl dimethoxy silane was added to an ethanol solvent and stirred and dispersed, 0.5 mol of intermediate 1 was added at 50°C, and reacted for 12 h. After the reaction was completed, it was cooled to room temperature, rotary evaporated, washed with diethyl ether, and dried to obtain intermediate 2.

[0045] (4) 50 g of intermediate 2 was added to a toluene solvent and stirred and dispersed, 10 g of nano-silica was added and stirred for another 30 min, mass fraction 75% ethanol aqueous solution was added, heated to reflux for 2 h, cooled to room temperature after completion, suction filtered, washed with toluene and diethyl ether in sequence, and dried to obtain benzoxazine-based bis-nano-silica.

[0046] (5) 100 g of polyether polyol (LY-4110), 1 g of foam stabilizer (AK8814), 2 g of dibutyltin dilaurate catalyst, 22 g of hydrofluorocarbon blowing agent (HFC-365mfc), 1 g of deionized water were stirred for 5 min and mixed uniformly, 15 g of benzoxazine-based bis-nano-silica and 6 g of benzoxazine-based bis-PEPA were added and stirred and mixed uniformly, 100 g of polyphenyl polymethylene polyisocyanate (PM-200) curing agent was added, stirred at a speed of 3000 rpm for 10 s, and then quickly poured into a 300 mm x 300 mm x 150 mm mold, foamed and molded, the mold temperature was controlled at 50°C, and a nano-silica modified polyurethane thermal insulation material was obtained.

[0047] Example 4

[0048] (1) 0.2 mol of 4-chloro-1-butylamine and 0.65 mol of formaldehyde were added to a dioxane solvent, stirred at room temperature for 35 min, 0.1 mol of diphenylol was added, heated to 90°C, and reacted for 8 h. After the reaction was completed, it was cooled to room temperature, rotary evaporated, and dried to obtain intermediate 1.

[0049] (2) 1.25 mol of PEPA was added to an acetonitrile solvent and stirred and dispersed, heated to 55°C, 0.5 mol of intermediate 1 was added, stirred and mixed uniformly, heated to 90°C, 0.3 mol of pyridine was added, and refluxed for 26 h. After the reaction was completed, it was filtered while hot, washed with ethanol, and dried to obtain benzoxazine-based bis-PEPA.

[0050] (3) Under nitrogen protection, 1.2 mol of N,N-diethyl-aminopropyl methyl dimethoxy silane was added to an ethanol solvent, stirred and dispersed, 0.5 mol of intermediate 1 was added at 55°C, reacted for 10 h, cooled to room temperature after the reaction was completed, rotary evaporated, washed with diethyl ether, and dried to obtain intermediate 2.

[0051] (4) 60 g of intermediate 2 was added to a toluene solvent and stirred and dispersed, 10 g of nano-silica was added, continued to be stirred for 40 min, 75% mass fraction of ethanol aqueous solution was added, heated to reflux for 3 h, cooled to room temperature after the reaction was completed, suction filtered, washed with toluene and diethyl ether in sequence, and dried to obtain benzoxazine-based bis-nano-silica.

[0052] (5) 95 g of polyether polyol (LY-4110), 1 g of foam stabilizer (AK8814), 2 g of N,N-dimethylcyclohexylamine catalyst, 22 g of hydrofluorocarbon blowing agent (HFC-365mfc), 1 g of deionized water were stirred for 10 min to mix uniformly, 20 g of benzoxazine-based bis-nano-silica, 10 g of benzoxazine-based bis-PEPA were stirred and mixed uniformly, 100 g of polyphenyl polymethylene polyisocyanate (PM-200) curing agent was added thereto, stirred at a speed of 3000 rpm for 15 s, and then quickly poured into a 300 mm x 300 mm x 150 mm mold to form a foam, and the mold temperature was controlled at 50°C to obtain a nano-silica modified polyurethane thermal insulation material.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is that nano-silica is used instead of benzoxazine-based bis-nano-silica in step (5).

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that benzoxazine-based bis-PEPA is not contained in step (5).

[0057] Flame retardant performance test:

[0058] Oxygen index test was performed using an oxygen index tester.

[0059] UL-94 grade was tested using a horizontal and vertical burning apparatus.

[0060] Table 1:

[0061] Oxygen index (%) UL-94 rating Example 1 27.9 V-0 Example 2 29.4 V-0 Example 3 31.3 V-0 Example 4 32.2 V-0 Comparative Example 1 27.0 V-0 Comparative Example 2 24.2 V-1

[0062] As can be seen from the table, the flame retardant effect of Examples 1-4 is better than that of Comparative Examples 1-2, because benzoxazine-based bis-nano-silica and benzoxazine-based bis-PEPA structure are added in Examples 1-4. As can be seen from Examples 1-4, the flame retardant effect is better as the amount of benzoxazine-based bis-nano-silica and benzoxazine-based bis-PEPA increases. As can be seen from Comparative Example 1 and Example 1, the difference between the two is that Comparative Example 1 uses nano-silica and Example 1 uses benzoxazine-based bis-nano-silica. The flame retardant effect of Example 1 is better than that of Comparative Example 1, because nano-silica itself is prone to agglomeration, while modified nano-silica can be uniformly dispersed in the material matrix, and a larger specific surface area and smaller particle size can better play a heat and oxygen isolation effect. Therefore, the effect of Example 1 is better than that of Comparative Example 1.

[0063] Antibacterial performance test:

[0064] (1) The polyurethane thermal insulation material is cut into 1cm*1cm sample, washed by ethanol, and dried.

[0065] (2) The E. coli is activated and configured into 1*104cfu / ml-5*104cfu / ml bacterial suspension, the cut sample is placed into a triangular flask containing the bacterial suspension, fixed on a shaking table, shaken at 25 DEG C and 300r / min for 5min, and 1mL bacterial suspension is taken to be diluted by 100 times.

[0066] (3) 1mL of the above bacterial suspension is inoculated in an agar culture dish, cultured at 37 DEG C under natural light for 48h, and the colony counting is carried out according to the method in GB15979-2003.

[0067] The antibacterial rate (%) = (the average number of bacteria before sample shaking-the average number of bacteria after sample shaking) / the average number of bacteria before sample shaking * 100%.

[0068] Table 2:

[0069] Bacterial inhibition rate (%) Example 1 85.6 Example 2 92.3 Example 3 98.4 Example 4 99.9 Comparative Example 1 -

[0070] It can be known from the table that the thermal insulation material prepared by the application has good antibacterial effect, and the antibacterial rate can reach 99.9% at most. This is because the benzoxazine-based double nanosilica contains a gemini quaternary ammonium salt structure, and has good antibacterial effect, therefore, the antibacterial effect of examples 1-4 is better than that of comparative example 1.

[0071] Thermal stability test:

[0072] The thermal stability of the material is tested by using a thermal gravimetric analyzer, the sample mass is 10mg, under nitrogen atmosphere, the gas flow rate is 20mL / min, the temperature raising rate is 10 DEG C / min, and the temperature range is 40-800 DEG C.

[0073] Table 3:

[0074] T 10% / ℃]] [CAT 800 wt% Example 1 308 19.4 Example 2 314 22.3 Example 3 319 26.7 Example 4 320 28.1 Comparative Example 1 289 15.1 Comparative Example 2 301 18.2

[0075] As shown in the table, the heat stability of the heat preservation material prepared by the application is good, the heat stability of examples 1-4 is greater than that of comparative examples 1-2, because the examples 1-4 contain benzoxazine-based double nano-silica and benzoxazine-based double PEPA structure, and the heat stability increases with the increase of the amount of the two, the difference between example 1 and comparative example 1 is that example 1 adds benzoxazine-based double nano-silica, and comparative example 1 uses nano-silica instead of benzoxazine-based double nano-silica, wherein example 1 contains the benzoxazine structure with good heat stability, and comparative example 1 does not contain the benzoxazine structure, so the effect of comparative example 1 is poor. The difference between comparative example 2 and example 1 is that comparative example 2 does not contain benzoxazine-based double PEPA structure, so the effect of comparative example 2 is poorer than that of example 1. Therefore, the heat preservation material prepared by the application has good heat stability.

[0076] Mechanical property test: the tensile strength of the material was tested according to GB / T6344-2008.

[0077] Table 4:

[0078] Tensile strength / kPa Example 1 135 Example 2 148 Example 3 160 Example 4 164 Comparative Example 1 118 Comparative Example 2 129

[0079] As shown in the table, the heat stability of the heat preservation material prepared by the application is good, the heat stability of examples 1-4 is greater than that of comparative examples 1-2, because the examples 1-4 contain benzoxazine-based double nano-silica and benzoxazine-based double PEPA structure, and the heat stability increases with the increase of the amount of the two, the difference between example 1 and comparative example 1 is that example 1 adds benzoxazine-based double nano-silica, and comparative example 1 uses nano-silica instead of benzoxazine-based double nano-silica, wherein example 1 contains the benzoxazine structure with good heat stability, and comparative example 1 does not contain the benzoxazine structure, so the effect of comparative example 1 is poor. The difference between comparative example 2 and example 1 is that comparative example 2 does not contain benzoxazine-based double PEPA structure, so the effect of comparative example 2 is poorer than that of example 1. Therefore, the heat preservation material prepared by the application has good heat stability.

[0076] Mechanical property test: the tensile strength of the material was tested according to GB / T6344-2008.

[0077] Table 4:

[0078] Tensile strength / kPa Example 1 135 Example 2 148 Example 3 160 Example 4 164 Comparative Example 1 118 Comparative Example 2 129

[0079] As shown in the table, the heat stability of the heat preservation material prepared by the application is good, the heat stability of examples 1-4 is greater than that of comparative examples 1-2, because the examples 1-4 contain benzoxazine-based double nano-silica and benzoxazine-based double PEPA structure, and the heat stability increases with the increase of the amount of the two, the difference between example 1 and comparative example 1 is that example 1 adds benzoxazine-based double nano-silica, and comparative example 1 uses nano-silica instead of benzoxazine-based double nano-silica, wherein example 1 contains the benzoxazine structure with good heat stability, and comparative example 1 does not contain the benzoxazine structure, so the effect of comparative example 1 is poor. The difference between comparative example 2 and example 1 is that comparative example 2 does not contain benzoxazine-based double PEPA structure, so the effect of comparative example 2 is poorer than that of example 1. Therefore, the heat preservation material prepared by the application has good heat stability.

Claims

1. A method for preparing a nano-silica modified polyurethane thermal insulation material, characterized in that, The preparation method is as follows: Mix polyether polyol, foam stabilizer, catalyst, foaming agent, and deionized water for 5-10 minutes until homogeneous. Then add benzoxazine-based double nano silica and benzoxazine-based double PEPA and mix until homogeneous. Add curing agent and stir at 3000 rpm for 10-20 seconds. Quickly pour into a 300mm×300mm×150mm mold and foam to form. Control the mold temperature at 50℃ to obtain nano silica-modified polyurethane insulation material. The mass ratio of the polyether polyol, foam stabilizer, catalyst, foaming agent, deionized water, benzoxazine-based double nano silica, benzoxazine-based double PEPA, and curing agent is 80-100:1-2:1-2:20-25:1-2:5-20:1-10:

100. The preparation method of the benzoxazine-based bis-PEPA is as follows: (1) Add 4-chloro-1-butanamine and formaldehyde to dioxane solvent, stir at room temperature for 30-40 min, then add biphenyl hydroquinone, heat to 80-90℃, react for 8-12 h, after the reaction is completed, cool to room temperature, rotary evaporate, dry to obtain intermediate 1; (2) Add PEPA to acetonitrile solvent, stir and disperse, heat to 55-65℃, add intermediate 1, stir and mix evenly, heat to 85-90℃, add pyridine, reflux reaction for 22-26h, after the reaction is completed, filter while hot, wash with ethanol, dry to obtain benzoxazine bis PEPA. The preparation method of the benzoxazine-based double nano-silica is as follows: S1. Under nitrogen protection, N,N-diethyl-aminopropylmethyldimethoxysilane was added to ethanol solvent and stirred to disperse. Intermediate 1 was added to the mixture at 50-55°C and reacted for 8-12 hours. After the reaction was completed, the mixture was cooled to room temperature, rotary evaporated, washed with diethyl ether, and dried to obtain intermediate 2. S2. Add intermediate 2 to toluene solvent, stir and disperse, then add nano-silica, continue stirring for 20-40 min, add 75% ethanol aqueous solution, heat under reflux for 2-3 h, after which cool to room temperature, filter, wash with toluene and diethyl ether in sequence, and dry to obtain benzoxazine-based bis-nano-silica.

2. The method of claim 1, wherein the nano-silica modified polyurethane thermal insulation material is prepared by mixing the nano-silica with the polyurethane prepolymer, and then adding the blowing agent and the catalyst. The catalyst is one of N,N-dimethylcyclohexylamine and dibutyltin dilauric acid.

3. The preparation method of the nano-silica modified polyurethane thermal insulation material according to claim 1, characterized in that, In (1), the molar ratio of 4-chloro-1-butamine, formaldehyde, and biphenyl is 2-2.5:6-7:

1.

4. The method of claim 1, wherein the nano-silica modified polyurethane thermal insulation material is prepared by mixing the nano-silica with the polyurethane, and then adding the blowing agent. In (2), the molar ratio of PEPA, intermediate 1, and pyridine is 2-2.5:1:0.4-0.

6.

5. The preparation method of the nano-silica modified polyurethane thermal insulation material according to claim 1, characterized in that, In S1, the molar ratio of N,N-diethyl-aminopropylmethyldimethoxysilane to intermediate 1 is 2-2.4:

1.

6. The method of claim 1, wherein the nano-silica modified polyurethane thermal insulation material is prepared by mixing the nano-silica with the polyurethane, and then adding the blowing agent. In S2, the mass ratio of intermediate 2 to nano-silica is 4-6:1.

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