Silicon-containing polyurethane hybrid phenolic aerogel and preparation method thereof

Abstract

The invention discloses a silicon-containing polyurethane hybrid phenolic aerogel and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a phenol ring-terminated silicon-containing polyurethane prepolymer; (2) mixing the phenol ring-terminated silicon-containing polyurethane prepolymer with phenolic resin to prepare a mixed solution, adding a curing agent, and carrying out gel reaction to prepare silicon-containing polyurethane hybrid phenolic aldehyde wet gel; and (3) removing a liquid phase in the silicon-containing polyurethane hybrid phenolic aldehyde wet gel to obtain the silicon-containing polyurethane hybrid phenolic aldehyde aerogel. According to the invention, a phenol ring-terminated silicon-containing polyurethane prepolymer is synthesized, an organosilicon component is introduced into phenolic resin through a phenol ring, the heat resistance and flexibility of a linear polysiloxane structure are utilized to improve the mechanical properties and high-temperature oxidation resistance of phenolic aerogel, and the hydrophobic property of the phenolic aerogel is also improved.

Description

A silicone-containing polyurethane hybrid phenolic aerogel and its preparation method Technical Field

[0001] This invention belongs to the field of aerogel materials technology, specifically, it relates to a silicon-containing polyurethane hybrid phenolic aerogel and its preparation method. Background Technology

[0002] With the development of materials science and nanotechnology, organic aerogels have attracted widespread attention due to their unique physicochemical properties. These materials consist of a lightweight, porous network structure, typically exhibiting extremely high specific surface area and extremely low thermal conductivity. The preparation of organic aerogels usually involves steps such as solvent replacement, supercritical drying, or freeze-drying. These steps preserve the porous structure of the material while removing the solvent, preventing pore collapse. In 1989, Pekala pioneered the development of organic aerogels by preparing an aerogel from resorcinol and formaldehyde via the sol-gel method and supercritical drying. Phenolic aerogels, as a type of organic polymer aerogel, have become a research hotspot due to their widely available raw materials, low cost, good chemical stability, and processability, and are mainly used in aerospace thermal protection materials. However, traditional phenolic aerogels also have some limitations, such as low mechanical strength, poor high-temperature oxidation resistance, and hydrophilicity issues caused by the large number of polar phenolic hydroxyl groups.

[0003] To improve the overall performance of phenolic aerogels, a common method is to modify the phenolic resin. For example, the introduction of organosilicon can enhance the antioxidant properties, hydrophobicity, and thermal stability of phenolic aerogels. Organosilicon molecules contain silicon-carbon bonds (Si-C), which have low surface energies, making it difficult for the surface of organosilicon materials to form strong interactions with other polar molecules such as water. Among them, the Si-O bond (443.7 KJ / mol) has a higher bond energy and better molecular chain flexibility than the C-C bond (347.4 KJ / mol). However, considering the significant difference between the solubility parameters of organosilicon (7.3-7.5) and phenolic resin (10.5-11.5), the poor compatibility leads to macroscopic phase separation in the prepared hybrid aerogels, preventing the organosilicon component from being effectively introduced into the skeletal structure of the phenolic aerogel and thus failing to achieve the desired modification effect.

[0004] Therefore, it is extremely important to design the molecular structure so that it can form a stable sol with phenolic resin, and further introduce the organosilicon component into the phenolic aerogel framework through the gelation and solidification of the sol, in order to match the aerogel preparation process.

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

[0006] The technical problem to be solved by the present invention is to overcome at least one of the shortcomings of the prior art and provide a silicon-containing polyurethane hybrid phenolic aerogel and its preparation method. The present invention introduces linear siloxanes into the phenolic aerogel skeleton structure, which not only greatly improves the mechanical strength and antioxidant properties of phenolic aerogel, but also solves the moisture absorption problem of phenolic aerogel.

[0007] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a silicon-containing polyurethane hybrid phenolic aerogel, comprising:

[0009] (1) Preparation of phenol ring-terminated silicone polyurethane prepolymer;

[0010] (2) A mixed solution was prepared by mixing the phenol ring-terminated silicone polyurethane prepolymer with phenolic resin, a curing agent was added, and a gel reaction was carried out to obtain silicone polyurethane hybrid phenolic wet gel.

[0011] (3) Remove the liquid phase from the silicon-containing polyurethane hybrid phenolic wet gel to obtain silicon-containing polyurethane hybrid phenolic aerogel.

[0012] In this invention, a phenol ring-terminated silicone polyurethane prepolymer is introduced into the phenolic aerogel system. The hydrogen ions on the phenol ring undergo an electrophilic substitution reaction with the formaldehyde produced by the decomposition of the curing agent, and co-curing with linear phenolic resin. This solves the problem of macroscopic phase separation caused by the poor compatibility of organosilicon and phenolic resins. The siloxane component is successfully introduced into the aerogel skeleton structure, which effectively improves the mechanical strength, high-temperature oxidation resistance and hydrophobicity of the aerogel. Furthermore, in terms of molecular structure design, the urea bond formed by the reaction of the phenol ring and isocyanate can enhance the intermolecular forces, achieving a combination of chemical and physical effects, and improving the mechanical strength and hydrophobicity of the hybrid phenolic aerogel through synergistic action.

[0013] Therefore, by introducing linear siloxanes into the phenolic aerogel framework structure, this invention not only greatly improves the mechanical strength and antioxidant properties of phenolic aerogel, but also solves the moisture absorption problem of phenolic aerogel.

[0014] In addition, the method for preparing silicon-containing polyurethane hybrid phenolic aerogels described in this invention can be successfully prepared by using the basic sol-gel method and drying under normal pressure. The raw materials are inexpensive, fully compatible with existing aerogel preparation processes, and can also be used for large-scale industrial production.

[0015] In a further embodiment, in step (1), amino- or hydroxyl-terminated polydimethylsiloxane is reacted with diisocyanate to obtain a silicone-containing polyurethane prepolymer, and then phenolic compounds are used to end-cap the silicone-containing polyurethane prepolymer to obtain a phenol ring-terminated silicone-containing polyurethane prepolymer.

[0016] In a further embodiment, the phenolic compound contains a phenolic hydroxyl group and at least one functional group that is reactive with isocyanate.

[0017] In this invention, the phenolic compound is defined to have at least one phenolic hydroxyl group and at least one functional group capable of reacting with isocyanate. This allows the phenolic compound to be capped with a polyurethane prepolymer by the functional group that is reactive with isocyanate, while the phenolic ring at the end still has a hydroxyl group. This enables the phenolic ring to be co-cured with phenolic resin, introducing silicon components into the phenolic resin system and improving properties beyond the intrinsic properties of phenolic resin.

[0018] Furthermore, the functional groups that are reactive between the phenolic compounds and isocyanates include hydroxyl, amino, phenolic hydroxyl, mercapto, hydroxymethyl, and aminomethyl groups.

[0019] Regarding the differences in reactivity of different functional groups, technical researchers have found that amino functional groups have high reactivity with isocyanates and can react more rapidly at room temperature.

[0020] Furthermore, the functional group is located on the phenolic ring in an ortho, meta, or para position, preferably in a meta position.

[0021] Preferably, the phenolic compound is selected from ortho-functionalized phenols such as salicylol, meta-functionalized phenols such as resorcinol or m-aminophenol, and para-functionalized phenols such as 4-mercaptophenol.

[0022] This invention discovers that phenolic molecules with meta-functional group structures have higher reactivity at the reaction sites on the benzene ring, which is beneficial for further curing reactions.

[0023] Preferably, the phenolic compound is m-aminophenol.

[0024] In the above scheme, the selected phenolic compound is m-aminophenol, which has a high reactivity because the amino group of m-aminophenol can react rapidly with the isocyanate group.

[0025] In a further embodiment, in step (1), the polydimethylsiloxane is selected from diamino-terminated polydimethylsiloxane or dihydroxy-terminated polydimethylsiloxane.

[0026] Preferably, the polydimethylsiloxane is a diamino-terminated polydimethylsiloxane.

[0027] In the above scheme, the diamino-terminated polydimethylsiloxane has high reactivity when reacting with isocyanate. The amino group, as a nucleophile, can react rapidly with isocyanate at a relatively low temperature to form substituted urea. If the dihydroxy-terminated polydimethylsiloxane is selected, a higher temperature or a catalyst is required to accelerate the reaction, and the reaction conditions are relatively harsh.

[0028] Furthermore, the molecular weight range of the diamino-terminated or dihydroxy-terminated polydimethylsiloxane is 1000-5000.

[0029] The molecular weight range defined in this invention is a suitable range discovered by technicians based on extensive research and experimentation. When the molecular weight is too low, the improvement effect on the mechanical properties of the aerogel is poor, and the modified phenolic aerogel still exhibits the inherent brittleness and fragility of phenolic aerogel. When the molecular weight is too high, the elasticity of the material increases, the modulus and mechanical strength decrease, and the compatibility with phenolic resin deteriorates. At the same time, a suitable molecular weight is conducive to the refinement of the aerogel pore size, thereby ensuring that the aerogel has higher strength.

[0030] In a further embodiment, in step (1), the diisocyanate is selected from at least one of aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates.

[0031] In this invention, aromatic diisocyanates are preferably used. Preferably, the diisocyanate is toluene diisocyanate.

[0032] Aromatic diisocyanates exhibit strong electrophilicity due to the conjugation between the phenyl group and the isocyanate group, thus possessing high reactivity.

[0033] In a further step, in step (1), amino- or hydroxyl-terminated polydimethylsiloxane and diisocyanate are dissolved in tetrahydrofuran and reacted at 75°C for 2 hours. Then, phenolic compounds are added to continue the reaction. The temperature is lowered to 50°C and the reaction is continued for 1 hour. The solvent is removed by vacuum distillation to obtain phenol ring-terminated polyurethane prepolymer.

[0034] Furthermore, the solvent includes tetrahydrofuran.

[0035] In one preferred embodiment, diamino-terminated polydimethylsiloxane and toluene 2,4-diisocyanate (2,4-TDI) are dissolved in tetrahydrofuran and reacted at 75°C for 2 hours. Then, m-aminophenol is added and reacted at 50°C for 1 hour. The solvent tetrahydrofuran is removed by vacuum distillation to obtain a phenol ring-terminated polyurethane prepolymer.

[0036] In a further embodiment, the molar ratio of diamino-terminated polydimethylsiloxane to toluene 2,4-diisocyanate is 1:2.

[0037] The molar ratio of added m-aminophenol to diamino-terminated polydimethylsiloxane is 2:1.

[0038] In a further embodiment, in step (2), the phenolic resin is selected from linear phenolic resins with a softening point of 90-120℃.

[0039] Preferably, the phenolic resin softening point is 100-110℃.

[0040] In this invention, based on extensive research and experimentation, technicians discovered that using linear phenolic resins with a softening point of 90-120℃ can improve their mechanical properties and oxidation resistance. Specifically, using linear phenolic resins with a softening point greater than 90℃ significantly improves mechanical properties and thermogravimetric analysis (TGA) carbon residue in air. However, if the softening point is higher than 120℃, heating is required to dissolve the resin solution, which is detrimental to the overall simplicity of the preparation process. Considering both performance and processability, a resin softening point temperature of 100-115℃ is preferred.

[0041] In a further embodiment, in step (2), the mass ratio of the phenol ring-terminated silicone polyurethane prepolymer to the phenolic resin is (5-30):100.

[0042] In the above scheme, the mixing ratio of phenol ring-terminated silicone polyurethane prepolymer to phenolic resin is a relatively excellent range determined by technicians based on extensive experiments and research. Within this range, the phenol ring-terminated silicone polyurethane prepolymer can significantly improve the mechanical properties, antioxidant properties, and hydrophobicity of phenolic aerogel. When the phenolic resin content is 100 parts, if the amount of phenol ring-terminated silicone polyurethane prepolymer is greater than 30 parts, the prepared hybrid aerogel will experience gel skeleton collapse during normal pressure drying, leading to increased aerogel bulk density due to volume shrinkage. If the amount of phenol ring-terminated polyurethane prepolymer is less than 5 parts, the hybrid aerogel, without modification, will still exhibit the inherent brittleness and powdering problems of phenolic aerogel.

[0043] In a further embodiment, in step (2), the curing agent is selected from hexamethylenetetramine, formaldehyde, or paraformaldehyde.

[0044] Among the above options, hexamethylenetetramine is a better choice as a curing agent. Its raw materials are readily available, and it is less toxic and non-volatile than formaldehyde. Its decomposition rate is temperature-dependent, which is beneficial for controlling the curing reaction rate.

[0045] In a further embodiment, in step (2), the gelation reaction is carried out in a closed reactor at a temperature of 70-110℃ for a duration of 12-48h.

[0046] Preferably, the reaction temperature for the gelation reaction is 90°C and the reaction time is 24 hours.

[0047] In a further step, in step (3), the liquid phase in the siloxane-modified phenolic resin gel is removed by high-temperature and atmospheric-pressure drying at a temperature of 50-90°C for 12-48 hours.

[0048] Preferably, the drying temperature is 90℃ and the drying time is 12h.

[0049] Secondly, the present invention provides a silicon-containing polyurethane hybrid phenolic aerogel obtained by the preparation method described above or in combination thereof.

[0050] Preferably, the silicone polyurethane hybrid phenolic aerogel has a compressive modulus ≥70MPa, compressive strength ≥20MPa, compressive strain ≥50%, residual carbon content >15% in air at 1000℃, and static water contact angle ≥150°.

[0051] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0052] 1. This invention designs and synthesizes a phenol ring-terminated silicone-containing polyurethane prepolymer. The organosilicon component is introduced into the phenolic resin through the phenol ring, and the heat resistance and flexibility of its linear polysiloxane structure are utilized to improve the mechanical properties and high-temperature oxidation resistance of the phenolic aerogel. The methyl groups attached to the silicon atoms in the polysiloxane reduce the polarity of the molecular surface, enhancing hydrophobicity. Furthermore, the phenol ring-terminated silicone-containing polyurethane prepolymer contains abundant urea bonds, which readily form intermolecular hydrogen bonds, significantly improving the mechanical strength, high-temperature oxidation resistance, and hydrophobicity of the phenolic aerogel.

[0053] 2. In a preferred embodiment, since the polyurethane prepolymer is end-capped with phenolic rings, the diamino-terminated polydimethylsiloxane can be directly cured by hexamethylenetetramine and phenolic gel without reacting with alcohol solvent. That is, there is no need to change the preparation process of phenolic aerogel. Aerogel can be prepared by existing conventional sol-gel and atmospheric pressure drying processes, which is easy to realize industrial production.

[0054] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0055] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0056] Figure 1 shows the compressive stress-strain curves of the silicon-containing polyurethane hybrid phenolic aerogel and the pure phenolic aerogel prepared by the preparation method of the present invention in Example 1.

[0057] Figure 2 shows the static water contact angle results of the silicon-containing polyurethane hybrid phenolic aerogel and the pure phenolic aerogel prepared by the preparation method of the present invention in Example 1.

[0058] Figure 3 shows the residual carbon content of the silicon-containing polyurethane hybrid phenolic aerogel and the pure phenolic aerogel prepared by the preparation method of the present invention in Example 3 under an air atmosphere.

[0059] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0061] Detection method:

[0062] In this invention, all compression tests were conducted using an Instron universal testing machine (model Instron 5567) at a compression rate of 1 mm / min. The specimens were cut into cylindrical blocks with a diameter of 17 mm and a height of 17 mm. The aerogel compression test method was based on the standard GB / T 18942.1-2003, "Porous Elastic Polymers - Determination of Compressive Stress-Strain Characteristics".

[0063] The compressive modulus is determined based on the slope of the initial linear portion of the stress-strain curve. The compressive stress is taken from the measured value of the maximum stress that the sample bears during compression, and the compressive strain is taken from the corresponding value of the compressive stress.

[0064] The hydrophobic properties of the aerogel samples were analyzed by the static water contact angle. The static water contact angle was obtained by measuring the angle between the droplet and the solid surface of the material when the volume of water was 2 μL using a KRUSS contact angle meter (model: DSA100).

[0065] The volume of the aerogel was calculated by measuring the mass, diameter, and height of a completely dried aerogel sample at ambient pressure, and the density was obtained by the mass-to-volume ratio (all measurements were performed at room temperature).

[0066] The drugs used in the following examples and their sources are shown in the table below:

[0067] Table 1

[0068]

[0069]

[0070] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0071] Example 1

[0072] (1) Preparation of polyurethane prepolymer

[0073] 10 g of diamino-terminated polydimethylsiloxane (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran and reacted at 75 °C for 2 hours. Then, 2.1 g of m-aminophenol was added and reacted at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a phenol ring-terminated polyurethane prepolymer.

[0074] (2) Preparation of silicone-containing polyurethane hybrid phenolic aerogel

[0075] A stable and homogeneous mixed solution was obtained by mixing phenol ring-terminated polyurethane prepolymer, linear phenolic resin (softening point 105℃), hexamethylenetetramine, and ethanol in a mass ratio of 5:95:15:300 and stirring until fully dissolved. The sol was then cured at 90℃ for 24 hours under sealed conditions to obtain a silicone polyurethane hybrid phenolic wet gel. The wet gel was then dried at 90℃ for 12 hours to obtain a silicone polyurethane hybrid phenolic aerogel.

[0076] The silicone polyurethane hybrid phenolic aerogel has good mechanical properties. Figure 1 shows the compressive stress-strain curves of the aerogel and pure phenolic aerogel (comparative example). It can be seen that compared with pure phenolic aerogel, the compressive strength, compressive modulus and compressive strain of the silicone polyurethane hybrid phenolic aerogel have been greatly improved.

[0077] Figure 2 shows the static water contact angle between the aerogel and the pure phenolic aerogel. The measured static water contact angle is 171.9°. The static water contact angle is greater than 150°, which proves that the aerogel has superhydrophobicity.

[0078] Example 2

[0079] (1) Preparation of polyurethane prepolymer

[0080] 10 g of diamino-terminated polydimethylsiloxane (molecular weight 2000 g / mol) and 1.74 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran and reacted at 75 °C for 2 hours. Then, 0.92 g of m-aminophenol was added and reacted at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a phenol ring-terminated polyurethane prepolymer.

[0081] (2) Preparation of silicone-containing polyurethane hybrid phenolic aerogel

[0082] A stable and homogeneous mixed solution was obtained by mixing phenol ring-terminated polyurethane prepolymer, linear phenolic resin (softening point 105℃), hexamethylenetetramine, and ethanol in a mass ratio of 5:95:15:300 and stirring until fully dissolved. The sol was then cured at 90℃ for 24 hours under sealed conditions to obtain a silicone polyurethane hybrid phenolic wet gel. The wet gel was then dried at 90℃ for 12 hours to obtain a silicone polyurethane hybrid phenolic aerogel.

[0083] Example 3

[0084] (1) Preparation of polyurethane prepolymer

[0085] 10 g of diamino-terminated polydimethylsiloxane (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran and reacted at 75 °C for 2 hours. Then, 2.1 g of m-aminophenol was added and reacted at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a phenol ring-terminated polyurethane prepolymer.

[0086] (2) Preparation of silicone-containing polyurethane hybrid phenolic aerogel

[0087] A stable and homogeneous mixed solution was obtained by mixing phenol ring-terminated polyurethane prepolymer, linear phenolic resin (softening point 105℃), hexamethylenetetramine, and ethanol in a mass ratio of 20:80:15:300 and stirring until fully dissolved. The sol was then cured at 90℃ for 24 hours under sealed conditions to obtain a silicone polyurethane hybrid phenolic wet gel. The wet gel was then dried at 90℃ for 12 hours to obtain a silicone polyurethane hybrid phenolic aerogel.

[0088] This silicone-containing polyurethane hybrid phenolic aerogel exhibits excellent antioxidant properties. As shown in Figure 3, the thermal weight loss at 1000°C in air increased from 2.87% to 16.71%, with a silicon content of only 4 wt%. The significant increase in residual carbon can be attributed to the fine control of the curing rate, which further demonstrates the importance of the molecular structure design of phenolic ring end-capping for performance improvement.

[0089] Example 4

[0090] (1) Preparation of polyurethane prepolymer

[0091] 10 g of dihydroxyl-terminated polydimethylsiloxane (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran and reacted at 75 °C for 2 hours. Then, 2.1 g of m-aminophenol was added and reacted at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a phenol ring-terminated polyurethane prepolymer.

[0092] (2) Preparation of silicone-containing polyurethane hybrid phenolic aerogel

[0093] A stable and homogeneous mixed solution was obtained by mixing phenol ring-terminated polyurethane prepolymer, linear phenolic resin (softening point 105℃), hexamethylenetetramine, and ethanol in a mass ratio of 20:80:15:300 and stirring until fully dissolved. The sol was then cured at 90℃ for 24 hours under sealed conditions to obtain a silicone polyurethane hybrid phenolic wet gel. The wet gel was then dried at 90℃ for 12 hours to obtain a silicone polyurethane hybrid phenolic aerogel.

[0094] Example 5

[0095] (1) Preparation of polyurethane prepolymer

[0096] 10 g of diamino-terminated polydimethylsiloxane (molecular weight 1000 g / mol) and 3.48 g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20 g of tetrahydrofuran and reacted at 75 °C for 2 hours. Then, 2.43 g of salicylol was added and reacted at 50 °C for 1 hour. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a phenol ring-terminated polyurethane prepolymer.

[0097] (2) Preparation of silicone-containing polyurethane hybrid phenolic aerogel

[0098] A stable and homogeneous mixed solution was obtained by mixing phenol ring-terminated polyurethane prepolymer, linear phenolic resin (softening point 105℃), hexamethylenetetramine, and ethanol in a mass ratio of 20:80:15:300 and stirring until fully dissolved. The sol was then cured at 90℃ for 24 hours under sealed conditions to obtain a silicone polyurethane hybrid phenolic wet gel. The wet gel was then dried at 90℃ for 12 hours to obtain a silicone polyurethane hybrid phenolic aerogel.

[0099] Comparative Example 1

[0100] Preparation of pure phenolic aerogel

[0101] Linear phenolic resin (softening point 105℃), hexamethylenetetramine, and ethanol were mixed in a mass ratio of 100:15:300 to obtain a stable and homogeneous phenolic sol. The sol was cured into a gel at 90℃ for 24 hours under sealed conditions to obtain a phenolic wet gel. The wet gel was dried at 90℃ for 12 hours to obtain a pure phenolic aerogel.

[0102] Comparative Example 2

[0103] (1) Preparation of polyurethane prepolymers with nonphenol ring-terminated ends

[0104] The difference between this comparative example and the previous example is that a polyurethane prepolymer with a non-phenol ring-terminated structure was used. 10g of diamino-terminated polydimethylsiloxane (molecular weight 1000g / mol) and 3.48g of toluene 2,4-diisocyanate (2,4-TDI) were dissolved in 20g of tetrahydrofuran and reacted at 75°C for 2 hours. After discharging, the tetrahydrofuran solvent was removed by direct vacuum distillation to obtain the non-phenol ring-terminated polyurethane prepolymer.

[0105] (2) Preparation of silicone-containing polyurethane hybrid phenolic aerogel

[0106] A stable and homogeneous mixed solution was obtained by mixing a polyurethane prepolymer with a phenol ring-terminated end, a linear phenolic resin (softening point 105℃), hexamethylenetetramine, and tetrahydrofuran in a mass ratio of 5:95:15:300. The sol was then cured at 60℃ for 24 hours under sealed conditions to obtain a silicone polyurethane hybrid phenolic wet gel. The wet gel was then dried at room temperature for 12 hours to obtain a silicone polyurethane hybrid phenolic aerogel.

[0107] Since polyurethane prepolymers with phenol ring-terminated ends will react chemically with alcohol solvents, and considering the simplicity of the preparation process, tetrahydrofuran was chosen as the sol solvent. However, tetrahydrofuran has a low boiling point of 66℃, and the curing gel temperature was determined to be 60℃. This temperature range is not conducive to the crosslinking reaction of phenolic resins, resulting in poor mechanical properties of the final aerogel due to excessive phase separation scale, and it still retains the inherent brittleness of pure phenolic aerogels.

[0108] The properties of the aerogels prepared in Examples 1-5 and Comparative Examples 1-2 were tested, and the results are shown in the table below:

[0109] Table 2

[0110]

[0111]

[0112] Results analysis:

[0113] As can be seen from the table above, compared with Comparative Example 1, the hybrid aerogels prepared by the method described in Examples 1-5 show significantly improved compressive strength and compressive strain compared with pure phenolic aerogels; their density is also lower than that of pure phenolic aerogels. Because the Si-CH3 on the siloxane in the prepared phenol ring-terminated polyurethane prepolymer has a lower surface energy, the hybrid aerogels of Examples 1-5 all exhibit superhydrophobicity, with static water contact angles greater than 150°. Furthermore, the presence of Si-CH3 can reduce the intermolecular forces between the phenolic hydroxyl groups and the alcohol solvent in phenolic resins, maintaining the integrity of the gel skeleton during drying and preventing shrinkage, thus reducing the final density of the hybrid aerogel.

[0114] The difference between Example 1 and Example 3 is that the ratio of the phenol ring-terminated polyurethane prepolymer to the linear phenolic resin is different. In Example 1, it is 5:95, while in Example 3 it is 20:80.

[0115] A comparison of Examples 1 and 3 shows that the proportion of linear phenolic resin in Example 1 is higher than that in Example 3, resulting in higher compressive modulus and compressive strength. However, the compressive strain in Example 3 is higher than that in Example 1, indicating that within the formulation range defined by this invention, as the amount of phenolic ring-terminated polyurethane prepolymer increases, the hybrid aerogel exhibits enhanced toughness while maintaining a certain level of mechanical strength. Furthermore, with the increase in the amount of phenolic ring-terminated polyurethane prepolymer, the antioxidant properties of Example 3 are significantly enhanced. With a silicon content of only 4%, the residual carbon rate reaches 16.71%, indicating that carbon in phenolic resin is retained to some extent in high-temperature environments. Performance improvement is achieved through precise molecular structure design.

[0116] The difference between Example 1 and Example 2 is that the aminosiloxane in the phenol ring-terminated polyurethane prepolymer prepared in Example 2 has a higher molecular weight. In both examples, the molar ratio of toluene 2,4-diisocyanate and m-aminophenol is the same, in order to end all end groups.

[0117] A comparison of Examples 1 and 2 shows that Example 2 has a higher compressive strain, indicating that flexible molecular chain segments are beneficial for the hybrid aerogel to exhibit better deformation capabilities.

[0118] Examples 3-5 share the same ratio of phenolic ring-terminated polyurethane prepolymer to phenolic resin. The difference lies in that Example 4 uses dihydroxy polydimethylsiloxane, while Example 5 uses salicylol as the end-capping agent.

[0119] The data in Table 2 shows that the mechanical properties of Examples 3-5 are not significantly different, and all three exhibit superhydrophobicity. This confirms that the molecular structure of this invention is independent of the selection of the end-capping agent, but only related to the reaction sites on the phenolic hydroxyl benzene ring. The substitution site of the functional group in salicylol that can react with isocyanate on the benzene ring is still the meta position of the phenolic hydroxyl group, which is the same as that of m-aminophenol, and can enhance the curing reaction activity.

[0120] Experimental Example 1

[0121] Effect of phenolic resin softening point

[0122] This experimental example follows the preparation method of Example 1, using linear phenolic resins with different softening points at 85℃, 90℃, 95℃, 105℃, 115℃, 120℃, and 125℃ to investigate their effect on the preparation properties of hybrid phenolic aerogels. The results are shown in the table below:

[0123] Table 3

[0124] Softening Point, Compression Modulus (MPa), Compression Strength (MPa), Residual Air Weight (%) 85℃ 43.08 14.73 7.86 90℃ 48.62 17.93 11.20 95℃ 53.75 19.37 12.60 105℃ 74.78 21.04 16.71 115℃ 78.35 22.11 18.44 120℃ 76.71 22.01 18.65 125℃ 76.38 20.73 18.95 surface

[0125] The results in the table above show that, compared to using linear phenolic resin with a softening point of 85℃, using linear phenolic resin with a softening point of 90℃ or higher significantly improves mechanical properties and thermogravimetric analysis (TGA) carbon residue in air. However, if the softening point is higher than 120℃, heating is required to dissolve the resin solution, which is detrimental to the overall simplicity of the preparation process. Therefore, using linear phenolic resin with a softening point of 90-120℃ can improve its mechanical properties and oxidation resistance. Considering both performance and processability, a resin softening point temperature of 100-115℃ is preferred.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a silicon-containing polyurethane hybrid phenolic aerogel, characterized in that, include: (1) Prepare a phenol ring-terminated silicone polyurethane prepolymer; (2) Mix the phenol ring-terminated silicone polyurethane prepolymer with phenolic resin to obtain a mixed solution, add a curing agent, and carry out a gel reaction to obtain a silicone polyurethane hybrid phenolic wet gel; (3) Remove the liquid phase from the silicone polyurethane hybrid phenolic wet gel to obtain a silicone polyurethane hybrid phenolic aerogel.

2. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to claim 1, characterized in that, In step (1), amino- or hydroxyl-terminated polydimethylsiloxane is reacted with diisocyanate to obtain a silicone polyurethane prepolymer. Then, phenolic compounds are used to end-cap the silicone polyurethane prepolymer to obtain a phenol ring-terminated silicone polyurethane prepolymer.

3. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to claim 2, characterized in that, The phenolic compound contains a phenolic hydroxyl group and at least one functional group that is reactive with isocyanate. Preferably, the functional group that is reactive with isocyanate includes hydroxyl, amino, phenolic hydroxyl, mercapto, hydroxymethyl, and aminomethyl. Preferably, the functional group is located at the ortho, meta, or para position on the phenolic ring, preferably at the meta position. Preferably, the phenolic compound is selected from at least one of salicylol, resorcinol, m-aminophenol, and 4-mercaptophenol. Preferably, the phenolic compound is m-aminophenol.

4. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to claim 2, characterized in that, In step (1), the polydimethylsiloxane is selected from diamino-terminated polydimethylsiloxane or dihydroxy-terminated polydimethylsiloxane; preferably, the molecular weight range of the diamino-terminated polydimethylsiloxane or the dihydroxy-terminated polydimethylsiloxane is 1000-5000; preferably, the polydimethylsiloxane is diamino-terminated polydimethylsiloxane.

5. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to claim 2, characterized in that, In step (1), the diisocyanate is selected from at least one of aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate; preferably, the diisocyanate is toluene diisocyanate.

6. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to any one of claims 1-5, characterized in that, In step (2), the phenolic resin is selected from linear phenolic resins with a softening point of 90-120℃; preferably, the softening point of the phenolic resin is 100-115℃.

7. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to any one of claims 1-5, characterized in that, In step (2), the mass ratio of the phenol ring-terminated silicone polyurethane prepolymer to the phenolic resin is (5-30):

100.

8. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to any one of claims 1-5, characterized in that, In step (2), the curing agent is selected from hexamethylenetetramine, formaldehyde or paraformaldehyde; preferably, the curing agent is hexamethylenetetramine.

9. The method for preparing silicon-containing polyurethane hybrid phenolic aerogel according to any one of claims 1-5, characterized in that, In step (2), the gelation reaction is carried out in a closed reactor at a temperature of 70-110°C for 12-48 hours; preferably, the gelation reaction temperature is 90°C and the reaction time is 24 hours.

10. A silicone polyurethane hybrid phenolic aerogel obtained by the preparation method according to any one of claims 1-9; preferably, the silicone polyurethane hybrid phenolic aerogel has a compressive modulus ≥70MPa, a compressive strength ≥20MPa, a compressive strain ≥50%, residual carbon >15% in air at 1000℃, and a static water contact angle ≥150°.

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