A method for preparing polyimide-based phase change aerogel

Abstract

This invention discloses a method for preparing polyimide-based phase change aerogels, comprising: adding dianhydride to a diamine solution for polymerization, then adding a crosslinking agent solution and mixing evenly, then adding a phase change solution for grafting reaction to obtain a crosslinked polyamic acid phase change solution; then mixing the crosslinked polyamic acid phase change solution with deionized water for solvent replacement to obtain a crosslinked polyamic acid phase change precursor; then freezing the crosslinked polyamic acid phase change precursor, then removing it, dissolving it in a solvent and neutralizing it, and after complete dissolution, freeze-drying it to obtain an uniminated crosslinked polyamide phase change aerogel; and then thermally amidating the uniminated crosslinked polyamide phase change aerogel to obtain a polyimide-based phase change aerogel. Using the polyimide precursor as a matrix, a crosslinking agent is introduced, and its active groups at both ends react with the polyimide segments and the phase change material to form stable covalent bonds.

Description

Technical Field

[0001] This invention belongs to the field of composite phase change materials, specifically a method for preparing polyimide-based phase change aerogels. Background Technology

[0002] With the increasing severity of the energy crisis and environmental problems, the development of multifunctional materials has become a key direction for solving many practical problems. Phase change materials (PCMs) can store and release energy by absorbing or releasing latent heat when the temperature changes, and have broad application prospects in the field of thermal insulation and energy storage. However, traditional PCMs have some limitations, such as easy leakage during the phase change process, poor mechanical properties, and single function, which limit their further promotion and application. In addition, in practical application scenarios, single-function materials can no longer meet diverse needs. There is an urgent need to develop new materials with multiple integrated functions to maximize the utilization of material performance and meet the urgent needs of high-performance materials in fields such as construction, electronics, and aerospace.

[0003] Polyimide is a class of polymeric materials with excellent comprehensive properties, including high strength, high temperature resistance, and chemical corrosion resistance. However, polyimide itself does not possess phase change energy storage capabilities. In existing technologies, the preparation of polyimide-based composite phase change material aerogels is divided into physical blending and chemical grafting methods, with physical blending being the most common method. While physical blending is simple and easy to operate, the encapsulation of the phase change material is not robust and prone to leakage, making it unreusable.

[0004] To address the aforementioned issues, a chemical grafting method is employed to prepare composite aerogels. For example, application number 202410689863.8 discloses a method for preparing a high thermal conductivity, shape-stabilized composite phase change material using erythritol-expanded graphite. This method involves in-situ grafting and thermal imidization to prepare a polyimide-grafted erythritol (PIET) composite material, introducing oxidized expanded graphite (EG-OH). The prepared material not only solves the problem of phase change material leakage and reduces encapsulation costs, but also significantly improves thermal conductivity, effectively reduces supercooling, exhibits high latent heat of phase change, and has good formability. However, erythritol has poor heat resistance (<100℃), and the interfacial bonding between erythritol and polyimide is weak, making it prone to phase separation with long-term use. EG-OH is a rigid inorganic filler, and its addition disrupts the continuity of the PI matrix. When the filler content exceeds a certain threshold (e.g., >10wt%), the impact strength and flexibility of the composite material significantly decrease, making it prone to cracking during bending or vibration.

[0005] Application No. 202410487245.5 discloses a polyimide aerogel / phase change composite material with energy storage, temperature control, wave transmission, and thermal insulation functions, and its preparation method. It utilizes the low thermal conductivity and three-dimensional porous structure of polyimide aerogel to construct a "sandwich-type" multilayer composite structure through vacuum impregnation of n-alkane phase change materials. However, it mainly focuses on the energy storage and thermal insulation properties of the material, and has not fully explored the potential of polyimide in terms of mechanical properties and chemical resistance. To date, no research has been reported on the one-step construction of polyimide phase change aerogel composite materials with integrated thermal insulation, energy storage, noise reduction, flame retardancy, adsorption, and radiative cooling functions. Therefore, developing a high-performance polyimide-based material that can simultaneously achieve multifunctional integration of energy storage, thermal insulation, and flame retardancy is a crucial problem that urgently needs to be solved. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing polyimide-based phase change aerogel.

[0007] The technical solution of the present invention to solve the aforementioned technical problem is to provide a method for preparing polyimide-based phase change aerogels, characterized in that the method includes the following steps: Step 1: Dissolve the diamine in a solvent to obtain a diamine solution; dissolve the crosslinking agent in a solvent to obtain a crosslinking agent solution; dissolve the phase change material in a solvent to obtain a phase change solution. Step 2: Add dianhydride to diamine solution for polymerization reaction to obtain polyamic acid solution; then add crosslinking agent solution to polyamic acid solution and mix evenly to obtain crosslinked polyamic acid solution; then add phase change solution to crosslinked polyamic acid solution for grafting reaction to obtain crosslinked polyamic acid phase change solution; Step 3: Mix the cross-linked polyamic acid phase change solution with deionized water to perform solvent replacement until all the solvent is replaced, thereby obtaining the cross-linked polyamic acid phase change precursor. Step 4: Freeze the cross-linked polyamic acid phase change precursor, then take out the frozen cross-linked polyamic acid phase change precursor, dissolve it in a solvent and neutralize it. After complete dissolution, freeze dry it to obtain uniminoized cross-linked polyamic acid phase change aerogel. Step 5: Thermal amidation of the uniminoized crosslinked polyamide phase change aerogel to obtain polyimide-based phase change aerogel.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a method for preparing an aerogel composite material of polyimide grafted with phase change material (PCM). The method uses a polyimide precursor as a matrix, introduces a crosslinking agent, and utilizes the active groups at both ends of the crosslinking agent to react with polyimide segments (containing amino and carboxyl groups) and PCM (containing hydroxyl or carboxyl groups), respectively, to form stable covalent bonds. The crosslinking agent not only acts as a molecular bridge to achieve chemical grafting of PCM onto the polyimide matrix, but also constructs a three-dimensional network structure through intermolecular crosslinking, effectively suppressing leakage of the PCM during cycling. Combining the sol-gel process with supercritical drying, a composite material is finally obtained that combines the high-temperature resistance of polyimide, the lightweight and porous properties of aerogel, and the heat storage and release functions of PCM. Through the above structural design and process optimization, this invention effectively solves the technical pain points of traditional PCM such as single function, easy leakage, and unstable performance. It also has advantages such as convenient preparation, controllable cost, and wide application scenarios. Specific beneficial effects are summarized as follows: 1. Innovative preparation process, combining stability, controllability, and economy; (1) More stable grafting mechanism: Compared with the traditional physical blending method, the present invention achieves a strong bond between the phase change material and the polyimide matrix at the molecular level by constructing covalent bonds through crosslinking agent, which completely solves the core pain points of leakage and poor stability of phase change material during long-term service in the prior art. (2) The process is highly controllable and simple: By adjusting the amount of crosslinking agent, reaction temperature and time, the grafting rate and network density can be precisely controlled, and the preparation process is precise and controllable; the self-supporting phase change aerogel is prepared by a two-step method, without the need for solvent extraction and adsorption stages, and the process has good repeatability and strong compatibility; the precursor preparation adopts the ice-water bath method, which can precisely control the polymerization reaction rate, suppress local overheating and premature gelation, improve the molecular weight and distribution uniformity of polyamic acid, reduce side reactions, ensure product purity, and further improve the performance stability of composite materials; (3) Significant cost advantage: The equipment investment cost is reduced by about 30% compared with the traditional supercritical drying process, laying a solid economic foundation for large-scale production.

[0009] 2. Energy storage and cycle stability are superior to existing technologies: The chemical grafting method firmly anchors the phase change material to the three-dimensional network skeleton of polyimide, and the phase change enthalpy is increased by about 10% compared with the traditional physical blending method; the material has outstanding structural stability, and after 1000 cycles of use, the phase change performance decay rate is less than 5%, which significantly improves the problem of energy storage efficiency decline of phase change materials in the long-term use of existing technologies and greatly extends the service life of the material.

[0010] 3. Outstanding thermal management and safety performance, suitable for harsh application scenarios: The material integrates the high temperature resistance of polyimide with the lightweight and porous advantages of aerogel, with a thermal conductivity as low as 0.02W / (m·K), which can effectively block heat transfer; the thermal decomposition temperature is higher than 300℃, which can adapt to high temperature and harsh working environments; at the same time, it has good flame retardant properties. Compared with existing single-function thermal management materials, it can simultaneously achieve temperature buffering, efficient heat insulation and safety protection, meeting the thermal management needs of high-end scenarios such as aerospace and electronic equipment thermal protection.

[0011] 4. It has a high degree of functional integration, strong environmental adaptability, and a wide range of application scenarios; (1) Multifunctional Synergistic Effect: Breaking through the limitation of single function of phase change materials in existing technologies, it simultaneously realizes multiple functions such as heat insulation, energy storage, noise reduction, and CO2 adsorption, among which the CO2 adsorption capacity can reach 90 cm³. 3 / g or more can directly contribute to the achievement of carbon neutrality goals; (2) Good adaptability to multiple fields: Its application prospects cover multiple fields such as building energy conservation, industrial thermal management, aerospace and electronic equipment, which is more extensive than the existing technology. Specific examples include: as a smart exterior wall material in green buildings, it can simultaneously realize thermal energy storage, CO2 adsorption and efficient heat insulation; in the thermal protection system of electronic devices, it can buffer temperature fluctuations and provide flame retardancy and noise reduction; in the aerospace field, it can be used for cabin CO2 purification and thermal control management to improve the overall efficiency of the environmental control system.

[0012] 5. Adjustable structure and performance, with ample support for large-scale promotion: Through precise control of crosslinking agent dosage, reaction parameters, etc., key performance parameters such as material pore distribution, mechanical strength, and grafting rate can be optimized to flexibly adapt to the application needs of different scenarios; at the same time, the material preparation cost is low and the process is highly repeatable, which provides solid technical and economic support for the large-scale application and multi-scenario promotion of the material compared with existing complex preparation technologies. Attached Figure Description

[0013] Figure 1 The thermal conductivity diagrams of the polyimide-based phase change aerogel of Example 1 and the polyimide aerogel of Comparative Example 1 as a function of temperature are shown. Figure 2 The thermal conductivity diagrams at room temperature are for the polyimide-based phase change aerogel of Example 1 and the polyimide aerogel of Comparative Example 1. Figure 3 The graph shows the heat release rate curves of the polyimide-based phase change aerogel of Example 1 and the polyimide aerogel of Comparative Example 1. Figure 4 The noise reduction coefficient diagram shows the polyimide-based phase change aerogel of Example 1 and the polyimide aerogel of Comparative Example 1. Figure 5The CO2 adsorption curves of the polyimide-based phase change aerogel of Example 1 and the polyimide aerogel of Comparative Example 1 are shown. Figure 6 This is a physical image of the polyimide-based phase change aerogel of Example 1 of the present invention. Detailed Implementation

[0014] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0015] This invention provides a method for preparing polyimide-based phase change aerogels (hereinafter referred to as the method), characterized in that the method includes the following steps: Step 1: Dissolve the diamine in a solvent to obtain a diamine solution; The crosslinking agent is dissolved in a solvent to obtain a crosslinking agent solution; The phase change material is dissolved in a solvent to obtain a phase change solution; Preferably, in step 1, the diamine is one of 4,4'-diaminodiphenyl ether (ODA), m-phenylenediamine (MPD), p-phenylenediamine (PPD), 2,2'-bis(trifluoromethyl)benzidine (TFMB), or 1,4-bis(4-aminophenoxy)benzene (TPE-Q).

[0016] Preferably, in step 1, the mass ratio of diamine to solvent is 1:20~50.

[0017] Preferably, in step 1, the diamine dissolution process is as follows: the temperature is an ice-water bath (-10℃±5℃), and the time is 20~30min.

[0018] Preferably, in step 1, the crosslinking agent is one of the following: isocyanate crosslinking agent, epoxy crosslinking agent, dianhydride crosslinking agent, carbodiimide crosslinking agent, diamine crosslinking agent, 1,3,5-tris(4-aminophenyl)benzene, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), polyisocyanate crosslinking agent, formaldehyde derivative crosslinking agent, titanate crosslinking agent, polyol crosslinking agent, peroxide crosslinking agent, or polyfunctional olefin crosslinking agent.

[0019] Preferably, in step 1, the isocyanate crosslinking agent is diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), or hexamethylene diisocyanate (HDI); the epoxy crosslinking agent is epoxy resin E51, bisphenol A epoxy resin, or epichlorohydrin derivative; the dianhydride crosslinking agent is phthalic anhydride or pyromellitic dianhydride (PMDA); and the carbodiimide crosslinking agent is N,N'-dicyclohexylcarbodiimide (DCC) or N,N'-diisopropylcarbodiimide. Imine (DIC); diamine crosslinking agents are ethylenediamine or p-phenylenediamine; polyisocyanate crosslinking agents are polymethylbenzene isocyanate (PAPI); formaldehyde derivative crosslinking agents are hexamethylenetetramine or hydroxymethylurea; titanate crosslinking agents are tetrabutyl titanate or tetraisopropyl titanate; polyol crosslinking agents are glycerol or pentaerythritol; peroxide crosslinking agents are benzoyl peroxide (BPO) or di-tert-butyl peroxide; polyfunctional olefin crosslinking agents are divinylbenzene or triallyl isocyanurate.

[0020] Preferably, in step 1, the mass ratio of crosslinking agent to solvent is 0.7~1.3:10.

[0021] Preferably, in step 1, the crosslinking agent dissolution process is as follows: the temperature is room temperature (20~30℃) and the time is 5~10 min.

[0022] Preferably, in step 1, the phase change material is one of hydroxyl (-OH) phase change materials, carboxyl (-COOH) phase change materials, amide (-CONH-) phase change materials, ester (-COO-) phase change materials, or alkyl (-R) phase change materials.

[0023] Preferably, in step 1, the hydroxyl-based phase change material is polyethylene glycol or octadecyl alcohol; the carboxyl-based phase change material is palmitic acid, stearic acid, or lauric acid; the amide-based phase change material is polyacrylamide; the ester-based phase change material is polyethylene glycol laurate or fatty acid ester; and the alkyl-based phase change material is n-alkyl acrylate.

[0024] Preferably, in step 1, the selected crosslinking agent and the selected phase change material need to have reactive groups that can carry out a grafting reaction.

[0025] Preferably, in step 1, the mass ratio of phase change material to solvent is 1~5:10.

[0026] Preferably, in step 1, the phase change material dissolution process is as follows: the temperature is room temperature and the time is 5~10 min.

[0027] Preferably, in step 1, the solvent is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO); preferably, all three solutions use the same solvent.

[0028] Step 2: Add dianhydride to the diamine solution one by one to carry out the polymerization reaction, and obtain a polyamic acid solution; then add the crosslinking agent solution to the polyamic acid solution and mix evenly to obtain a crosslinked polyamic acid solution; then slowly add the phase change solution to the crosslinked polyamic acid solution to carry out the grafting reaction, and obtain a crosslinked polyamic acid phase change solution. Preferably, in step 2, the dianhydride is one of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), diphenyl ether dianhydride (ODPA), hexafluorodianhydride (6FDA), or 3,3',4,4'-benzophenone dianhydride (BTDA).

[0029] Preferably, in step 2, the dianhydride is added to the diamine solution in batches for polymerization, with the number of batches being 2 to 5.

[0030] Preferably, in step 2, the molar ratio of diamine to dianhydride is 1:1; Preferably, in step 2, the polymerization reaction process is as follows: the temperature is an ice-water bath, and the time is 1~3h (preferably 1~2h).

[0031] Preferably, in step 2, the crosslinking agent solution is added dropwise to the polyamic acid solution and mixed evenly.

[0032] Preferably, in step 2, the ratio of the mass of the crosslinking agent to the sum of the masses of the diamine and dianhydride is 0.009 to 0.015:1.

[0033] Preferably, in step 2, the mixing is carried out by stirring, and the stirring process is as follows: the temperature is an ice water bath, the speed is 300~500 rpm, and the time is 1~3 hours.

[0034] Preferably, in step 2, the ratio of the mass of the phase change material to the sum of the masses of the diamine and dianhydride is 5:1~6.

[0035] Preferably, in step 2, the grafting reaction process is as follows: the temperature is an ice-water bath, and the time is 2.5~4.5h (preferably 2.5~3.5h).

[0036] Step 3: Mix the cross-linked polyamic acid phase change solution with deionized water to perform solvent replacement until all the solvent is replaced, thereby obtaining the cross-linked polyamic acid phase change precursor. Preferably, in step 3, the solvent replacement process is as follows: the temperature is room temperature (20~30℃), the replacement time is 30~40 min each time, and the number of replacements is 6~8 times.

[0037] Step 4: Freeze the cross-linked polyamic acid phase change precursor, then take out the frozen cross-linked polyamic acid phase change precursor, dissolve it in a solvent and neutralize it. After complete dissolution, freeze dry it to obtain uniminoized cross-linked polyamic acid phase change aerogel. Preferably, in step 4, the freezing process is as follows: the freezing temperature is -15℃ to -18℃, and the time is 5 to 7 hours, until it is completely frozen.

[0038] Preferably, in step 4, the solvent is deionized water; the mass of the frozen cross-linked polyamic acid phase change precursor is 1 to 50% of the mass of deionized water.

[0039] Preferably, in step 4, triethylamine is added for neutralization; the mass of triethylamine is 0.1-5% (preferably 1-5%) of the mass of deionized water.

[0040] Preferably, in step 4, the freeze-drying process is as follows: temperature is -55℃ to -45℃, time is 24 to 36 hours, and vacuum degree is 30 to 50 Pa.

[0041] Preferably, in step 4, after complete dissolution, the mixture is poured into a mold for freeze-drying.

[0042] Step 5: Thermal amidation of the uniminoized crosslinked polyamide phase change aerogel to obtain polyimide-based phase change aerogel.

[0043] Preferably, in step 5, the thermal amidation process is as follows: in an oxygen-free environment, the thermal amidation temperature is 200~300℃, the time from room temperature to the thermal amidation temperature is 2~4h, and the holding time is 2~4h; preferably, it is carried out in a muffle furnace.

[0044] Preferably, in step 5, the oxygen-free environment is a nitrogen environment or an inert gas environment; the inert gas is argon or helium.

[0045] Example 1: Step 1: Dissolve 2.4 g of ODA in 48 mL of DMAC at -15°C in an ice-water bath for 30 min until completely dissolved to obtain a diamine solution; dissolve 0.0168 g of TAPOB in 1 mL of DMAC at room temperature for 8 min until completely dissolved to obtain a crosslinking agent solution; dissolve 1 g of palmitic acid in 10 mL of DMAC at room temperature for 8 min until completely dissolved to obtain a phase transition solution. Step 2: Add 2.6g of PMDA in portions to the diamine solution at a rate of 2g / min, and react in an ice-water bath for 1h to obtain a polyamic acid solution; then add the crosslinking agent solution dropwise to the polyamic acid solution, and stir at 400rpm for 1h in an ice-water bath to obtain a crosslinked polyamic acid solution; then slowly add the phase change solution to the crosslinked polyamic acid solution, and react in an ice-water bath for 2.5h to obtain a crosslinked polyamic acid phase change solution. Step 3: Pour the cross-linked polyamic acid phase change solution into deionized water at room temperature for solvent replacement. Each replacement takes 30 minutes and is repeated 6 times until all the solvent is removed, thus obtaining the cross-linked polyamic acid phase change precursor. Step 4: Freeze the cross-linked polyamic acid phase change precursor at -18°C for 6 hours. Then, take out 1g of the frozen cross-linked polyamic acid phase change precursor, dissolve it in 19mL of deionized water, and add 1mL of triethylamine for neutralization. After complete dissolution, pour it into a mold and freeze-dry it at -50°C and 45Pa for 24 hours to obtain uniminoized cross-linked polyamic acid phase change aerogel. Step 5: Place the completely dried, uniminoized crosslinked polyamide phase change aerogel into a muffle furnace. In an oxygen-free environment, heat the aerogel from room temperature to 200°C for 2 hours, and then hold it at 200°C for 2 hours to ensure complete iminoization reaction, reduce structural defects caused by rapid release of volatiles, and enable the polyimide molecular chain to form a stable imide ring structure, thereby improving the high temperature resistance and mechanical strength of the material, and obtaining a polyimide-based phase change aerogel (named PI-PA@5).

[0046] Example 2: This embodiment is exactly the same as Embodiment 1, except that in step 1, 2g of palmitic acid is added.

[0047] Example 3: This embodiment is exactly the same as Embodiment 1, except that in step 1, 3g of palmitic acid is added.

[0048] Example 4: This embodiment is exactly the same as Embodiment 1, except that in step 1, 4g of palmitic acid is added.

[0049] Example 5: This embodiment is exactly the same as Embodiment 1, except that in step 1, 5g of palmitic acid is added.

[0050] Example 6: This embodiment is exactly the same as Embodiment 1, except that in step 1, the phase change material is replaced with 2g of stearic acid.

[0051] Example 7: This embodiment is exactly the same as Embodiment 1, except that in step 1, the phase change material is replaced with 3g of stearic acid.

[0052] Example 8: This embodiment is exactly the same as Embodiment 1, except that in step 1, the phase change material is replaced with 5g of stearic acid.

[0053] Example 9: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to hexamethylene diisocyanate (HDI) and the phase change material is changed to 2g of polyethylene glycol.

[0054] Example 10: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to hexamethylene diisocyanate (HDI) and the phase change material is changed to 3g of polyethylene glycol.

[0055] Example 11: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to hexamethylene diisocyanate (HDI) and the phase change material is changed to 5g of polyethylene glycol.

[0056] Example 12: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to hexamethylene diisocyanate (HDI) and the phase change material is changed to 6g of polyethylene glycol.

[0057] Example 13: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to polymethyl phenyl isocyanate (PAPI) and the phase change material is changed to 2g of polyacrylamide.

[0058] Example 14: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to polymethyl phenyl isocyanate (PAPI) and the phase change material is changed to 3g of polyacrylamide.

[0059] Example 15: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to polymethyl phenyl isocyanate (PAPI) and the phase change material is changed to 5g of polyacrylamide.

[0060] Example 16: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to polymethyl phenyl isocyanate (PAPI) and the phase change material is changed to 6g of polyacrylamide.

[0061] Example 17: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to pentaerythritol (PETP) and the phase change material is changed to 2g of polyethylene glycol laurate.

[0062] Example 18: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to pentaerythritol (PETP) and the phase change material is changed to 3g of polyethylene glycol laurate.

[0063] Example 19: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to pentaerythritol (PETP) and the phase change material is changed to 5g of polyethylene glycol laurate.

[0064] Example 20: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to pentaerythritol (PETP) and the phase change material is changed to 6g of polyethylene glycol laurate.

[0065] Example 21: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to benzoyl peroxide (BPO) and the phase change material is changed to 2g of n-alkyl acrylate.

[0066] Example 22: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to benzoyl peroxide (BPO) and the phase change material is changed to 3g of n-alkyl acrylate.

[0067] Example 23: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to benzoyl peroxide (BPO) and the phase change material is changed to 5g of n-alkyl acrylate.

[0068] Example 24: This embodiment is exactly the same as Embodiment 1, except that in step 1, the crosslinking agent is changed to benzoyl peroxide (BPO) and the phase change material is changed to 6g of n-alkyl acrylate.

[0069] Example 25: This embodiment is exactly the same as Embodiment 1, except that in step 2, the grafting reaction time is 3 hours.

[0070] Example 26: This embodiment is exactly the same as Embodiment 1, except that in step 2, the grafting reaction time is 3.5 hours.

[0071] Example 27: This embodiment is exactly the same as Embodiment 1, except that in step 4, the freeze-drying time is 30 hours.

[0072] Example 28: This embodiment is exactly the same as Embodiment 1, except that in step 4, the freeze-drying time is 36 hours.

[0073] Example 29: This embodiment is exactly the same as Embodiment 1, except that in step 4, the vacuum degree is 40 Pa.

[0074] Example 30: This embodiment is exactly the same as Embodiment 1, except that in step 4, the vacuum degree is 50 Pa.

[0075] Example 31: This embodiment is exactly the same as Embodiment 1, except that in step 5, the thermal amidation temperature is 250°C, the time to heat from room temperature to the thermal amidation temperature is 3 hours, and the holding time is 3 hours.

[0076] Example 32: This embodiment is exactly the same as Embodiment 1, except that in step 5, the thermal amidation temperature is 250°C, the time to heat from room temperature to the thermal amidation temperature is 4 hours, and the holding time is 4 hours.

[0077] Example 33: This embodiment is exactly the same as Embodiment 1, except that in step 5, the thermal amidation temperature is 300°C, the time to heat from room temperature to the thermal amidation temperature is 3 hours, and the holding time is 3 hours.

[0078] Example 34: This embodiment is exactly the same as Embodiment 1, except that in step 5, the thermal amidation temperature is 300°C, the time to heat from room temperature to the thermal amidation temperature is 4 hours, and the holding time is 4 hours.

[0079] The test results of the polyimide-based phase change aerogels prepared in Examples 1-34 are shown in Table 1.

[0080] Table 1

[0081]

[0082] Comparative Example 1: This embodiment is exactly the same as Example 1, except that no crosslinking agent and phase change material are added, and the final product is polyimide aerogel (named PI).

[0083] Comparative Example 2: This embodiment is exactly the same as Embodiment 1, except that no phase change material is added.

[0084] Comparative Example 3: This embodiment is exactly the same as Embodiment 9, except that the phase change material polyethylene glycol is not added.

[0085] Comparative Example 4: This embodiment is exactly the same as Embodiment 13, except that the phase change material polyacrylamide is not added.

[0086] Comparative Example 5: This embodiment is exactly the same as Embodiment 17, except that the phase change material polyethylene glycol laurate is not added.

[0087] Comparative Example 6: This embodiment is exactly the same as Embodiment 21, except that no phase change material, n-alkyl acrylate, is added.

[0088] The test results of the aerogels prepared in Comparative Examples 1-6 are shown in Table 2.

[0089] Table 2

[0090] Performance testing: Thermal conductivity was tested using a thermal constant analyzer (Hot Disck TP 2500S, HotDisk GmbH, Sweden), starting from an initial measurement of 0.001W and 0.1s and gradually increasing, using a polyimide-coated probe with a diameter of R=2.001 mm and model number 7577.

[0091] Cone calorimetry was performed, and the experimental results are shown below. Figure 3 .

[0092] Depend on Figure 1-6As shown in Tables 1 and 2, firstly, TAPOB's unique multifunctional structure can efficiently covalently crosslink with polyimide segments and palmitic acid molecules under mild conditions, forming a dense and stable network structure. This results in a compressive strength of 0.8 mPa and a palmitic acid leakage rate of less than 0.1% at 80°C. Secondly, the freeze-drying process, using ice crystals as templates in a low-temperature environment, avoids solvent surface tension from damaging the aerogel skeleton, ultimately forming a three-dimensional nanoporous structure with a porosity of 95% and a pore size of 10-50 nm. This imparts an ultra-low thermal conductivity of 0.011 W / (m·K), significantly improving thermal insulation and phase change energy storage efficiency. Thirdly, the grafting method promotes uniform molecular-level composite formation of palmitic acid and polyimide, eliminating interfacial defects and raising the thermal decomposition initiation temperature of the material to 320°C, far exceeding that of traditional physical blends. Furthermore, the preparation process uses water as a solvent, eliminating the need for high temperature, high pressure, and toxic solvents. The preparation from sol to finished product can be completed within 48 hours using general-purpose equipment, significantly reducing equipment and energy costs. By flexibly adjusting the amount of TAPOB, the degree of grafting, and the freeze-drying parameters, the pore structure, mechanical and phase change properties of aerogels can be precisely designed, making them widely adaptable to various application needs in fields such as building insulation and electronic heat dissipation.

[0093] This invention, through the synergistic innovation of freeze-drying, cross-linking, and grafting technologies, endows the material with outstanding multifunctional properties and wide applicability. Leveraging the high phase change enthalpy of palmitic acid and the thermal stability of polyimide, the material achieves efficient energy storage and thermal insulation, with a thermal conductivity as low as 0.011 W / (m·K). Its three-dimensional nanoporous structure (95% porosity, pore size 10~50 nm) not only enhances thermal insulation performance but also achieves a noise reduction coefficient of over 0.95 through multiple sound wave reflections and dissipation. After special modification, the aerogel's oxygen index is increased to 28%, meeting the UL94 V-0 flame retardant standard. Simultaneously, its abundant pores and surface-active groups endow it with excellent adsorption capacity, achieving a CO2 adsorption capacity of up to 87 cm³. 3 / g. The aforementioned multifunctional properties enable this aerogel to be widely used in various fields such as integrated energy storage, heat insulation, and noise reduction walls in the construction industry, heat dissipation and flame retardant encapsulation materials for electronic devices, and pollutant adsorption and purification devices in the environmental protection industry. It effectively solves the application problem of traditional single-function materials requiring multiple components, significantly reduces system costs and complexity, and demonstrates extremely high practical value and market potential.

[0094] Depend on Figure 6 As can be seen, when the polyimide-based phase change aerogel prepared in Example 1 is placed on the flower stamen, the stamen bears the weight. Since the stamen has a weak load-bearing capacity, the sample is very light and will not crush the stamen.

[0095] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing a polyimide-based phase change aerogel, characterized in that, The method includes the following steps: Step 1: Dissolve the diamine in a solvent to obtain a diamine solution; dissolve the crosslinking agent in a solvent to obtain a crosslinking agent solution; dissolve the phase change material in a solvent to obtain a phase change solution. Step 2: Add dianhydride to diamine solution for polymerization reaction to obtain polyamic acid solution; then add crosslinking agent solution to polyamic acid solution and mix evenly to obtain crosslinked polyamic acid solution; then add phase change solution to crosslinked polyamic acid solution for grafting reaction to obtain crosslinked polyamic acid phase change solution; Step 3: Mix the cross-linked polyamic acid phase change solution with deionized water to perform solvent replacement until all the solvent is replaced, thereby obtaining the cross-linked polyamic acid phase change precursor. Step 4: Freeze the cross-linked polyamic acid phase change precursor, then take out the frozen cross-linked polyamic acid phase change precursor, dissolve it in a solvent and neutralize it. After complete dissolution, freeze dry it to obtain uniminoized cross-linked polyamic acid phase change aerogel. Step 5: Thermal amidation of the uniminoized crosslinked polyamide phase change aerogel to obtain polyimide-based phase change aerogel.

2. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 1, the diamine is one of 4,4'-diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 2,2'-bis(trifluoromethyl)biphenylenediamine or 1,4-bis(4-aminophenoxy)benzene; In step 1, the mass ratio of diamine to solvent is 1:20~50; In step 1, the diamine dissolution process is as follows: the temperature is an ice-water bath, and the time is 20~30 minutes.

3. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 1, the crosslinking agent is one of the following: isocyanate crosslinking agent, epoxy crosslinking agent, dianhydride crosslinking agent, carbodiimide crosslinking agent, diamine crosslinking agent, 1,3,5-tris(4-aminophenyl)benzene, 1,3,5-tris(4-aminophenoxy)benzene, polyisocyanate crosslinking agent, formaldehyde derivative crosslinking agent, titanate crosslinking agent, polyol crosslinking agent, peroxide crosslinking agent, or polyfunctional olefin crosslinking agent; In step 1, the mass ratio of crosslinking agent to solvent is 0.7~1.3:10; In step 1, the crosslinking agent dissolution process is as follows: the temperature is room temperature, and the time is 5~10 min; In step 1, the phase change material is one of the following: hydroxyl-based phase change material, carboxyl-based phase change material, amide-based phase change material, ester-based phase change material, or alkyl-based phase change material; In step 1, the mass ratio of phase change material to solvent is 1~5:10; In step 1, the phase change material dissolution process is as follows: the temperature is room temperature, and the time is 5~10 min; In step 1, the selected crosslinking agent and the selected phase change material can undergo a grafting reaction; In step 1, the solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, or dimethyl sulfoxide.

4. The method for preparing polyimide-based phase change aerogel according to claim 3, characterized in that, In step 1, the isocyanate crosslinking agent is diphenylmethane diisocyanate, toluene diisocyanate, or hexamethylene diisocyanate; the epoxy crosslinking agent is epoxy resin E51, bisphenol A epoxy resin, or epichlorohydrin derivative; the dianhydride crosslinking agent is phthalic anhydride or pyromellitic dianhydride; the carbodiimide crosslinking agent is N,N'-dicyclohexylcarbodiimide or N,N'-diisopropylcarbodiimide; the diamine crosslinking agent is ethylenediamine or p-phenylenediamine; the polyisocyanate crosslinking agent is polymethylphenyl isocyanate; the formaldehyde derivative crosslinking agent is hexamethylenetetramine or hydroxymethylurea; the titanate crosslinking agent is tetrabutyl titanate or tetraisopropyl titanate; the polyol crosslinking agent is glycerol or pentaerythritol; the peroxide crosslinking agent is benzoyl peroxide or di-tert-butyl peroxide; and the polyfunctional olefin crosslinking agent is divinylbenzene or triallyl isocyanurate. In step 1, the hydroxyl-based phase change material is polyethylene glycol or octadecyl alcohol; the carboxyl-based phase change material is palmitic acid, stearic acid, or lauric acid; the amide-based phase change material is polyacrylamide; the ester-based phase change material is polyethylene glycol laurate or fatty acid ester; and the alkyl-based phase change material is n-alkyl acrylate.

5. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 2, the dianhydride is one of pyromellitic dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, hexafluoro dianhydride, or 3,3',4,4'-benzophenone dianhydride. In step 2, the dianhydride is added to the diamine solution in batches to carry out the polymerization reaction, with 2 to 5 batches being added in total; In step 2, the molar ratio of diamine to dianhydride is 1:1; In step 2, the polymerization reaction process is as follows: the temperature is an ice-water bath, and the time is 1~3 hours.

6. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 2, the ratio of the mass of the crosslinking agent to the sum of the masses of the diamine and dianhydride is 0.009~0.015:1; In step 2, the mixture is stirred to ensure uniformity. The stirring process is as follows: the temperature is an ice-water bath, the speed is 300~500 rpm, and the time is 1~3 hours. In step 2, the ratio of the mass of the phase change material to the sum of the masses of the diamine and dianhydride is 5:1~6; In step 2, the grafting reaction process is as follows: the temperature is an ice-water bath, and the time is 2.5~4.5h.

7. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 3, the solvent replacement process is as follows: the temperature is room temperature, the replacement time is 30~40 min each time, and the number of replacements is 6~8 times.

8. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 4, the freezing process is as follows: the freezing temperature is -15℃ to -18℃, and the time is 5 to 7 hours; In step 4, the solvent is deionized water; the mass of the frozen cross-linked polyamic acid phase change precursor is 1-50% of the mass of deionized water. In step 4, triethylamine is added for neutralization; the mass of triethylamine is 0.1-5% of the mass of deionized water. In step 4, the freeze-drying process is as follows: temperature is -55℃ to -45℃, time is 24 to 36 hours, and vacuum degree is 30 to 50 Pa.

9. The method for preparing polyimide-based phase change aerogel according to claim 1, characterized in that, In step 5, the thermal amidation process is as follows: in an oxygen-free environment, the thermal amidation temperature is 200~300℃, the time from room temperature to the thermal amidation temperature is 2~4h, and the holding time is 2~4h.

10. The method for preparing polyimide-based phase change aerogel according to claim 9, characterized in that, In step 5, the oxygen-free environment is either a nitrogen environment or an inert gas environment; the inert gas is either argon or helium.

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