A cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material and its preparation method

Abstract

This invention provides a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material and its preparation method. This invention prepares the cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material by physically entangled a three-dimensional network structure of cross-linked polyimide within a thermoplastic shape memory polyimide three-dimensional network structure. The polyimide porous material obtained by this invention exhibits stable performance, high strength, low density, light weight, low thermal conductivity, small pore size, and uniform cell size, meeting the requirements for flame retardancy, sound absorption, and heat insulation, and has good application prospects in aerospace, construction, flexible robotics, and electronic devices.

Description

Technical Field

[0001] This invention relates to a cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus responsive shape memory polyimide porous material and its preparation method. Background Technology

[0002] Shape memory polymers (SMPs) are a new type of smart material that can autonomously return to their original shape when exposed to external stimuli such as heat, light, electricity, magnetism, and solvents. After decades of development, ester-based SMPs, epoxy-based SMPs, and styrene-based SMPs have seen widespread development, and their foamed materials have attracted considerable attention. Shape memory foams based on ester-based, epoxy-based, and styrene-based SMPs possess advantages such as large deformation capacity, ease of shaping, tunable stimulus response temperature, light weight, low relative density, large specific surface area, and ease of surface chemical modification, as well as the characteristics of porous polymer materials. They have high application value in fields such as thermal insulation, cushioning and shock absorption, catalyst carriers, adsorption and separation, biological tissue materials, and microelectronic materials. However, shape memory foams prepared from existing SMP materials suffer from problems such as low glass transition temperature, poor mechanical properties, poor resistance to harsh environments, and high cost.

[0003] Polyimides, with their unique chemical structure, possess excellent mechanical properties, rigidity, heat resistance, toughness, impact resistance, and dynamic fatigue resistance. Polyimide foam materials retain these superior properties while also offering lightweight, heat insulation, and sound absorption characteristics. However, the preparation of traditional polyimide foam materials primarily relies on conventional polyimide materials lacking shape memory properties, limiting their application in fields requiring intelligent characteristics. Shape memory polyimide (SMPI) is a smart material developed in the last decade or so, exhibiting high thermal stability, high mechanical strength, and high resistance to harsh environments. However, due to the high glass transition temperature of SMPI, achieving shape memory functionality under external stimuli such as heat, light, electricity, and magnetism presents certain challenges. For example, patent document CN111303425A discloses a photothermal responsive three-dimensional shape memory polyimide, its preparation method, and its applications. This invention mixes photothermal nanoparticles with diamine and dianhydride, and synthesizes them into polyamic acid through in-situ condensation polymerization. The photothermal nanoparticles are then dispersed in the polyamic acid, which is then coated onto a rigid thin-film substrate. After solvent evaporation, a polyamic acid film is obtained. Subsequently, the polyamic acid film and the underlying rigid thin-film substrate are fabricated into a three-dimensional structure. After thermal imidization, the substrate is removed to obtain a photothermal responsive three-dimensional shape memory polyimide. This invention can obtain shape memory polyimides with complex three-dimensional structures, and the resulting shape memory polyimides can achieve dual responses to light and heat. However, this invention only achieves shape memory function under light and heat conditions, and the stimulus response conditions are relatively simple. Moreover, this invention is post-cured into a three-dimensional shape, making the preparation process complex and costly. In addition, this invention relies on simple stacking with external force to form a three-dimensional shape and does not have excellent flame retardant and sound absorption properties.

[0004] Therefore, multi-stimulus responsive polyimides and their porous materials with excellent properties deserve further research. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material and its preparation method. This invention controls the structure of diamine and dianhydride monomers, thereby regulating the ratio of hard to soft segments in the polyimide (PI) structure to impart shape memory properties to PI. Multi-stimulus responsive behavior of SMPI is achieved by adding light-absorbing, conductive, and magnetic reinforcing phases to the matrix material. The multi-stimulus responsive SMPI porous material is prepared using traditional polyimide foaming methods. This invention prepares the cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material by physically entangled a three-dimensional network structure of cross-linked polyimide within a thermoplastic shape memory polyimide three-dimensional network structure. The polyimide porous material obtained by this invention exhibits stable performance, high strength, low density, light weight, low thermal conductivity, small pore size, and uniform pore size, meeting the requirements for flame retardancy, sound absorption, and heat insulation. It has promising application prospects in aerospace, construction, flexible robotics, and electronic devices.

[0006] The technical solution of the present invention is as follows:

[0007] A cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus responsive shape memory polyimide porous material, wherein the polyimide porous material can recover its shape under the stimulation of light, electricity, magnetism or heat.

[0008] According to a preferred embodiment of the present invention, the polyimide porous material has the following characteristics: thermal conductivity: 0.03–0.05 W / m·K; flame retardancy: oxygen index > 27; sound absorption: noise reduction coefficient > 0.21; stimulus response characteristics: recovery rate 97–100%; and bulk density: 5–8 kg / m³. 3 Thermal decomposition temperature: 530~600℃.

[0009] The preparation method of the above-mentioned cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material includes the following steps:

[0010] (1) Disperse dianhydride a, diamine a and crosslinking agent fully in organic solvent a, add light-absorbing phase, conductive phase and magnetic phase, mix evenly, and obtain polyimide acid (PAA) through reaction;

[0011] (2) Dissolve the polyimide acid (PAA) obtained in step (1) in organic solvent b, add catalyst, dianhydride b and lower fatty alcohol, and react dianhydride b and lower fatty alcohol to obtain esterified dianhydride; add diamine b, and react esterified dianhydride and diamine b to obtain polyester ammonium salt intermediate product; add foam stabilizer and mix evenly to obtain polyimide foaming precursor material; the polyimide foaming precursor material undergoes thermal imide cyclization reaction to obtain cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus responsive shape memory polyimide porous material.

[0012] According to a preferred embodiment of the present invention, in steps (1) and (2), organic solvent a and organic solvent b are each independently selected from one or more combinations of tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone or dimethyl sulfoxide; preferably, organic solvent a is N,N-dimethylformamide and organic solvent b is tetrahydrofuran or N,N-dimethylformamide.

[0013] According to a preferred embodiment of the present invention, in steps (1) and (2), diamine a and diamine b are independently selected from m-phenylenediamine, p-phenylenediamine, 4,4-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, 4,4-diaminodiphenyl sulfide, 4,4-diaminodiphenol, 4,4-diaminodibenzophenone, 3,3-diaminodiphenyl ether, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl or... One or more of 1,3-bis(4-aminophenyl)propane; preferably, diamine a is 4,4-diaminodiphenyl ether or a combination of 1,3-bis(3-aminophenoxy)benzene and 4,4'-bis(4-aminophenoxy)diphenyl ether; diamine b is 4,4-diaminodiphenyl ether or a combination of 1,3-bis(3-aminophenoxy)benzene and 4,4'-bis(4-aminophenoxy)diphenyl ether, wherein the molar ratio of 1,3-bis(3-aminophenoxy)benzene and 4,4'-bis(4-aminophenoxy)diphenyl ether is 1.4-1.6:1.

[0014] According to a preferred embodiment of the present invention, in steps (1) and (2), dianhydride a and dianhydride b are each independently selected from one or more combinations of bisphenol A type diether dianhydride, 4,4'-oxophthalic anhydride, pyromellitic dianhydride, 3,3,4,4-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-diphenylmethyl ether tetracarboxylic dianhydride, 2,2-bis(3,4-phthalic anhydride)hexafluoropropane or 1,3-bis(3,4-phthalic acid)hexafluoropropane; preferably, dianhydride a is pyromellitic dianhydride or bisphenol A type diether dianhydride, and dianhydride b is bisphenol A type diether dianhydride or 3,3,4,4-benzophenone tetracarboxylic dianhydride.

[0015] According to a preferred embodiment of the present invention, in step (1), the crosslinking agent is one or a combination of two or more of tris(4-aminophenyl)amine, 4,4'4”-triaminotriphenylamine, 1,3,5-tris(4-aminophenoxy)benzene, alkynylaniline or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, preferably tris(4-aminophenyl)amine or 1,3,5-tris(4-aminophenoxy)benzene.

[0016] According to a preferred embodiment of the present invention, in step (1), the molar ratio of dianhydride a, diamine a and crosslinking agent is 1-1.2:1:1-3.

[0017] According to a preferred embodiment of the present invention, in step (1), the molar ratio of dianhydride a to the volume ratio of organic solvent a is 0.05-1 mol / L.

[0018] According to a preferred embodiment of the present invention, in step (1), the light-absorbing phase is one or a combination of two or more of dopamine, carbon nanotubes, silver nanowires or graphene.

[0019] According to a preferred embodiment of the present invention, in step (1), the conductive phase is one or a combination of two or more of carbon nanotubes, carbon black, silver nanoparticles, gold nanoparticles or silver nanowires.

[0020] According to a preferred embodiment of the present invention, in step (1), the magnetic phase is one or a combination of two or more of the following: ferric oxide, iron tetroxide, nickel powder, iron-cobalt alloy, or nickel-aluminum alloy.

[0021] According to a preferred embodiment of the present invention, in step (1), the mass ratio of the light-absorbing phase, the conductive phase, and the magnetic phase is 1:1-2:1; and the total mass ratio of dianhydride a to the light-absorbing phase, the conductive phase, and the magnetic phase is 1:1-3.

[0022] According to the present invention, in step (1), the light-absorbing phase, conductive phase, and magnetic phase all need to undergo surface activation treatment before use. The surface treatment methods for the light-absorbing phase, conductive phase, and magnetic phase include gas phase oxidation, liquid phase oxidation, electrochemical oxidation, in-situ modification of nanoparticles, plasma treatment, coupling agent treatment, solubilization treatment, chemical grafting treatment, and vapor deposition, etc., to improve the micro / nano interfacial forces between the added phases and between the added phase and the matrix material, enhance the adhesion strength between the added phases and between the added phase and the matrix material, and optimize the comprehensive performance of the obtained material. Preferably, the surface activation treatment method is as follows: the light-absorbing phase, conductive phase, and magnetic phase are treated in an air atmosphere at 400°C for 2 to 4 hours.

[0023] According to a preferred embodiment of the present invention, in step (1), the reaction temperature is 0–30°C, the reaction time is 10–36 h, and the reaction is carried out under inert gas protection and stirring conditions; preferably, the reaction temperature is 10–15°C, and the reaction time is 24–36 h. The reaction is a polycondensation and crosslinking reaction.

[0024] According to a preferred embodiment of the present invention, in step (1), the reactants obtained from the reaction are precipitated with anhydrous ethanol, dried, ground into powder, and passed through a 60-100 mesh sieve to obtain SMPI precursor material - polyimide acid (PAA) powder with a cross-linked network structure.

[0025] According to a preferred embodiment of the present invention, in step (2), the catalyst is one or a combination of two or more of α-methylimidazolium, 1-H-3-methylimidazolium chloride, 2-ethyl-4-methylimidazolium, 2-cyanomethylbenzimidazole, 1-hexyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 2-methylimidazolium, 3-methylimidazolium, 4-methylimidazolium, and 5-methylimidazolium; the mass of the catalyst is 0.1-2% of the mass of dianhydride b.

[0026] According to a preferred embodiment of the present invention, in step (2), the lower fatty alcohol is one or a combination of two or more of methanol, ethanol, n-propanol or butanol, preferably methanol; the molar ratio of dianhydride b to the lower fatty alcohol is 1:30-70.

[0027] According to a preferred embodiment of the present invention, in step (2), the molar ratio of dianhydride b to the volume ratio of organic solvent b is 0.1-1 mol / L.

[0028] According to a preferred embodiment of the present invention, in step (2), the mass ratio of dianhydride b to polyimide acid (PAA) is 3-10:1.

[0029] According to a preferred embodiment of the present invention, in step (2), the reaction temperature of dianhydride b and lower fatty alcohol is 60-70°C, the reaction time is 4-8h, the heating rate is 0.5-5°C / min, and the reaction is carried out under inert gas protection and stirring conditions.

[0030] According to a preferred embodiment of the present invention, in step (2), dianhydride b reacts with a lower fatty alcohol to obtain esterified dianhydride, and after cooling to 20-40°C, the next step is carried out.

[0031] According to a preferred embodiment of the present invention, in step (2), the molar ratio of dianhydride b to diamine b is 0.94-1.2:1.

[0032] According to a preferred embodiment of the present invention, in step (2), the reaction temperature of the esterified dianhydride and diamine b is 60-70°C, the reaction time is 1-3 h, the heating rate is 0.5-5°C / min, and the reaction is carried out under inert gas protection and stirring conditions.

[0033] According to a preferred embodiment of the present invention, in step (2), the foam stabilizer is one or a combination of two or more of AK-8005, silicone oil, cellulose, dodecyl dimethylamine oxide, sodium fatty alcohol polyoxyethylene ether sulfate or sodium α-alkenyl sulfonate; the mass ratio of the foam stabilizer to dianhydride b is 0.19-0.89:1.

[0034] According to a preferred embodiment of the present invention, in step (2), after adding the foam stabilizer and mixing evenly, the mixture is dried, ground into powder, and passed through a 60-100 mesh sieve to obtain the polyimide foaming precursor material.

[0035] According to a preferred embodiment of the present invention, in step (2), the thermal imide cyclization reaction conditions are as follows: the temperature is gradually increased to 80°C, 110°C, 180°C, 200°C, 250°C, and 300°C at a heating rate of 1-2°C / min, and each of the above temperatures is maintained for 1-2 hours.

[0036] Technical features and beneficial effects of the present invention:

[0037] 1. This invention regulates the structure of diamine and dianhydride monomers, thereby controlling the ratio of hard to soft segments in the polyimide (PI) structure to impart shape memory properties to PI. Furthermore, by adding light-absorbing, conductive, and magnetic reinforcing phases to the matrix material, the multi-stimulus responsive behavior of SMPI is achieved. The invention utilizes traditional polyimide foaming methods to prepare multi-stimulus responsive shape memory polyimide porous materials. The preparation method of the multi-stimulus responsive shape memory polyimide porous material provided by this invention is simple, energy-efficient, and cost-effective. The foaming process is simple and easy to control, and the foamed products do not exhibit defects such as bubble cracking, collapse, uneven pore size, or incomplete imidization. Due to the interpenetration of polyimides with a cross-linked network structure, the obtained polyimide porous material exhibits stable performance, high thermal stability, high resistance to harsh environments, high strength, low density, light weight, low thermal conductivity, small pore size, uniform pore size, sound absorption and noise reduction, and meets the requirements for flame retardancy, sound absorption, and heat insulation. It has good application prospects in aerospace, construction, flexible robotics, and electronic devices.

[0038] 2. This invention utilizes methods such as gas-phase oxidation, liquid-phase oxidation, electrochemical oxidation, in-situ modification with nanoparticles, plasma treatment, coupling agent treatment, solubilization treatment, chemical grafting treatment, and vapor deposition to activate the surfaces of the light-absorbing, conductive, and magnetic additive phases. The surface-active functional groups generated by the additive phases form intermolecular hydrogen bonds with the matrix material, enhancing the micro / nano interfacial forces between additive phases and between the additive phases and the matrix material. This avoids physical separation caused by shape memory deformation between additive phases and between the additive phases and the matrix material, significantly improving the compressive strength, high-temperature resistance, sound absorption, and thermal insulation properties of the foam material.

[0039] 3. This invention first prepares a chemically cross-linked polyimide, and then in-situ polymerizes a thermoplastic shape memory polyimide network structure on the three-dimensional network structure of the chemically cross-linked polyimide. Thus, the chemically cross-linked polyimide three-dimensional network structure permeates and is physically entangled within the shape memory polyimide three-dimensional network structure formed by physical entanglement. After a foaming process using a gradual heating and heat preservation method, the chemically cross-linked polyimide molecular chains interpenetrate within the three-dimensional network structure of the thermoplastic shape memory polyimide porous material. The interpenetrating network structure generally contains two or more network structures. Because the two polyimide network structures are intertwined, maintaining the material properties of the original network structure, the interpenetration of the cross-linked polyimide network structure can enhance the strength, thermal stability, dimensional stability, and resistance to harsh environments of the thermoplastic shape memory polyimide porous material.

[0040] 4. In step (2) of the present invention, dianhydride b first reacts with a lower fatty alcohol to obtain esterified dianhydride, and then reacts with diamine b to further form polyamide ester. Compared with the direct reaction of dianhydride b and diamine b to prepare polyamic acid, polyamide ester is more stable, providing a solid foundation for the subsequent preparation of cross-linked polyimide molecular chain interpenetrating shape memory polyimide porous materials. The amount of the added phase in the present invention needs to be appropriate. If the amount of added phase is too low, it cannot achieve its function; if the amount of added phase is too high, it will lead to poor adhesion between the added phase and the matrix, and breakage or delamination will occur during deformation and recovery. In addition, the method of the present invention is applicable to different types of dianhydrides and diamines, and the appropriate type of diamine and dianhydride can be selected according to the specific application requirements. The preparation method of the present invention is a whole, and the excellent effects of the present invention can only be achieved by the combined action of each step and condition.

[0041] 5. The multi-stimulus responsive shape memory polyimide porous material prepared by the method of this invention has a high surface area and porosity, and exhibits significant light absorption, conductivity, and magnetism. Under light irradiation, the light absorption capacity of the polyimide porous material is enhanced, generating sufficient heat to drive the polyimide porous material to return to its original initial shape; under electrical current, the interconnected conductive particles inside the polyimide porous material generate heat, thereby driving the polyimide porous material to return to its original initial shape; in a magnetic field environment, the magnetic particles inside the polyimide porous material generate electromagnetic heat, thereby driving the polyimide porous material to return to its original initial shape; furthermore, some light-absorbing materials also have conductive properties, which will produce a synergistic effect in a single external environment, thereby shortening the shape recovery time; this multi-stimulus responsive polyimide porous material is not limited to heating environments, but can also be remotely driven in light, electric, and magnetic environments, greatly expanding the application fields of polyimide porous materials. Furthermore, this multi-stimulus responsive porous material can be fabricated into devices with complex shapes, and by controlling the sequence of light, electricity, magnetism, and heat stimulation, it can achieve the recovery of specific shapes, showing great application potential in the controllable complex deformation of future artificial intelligence devices. In addition, the addition of inorganic fillers can also increase the pore size, improve the foaming capacity, and reduce the density of the foamed material. Attached Figure Description

[0042] Figure 1 The images show a comparison of the original shape (a), the compression-deformed shape (b), and the shape (c) after shape recovery under thermal stimulation of the cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material prepared in Example 1 of this invention.

[0043] Figure 2 The diagram shows the pore structure of the cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material prepared in Example 1 of this invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0045] In addition, the experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0046] Example 1

[0047] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material, comprising the following steps:

[0048] Step 1: Install the three-necked flask, condenser, and magnetic stirrer, and introduce nitrogen as an inert protective gas.

[0049] Step 2: Add 10 mmol / L pyromellitic dianhydride, 15 mL N,N-dimethylformamide, 10 mmol / L 4,4-diaminodiphenyl ether, and 15 mmol / L 1,3,5-tris(4-aminophenoxy)benzene to the mixture from Step 1, and mix thoroughly and disperse evenly. Then add 1.5 g of surface-activated silver nanowires (diameter: ~70 nm, length: ~40 μm), 1.5 g of surface-activated graphene, and 1.5 g of surface-activated iron oxide, and mix evenly at 15°C. Under nitrogen protection and stirring, allow the mixture to undergo condensation and cross-linking reactions at 15°C for 30 h. The resulting reactants precipitate in anhydrous ethanol, dry at 70°C, grind into powder, and pass through a 60-mesh sieve to obtain polyimide (PAA) powder. The surface activation treatment method is as follows: place the silver nanowires, graphene, and iron oxide in a muffle furnace at 400°C in an air atmosphere for 2 h.

[0050] Step 3: Install another synthesis apparatus containing a three-necked flask, a condenser, and a magnetic stirrer, and introduce nitrogen gas as an inert protective gas into it. Add 25 mL of tetrahydrofuran, 15 mL (0.37 mol) of methanol, 10 mol (5.2 g) of bisphenol A diether dianhydride (BPADA), 0.04 g of α-methylimidazole, and 1 g of polyimide acid (PAA) powder prepared in Step 2, and mix and disperse thoroughly.

[0051] Step 4: The system from Step 3 is heated to 65°C at a heating rate of 1°C / min, and then refluxed for 6 hours under nitrogen protection and stirring conditions to obtain a pale yellow transparent liquid.

[0052] Step 5: Cool the above pale yellow transparent reaction solution to 40°C.

[0053] Step 6: Add 6 mmol / L 1,3-bis(3-aminophenoxy)benzene and 4 mmol / L 4,4'-bis(4-aminophenoxy)benzene to the system from Step 5, and heat to 65°C at a rate of 1°C / min. Continue the reaction at this temperature under nitrogen protection and stirring for 2 hours.

[0054] Step 7: Add 1.5g of AK-8805 foaming agent to the system in Step 6 and disperse it evenly. Pour the resulting product into a tray, place it in a vacuum drying oven and dry it at 70℃. Grind it into powder and pass it through a 60-mesh sieve to obtain the polyimide foaming precursor material.

[0055] Step Nine: Place the polyimide foaming precursor material in an aluminum mold and gradually heat it at a rate of 1℃ / min to 80℃ and hold for 2 hours, 110℃ and hold for 2 hours, 180℃ and hold for 2 hours, 200℃ and hold for 2 hours, 250℃ and hold for 2 hours, and 300℃ and hold for 2 hours, finally obtaining a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material.

[0056] The pore structure diagram of the polyimide porous material prepared in this embodiment is shown below. Figure 2 As shown in the figure, the polyimide porous material prepared by this invention has loose and uniform pores of consistent size.

[0057] Example 2

[0058] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that: in step two, the 10 mmol / L pyromellitic dianhydride and 10 mmol / L 4,4'-diaminodiphenyl ether are replaced with 10 mmol / L bisphenol A type diether dianhydride (BPADA), 6 mmol / L 1,3'-bis(3-aminophenoxy)benzene, and 4 mmol / L 4,4'-bis(4-aminophenoxy)benzene. The other steps and conditions are the same as in Example 1.

[0059] Example 3

[0060] A method for preparing a cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that the 15 mmol / L 1,3,5-tris(4-aminophenoxy)benzene crosslinking agent in step two is replaced with 17 mmol / L tris(4-aminophenyl)amine, and the other steps and conditions are the same as in Example 1.

[0061] Example 4

[0062] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that the 10 mmol / L bisphenol A type diether dianhydride in step three is replaced with 10 mmol / L 3,3,4,4-benzophenone tetracarboxylic dianhydride, and the other steps and conditions are the same as in Example 1.

[0063] Example 5

[0064] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that in step three, 25 mL of tetrahydrofuran is replaced with 30 mL of N,N-dimethylformamide, and methanol is 25 mL. Other steps and conditions are the same as in Example 1.

[0065] Example 6

[0066] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that the temperature in step five is reduced to 20°C, while the other steps and conditions are the same as in Example 1.

[0067] Example 7

[0068] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that: in step six, the 1,3-bis(3-aminophenoxy)benzene and 4,4'-bis(4-aminophenoxy) are replaced with 10 mmol / L 4,4'-diaminodiphenyl ether; the other steps and conditions are the same as in Example 1.

[0069] Example 8

[0070] A method for preparing a cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that the mass of the foaming agent in step eight is 1.0 g, and the other steps and conditions are the same as in Example 1.

[0071] Example 9

[0072] A method for preparing a cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that the sieve aperture in steps two and seven is 100 mesh, and the other steps and conditions are the same as in Example 1.

[0073] Comparative Example 1

[0074] A method for preparing a polyimide porous material, as described in Example 1, except that steps one and two are omitted, and polyimide acid (PAA) powder is not added in step three.

[0075] Specifically as follows:

[0076] (1) Install another synthesis apparatus containing a three-necked flask, a condenser, and a magnetic stir bar, and introduce nitrogen gas as an inert protective gas into it. Add 25 mL of tetrahydrofuran, 15 mL (0.37 mol) of methanol, 10 mmol (5.2 g) of bisphenol A diether dianhydride (BPADA), and 0.04 g of α-methylimidazole, and mix thoroughly and disperse evenly.

[0077] (2) The system in step (1) was heated to 65°C at a heating rate of 1°C / min, and refluxed for 6 hours under nitrogen protection and stirring conditions to obtain a pale yellow transparent liquid.

[0078] (3) Cool the above reaction solution to 40°C.

[0079] (4) Add 6 mmol / L 1,3-bis(3-aminophenoxy)benzene and 4 mmol / L 4,4'-bis(4-aminophenoxy)benzene to the system in step (3), and heat to 65°C at a heating rate of 1°C / min. Continue the reaction for 2 h at this temperature under nitrogen protection and stirring.

[0080] (5) Add 1.5g of AK-8805 foaming agent to the system in step (4) and disperse it evenly. Pour the obtained product into a tray, put it into a vacuum drying oven and dry it at 70℃. Grind it into powder and pass it through a 60-mesh sieve to obtain polyimide foaming precursor material.

[0081] (6) The polyimide foaming precursor material was placed in an aluminum mold and gradually heated to 80℃ for 2 hours at a heating rate of 1℃ / min, then held at 110℃ for 2 hours, 180℃ for 2 hours, 200℃ for 2 hours, 250℃ for 2 hours, and 300℃ for 2 hours to obtain the polyimide porous material.

[0082] Comparative Example 2

[0083] A method for preparing a polyimide porous material, as described in Example 1, except that the crosslinking agent 15 mmol / L 1,3,5-tris(4-aminophenoxy)benzene in step two is removed, while the other steps and conditions remain unchanged.

[0084] Comparative Example 3

[0085] A method for preparing a polyimide porous material, as described in Example 1, except that: no crosslinking agent is added in step two; 15 mmol / L of 1,3,5-tris(4-aminophenoxy)benzene crosslinking agent is added in step three; other steps and conditions remain unchanged.

[0086] Comparative Example 4

[0087] A method for preparing a polyimide porous material, as described in Example 1, differs in that the reaction of dianhydride and lower fatty alcohol in step three is omitted, and the material is directly reacted with diamine; the other steps remain unchanged. Details are as follows:

[0088] Step 1: Install the three-necked flask, condenser, and magnetic stirrer, and introduce nitrogen as an inert protective gas.

[0089] Step 2: Add 10 mmol / L pyromellitic dianhydride, 15 mL N,N-dimethylformamide, 10 mmol / L 4,4-diaminodiphenyl ether, and 15 mmol / L 1,3,5-tris(4-aminophenoxy)benzene to the mixture from Step 1, and mix thoroughly and disperse evenly. Then add 1.5 g of surface-activated silver nanowires (diameter: ~70 nm, length: ~40 μm), 1.5 g of surface-activated graphene, and 1.5 g of surface-activated iron oxide, and mix evenly at 15°C. Under nitrogen protection and stirring, allow the mixture to undergo condensation and cross-linking reactions at 15°C for 30 h. The resulting reactants precipitate in anhydrous ethanol, dry at 70°C, grind into powder, and pass through a 60-mesh sieve to obtain polyimide (PAA) powder. The surface activation treatment method is as follows: place the silver nanowires, graphene, and iron oxide in a muffle furnace at 400°C in an air atmosphere for 2 h.

[0090] Step 3: Install another synthesis apparatus containing a three-necked flask, a condenser, and a magnetic stirrer, and introduce nitrogen gas as an inert protective gas into it. Add 25 mL of tetrahydrofuran, 10 mmol of bisphenol A diether dianhydride (BPADA), 0.04 g of α-methylimidazole, 6 mmol of 1,3-bis(3-aminophenoxy)benzene, 4 mmol of 4,4'-bis(4-aminophenoxy)bidioxanone, and 1 g of polyimide acid (PAA) powder prepared in Step 2. Mix and disperse evenly, and then heat to 65 °C at a heating rate of 1 °C / min. Continue the reaction at this temperature under nitrogen protection and stirring conditions for 6 h.

[0091] Step 4: Cool the above reaction solution to 40°C.

[0092] Step 5: Add 1.5g of AK-8805 foaming agent to the system in Step 4 and disperse it evenly. Pour the resulting product into a tray, place it in a vacuum drying oven and dry it at 70℃. Grind it into powder and pass it through a 60-mesh sieve to obtain the precursor powder.

[0093] Step 7: Place the obtained powder into an aluminum mold and gradually heat it at a rate of 1℃ / min to 80℃ and hold for 2 hours, 110℃ and hold for 2 hours, 180℃ and hold for 2 hours, 200℃ and hold for 2 hours, 250℃ and hold for 2 hours, and 300℃ and hold for 2 hours to finally obtain a polyimide porous material.

[0094] Comparative Example 5

[0095] A method for preparing a polyimide porous material, as described in Example 1, except that the ratio of light-absorbing phase, conductive phase, and magnetic phase is 1:3:1, the total amount of added phase is 4.5g, and other steps and conditions remain unchanged.

[0096] Comparative Example 6

[0097] A method for preparing a polyimide porous material, as described in Example 1, except that: an additive phase is added to the preparation of the polyester ammonium salt intermediate (step three);

[0098] The specific steps are as follows:

[0099] Step 1: Install the three-necked flask, condenser, and magnetic stirrer, and introduce nitrogen as an inert protective gas.

[0100] Step 2: Add 10 mmol / L pyromellitic dianhydride, 15 mL N,N-dimethylformamide, 10 mmol / L 4,4-diaminodiphenyl ether, and 15 mmol / L 1,3,5-tris(4-aminophenoxy)benzene to Step 1, and mix thoroughly and disperse evenly; under nitrogen protection and stirring, allow the polycondensation and crosslinking reaction to occur at 15°C for 30 h; precipitate the resulting reactant in anhydrous ethanol, dry at 70°C, grind into powder, and pass through a 60-mesh sieve to obtain polyimide (PAA) powder.

[0101] Step 3: Install another synthesis apparatus containing a three-necked flask, a condenser, and a magnetic stirrer, and introduce nitrogen as an inert protective gas. Add 25 mL of tetrahydrofuran, 15 mL (0.37 mol) of methanol, 10 mmol (5.2 g) of bisphenol A diether dianhydride (BPADA), 0.04 g of α-methylimidazole, and 1 g of polyimide acid (PAA) powder prepared in Step 2, and mix thoroughly and disperse evenly. Then add 1.5 g of surface-activated silver nanowires (diameter: ~70 nm, length: ~40 μm), 1.5 g of surface-activated graphene, and 1.5 g of surface-activated iron oxide, and stir at room temperature to mix thoroughly and disperse evenly. The surface activation treatment method is as follows: place the silver nanowires, graphene, and iron oxide in a muffle furnace at 400 °C in an air atmosphere for 2 h.

[0102] Steps four through nine are the same as in Example 1, and finally a polyimide porous material is obtained.

[0103] Comparative Example 7

[0104] A method for preparing a cross-linked polyimide macromolecular chain interpenetrating multi-stimulus responsive shape memory polyimide porous material is as described in Example 1, except that the silver nanowires, graphene, and iron oxide in step two are not subjected to surface activation treatment, while the other steps and conditions are the same as in Example 1.

[0105] Experimental Example 1

[0106] The polyimide porous materials prepared in the examples and comparative examples were tested for thermal insulation performance, flame retardancy performance, sound absorption performance, thermal stimulus response characteristics, bulk density and high temperature resistance. The test data are shown in Table 1 below.

[0107] Table 1. Thermal insulation, flame retardancy, sound absorption, bulk density, high temperature resistance, glass transition temperature, compressive strength, and thermal response characteristics of polyimide porous materials.

[0108]

[0109] Note: The test method for thermal stimulation response characteristics is the same as in Experiment 2.

[0110] Compared to the performance of the polyimide porous material in Comparative Example 3, the cross-linked polyimide macromolecular chain in Example 1 has higher rigidity. Therefore, among polyimide porous materials, Example 1 exhibits better thermal stability, compressive strength, shape recovery rate, thermal insulation, and sound absorption performance, and is also lighter. Compared to the performance of the polyimide porous material in Comparative Example 2, Example 1 has an interpenetrating and physically entangled three-dimensional chemically cross-linked network structure and a thermoplastic three-dimensional shape memory polyimide network structure formed by physical entanglement. In contrast, Comparative Example 2 has two types of physically entangled three-dimensional polyimide network structures that interpenetrate and entangle. Therefore, Example 1 has superior thermal insulation performance, flame retardant performance, sound absorption performance, stimulus response characteristics, high temperature resistance, and lower density. The interpenetrating structure of rigid cross-linked polyimide macromolecular chains within thermoplastic shape memory polyimide porous materials effectively improves compressive strength, thermal stability, shape recovery rate, and promotes the formation of uniform cells, while reducing the thermal conductivity and bulk density of the polyimide porous material and enhancing its sound absorption performance. However, the rigidity of the structure in the thermoplastic shape memory polyimide porous material cannot be further improved compared to Example 1, possibly because the higher rigidity of the molecular chain structure makes the polyimide porous material more brittle, leading to a decrease in compressive strength. In addition, unsuitable cross-linking agents with rigid structures, the type and content of organic solvents, temperature, the presence or absence of surface treatment of the added phases, and the ratio between the added phases all affect the performance of the polyimide porous material.

[0111] Experimental Example 2

[0112] The shape memory function of the polyimide porous material prepared in Example 1 was tested.

[0113] The testing method is as follows:

[0114] Polyimide porous material was placed in an oven at a temperature 10°C above its glass transition temperature. After the polyimide porous material softened completely, pressure was applied directly above it to compress it, and the height L of the compressed polyimide porous material was recorded. The material was then removed from the oven and cooled for 10 minutes under continuous pressure, and the height L' at this time was recorded. After removing the external pressure, the compressed and deformed polyimide porous material was placed back in the oven at the above temperature, or irradiated with a voltage of 3–15V, or under a UV lamp with a power of 5–100W, or placed in a magnetic field with an alternating magnetic field of 20–50kHz. The recovery height and recovery time of the polyimide porous material were observed and recorded, and the shape recovery rate of the polyimide porous material was calculated to verify its multi-stimulus response characteristics.

[0115] Test results under heat stimulation are as follows Figure 1 As shown, Figure 1 (a) shows the original shape of the polyimide porous material. Figure 1 (b) is the shape of compression deformation. Figure 1 (c) shows the shape after shape recovery under the above thermal stimulation. The compressed polyimide porous material can completely recover to its original initial height within 30 seconds under thermal stimulation.

[0116] The polyimide porous material prepared in Example 1 of this invention can completely recover to its original height after being irradiated with 50W ultraviolet light for 20s, or with a 3V voltage for 10s, or in an alternating magnetic field of 30kHz for 30s, demonstrating excellent stimulus response characteristics.

Claims

1. A method for preparing a cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus response shape memory polyimide porous material, comprising the steps of: (1) dispersing a dianhydride a, a diamine a and a cross-linking agent in an organic solvent a, adding an optical absorption phase, a conductive phase and a magnetic phase, mixing uniformly, and obtaining a polyimide acid (PAA) through a reaction; the diamine a is 4, 4-diamino diphenyl ether; the dianhydride a is pyromellitic dianhydride; the cross-linking agent is one or a combination of more than two of tri (4-aminophenyl) amine, 4, 4' 4''-triaminotriphenylamine, 1, 3, 5-tri (4-aminophenoxy) benzene, acetylenic aniline or 2, 4, 6-tri (4-aminophenyl) -1, 3, 5-triazine; the optical absorption phase is one or a combination of more than two of carbon nanotubes or graphene; the conductive phase is one or a combination of more than two of carbon black, nano silver particles, nano gold particles or silver nanowires; the magnetic phase is one or a combination of more than two of ferroferric oxide, magnetite, nickel powder, iron-cobalt alloy or nickel-aluminum alloy; the mass ratio of the optical absorption phase, the conductive phase and the magnetic phase is 1: 1-2: 1; the optical absorption phase, the conductive phase and the magnetic phase all need to be surface-activated before use, and the surface-activation method is as follows: the optical absorption phase, the conductive phase and the magnetic phase are respectively treated at 400℃ for 2-4 h in an air atmosphere; the total mass ratio of the dianhydride a and the optical absorption phase, the conductive phase and the magnetic phase is 1: 1-3; (2) dissolving the polyimide acid (PAA) obtained in step (1) in an organic solvent b, adding a catalyst, a dianhydride b and a lower aliphatic alcohol, and obtaining an esterified dianhydride through a reaction of the dianhydride b and the lower aliphatic alcohol; adding a diamine b, and obtaining a polyester ammonium salt intermediate product through a reaction of the esterified dianhydride and the diamine b; adding a foam stabilizer and mixing uniformly to obtain a polyimide foaming precursor material; and obtaining a cross-linked polyimide macromolecular chain structure interpenetrating multi-stimulus response shape memory polyimide porous material through a thermal imide ring-opening reaction of the polyimide foaming precursor material; the catalyst is one or a combination of more than two of α-methyl imidazole, 1-H-3-methyl imidazole chloride, 2-ethyl-4-methyl imidazole, 2-cyanomethyl benzimidazole, 1-hexyl-3-methyl imidazole chloride, 1-butyl-3-methyl imidazole chloride, 2-methyl imidazole, 3-methyl imidazole, 4-methyl imidazole and 5-methyl imidazole; the dianhydride b is a bisphenol A type diether dianhydride or 3, 3, 4, 4, -benzophenone tetracarboxylic dianhydride; the lower aliphatic alcohol is methanol; the diamine b is a combination of 4, 4-diamino diphenyl ether or 1, 3-bis (3-aminophenoxy) benzene and 4, 4'-bis (4-aminophenoxy) biphenyl, and the molar ratio of 1, 3-bis (3-aminophenoxy) benzene and 4, 4'-bis (4-aminophenoxy) biphenyl is 1.4-1.6: 1; the foam stabilizer is one or a combination of more than two of silicone oil, cellulose, dodecyl dimethyl amine oxide, fatty alcohol polyoxyethylene ether sodium sulfate or α-alkenyl sulfonic acid sodium; and the mass ratio of the foam stabilizer and the dianhydride b is 0.19-0.89:

1. ​ ​ ​ ​ 2. The method of claim 1, wherein the crosslinking of the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material is performed by a process selected from the group consisting of a thermal process, a photo process, a chemical process, and a combination thereof. In steps (1) and (2), the organic solvent a and the organic solvent b are independently selected from one or a combination of two or more of tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone or dimethyl sulfoxide.

3. The method of claim 2, wherein the crosslinking of the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material is performed by irradiation of electron beams. The organic solvent a is N,N-dimethylformamide, and the organic solvent b is tetrahydrofuran or N,N-dimethylformamide.

4. The method of claim 1, wherein the crosslinking of the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material is performed by a process comprising: (a) dissolving the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material in a solvent; (b) adding a crosslinking agent to the solution; and (c) removing the solvent from the solution. In step (1), one or more of the following conditions is included: i. the cross-linking agent is tris(4-aminophenyl)amine or 1,3,5-tris(4-aminophenoxy)benzene; ii. the molar ratio of the dianhydride a, the diamine a and the cross-linking agent is 1-1.2:1:1-3; iii. the molar amount of the dianhydride a and the volume of the organic solvent a are in a ratio of 0.05-1 mol / L.

5. The method of claim 1, wherein the crosslinking of the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material is performed by a process comprising: (a) dissolving the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material in a solvent; (b) adding a crosslinking agent to the solution; and (c) removing the solvent from the solution. In step (1), one or more of the following conditions is included: i. the reaction temperature is 0-30°C, the reaction time is 10-36 h, and the reaction is carried out under inert gas protection and stirring; ii. the reaction product obtained by reaction is precipitated by anhydrous ethanol, dried, ground, and sieved through a 60-100 mesh sieve to obtain a SMPI precursor material-polyimide acid (PAA) powder having a cross-linked network structure.

6. The method of claim 1, wherein the crosslinking of the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material is performed by a process comprising: (a) dissolving the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material in a solvent; (b) adding a crosslinking agent to the solution; and (c) removing the solvent from the solution. In step (2), one or more of the following conditions is included: i. the mass of the catalyst is 0.1-2% of the mass of the dianhydride b; ii. the molar ratio of the dianhydride b and the lower aliphatic alcohol is 1:30-70; iii. the molar amount of the dianhydride b and the volume of the organic solvent b are in a ratio of 0.1-1 mol / L; iv. the mass ratio of the dianhydride b and the polyimide acid (PAA) is 3-10:1; v. the reaction temperature of the dianhydride b and the lower aliphatic alcohol is 60-70°C, the reaction time is 4-8 h, the heating rate is 0.5-5°C / min, and the reaction is carried out under inert gas protection and stirring; vi. the dianhydride b and the lower aliphatic alcohol are reacted to obtain an esterified dianhydride, and after cooling to 20-40°C, the next step is performed; vii. the molar ratio of the dianhydride b and the diamine b is 0.94-1.2:1; viii. the reaction temperature of the esterified dianhydride and the diamine b is 60-70°C, the reaction time is 1-3 h, and the heating rate is 0.5-5°C / min, and the reaction is carried out under inert gas protection and stirring.

7. The method of claim 1, wherein the crosslinking of the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material is performed by a process comprising: (a) dissolving the polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material in a solvent; (b) adding a crosslinking agent to the solution; and (c) removing the solvent from the solution. In step (2), one or more of the following conditions is included: i. after adding a foam stabilizer and uniformly mixing, drying, grinding and sieving through a 60-100 mesh sieve to obtain a polyimide foaming precursor material; ii. the thermal imide ring-opening reaction conditions are as follows: gradually increasing the temperature to 80°C, 110°C, 180°C, 200°C, 250°C and 300°C at a heating rate of 1-2°C / min, and maintaining each temperature for 1-2 h.

8. The crosslinked polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material prepared by the method of any one of claims 1-7, characterized in that, The polyimide porous material can realize shape recovery under the stimulation of light, electricity, magnetism or heat.

9. The crosslinked polyimide macromolecular chain structure interpenetrating multi-stimuli responsive shape memory polyimide porous material according to claim 8, characterized in that, The thermal conductivity of the polyimide porous material is 0.03-0.05 W / m*K, the flame retardant performance is that the oxygen index is >27, the sound absorption performance is that the noise reduction coefficient is >0.21, the stimulus response characteristic is that the recovery rate is 97-100%, the bulk density is 5-8 Kg / m 3 , and the thermal decomposition temperature is 530-600℃.

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