A polypyrrole reinforced polyimide aerogel and a preparation method and application thereof

Abstract

The application belongs to the technical field of aerogels, and particularly relates to a polypyrrole reinforced polyimide aerogel and a preparation method and application thereof. The application directly uses a macroscopic ice block as a hard template for preparation of polypyrrole, and through introduction of a cyclic molecule hydroxypropyl-beta-cyclodextrin with a hydrophilic-hydrophobic dual function as an array growth aid, a polypyrrole array with a self-supporting structure is prepared. The array is in-situ compounded with polyamic acid, and through freeze drying and thermal imidization, a polypyrrole reinforced polyimide aerogel is prepared. The aerogel has high mechanical strength and high conductivity, and can be used as a conductive reinforcing filler for polyurethane in the technical field of 3D printing, solves the compatibility problem of the conductive polypyrrole and a polyurethane resin matrix, and further improves the mechanical properties of the polyurethane on the basis of improving the antistatic performance of the polyurethane.

Description

Technical Field

[0001] This invention belongs to the field of aerogel technology, specifically relating to a polypyrrole-reinforced polyimide aerogel, its preparation method, and its application. Background Technology

[0002] 3D printing technology, as a revolutionary manufacturing method, exhibits numerous significant advantages over traditional manufacturing techniques. Traditional manufacturing techniques are often limited by mold preparation and processing methods, resulting in high manufacturing costs, long production cycles, and difficulty in achieving free design of product structures. 3D printing, with its unique layer-by-layer manufacturing method, enables controlled material arrangement during the printing process, effectively solving these bottlenecks. In practical applications, 3D printing technology can address the high costs of traditional processes through small-batch customized production, freeing users from the constraints of structural design. The most crucial aspect of 3D printing is the preparation of the printing material. Thermoplastic engineering plastics do not undergo chemical bonding during 3D printing, allowing for recycling, melting, and reuse, making them the most common materials used in 3D printing.

[0003] Polyurethane is a class of polymeric materials prepared through chemical reactions from raw materials such as isocyanates, polyols, and chain extenders. Its unique molecular structure and tunable chemical composition endow it with an extremely wide range of performance characteristics. Since the industrial production of polyurethane, its elastomer form has established an important position due to its unique performance advantages. This material combines the high elasticity of rubber with the high strength of plastics, and through flexible molecular design, it can meet the needs of different application scenarios. It is now widely used in key fields such as automobile manufacturing, medical devices, sports equipment, and aerospace. The core feature of polyurethane lies in its microphase separation structure. This interpenetrating network structure ensures both high load-bearing capacity and excellent deformation recovery properties. Precise control of this special morphology allows polyurethane to maintain stable mechanical properties over a wide temperature range, making it a polymeric system with high application value in the field of engineering materials. The hard segments of polyurethane consist of rigid urethane units formed by the stepwise polymerization of isocyanates and chain extenders, forming a physical cross-linked network through multiple hydrogen bonds; the soft segments consist of long chains of polyols with conformational freedom, imparting elastic response characteristics to the material through chain segment movement. This combination of rigidity and flexibility allows the material to effectively disperse stress while resisting permanent deformation. By adjusting the ratio of hard to soft segments, selecting different types of polyols (such as polyester, polyether, and polycarbonate types), and controlling the synthesis process, it is possible to precisely customize the crystallinity, crosslinking density, and microstructure of the material, thereby obtaining a continuous performance spectrum from ultra-soft elastomers to rigid structural components.

[0004] Currently, the development of 3D printing polyurethane materials mainly focuses on optimizing the material's mechanical properties; however, research on the antistatic properties of 3D printing polyurethane materials is still lacking. Existing technologies mostly employ the addition of various conductive polymer fillers to address the poor antistatic properties of polyurethane. However, the interfacial bonding force between conductive polymer fillers and polyurethane is low, making direct printing through blending difficult. Summary of the Invention

[0005] The purpose of this invention is to provide a polypyrrole-reinforced polyimide aerogel, its preparation method, and its application. Macroscopic ice blocks are directly used as a hard template for polypyrrole preparation. A self-supporting polypyrrole nanosheet array is prepared by introducing hydroxypropyl-β-cyclodextrin, a cyclic molecule with both hydrophilic and hydrophobic functions, as an array growth aid. This array is then in-situ composited with polyamic acid to prepare the polypyrrole-reinforced polyimide aerogel. This aerogel is used as a conductive reinforcing filler for polyurethane in the field of 3D printing technology, solving the compatibility problem between conductive polypyrrole and the polyurethane resin matrix. In addition to improving the antistatic properties of polyurethane, its mechanical properties are further enhanced.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0008] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the ice surface, then add pyrrole monomer, and let it stand to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is (1-3):1;

[0009] (2) Add an acid solution containing an oxidant to the dispersion, and after the reaction, wash and dry to obtain a self-supporting polypyrrole nanoarray;

[0010] (3) Polyamic acid powder was prepared by precipitation method using dianhydride monomer and diamine monomer as raw materials;

[0011] (4) Add polyamic acid powder, tertiary amine compound, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation;

[0012] (5) Dry the polyamic acid hydrogel and heat imidize it to obtain polypyrrole-reinforced polyimide aerogel.

[0013] Polypyrrole (PP) is a heterocyclic polymer formed by the polymerization of pyrrole monomers. Its basic structural unit is the pyrrole ring, and each pyrrole molecule consists of one nitrogen atom and four carbon atoms. During polymerization, pyrrole monomers are interconnected through α-carbon atoms, forming linear or branched structures. This structure endows PPI with unique physicochemical properties. In the PPI molecule chain, the pyrrole rings are connected through α-carbon atoms, forming a continuous conjugated π-electron system. This conjugated structure allows electrons to move freely within the polymer chain, thus giving PPI excellent electrical conductivity. Furthermore, the conductivity of PPI can be further modulated by doping. However, PPI contains rigid groups within its molecule, making it difficult to melt and dissolve, thus hindering its processing. Current technologies mostly use one-dimensional PPI nanoparticles or two-dimensional PPI nanosheets as conductive fillers in polyurethane. However, PPI nanoparticles or PPI nanosheets are difficult to disperse in molten resin, making it difficult to effectively construct a spatial structure and affecting the formation of the conductive network. On the other hand, adding large amounts of PPI can lead to a decrease in the mechanical properties of the composite material.

[0014] In previous work (CN121182184A, CN121203232A, etc.), the inventors prepared curved polyaniline using ice micropowder as a template and used curved polyaniline as a conductive filler for polyurethane. However, this process requires the preparation of micron-sized ice powder, which is energy-intensive. Furthermore, the polymerization of aniline is carried out in an aqueous solution of ice micropowder. Due to the limitations of the size and morphology of ice micropowder, it is impossible to prepare curved polyaniline on a large scale, making it difficult to promote its industrial use. More importantly, two-dimensional nanosheets have a large specific surface area and high surface energy, and tend to spontaneously aggregate to reduce energy. Under external forces, they are prone to slippage or debonding from the resin matrix, resulting in the destruction of conductive pathways. At the same time, the two-dimensional sheet structure is difficult to form an effective conductive network at low concentrations; at high concentrations, it will damage the film-forming properties of polyurethane, making the material brittle and rough, affecting the improvement of 3D printed product performance.

[0015] To further improve the electrical and mechanical properties of polypyrrole materials, this invention directly uses macroscopically structured ice as a hard template for polypyrrole preparation, and introduces hydroxypropyl-β-cyclodextrin, a cyclic molecule with both hydrophilic and hydrophobic functions, as an array growth aid. A self-supporting polypyrrole nanosheet array is prepared via a one-step polymerization method. The type of ice is not particularly limited, as long as it can provide a large, smooth planar structure to facilitate the formation of a thin liquid film from the mixed solution.

[0016] In traditional particulate-filled systems, conductive pathways rely on the physical contact between filler particles or sheets. Only when the filler content reaches the percolation threshold and the distance between particles or sheets is sufficiently close can a conductive network be formed throughout the entire material. In contrast to zero-dimensional polypyrrole nanoparticles or nanosheets, the array structure itself is a pre-constructed continuous conductive pathway, independent of random contact between fillers. Even at low addition levels, as long as the network structure remains intact in the resin, electrons can be transported along the network skeleton over long distances. During deformation, the array can adapt to deformation through bending, twisting, and sliding of the skeleton, rather than breaking. Even if local microstructural reorganization occurs, the overall conductive pathway can still be maintained. Furthermore, the network structure of the self-supporting polypyrrole nanosheet array can interpenetrate with the resin matrix, uniformly transfer stress, inhibit crack propagation, and easily form continuous conductive pathways, achieving high conductivity with low addition levels. Among these, the three-dimensional polypyrrole array, as a continuous reinforcing phase, forms an interpenetrating network structure in the resin matrix, which can efficiently conduct electrons and transfer loads through mechanical interlocking and interfacial bonding.

[0017] In this invention, ice acts as a macroscopic hard template. Compared to the ice micropowder used in patent technologies CN121182184A and CN121203232A, it has no special requirements for structure and morphology, only needing to provide a large plane, making it easier to prepare on a large scale. Typically, existing technologies for preparing conductive array structures require two-dimensional materials such as graphene, graphene oxide, and boron nitride as a substrate, utilizing the surface provided by inorganic two-dimensional field materials as a reaction substrate, on which conductive polymer arrays are grown. On the one hand, these technologies not only involve the preparation of complex substrates, but the conductive polymer arrays grown on these substrates are organic materials, resulting in low interaction with the inorganic substrate, easy detachment, and poor structural stability. On the other hand, the substrates in these technologies cannot be removed, preventing the preparation of simple conductive polymer arrays.

[0018] This invention uses ice as a hard template, where pyrrole monomers self-assemble on the ice surface under the action of hydroxypropyl-β-cyclodextrin to form an array structure. The macroscopic ice structure is not only easy to prepare but also easy to remove. After the reaction is complete, the ice substrate can be removed simply by heating, without damaging the array structure.

[0019] Hydroxypropyl-β-cyclodextrin acts as a molecular template in the early stages of polymerization. Unlike typical cyclodextrins, hydroxypropyl-β-cyclodextrin possesses a hydrophobic cavity and a hydrophilic shell (hydroxypropyl substituents). In the aqueous phase, hydrophobic pyrrole monomers tend to enter the hydrophobic cavity of hydroxypropyl-β-cyclodextrin, forming inclusion complexes; furthermore, the hydroxyl groups on hydroxypropyl-β-cyclodextrin readily form hydrogen bonds with pyrrole monomers. This inclusion and hydrogen bonding anchors the pyrrole monomers to the cyclodextrin molecules, preventing their disordered migration in solution. The pyrrole molecules are confined around the cavity, and their polymerization reaction can only proceed along the cavity opening, inducing polymer growth. The arrangement of pyrrole molecules within the cyclodextrin lays the molecular foundation for the subsequent formation of a regular three-dimensional array structure.

[0020] Dispersing the reaction solution onto the ice surface effectively constructs a solid (ice)-liquid (reaction solution) two-phase interface. The ice surface provides a rigid, flat two-dimensional substrate at extremely low temperatures. In low-temperature environments, the viscosity of water increases significantly, and its molecular diffusion ability weakens. Furthermore, the ice surface typically exhibits microscopic irregularities and grain boundary structures. These surface defects and grain boundaries act as physical barriers during liquid film spreading. The reaction solution also contains solutes such as hydroxypropyl-β-cyclodextrin, pyrrole monomers, and oxidants, the presence of which further influences the spreading behavior of water. Their adsorption further reduces the wettability of the ice surface, helping the liquid film maintain a stable state within a confined area. Forming a liquid film of a certain thickness and limited size on the ice surface ensures that the polymerization reaction can proceed within a confined space, thereby inducing two-dimensional anisotropic growth and ultimately forming an ordered array structure with self-supporting capabilities.

[0021] The reaction liquid spreads into a thin liquid film on the ice surface, greatly restricting the physical space of the polymerization reaction (from a three-dimensional bulk phase to a two-dimensional plane). Within the thin liquid film, the hydroxypropyl-β-cyclodextrin-pyrrole inclusion complex, driven by the minimization of interfacial energy, tends to accumulate and oriented at the ice-liquid interface (solid substrate) or liquid-gas interface (surface), with its hydrophilic shell facing outward and its hydrophobic cavities facing in the same direction. This arrangement forces the polymerization of pyrrole monomers along specific crystal planes, avoiding random, isotropic homogeneous nucleation, suppressing disordered three-dimensional aggregation in the bulk phase, and thus promoting the lateral growth of the lamellar array.

[0022] Moreover, the surface of ice is not perfectly flat, but rather has micron / nanoscale grain boundaries and steps. When the reaction solution freezes or partially freezes on the ice surface, the hydroxypropyl-β-cyclodextrin and pyrrole complex is repelled and enriched at the grain boundaries between ice crystals. These grain boundaries form a natural array of nanochannels. When the polymerization reaction occurs within these confined channels, polypyrrole is forced to grow along the direction of the channels (i.e., the orientation of the ice crystals), forming the initial "array" prototype. During polymerization, the ice is not only a low-temperature substrate but also a dynamic sacrificial template. The channels formed by the tiny cracks on the ice surface are interconnected, forming a continuous network template. Under the action of hydroxypropyl-β-cyclodextrin, polypyrrole grows along the walls of these channels, forming a continuous three-dimensional network that replicates the gaps between ice crystals; different polypyrrole chains are interconnected through the physical entanglement or hydrogen bond network of cyclodextrin molecules, enhancing the interlayer bonding strength. When the ice melts, the remaining polypyrrole network (which can also be directly removed from the ice surface) is a three-dimensional nanosheet array structure with self-supporting capabilities.

[0023] In their previous work, the inventors directly used polypyrrole nanosheet arrays as conductive fillers for polyurethane. Polypyrrole, as a conductive polymer, has polar properties that differ somewhat from the polyurethane matrix. Direct blending often results in weak bonding at the interface, easily leading to microscopic defects or voids. These defects not only hinder carrier migration but also become stress concentration points, degrading the mechanical properties of the composite material. Furthermore, in the shear flow field of 3D printing, polypyrrole sheets are prone to migration and aggregation, resulting in uneven conductivity across different regions of the printed part. In contrast, polyimide aerogel possesses extremely low density and extremely high specific surface area. This means that, with the same mass fraction added, the aerogel occupies a much higher volume fraction in the polyurethane than the nanosheet array, enabling the construction of a conductive network at a lower mass cost, thus keeping the increase in matrix viscosity within an acceptable range. Furthermore, the polyimide aerogel framework itself possesses excellent mechanical strength, flexibility, and outstanding thermal stability. When dispersed in polyurethane as a filler, it can simultaneously exert a fiber-reinforcing effect, improving the tensile strength and tear resistance of the composite material. Moreover, under high-temperature or frictional conditions, the polyimide framework can provide effective thermal protection for polypyrrole, delaying the degradation of conductivity. This structural design achieves a synergistic improvement in conductivity, mechanical reinforcement, and thermal stability, which cannot be achieved by directly adding a single polypyrrole nanosheet array. Simultaneously, by introducing polyimide aerogel as an intermediate carrier, polyimide and polyurethane, both being polar polymers, exhibit good compatibility and interfacial affinity, forming strong physical entanglements or chemical bonds. Polypyrrole adheres to the polyimide framework through a strong coating layer, transforming the previously poorly contacted polypyrrole-polyurethane interface into a superior polyimide-polyurethane interface, significantly reducing interfacial defects and contact resistance. Meanwhile, the prepared polypyrrole-reinforced polyimide aerogel was pulverized and mixed with polyurethane material for 3D printing. The aerogel particles served as the dispersed phase in the polyurethane, and their stability during the printing process was much higher than that of nanoscale fillers, which could ensure the consistency of the microstructure and conductivity of the printed parts.

[0024] Furthermore, the standing time in step (1) is 5-10 minutes. By standing for a period of time, hydroxypropyl-β-cyclodextrin can better bind to the ice template through hydrogen bonding or electrostatic interactions.

[0025] Furthermore, in step (1), the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is (1.5-2.5):1. Specifically, it can be 1.5:1, 1.7:1, 1.9:1, 2.1:1, 2.3:1, or 2.5:1. Insufficient hydroxypropyl-β-cyclodextrin will not fully function as a template agent, resulting in an incomplete array structure. Excessive hydroxypropyl-β-cyclodextrin leads to a high nucleation density, preventing polypyrrole from fully expanding in the two-dimensional direction. Simultaneously, during polymerization, hydroxypropyl-β-cyclodextrin tightly binds to the polypyrrole network through hydrogen bonds and physical entanglement. When the amount of hydroxypropyl-β-cyclodextrin is appropriate, some of it can be removed during washing, and the remaining small amount can act as a structural reinforcing agent, strengthening the connection between layers through hydrogen bond bridging. However, when hydroxypropyl-β-cyclodextrin is used in excess, a large number of hydroxypropyl-β-cyclodextrin molecules are physically embedded in the polypyrrole network and cannot be completely removed by conventional washing. These residual insulating molecules are distributed on the surface and between the polypyrrole sheets. On the one hand, they act as physical barriers, hindering electronic transitions between polypyrrole chains and charge transport between sheets, increasing contact resistance. On the other hand, the numerous hydroxyl groups on the hydroxypropyl-β-cyclodextrin molecules can form hydrogen bonds with the positive charge centers on the polypyrrole chains, partially shielding the effect of dopants and reducing the effective doping degree. Therefore, in the process optimization of preparing self-supporting polypyrrole arrays by ice-surface polymerization, the amount of hydroxypropyl-β-cyclodextrin needs to be controlled to avoid performance degradation caused by excessive dosage while ensuring sufficient template coverage and structure guidance.

[0026] The method of adding the reaction raw materials is not particularly limited and can be common in the field, such as dripping, pouring, or coating. The reason for first dispersing the hydroxypropyl-β-cyclodextrin solution onto the ice surface is that the ice template surface contains a large number of hydroxyl groups, which have strong hydrogen bond donor and acceptor capabilities. The outer shell of the hydroxypropyl-β-cyclodextrin molecule is rich in hydroxypropyl groups and unsubstituted hydroxyl groups, which can form a dense hydrogen bond network with the hydroxyl groups on the ice surface. This hydrogen bonding firmly anchors the hydroxypropyl-β-cyclodextrin molecules to the ice-liquid interface, while also connecting the hydroxypropyl-β-cyclodextrin molecules to each other, forming an ordered molecular layer. Orienting the hydrophobic cavities of the hydroxypropyl-β-cyclodextrin provides an ideal molecular platform for the subsequent pre-organization of pyrrole monomers and also provides ordered inclusion sites for the pyrrole monomers, controlling the thickness and interlayer spacing of the polypyrrole nanosheets. Then, pyrrole monomers are added, which are captured by the anchored hydroxypropyl-β-cyclodextrin, achieving in-situ pre-organization. After the addition of ammonium persulfate, the polymerization reaction occurs on the surface of the template layer. At the same time, the introduction of hydroxypropyl-β-cyclodextrin also promotes the regularity of the polypyrrole structure, greatly improving the thermal stability of polypyrrole and making it more suitable for resin processing.

[0027] Furthermore, in step (2), the oxidant is one or more of ammonium persulfate, potassium persulfate, sodium persulfate, ferric chloride, and hydrogen peroxide. Specifically, ammonium persulfate can be used as an initiator. Ammonium persulfate acts as a single-electron oxidant, initiating the oxidative polymerization of pyrrole; simultaneously, the sulfate or bisulfate ions generated from the decomposition of ammonium persulfate also have a doping effect, improving the conductivity of polypyrrole. The acid solution containing the oxidant is added dropwise to the dispersion, ultimately forming a mixed liquid film on the surface of the ice block, where the pyrrole monomers complete the polymerization reaction. Specifically, the ice block is placed horizontally to facilitate the stability of the liquid film. The method of adding the oxidant is not particularly limited; however, it can be added in a dispersed manner according to the size of the dispersion film containing the monomers to better promote the dispersion of the substances.

[0028] Further, in step (2), the mass ratio of the oxidant to the pyrrole monomer is (1-5):1. Specifically, it can be 1:1, 2:1, 3:1, 4:1, or 5:1. In particular, the mass ratio of the oxidant to the pyrrole monomer is (2-4):1 or (2.5-3.5):1. After the acid solution containing the oxidant is added dropwise to the dispersion to form a mixed solution, the reaction can begin. The concentration of the mixed solution is not particularly limited, but in particular, the concentration of pyrrole monomer in the mixed solution is 0.1-1.5 g / 100 ml. Specifically, in this invention, the concentration of pyrrole monomer does not need to be precisely controlled and can be adjusted to approximately 0.5-1.1 g / 100 ml by using deionized water. A lower monomer concentration can prevent the overgrowth of the self-supporting polypyrrole structure and improve the regularity of the array structure. Moreover, the reaction system of this invention uses water as a solvent, which facilitates the recovery and reuse of unreacted monomers and other raw materials in the mixed solution, effectively reducing the cost of industrial production. An appropriate amount of oxidant can effectively promote the polymerization of pyrrole monomers and improve the regularity of polypyrrole nanosheet arrays. However, when the amount of oxidant is too high, the excessively high core density restricts the full expansion of nanosheets in the two-dimensional direction, which is not conducive to the formation of large-sized nanosheets. This results in the loss of the continuous network characteristics unique to nanosheet arrays and a decrease in self-support.

[0029] Furthermore, in step (2), the molar ratio of acid to pyrrole monomer is (1-5):1. Specifically, it can be 1:1, 2:1, 3:1, 4:1, or 5:1. Adding acid to dope polypyrrole can significantly improve its electrical conductivity and enhance the conductivity uniformity of the network structure. Simultaneously, acid doping can strengthen the electrostatic interactions and hydrogen bond network between polypyrrole chains, helping to maintain the structural integrity of the self-supporting array during the drying process.

[0030] Furthermore, in step (2), the acid is one or more of organic or inorganic acids.

[0031] Furthermore, the organic acid is one or more of p-toluenesulfonic acid, dodecylbenzenesulfonic acid, sodium dodecyl sulfonate, camphorsulfonic acid, sulfosalicylic acid, and oxalic acid.

[0032] Furthermore, the inorganic acid is one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. Specifically, a 1 mol / L hydrochloric acid solution can be used.

[0033] Furthermore, the reaction temperature in step (2) is below 0°C. Controlling the ice surface polymerization temperature below 0°C can effectively improve the fineness and performance of the self-supporting polypyrrole array structure. Specifically, it can be -10 to 0°C. In particular, from the perspective of ease of operation, the reaction can be carried out at 0°C.

[0034] Furthermore, the reaction time in step (2) is 20-40 min. Specifically, it can be 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, 32 min, 34 min, 36 min, 38 min, or 40 min. The reaction time for preparing polypyrrole using the conventional aqueous solution method in existing technologies can typically reach several hours, or even more than ten hours, severely impacting production efficiency. However, in the system of this invention, due to the solid-liquid interface effect and the template-regulating effect of hydroxypropyl-β-cyclodextrin in the reaction liquid film, the vertical growth of polypyrrole is facilitated, and the pyrrole monomer can complete polymerization in a short time. Furthermore, the reaction time can be 25-35 min. Due to the presence of a smooth ice surface and the solid-liquid interface template formed by hydroxypropyl-β-cyclodextrin, within the aforementioned shorter reaction time, the pyrrole monomer preferentially grows along the bottom solid-liquid interface. If the reaction time is insufficient, it will lead to incomplete polymerization and the inability to form a continuous network structure. However, when the reaction time is too long, not only will excessive polymerization destroy the array structure, but the already formed polypyrrole chains will also be exposed to excessive oxidants, resulting in a peroxidation reaction. Oxidants have strong oxidizing properties and will continue to attack the conjugated double bonds on the polypyrrole backbone in the later stages of the polymerization reaction, destroying the conjugated structure of polypyrrole. This peroxidation reaction significantly reduces the electrical conductivity of polypyrrole and damages its self-supporting structure, making the entire network structure fragile. During subsequent washing and drying processes, this damaged array structure is more prone to collapse due to capillary forces, manifesting as decreased mechanical strength and flexibility of the self-supporting structure, and even an inability to maintain its intact shape.

[0035] Furthermore, in step (2), the washing process involves using deionized water.

[0036] Furthermore, the drying in step (2) is performed in a vacuum drying oven.

[0037] It is worth mentioning that, unlike the ice micropowder method previously used by the inventors to prepare polyaniline, this method is only applicable to the preparation of polypyrrole arrays. This is because the oxidative polymerization of pyrrole has the kinetic characteristics of rapid initiation and slow growth. Under the action of oxidants such as ammonium persulfate, pyrrole monomers are oxidized to generate cationic free radicals. These active species tend to grow chains on the surface of existing nuclei rather than continuously generating new nuclei. This kinetic characteristic allows for effective separation of nucleation and growth in the ice surface polymerization of pyrrole: initially, a limited number of nuclei are formed, and then these nuclei slowly expand along the two-dimensional direction, eventually forming a large-sized, interconnected nanosheet array. In contrast, the oxidative polymerization of aniline follows an autocatalytic mechanism; once initiated, the reaction rate increases exponentially, exhibiting strong burst nucleation characteristics. These nuclei collide with each other before they can undergo anisotropic growth, and the final product is a random particulate aggregate that cannot form a regular nanosheet array. Furthermore, pyrrole molecules possess good planarity, and their five-membered ring structure allows for ordered arrangement of molecules through π-π stacking interactions. The five-membered ring structure also makes its molecular size highly compatible with that of hydroxypropyl-β-cyclodextrin. Under the synergistic effect of the ice-surface template and hydroxypropyl-β-cyclodextrin, this self-assembly tendency facilitates the formation of a regular two-dimensional sheet structure. In contrast, aniline molecules have a six-membered ring structure, which has poor cavity compatibility with hydroxypropyl-β-cyclodextrin, and the π-π stacking interactions between benzene rings are weak, making it impossible to construct a self-supporting array structure.

[0038] Furthermore, in step (3), the polyamic acid powder is prepared by copolymerizing dianhydride monomers and diamine monomers to form a polyamic acid solution, which is then precipitated by dropping it into deionized water. Polyamic acid has poor stability and is generally prepared as needed. Specifically, it can be prepared from dianhydride monomers and diamine monomers in an organic solvent.

[0039] There are no particular limitations on the type of dianhydride monomer, diamine monomer, or organic solvent; any commonly used in the field may be used. Specifically, the molar ratio of dianhydride monomer to diamine monomer is (0.95-1.05):(0.95-1.05). In particular, multiple dianhydride monomers or diamine monomers can be used for copolymerization to improve the processing properties of polyimide.

[0040] For example, dianhydride monomers can be pyromellitic dianhydride (PMDA), oxydiphthalic anhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), diphenyl sulfone-3,4,3',4'-tetracarboxylic dianhydride (DSDA), bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-di... The following are at least one of the following: (carboxyphenyl)propane dianhydride, p-phenylenebis(triphenyltriacrylic acid monoester anhydride), p-biphenylenebis(triphenyltriacrylic acid monoester anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)phenyl dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, and 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride.

[0041] The diamine monomer can be p-phenylenediamine (PPD), m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid (DABA), 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (methylenediamine), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-Dicarboxy-4,4'-Diaminodiphenylmethane, 3,3',5,5'-Tetramethyl-4,4'-Diaminodiphenylmethane, bis(4-aminophenyl) sulfide, 4,4'-Diaminobenzoylaniline, 3,3'-Dimethoxybenzidine, 2,2'-Dimethoxybenzidine, 3,3'-Diaminodiphenyl ether, 3,4'-Diaminodiphenyl ether, 4,4'-Diaminodiphenyl ether, 3,3'-Diaminodiphenyl sulfide, 3,4'-Diaminodiphenyl sulfide, 4,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl sulfone, 3,4'-Diaminodiphenyl sulfone, 4,4'-Diaminodiphenyl sulfone, 3,3'-Diaminobenzophenone, 4,4'-Diaminobenzophenone, 3,3'-Diamino-4,4'-Dichlorobenzophenone, 3,3'-Diamino-4,4'-Dimethoxybenzophenone, 3,3'-Diaminodiphenylmethane, 3,4'-Diaminodiphenylmethane, 4,4'-Diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-Diaminodiphenyl sulfoxide, At least one of 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 1,3-bis(3-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene, 1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(3-aminophenoxy)benzene (TPE-Q), 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenyl)phenoxybenzophenone, 3,3'-diamino-4,4'-bis(4-phenylphenoxy)benzophenone, etc.

[0042] The organic solvent may be one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methylpyrrolidone (NMP), and γ-butyrolactone (GBL).

[0043] Furthermore, in step (4), the tertiary amine compound is one or more of triethylamine, tripropylamine, and triethanolamine; the mass ratio of the tertiary amine compound to the polyamic acid powder is (0.1-1):1.

[0044] Furthermore, in step (4), the mass ratio of polyamic acid powder to deionized water is 1-10 wt%. In particular, it can be 5 wt%.

[0045] Furthermore, in step (4), the mass ratio of the self-supporting polypyrrole nanoarray to the polyamic acid powder is (0.1-1):1. Specifically, the mass ratio of the self-supporting polypyrrole nanoarray to the polyamic acid powder can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1. In particular, the mass ratio of the self-supporting polypyrrole nanoarray to the polyamic acid powder is (0.4-0.8):1. An appropriate amount of self-supporting polypyrrole nanoarray can not only sufficiently improve the conductivity of polyimide, but also avoid the problem of dispersion difficulties caused by excessive polypyrrole.

[0046] Furthermore, in step (5), the drying method is freeze drying, and the thermal imidization adopts a gradient heating method. The specific heating steps can be 100℃-130℃ / 0.5-1.5h, 130℃-150℃ / 1-3h, 150℃-180℃ / 3-5h, or 180℃-200℃ / 0.5-1.5h.

[0047] On the other hand, the present invention also provides polypyrrole-reinforced polyimide aerogels prepared by the preparation method and their applications.

[0048] First, the polypyrrole prepared by the method of this invention exhibits a nanosheet array structure, which has significant advantages over the nanorod or nanowire arrays commonly used in the field: In terms of improving conductivity, nanosheets more easily form face-to-face overlaps during growth. This large contact area makes the electron transport resistance between layers much lower than the point-to-point contact between nanorods or nanowires. Therefore, at the same filler volume fraction, the conductive network formed by the nanosheet array is more continuous and dense, with a lower percolation threshold. In terms of improving mechanical properties, two-dimensional nanosheets have a large specific surface area, enabling them to establish broader hydrogen bonding interactions and physical entanglements with the matrix resin. When the composite material is subjected to external tensile force, these nanosheets do not exist as isolated rigid inclusions, but rather participate in deformation as an interconnected continuous layered network, uniformly dispersing concentrated stress throughout the large-area matrix. In contrast, while nanorod arrays can also provide reinforcement, their geometric limitations result in fewer connection points between rods, making them prone to localized stress concentration under external forces. Furthermore, the significant difference in mechanical properties between oriented and non-oriented directions in the rod-like structure can easily lead to performance degradation in specific directions of the composite material. Secondly, polyimide, as an intermediate, provides effective thermal protection for polypyrrole through its framework, delaying the degradation of conductivity. This structural design achieves a synergistic improvement in conductivity, mechanical reinforcement, and thermal stability, which cannot be achieved by directly adding a single polypyrrole nanosheet array. Simultaneously, the introduction of polyimide aerogel as an intermediate carrier leverages the fact that polyimide and polyurethane, both polar polymers, exhibit good compatibility and interfacial affinity, forming strong physical entanglements or chemical bonds. This significantly reduces interfacial defects and contact resistance, ensuring consistency in the microstructure and conductivity of the printed part.

[0049] Specifically, polypyrrole-reinforced polyimide aerogel can be used in 3D printing technologies such as photopolymerization, selective laser sintering, fused deposition modeling, or layered solid fabrication. Furthermore, this invention also discloses a 3D-printed polyurethane material comprising a polyurethane resin and polypyrrole-reinforced polyimide aerogel. Due to the limiting effect of the ice template and hydroxypropyl-β-cyclodextrin template, the self-supporting polypyrrole nanoarray prepared by this invention, with vertically arranged polypyrrole nanosheets and a micron-sized array substrate in the transverse direction, can serve as a conductive filler for the intermediate polyimide aerogel to improve the conductivity and mechanical properties of the polyurethane. Further, photopolymerization or fused deposition modeling can be used. Specifically, fused deposition modeling is used to prepare the polyurethane material. In the fused deposition modeling, the printing temperature is not particularly limited and can be between 180-200°C, or adjusted according to the specific production process. Furthermore, the 3D printing polyurethane material may also include inorganic reinforcing fillers, coupling agents, flow modifiers, lubricants, antioxidants, UV stabilizers, hydrolysis inhibitors, colorants, and other additives. Specifically, the type of inorganic reinforcing filler is not particularly limited and may include granular, fibrous, or sheet-like fillers. It should be noted that the types of raw materials used in this invention are not particularly limited; they can be prepared using conventional processes in the art or commercially available. For example, the thermoplastic polyurethane can be a common choice such as Wanhua Q / 0600.

[0050] Beneficial effects:

[0051] (1) This invention first uses ice as a hard template for polypyrrole preparation, and introduces hydroxypropyl-β-cyclodextrin, a cyclic molecule with both hydrophilic and hydrophobic functions, as an array growth aid to prepare a self-supporting polypyrrole nanosheet array through a one-step polymerization method. Simultaneously, polyimide aerogel is introduced as an intermediate carrier, transforming the originally poorly contacted polypyrrole-polyurethane interface into an excellent polyimide-polyurethane interface, significantly reducing interface defects and contact resistance. Furthermore, the aerogel particles, acting as a dispersed phase in the polyurethane, exhibit much higher stability during the printing process than nanoscale fillers, ensuring the consistency of the microstructure and conductivity of the printed parts.

[0052] (2) The polyimide aerogel skeleton has excellent mechanical strength, flexibility and excellent thermal stability. When it is dispersed in polyurethane as a filler, it can simultaneously exert the effect of fiber reinforcement, improve the tensile strength and tear resistance of the composite material, and provide effective thermal protection for polypyrrole under high temperature or friction conditions, delaying the decay of electrical conductivity, thus achieving a synergistic improvement of electrical conductivity, mechanical reinforcement and thermal stability. Attached Figure Description

[0053] Figure 1A scanning electron microscope image of the self-supporting polypyrrole nanoarray prepared in Example 8;

[0054] Figure 2 Here is a scanning electron microscope image of the polypyrrole prepared in Comparative Example 1;

[0055] Figure 3 The image shows a scanning electron microscope (SEM) image of polypyrrole prepared for Comparative Example 2. Detailed Implementation

[0056] In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the specific embodiments of the present invention will be described in further detail below with reference to specific examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0057] The performance testing method for the products prepared in the following examples and comparative examples is as follows: Under the same conditions, the effect of the polypyrrole-reinforced polyimide aerogels prepared in Examples 1-8 and Comparative Examples 1-2 on the performance of 3D printed polyurethane products is tested.

[0058] Specifically, the 3D printing polyurethane material comprises 100 parts thermoplastic polyurethane, 15 parts polypyrrole-reinforced polyimide aerogel, and 3 parts zinc stearate. The 3D printing polyurethane material is printed into specimens, and the elongation at break of the specimens is tested according to GB / T528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber," and its conductivity is tested using a conductivity meter.

[0059] Example 1

[0060] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0061] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, then add pyrrole monomer, let stand for 5 min to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 1:1;

[0062] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 20 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 3.5:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 2:1.

[0063] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminobenzophenone in a molar ratio of 1:1, and the dianhydride monomer was composed of pyromellitic dianhydride and oxydiphthalic anhydride in a molar ratio of 1:3. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0064] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.5:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0065] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 624%, and its electrical conductivity was 41.72 × 10⁻⁶. -4 S / cm.

[0066] Example 2

[0067] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0068] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, then add pyrrole monomer, let stand for 10 min to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 2.3:1;

[0069] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 35 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 2.3:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 4.5:1.

[0070] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone in a molar ratio of 1.5:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 1:2.5. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0071] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.7:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0072] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 617%, and its electrical conductivity was 43.34 × 10⁻⁶. -4 S / cm.

[0073] Example 3

[0074] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0075] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, and then add pyrrole monomer. Let it stand for 6 minutes to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 2:1.

[0076] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 40 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 3:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 3.5:1.

[0077] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 2:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 2:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0078] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.64:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0079] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 611%, and its electrical conductivity was 42.37 × 10⁻⁶. -4 S / cm.

[0080] Example 4

[0081] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0082] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, then add pyrrole monomer, let stand for 7 min to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 1.4:1;

[0083] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 23 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 2.6:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 2.5:1.

[0084] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 1:2, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride in a molar ratio of 1:3. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0085] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.55:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0086] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 620%, and its electrical conductivity was 41.63 × 10⁻⁶. -4 S / cm.

[0087] Example 5

[0088] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0089] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, then add pyrrole monomer, let stand for 6 min to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 3:1;

[0090] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 30 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 3:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 3.5:1.

[0091] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 2:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 2:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0092] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.64:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0093] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 608%, and its electrical conductivity was 42.54 × 10⁻⁶. -4 S / cm.

[0094] Example 6

[0095] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0096] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, then add pyrrole monomer, let stand for 8 min to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 1.7:1;

[0097] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 27 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 2.8:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 3:1.

[0098] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenylmethane and 3,3'-diaminodiphenyl ether in a molar ratio of 1:3, and the dianhydride monomer was composed of pyromellitic dianhydride and oxydiphthalic anhydride in a molar ratio of 3:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0099] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.73:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0100] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 605%, and its electrical conductivity was 43.45 × 10⁻⁶. -4 S / cm.

[0101] Example 7

[0102] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0103] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of horizontally placed ice, then add pyrrole monomer, let stand for 9 min to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 2.7:1;

[0104] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 32 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 3.2:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 4:1.

[0105] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenylmethane in a molar ratio of 3:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 3:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0106] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.6:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0107] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 618%, and its electrical conductivity was 42.82 × 10⁻⁶. -4 S / cm.

[0108] Example 8

[0109] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0110] (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the surface of ice placed horizontally, and then add pyrrole monomer. Let it stand for 6 minutes to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 2:1.

[0111] (2) A hydrochloric acid solution containing ammonium persulfate oxidant was added dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. The mixture was reacted at 0 °C for 30 min. The product was washed with deionized water and dried in a vacuum drying oven to obtain a self-supporting polypyrrole nanoarray. The mass ratio of oxidant to pyrrole monomer was 3:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer was 3.5:1.

[0112] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 2:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 2:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0113] (4) Add polyamic acid powder, triethylamine, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is 0.64:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0114] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 622%, and its electrical conductivity was 44.68 × 10⁻⁶. -4 S / cm.

[0115] Comparative Example 1

[0116] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0117] (1) First, disperse the aqueous solution of β-cyclodextrin on the surface of ice placed horizontally, then add pyrrole monomer, let stand for 6 min to form a dispersion; the mass ratio of β-cyclodextrin to pyrrole monomer is 2:1;

[0118] (2) Add hydrochloric acid solution containing ammonium persulfate oxidant dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. React at 0 °C for 30 min. Wash the product with deionized water and dry it in a vacuum drying oven to obtain polypyrrole. The mass ratio of oxidant to pyrrole monomer is 3:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer is 3.5:1.

[0119] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 2:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 2:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0120] (4) Add polyamic acid powder, triethylamine, and polypyrrole to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of polypyrrole to polyamic acid powder is 0.64:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0121] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 548%, and its electrical conductivity was 5.36×10⁻⁶. -4 S / cm.

[0122] Comparative Example 2

[0123] A method for preparing polypyrrole-reinforced polyimide aerogel includes the following steps:

[0124] (1) First, disperse the aqueous solution of pyrrole monomer on the surface of ice placed horizontally, and then add hydroxypropyl-β-cyclodextrin. Let it stand for 6 minutes to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is 2:1.

[0125] (2) Add hydrochloric acid solution containing ammonium persulfate oxidant dropwise to the dispersion to adjust the concentration of pyrrole monomer to 0.8 g / 100 ml. React at 0 °C for 30 min. Wash the product with deionized water and dry it in a vacuum drying oven to obtain polypyrrole. The mass ratio of oxidant to pyrrole monomer is 3:1. The molar ratio of hydrochloric acid (HCl) to pyrrole monomer is 3.5:1.

[0126] (3) The diamine monomer was dispersed in the organic solvent N,N-dimethylacetamide, and then the dianhydride monomer was added. The reaction was carried out at 25°C for 9 h to obtain a polyamic acid solution. The obtained polyamic acid solution was dropped into water for precipitation and filtered to obtain polyamic acid powder. The diamine monomer was composed of 4,4'-diaminodiphenyl ether and 3,3'-diaminodiphenyl ether in a molar ratio of 2:1, and the dianhydride monomer was composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride in a molar ratio of 2:1. The molar ratio of the diamine monomer to the dianhydride monomer was 1:1.02, and the mass ratio of the sum of the diamine monomer and the dianhydride monomer to the organic solvent was 5 wt%.

[0127] (4) Add polyamic acid powder, triethylamine, and polypyrrole to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of polypyrrole to polyamic acid powder is 0.64:1; the mass ratio of triethylamine to polyamic acid powder is 0.5:1; the mass ratio of polyamic acid powder to deionized water is 2wt%;

[0128] (5) The polyamic acid hydrogel was freeze-dried and then subjected to thermal imidization at 130℃ / 1h, 150℃ / 3h, 170℃ / 3h, and 190℃ / 1h to obtain polypyrrole-reinforced polyimide aerogel. When used as a conductive reinforcing filler for thermoplastic polyurethane, its elongation at break was tested to be 553%, and its electrical conductivity was 9.15×10⁻⁶. -4 S / cm.

[0129] Figure 1 The image shows a scanning electron microscope (SEM) image of the self-supporting polypyrrole nanoarray prepared in Example 8. As can be seen from the image, the polypyrroles are interconnected in a sheet-like structure, forming a three-dimensional nanosheet array with a self-supporting structure. This indicates that using ice as a hard template, the pyrrole monomers self-assembled on the ice surface under the action of hydroxypropyl-β-cyclodextrin to form an array structure.

[0130] Figure 2 The image shows a scanning electron microscope (SEM) image of the polypyrrole prepared for Comparative Example 1. From... Figure 2As can be seen, Comparative Example 1 did not form a nanosheet array, but instead exhibited a clearly aggregated stacked structure. This is because Comparative Example 1 used hydroxypropyl-free β-cyclodextrin as an adjuvant. Hydroxypropyl-β-cyclodextrin molecules are modified with hydroxypropyl groups on their periphery. These groups disrupt the hydrogen bond network between cyclodextrin molecules, giving them high water solubility and a certain degree of surface activity. When the solution is dispersed on an ice surface, hydroxypropyl-β-cyclodextrin can rapidly accumulate at the ice-water interface and form dynamic hydrogen bonds with ice through its peripheral hydroxyl groups, achieving stable anchoring. This anchoring not only fixes the cyclodextrin molecules to the ice surface but also orients their hydrophobic cavities, providing a molecular template for the ordered inclusion of pyrrole monomers and subsequent anisotropic growth. β-cyclodextrin is completely different. β-cyclodextrin molecules are composed of 7 glucose units, with a large number of hydroxyl groups distributed inside and outside the molecule, giving them a very strong tendency for intermolecular hydrogen bond association. In the low-temperature environment of ice, β-cyclodextrin not only exhibits poor dispersibility, but its molecules also rapidly form tight two-dimensional crystals or aggregates through hydrogen bonds, rather than anchoring themselves as individual molecules on the ice surface. This self-aggregating behavior prevents it from forming a uniformly oriented monolayer template on the ice surface; its cavity orientation is also disordered, failing to provide ordered inclusion sites for pyrrole monomers and thus preventing pyrrole from polymerizing into a regular array structure. When using this type of polypyrrole to prepare aerogels, its interfacial interaction with polyimide resin is low, which is detrimental to the formation of polyimide aerogels.

[0131] Figure 3 The scanning electron microscope image of the polypyrrole prepared in Comparative Example 2 also shows that it did not form a regularly arranged array structure. In Comparative Example 2, the aqueous solution of pyrrole monomer was first dispersed on the ice surface, and then hydroxypropyl-β-cyclodextrin was added. This resulted in a large amount of hydroxypropyl-β-cyclodextrin remaining in the bulk solution phase, which was not conducive to the uniform and sequential polymerization of pyrrole monomer and could not form an array structure.

[0132] The mechanical and electrical conductivity data from various embodiments and comparative examples also demonstrate that the well-organized, self-supporting polypyrrole nanoarray structure can significantly disperse the stress on polypyrrole, improving the elongation at break and electrical conductivity of the polyurethane composite material. This is because nanosheets more easily form surface-to-surface overlaps during growth. This large contact area makes the electron transport resistance between layers much lower than the point-to-point contact between nanorods or nanowires, achieving higher conductivity with less polypyrrole. Simultaneously, the two-dimensional nanosheets have a large specific surface area, enabling them to establish broader hydrogen bonding interactions and physical entanglements with the polyimide molecular chains, which is beneficial for uniformly dispersing concentrated stress across a large matrix area. Furthermore, the introduction of polyimide aerogel as an intermediate carrier, combined with the fact that polyimide and polyurethane are both polar polymers, exhibits good compatibility and interfacial affinity, allowing for the formation of strong physical entanglements or chemical bonds. Polypyrrole is firmly attached to the polyimide skeleton through a coating layer, thereby transforming the originally poorly contacted polypyrrole-polyurethane interface into an excellent polyimide-polyurethane interface. This significantly reduces interface defects and contact resistance, and greatly improves the mechanical properties and electrical conductivity of the composite material.

[0133] Specifically, compared to Example 8, Comparative Example 1, using hydroxypropyl-free β-cyclodextrin as an additive, failed to prepare a sheet-like polypyrrole array structure, instead forming an irregularly stacked structure. While the irregularly stacked polypyrrole structure can provide reinforcement, its geometric limitations result in fewer connection points, making it difficult to construct a conductive network. Furthermore, the irregularly stacked polypyrrole exhibits poor dispersibility and wettability, failing to fully disperse within the polyimide matrix and thus hindering the effective construction of a conductive and reinforcing network, leading to a decrease in the performance of the polyimide aerogel.

[0134] Compared to Example 8, in Comparative Example 2, an aqueous solution of pyrrole monomer was first dispersed on an ice surface before hydroxypropyl-β-cyclodextrin was added. The pyrrole monomer added first was in a free-diffusion state in the solution and could not form specific adsorption on the ice surface. It would occupy the anchoring sites of the subsequent hydroxypropyl-β-cyclodextrin, resulting in a large amount of hydroxypropyl-β-cyclodextrin remaining in the bulk solution phase due to ineffective anchoring. This formed empty templates or included free monomers in the solution, and the polymerization reaction took place in the bulk solution phase. This was not conducive to the uniform and sequential polymerization of pyrrole monomers, nor was it conducive to the formation of array structures. Consequently, the conductivity and reinforcing effect of the polyimide aerogel were reduced.

[0135] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing polypyrrole-reinforced polyimide aerogel, characterized in that, Includes the following steps: (1) First, disperse the aqueous solution of hydroxypropyl-β-cyclodextrin on the ice surface, then add pyrrole monomer, and let it stand to form a dispersion; the mass ratio of hydroxypropyl-β-cyclodextrin to pyrrole monomer is (1-3):1; (2) Add an acid solution containing an oxidant dropwise to the dispersion. After the reaction, wash and dry to obtain a self-supporting polypyrrole nanoarray. The oxidant is one or more of ammonium persulfate, potassium persulfate, sodium persulfate, ferric chloride, and hydrogen peroxide. (3) Polyamic acid powder was prepared by precipitation method using dianhydride monomer and diamine monomer as raw materials; the molar ratio of dianhydride monomer to diamine monomer was (0.95-1.05):(0.95-1.05). (4) Add polyamic acid powder, tertiary amine compound, and self-supporting polypyrrole nanoarray to deionized water and stir until homogeneous; obtain polyamic acid hydrogel by sol-gelation; the mass ratio of self-supporting polypyrrole nanoarray to polyamic acid powder is (0.1-1):1; (5) Dry the polyamic acid hydrogel and heat imidize it to obtain polypyrrole-reinforced polyimide aerogel.

2. The method for preparing a polypyrrole-reinforced polyimide aerogel as described in claim 1, characterized in that, In step (4), the tertiary amine compound is one or more of triethylamine, tripropylamine, and triethanolamine.

3. The method for preparing a polypyrrole-reinforced polyimide aerogel as described in claim 1, characterized in that, The drying method in step (5) is freeze drying.

4. The method for preparing a polypyrrole-reinforced polyimide aerogel as described in claim 1, characterized in that, In step (5), thermal imidization is performed using a gradient heating method.

5. A polypyrrole-reinforced polyimide aerogel, characterized in that, It is prepared by the method for preparing a polypyrrole-reinforced polyimide aerogel according to any one of claims 1-4.

6. An application of the polypyrrole-reinforced polyimide aerogel as described in claim 5, characterized in that, The polypyrrole-reinforced polyimide aerogel is used in 3D printing technologies such as photopolymerization, selective laser sintering, fused deposition modeling, or layered solid manufacturing.

7. A 3D printing polyurethane material, characterized in that, It comprises polyurethane resin material and polypyrrole-reinforced polyimide aerogel; the polypyrrole-reinforced polyimide aerogel is the polypyrrole-reinforced polyimide aerogel as described in claim 5.

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