Novel aza conjugated microporous polymer wave-absorbing material and preparation method thereof

Abstract

The invention relates to the field of wave-absorbing materials, in particular to a novel aza conjugated microporous polymer wave-absorbing material and a preparation method of the novel aza conjugated microporous polymer wave-absorbing material. The conjugated microporous polymer is prepared from a dibromopyridine monomer and a borate monomer through Suzuki coupling reaction under the action of a palladium catalyst, and the polypyrrole-aza conjugated microporous polymer material with a net structure is obtained through confinement polymerization of polypyrrole in holes of the conjugated microporous polymer. According to the preparation method, a conjugated microporous polymer containing pyridine groups is synthesized through a molecular design strategy of introducing nitrogen heterocyclic rings on a conjugated microporous molecular skeleton, and polypyrrole is introduced into nanopores of the conjugated microporous polymer through a confinement polymerization method, so that the novel nitrogen heterocyclic conjugated microporous polymer wave-absorbing material is prepared. The wave-absorbing characteristic of the wave-absorbing material is obviously improved.

Description

Technical Field

[0001] The invention relates to the field of wave absorbing materials, and in particular to a novel nitrogen-doped conjugated microporous polymer wave absorbing material and a preparation method thereof. Background Art

[0002] With the rapid development of electronic technology, electromagnetic radiation has gradually entered people's daily life. These electromagnetic radiations will not only interfere with the normal operation of various instruments, but also cause serious harm to human health. Therefore, in order to eliminate electromagnetic radiation, people have developed a variety of absorbing materials, such as magnetic materials, carbonaceous materials, ceramics, metal oxides / sulfides and conductive polymers. According to the different electromagnetic loss mechanisms, absorbing materials can be divided into two categories: magnetic loss materials and dielectric loss materials. Magnetic loss materials are generally magnetic metal oxides or alloys such as ferrites, carbonyl iron powders, carbonyl nickel powders, cobalt-nickel alloys, etc. Dielectric loss-absorbing materials are generally various mixed nanostructured composite materials composed of highly conductive carbonaceous nanoparticles, dielectric ceramic nanoparticles and metal semiconductor oxides. Compared with traditional inorganic absorbing materials such as ferrites or ceramics, metal oxides, organic absorbing materials have good chemical stability, low density, and are easy to functionalize and modify, so they have unique advantages in the field of absorbing. However, most organic materials have poor conductivity and cannot be used as excellent electromagnetic wave absorbing materials. Therefore, how to effectively enhance the conductive properties of organic absorbing materials is the key to improving the absorbing performance of such materials.

[0003] Conjugated microporous polymers are a type of reticular porous polymers with a π-conjugated system structure. This type of material has the characteristics of high specific surface area, permanent pores, good stability and easy chemical modification. As a multifunctional porous material, conjugated microporous polymers have good potential application value in many fields. Conductive polymers have the characteristics of adjustable conductivity, low density, good thermal stability and environmental stability, and have been widely used in many fields such as antibacterial / anticorrosive, temperature sensors, optoelectronic materials, energy storage, drug release and electromagnetic wave shielding. Polypyrrole, as a high-performance dielectric loss material, has high mass density and good flexibility, and its morphology is easy to control (such as polypyrrole nanotubes, or spherical, or bowl-shaped structures), so it is considered to be one of the most promising electromagnetic wave absorbers. Therefore, it is a hot topic in this field to introduce polypyrrole with excellent electrical properties into the pores of conjugated microporous polymers, control the pore size of porous materials through chemical synthesis, and the microscopic interaction between it and polypyrrole, and then develop composite materials with excellent wave absorption properties.

[0004] Generally speaking, magnetic loss-type absorbing materials have higher impedance matching and better magnetic loss capacity, so they have better absorbing performance. However, magnetic absorbers have a large density and need to be filled more in the coating to achieve ideal absorbing performance. In addition, magnetic metals and alloys have poor chemical stability and are easily corroded in a humid environment, resulting in a short lifespan. In contrast to magnetic loss-type absorbing materials, carbon-based absorbing materials are characterized by light weight and good chemical stability. At the same time, carbon-based materials have stronger microstructural designability, such as zero-dimensional carbon quantum dots, one-dimensional carbon nanotubes, and two-dimensional graphene. Therefore, carbon-based absorbing materials have received widespread attention.

[0005] Zeng et al. connected many ultra-small Fe3O4 particles to carbon nanotubes (CNTs), aggregated Fe3O4 to form microspheres, and formed a sea urchin-like structure on CNTs. The resulting composite material Fe3O4 / CNTs exhibited strong dielectric loss. When the sample thickness was 2 mm and the filling was only 5 wt%, the reflection loss at 11.12 GHz reached -56.8 dB. Zhang et al. used dicyandiamide as a raw material to grow carbon nanotubes on the surface of graphene sheets. Because graphene sheets and carbon nanotubes have high conductivity, and there are sufficient defects and interfaces between graphene sheets and carbon nanotubes, the unique three-dimensional structure makes its absorption peak width (EAB) reach 4.63 GHz when the thickness is 1.6 mm, and the maximum absorption peak reaches -44.23 dB at 2 mm. Ren et al. used wood ear as a carbon source and template to prepare Fe3O4 / nitrogen-doped porous carbon materials, and combined with freeze-drying to form pores, they simultaneously realized a three-dimensional conductive network of porous carbon in one sample. Due to the interface polarization of the composite material and the magnetism of Fe3O4, the minimum reflection loss reached -77.91 dB and the EAB reached 8.49 GHz.

[0006] The porous structure of conjugated microporous polymers helps to construct absorbing materials with good performance. Publication number: CN117842944A A metal conjugated microporous polymer-based absorbing material and its preparation and application. Liao Yaozu et al. used the microporous channels of CMP as a "cage" to anchor metal particles to achieve uniform dispersion of metal particles. By adjusting the content of single metal, bimetal and metal type, the electromagnetic parameters of the absorbing material can be controlled to optimize impedance matching. When the filling ratio of the absorbing material is 30wt% and the thickness is 3.0 mm, the minimum reflection loss of the absorbing material reaches -49.7 dB, the maximum effective absorption bandwidth below -10 dB is 5.8 GHz, and the frequency range is 11.8 to 17.6 GHz. Publication number: CN116003116B A ZnFe2O4-based composite absorbing material and its preparation method. Xie Zhipeng et al. first synthesized a conjugated microporous polymer, and then prepared a hyper-crosslinked conjugated microporous polymer through Friedel-Crafts reaction. It is then subjected to a hydrothermal reaction together with a precursor for synthesizing ZnFe2O4 nanoparticles, and finally carbonized at the target temperature to obtain a composite absorbing material. Utilizing the porous properties and tubular structure of the polymer, its maximum effective absorption bandwidth can reach 6.24 GHz and the maximum absorption reaches -59.56 dB.

[0007] Polypyrrole also has the ability to prepare materials with good microwave absorption properties due to its conductive and lightweight characteristics. Ritwik Panigrahi et al. prepared hollow polypyrrole and its silver nanocomposite using polystyrene (PS) as a template. Liu et al. prepared core-shell CoS@PPy microspheres by solvothermal and self-assembly polymerization. By successfully coating CoS microspheres with amorphous polypyrrole, the maximum reflection loss of the CoS@PPy composite material was -41.8 dB, the maximum bandwidth was 5.4 GHz, and the thickness was only 2 mm. Feng et al. first synthesized cellulose gel and then generated polypyrrole in situ. This composite material showed the best microwave absorption performance at a compression ratio of 65%, with a minimum reflection loss of -12.24 dB at 8.53 GHz and a thickness of 5 mm. In addition, the effective bandwidth can cover the entire X-band (8.2-12.4 GHz) by changing the thickness of the composite material in the range of 4-5 mm.

[0008] In order to further improve the wave-absorbing properties of wave-absorbing materials, it is urgent to develop new wave-absorbing materials and preparation methods thereof to solve the problem of poor wave-absorbing properties of wave-absorbing materials in the prior art. Summary of the invention

[0009] In view of this, the present invention aims to provide a novel nitrogen-based conjugated microporous polymer absorbing material and a preparation method thereof, so as to solve the problem of poor absorbing properties of absorbing materials in the prior art.

[0010] The present invention constructs a new CMP molecular skeleton by introducing pyridine nitrogen heterocycle into the molecular skeleton of CMP for the first time. The pyridine nitrogen heterocycle is an electron-deficient structure. Since the entire molecular skeleton is conjugated, pyridine will reduce the HOMO and LUMO energy levels of the CMP skeleton, which can regulate the molecular energy level and electromagnetic properties of the CMP skeleton and enhance the cross-sectional polarization effect and impedance matching of the material.

[0011] In addition, the electron-withdrawing properties of nitrogen heterocycles are more conducive to the in situ synthesis of polypyrrole. Therefore, the in situ generation of polypyrrole is easier to achieve in pyridine CMPs, the reaction site and reaction efficiency will be higher, and the electromagnetic properties of the final DA complex will be further regulated and optimized.

[0012] The present invention determines a reasonable stoichiometric relationship, specific reaction conditions and reaction rate through creative process design and a large number of experiments, prevents overheating of the reaction, ensures product purity, and has mild overall reaction conditions, high yield and easy control.

[0013] The technical solution of the present invention is achieved in this way:

[0014] An object of the present invention is to disclose a novel aza-conjugated microporous polymer absorbing material, comprising aza-conjugated microporous polymer containing pyridine units and polypyrrole, wherein the conjugated microporous polymer is prepared by Suzuki coupling reaction of dibromopyridine monomers and borate monomers under the action of a palladium catalyst, and a polypyrrole-aza-conjugated microporous polymer material having a network structure is obtained by confined polymerization of polypyrrole in the pores of the conjugated microporous polymer.

[0015] Furthermore, the structure of the conjugated microporous polymer is shown in Formula 1: ………1.

[0016] Furthermore, the structure of the absorbing material is shown in Formula 2: ………2.

[0017] Another object of the present invention is to disclose a method for preparing a novel nitrogen-containing conjugated microporous polymer absorbing material, characterized in that the method is used to prepare any of the novel nitrogen-containing conjugated microporous polymer absorbing materials described above, and specifically comprises the following steps:

[0018] S1: Mix dibromopyridine monomer, borate monomer, catalyst and carbonate according to a set ratio and perform oxygen-free treatment;

[0019] S2: adding organic solvent and water, the reaction temperature is 150°C and stirred, and the reaction time is 72h;

[0020] S3: After the reaction is completed, the temperature is lowered to room temperature, and after purification, an azo-conjugated microporous polymer containing pyridine units is obtained, which is named CMP-PY. The reaction formula for preparing the conjugated microporous polymer is shown in Formula 3:

[0021] …3;

[0022] S4: mixing the conjugated microporous polymer and the pyrrole monomer according to a set ratio and evaporating under reduced pressure to obtain a solid-liquid mixture;

[0023] S5: Add ferric chloride solution, stir and react at room temperature for 4 to 5 hours, and obtain the absorbing material after purification, named CMP-TH / PPy; the reaction formula for preparing the conjugated microporous polymer is shown in Formula 4: …4.

[0024] Furthermore, in step S1, the molar ratio of the dibromopyridine monomer to the borate ester monomer is 1.7:1.

[0025] Further, in step S1, the dibromopyridine monomer is one of 2,5-dibromopyridine, 2,6-dibromopyridine, and 3,5-dibromopyridine, and the borate monomer is one of 1,3,5-tris(4-phenylboronic acid pinacol ester)benzene, 4,4'-bis(phenylboronic acid pinacol ester)biphenyl, and 1,4-phenyldiboronic acid bispinacol ester.

[0026] Further, in step S1, the catalyst is one of tetrakistriphenylphosphine palladium (Pd(PPh3)4), [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium (Pd(dppf)Cl2), Pd(OAc)2 (palladium acetate), and PdCl2 (palladium chloride).

[0027] Furthermore, in step S2, the volume ratio of the organic solvent to water is 19:4.

[0028] Furthermore, in step S4, the mass ratio of the nitrogen-conjugated microporous polymer containing pyridine units to the pyrrole monomer is 1:(1-10).

[0029] Furthermore, in step S5, the concentration of the ferric chloride solution is 1 mol·L -1 .

[0030] Compared with the prior art, the novel nitrogen-based conjugated microporous polymer absorbing material and the preparation method thereof of the present invention have the following advantages:

[0031] 1. The present invention synthesizes a conjugated microporous polymer containing pyridine groups by introducing a molecular design strategy of nitrogen heterocycles into a conjugated microporous molecular skeleton, and introduces polypyrrole into the nanopores of the conjugated microporous polymer by the "confined polymerization" method to prepare a new type of nitrogen-based conjugated microporous polymer absorbing material, which significantly improves the absorbing properties of the absorbing material.

[0032] 2. The present invention obtains a novel nitrogen heterocyclic conjugated microporous polymer material with excellent electromagnetic wave absorption performance by adjusting the ratio of polypyrrole and conjugated microporous polymer, so that the minimum reflection loss reaches -70 dB and the wave absorption property is significantly enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 The figure is a flow chart of the preparation of conjugated microporous polymer CMP-PY;

[0035] Figure 2 The figure is a flow chart of the preparation of the conjugated microporous polymer absorber CMP-PY / PPy;

[0036] Figure 3 Schematic diagram of the structure of CMP-PY / Py conjugated microporous polymer composite material;

[0037] Figure 4 is a scanning electron microscope image of the conjugated microporous polymer CMP-PY;

[0038] Figure 5 is the solid-state NMR spectrum of the conjugated microporous polymer CMP-PY;

[0039] Figure 6 This is the photoelectron spectrum of the conjugated microporous polymer CMP-PY;

[0040] Figure 7 This is a scanning electron microscope image of the conjugated microporous absorber CMP-PY / PPy;

[0041] Figure 8 The infrared spectra of the conjugated microporous polymer absorber CMP-PY / Py with different ratios;

[0042] Fig. 9 This is the electromagnetic performance test diagram of reflection loss at different thicknesses of CMP-PY / PPy 1:5;

[0043] Fig.10 This is the electromagnetic performance test diagram of reflection loss at different thicknesses of CMP-PY / PPy 1:3;

[0044] Fig.11 This is the electromagnetic performance test diagram of reflection loss at different thicknesses of polypyrrole;

[0045] Fig.12 Comparison of the strongest absorption peaks of conjugated microporous polymer absorber materials CMP-PY / Py with different ratios. DETAILED DESCRIPTION

[0046] In order to make the technical means, objectives and effects of the present invention easy to understand, the embodiments of the present invention are described in detail below with reference to specific drawings.

[0047] It should be noted that all the terms used in the present invention to indicate directionality and positionality, such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside", "top", "lower", "lateral", "longitudinal", "center", etc., are only used to explain the relative positional relationship and connection status between the components in a certain state, and are only for the convenience of describing the present invention, rather than requiring the present invention to be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features.

[0048] In the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0050] Suzuki coupling reaction, also known as Suzuki-Miyaura coupling reaction, is a cross-coupling reaction widely used in organic synthesis. The basic principle of Suzuki coupling reaction is to cross-couple arenes or heteroarenes with halogen atoms (such as bromine or iodine) with boronic acid or boronic ester (usually aryl or alkenyl boronic acid / boronic ester) by palladium catalysis to form a new carbon-carbon bond.

[0051] DA-CMPs (Donor-Acceptor Conjugated Microporous Polymers) are a special type of conjugated microporous polymers, which are designed based on the alternating arrangement of donor (Donor, D) and acceptor (Acceptor, A) units. DA-CMPs exhibit excellent electronic properties, efficient microwave absorption performance, high specific surface area and porosity due to their unique donor-acceptor alternating structure. These characteristics make them have broad application prospects in many fields such as microwave absorbing materials, energy storage and conversion, gas adsorption and separation, photocatalysis and sensing.

[0052] ICT (Intramolecular Charge Transfer) refers to the transfer of electrons from the donor (Donor, D) part to the acceptor (Acceptor, A) part within the same molecule. This charge transfer usually occurs in molecules composed of different fragments with obvious electron-donating and electron-withdrawing abilities.

[0053] HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) are important concepts used in quantum chemistry to describe the electronic structure of molecules. HOMO refers to the molecular orbital with the highest energy occupied by electrons in a molecule. It represents the part of a molecule that is most likely to lose electrons; LUMO refers to the molecular orbital with the lowest energy not occupied by electrons in a molecule. It is the part of a molecule that is most likely to accept electrons.

[0054] An object of the present invention is to disclose a novel aza-conjugated microporous polymer absorbing material, comprising aza-conjugated microporous polymer containing pyridine units and polypyrrole, wherein the conjugated microporous polymer is prepared by Suzuki coupling reaction of dibromopyridine monomers and borate monomers under the action of a palladium catalyst, and a polypyrrole-aza-conjugated microporous polymer material having a network structure is obtained by confined polymerization of polypyrrole in the pores of the conjugated microporous polymer.

[0055] Conjugated microporous polymers have excellent structural controllability. As a conductive polymer, polypyrrole has good development prospects in the field of wave absorption. The polymerization of polypyrrole is limited by the porous structure of the conjugated microporous polymer to form a network structure of polypyrrole. This network structure can enhance the reflection of microwaves in the absorbing material, and further weaken the microwaves during the reciprocating reflection process of microwaves. The conjugated microporous polymer absorbing material prepared by this invention, as a fully organic absorbing material, has extremely high absorbing performance at specific wavelengths, and is also light in weight, has good compatibility with organic matter, and has adjustable absorbing performance. It has a wide range of usage scenarios and good practical value.

[0056] Nitrogen-doped conjugated microporous polymers containing pyridine units were synthesized through Suzuki coupling reaction, and polypyrrole was in situ polymerized in its pores to form a network structure. The "confined polymerization" strategy was used to ensure that polypyrrole grew in specific locations to avoid performance degradation caused by disordered growth. The Suzuki coupling reaction under anaerobic conditions and environmentally friendly solvents were used for purification to reduce environmental pollution.

[0057] This setting obtains a new type of pyridine DA-type conjugated microporous polymer material by introducing the design strategy of pyridine units. The introduction of pyridine units not only effectively improves the molecular planarity of the conjugated microporous molecular skeleton, but the introduction of DA structure can also effectively enhance the delocalization ability of its outer electrons through the ICT intramolecular charge transfer effect, while also being able to regulate the HOMO / LUMO energy levels and the intrinsic conductive properties of this type of microporous polymer.

[0058] In addition, the introduction of nitrogen heterocycles is beneficial to the interaction between conjugated microporous polymers and polypyrrole. Ultimately, through the above synergistic effect, the wave-absorbing properties of this type of composite materials are significantly improved. We have successfully developed nitrogen-doped conjugated microporous polymer-polypyrrole composite wave-absorbing materials with excellent wave-absorbing properties.

[0059] Specifically, the structure of the conjugated microporous polymer is shown in Formula 1: ………1.

[0060] Specifically, the structure of the absorbing material is shown in Formula 2: ………2.

[0061] Another object of the present invention is to disclose a novel nitrogen-based conjugated microporous polymer absorbing material and a preparation method thereof, which specifically comprises the following steps:

[0062] S1: Mix dibromopyridine monomer, borate monomer, catalyst and carbonate according to a set ratio and perform oxygen-free treatment;

[0063] By vacuuming and filling with nitrogen, oxygen in the reaction system is removed to ensure that the reaction is carried out under an inert atmosphere. The oxygen-free environment helps to maintain the activity of the catalyst, avoids side reactions caused by oxygen, and makes the reaction more controllable, thereby improving the reaction efficiency and product yield.

[0064] S2: adding organic solvent and water, the reaction temperature is 150°C and stirred, and the reaction time is 72h;

[0065] The use of appropriate organic solvents, such as N,N-dimethylformamide DMF and water, can fully dissolve the reactants and promote the reaction. High temperature of 150°C and long-term stirring for 72 hours can ensure that the reactants are fully in contact and complete the required chemical reaction. Long-term heating and stirring help the reaction to proceed completely and increase the generation ratio of the target product. Stirring makes the material distribution in the reaction system more uniform, reducing the impact of local concentration differences on the reaction.

[0066] S3: After the reaction is completed, the temperature is lowered to room temperature, and after purification, an aza-conjugated microporous polymer containing pyridine units is obtained, which is named CMP-PY. The reaction formula for preparing the conjugated microporous polymer is shown in the formula:

[0067]

[0068] Cooling to room temperature can stop the chemical reaction and prevent over-reaction or side reaction. Through washing and Soxhlet extraction, unreacted monomers, catalysts and other impurities can be removed to obtain pure target products.

[0069] S4: mixing the conjugated microporous polymer and the pyrrole monomer according to a set ratio and evaporating under reduced pressure to obtain a solid-liquid mixture;

[0070] The pyrrole monomer is absorbed into the micropores of the conjugated microporous polymer by the method of reduced pressure distillation, ensuring the uniform distribution of the pyrrole monomer and providing a good foundation for the subsequent polymerization reaction.

[0071] S5: Add ferric chloride solution, stir and react at room temperature for 4 to 5 hours, and obtain the absorbing material after purification, named CMP-TH / PPy; the reaction formula for preparing the conjugated microporous polymer is shown in the formula:

[0072]

[0073] Ferric chloride, as an oxidant, can initiate the polymerization reaction of pyrrole monomers to generate polypyrrole. By adjusting the reaction time and conditions, the amount and distribution of polypyrrole can be precisely controlled, so that polypyrrole grows in the pores of the conjugated microporous polymer and the performance of the composite material is optimized.

[0074] Specifically, in step S1, the dibromopyridine monomer can be one of 2,5-dibromopyridine, 2,6-dibromopyridine, and 3,5-dibromopyridine, the borate monomer can be one of 1,3,5-tris(4-phenylboronic acid pinacol ester)benzene, 4,4'-bis(phenylboronic acid pinacol ester)biphenyl, and 1,4-phenyldiboronic acid bispinacol ester, the catalyst can be one of tetrakistriphenylphosphine palladium (Pd(PPh3)4), [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium (Pd(dppf)Cl2), Pd(OAc)2 (palladium acetate), and PdCl2 (palladium chloride), and the carbonate can be one of potassium carbonate (K2CO3), (Cs2CO3), and sodium carbonate (Na2CO3).

[0075] This setting can obtain different polymer structures and properties by selecting different types of raw materials, adapt to different reaction conditions and scales, improve reaction efficiency and product purity, and ensure the smooth progress of the reaction.

[0076] Specifically, the molar ratio of the dibromopyridine monomer to the borate ester monomer is 1.7:1.

[0077] By setting the molar ratio of dibromopyridine monomer slightly higher than that of borate monomer, it is possible to ensure that the borate monomer fully participates in the reaction, avoid unreacted borate residue, improve the completeness of the reaction, reduce the generation of by-products, and thus improve the purity of the final product. Optimizing the cross-linking density of the polymer ensures that the material has good mechanical strength and appropriate porosity, which is conducive to the subsequent introduction of polypyrrole and the preparation of composite materials, obtaining polymers with high specific surface area and good pore structure, enhancing the overall conductivity and interfacial polarization effect of the material, and improving its electromagnetic wave absorption performance.

[0078] Preferably, the dibromopyridine monomer is: 441.5 mg of 2,5-dibromopyridine, the borate monomer is: 852 mg of 1,3,5-tris(4-phenylboronic acid pinacol ester)benzene, the catalyst is: 17 mg of tetrakistriphenylphosphine palladium (Pd(PPh3)4), and the carbonate is: 1031 mg of potassium carbonate (K2CO3).

[0079] This combination can efficiently complete the Suzuki coupling reaction under anaerobic conditions to generate high-quality nitrogen-conjugated microporous polymers containing pyridine units. By adjusting the selection and proportion of these components, the performance of the material can be further optimized to meet different application requirements.

[0080] Specifically, in step S2, the volume ratio of the organic solvent to water is 19:4.

[0081] Dibromopyridine monomers and borate monomers usually have different solubility characteristics. Organic solvents, such as N,N-dimethylformamide (DMF), can effectively dissolve these monomers. By adjusting the ratio of organic solvent to water, the solubility of the reaction system can be optimized, ensuring that all reactants are evenly dispersed, increasing the yield and purity of the target product, and promoting the efficient conduct of the reaction.

[0082] Specifically, in step S3, the purification method uses water and methanol to wash repeatedly, then extracts with cyclopentyl methyl ether for 3 days, and then vacuum-dries at 100°C for 12 hours.

[0083] Water can effectively remove water-soluble byproducts and incompletely reacted small molecule impurities generated during the reaction. Methanol, as an organic solvent, can dissolve and remove some organic solvent residues and some water-insoluble impurities. Through multiple washings, most water-soluble impurities and some organic solvent residues can be effectively removed, significantly improving the purity of the final product, reducing the burden of subsequent Soxhlet extraction, and making the Soxhlet extraction process more efficient.

[0084] Soxhlet extraction is a continuous extraction technology that can continuously remove small molecule impurities and unreacted monomers over a long period of time. Through long-term Soxhlet extraction, low molecular weight substances in the polymer can be removed, its pore structure can be optimized, the specific surface area can be increased, and as many impurities as possible can be removed to improve product quality. Cyclopentyl methyl ether is an environmentally friendly solvent with low toxicity and good biodegradability, which reduces the impact on the environment.

[0085] Under vacuum conditions, water and other volatile components are more easily evaporated, shortening the drying time. 100°C is a relatively mild temperature that will not cause significant damage to the structure and properties of the conjugated microporous polymer. It helps to maintain the high specific surface area and porosity of the material, and can completely remove residual solvents and water, which can significantly improve the stability and long-term storage performance of the final product.

[0086] Specifically, in step S4, the mass ratio of the nitrogen-conjugated microporous polymer containing pyridine units to the pyrrole monomer is 1:(1-10).

[0087] By adjusting the mass ratio of CMP-PY to pyrrole monomers, the growth of polypyrrole in the pores of CMP-PY can be controlled, thereby optimizing its conductive network, helping to form a uniform and efficient conductive network, enhancing the material's interfacial polarization effect and impedance matching, and improving the material's overall conductivity and electromagnetic wave absorption performance.

[0088] Preferably, the mass ratio of the nitrogen-conjugated microporous polymer containing pyridine units to the pyrrole monomer is 1:1, 1:3, or 1:5.

[0089] By changing the mass ratio of CMP-PY to pyrrole monomer, the performance of the composite material can be controlled in a wide range. When the mass ratio of CMP-PY to pyrrole monomer is 1:5, the minimum reflection loss can reach -70 dB, showing excellent absorption performance.

[0090] Specifically, in step S4, a rotary evaporator is used to perform reduced pressure distillation, and the solvent is methanol.

[0091] By heating the solution under reduced pressure using a rotary evaporator, unreacted pyrrole monomers, catalyst residues, and other small molecule impurities can be effectively removed, avoiding damage to the material structure and performance by high temperature, ensuring the high purity of the final product, and reducing the impact of by-products on material performance. Methanol is used as a solvent, and the evaporation process of the solvent is accelerated by rotation and reduced pressure to improve processing efficiency.

[0092] Specifically, in step S5, the concentration of the ferric chloride solution is 1 mol·L -1 .

[0093] Ferric chloride is a strong oxidant that can quickly oxidize pyrrole monomers and initiate their polymerization, ensuring that pyrrole monomers are quickly and completely converted into polypyrrole (PPy) to form the desired conductive network structure. A concentration of 1 mol·L⁻¹ provides a moderate oxidation intensity that can ensure the efficient reaction without causing over-oxidation or side reactions, helping to control the growth morphology and size of polypyrrole and avoid disordered growth, thereby building an ordered conductive network.

[0094] Specifically, in step S5, the specific method of purification is: repeatedly washing with a large amount of water and ethanol, and drying in a vacuum oven at 70°C to obtain a black powdery composite absorber of a conjugated microporous polymer and polypyrrole, which is named CMP-TH / PPy.

[0095] By repeatedly washing with a large amount of water and ethanol, impurities such as unreacted pyrrole monomer, ferric chloride and its by-products can be effectively removed to ensure the high purity of the final product and reduce the impact of by-products on material properties. Multiple washing and drying treatments can optimize the microstructure of the material and maintain its porosity and specific surface area. Vacuum drying at a lower temperature can avoid high temperature damage to the material structure and maintain its excellent physical and chemical properties.

[0096] Example 1

[0097] CMP-PY-1

[0098] In a 100 mL two-necked bottle, add 489 mg of 2,5-dibromopyridine, 953 mg of 1,3,5-tris(4-phenylboronic acid pinacol ester)benzene, 19 mg of tetrakistriphenylphosphine palladium, and 1142 mg of potassium carbonate, and perform oxygen-free treatment. Inject 27 mL of N,N-dimethylformamide and 5 mL of water into the reaction system, and heat and stir to 150°C. After 72 hours of reaction, stop the reaction, cool to room temperature, wash repeatedly with water and methanol, and then extract with cyclopentyl methyl ether as an eluent for 3 days. Dry under vacuum at 100°C for 12 hours to obtain a light gray product, which is named CMP-PY-1, as shown in Table 1 below.

[0099]

[0100] Example 2

[0101] CMP-PY-2, add 646 mg of 2,5-dibromopyridine, 1235 mg of 1,3,5-tris(4-phenylboronic acid pinacol ester)benzene, 16 mg of [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium, 3552 mg of cesium carbonate into a 100 mL two-necked bottle, do oxygen-free treatment, inject 27 mL of N,N-dimethylformamide and 5 mL of water into the reaction system, heat and stir to 150 ° C. After 72 h of reaction, stop the reaction, cool to room temperature, wash repeatedly with water and methanol, and then extract with cyclopentyl methyl ether for 3 days. Dry at 100 ° C in vacuum for 12 h to obtain a light gray product, which is named CMP-PY-2, as shown in Table 2 below.

[0102] Example 3

[0103] 100 mg of CMP-PY-1 and 300 mg of pyrrole were added to a 250 mL single-mouth bottle, and 100 mL of 1 mol·L-1 ferric chloride solution was injected into the reaction system. The mixture was stirred and reacted at room temperature for 4 h. The mixture was repeatedly washed with a large amount of water and ethanol, and dried in a vacuum oven at 70 °C to obtain a black powdery composite absorber of conjugated microporous polymer and polypyrrole, which was named CMP-PY / PPy 1:3, as shown in Table 3 below.

[0104] Taking paraffin as the matrix, the conjugated microporous polymer-based absorbing material CMP-PY / PPy 1:3 is uniformly dispersed in the paraffin. The mass ratio of paraffin to the absorbing material is 85:15. When the thickness is 3.94 mm, the maximum effective absorption bandwidth below -10 dB is 3.42 GHz, the frequency range is 10.52-13.94 GHz, and the minimum reflection loss of the absorbing material is -13.6 dB.

[0105] Example 4

[0106] 100 mg CMP-PY and 500 mg pyrrole were added to a 250 mL single-mouth bottle, and 100 mL 1 mol·L-1 ferric chloride solution was injected into the reaction system. The mixture was stirred and reacted at room temperature for 4 h. The mixture was repeatedly washed with a large amount of water and ethanol, and dried in a vacuum oven at 70 °C to obtain a black powdery composite absorber of conjugated microporous polymer and polypyrrole, which was named CMP-PY / PPy 1:5, as shown in Table 4 below.

[0107] Taking paraffin as the matrix, the conjugated microporous polymer-based absorbing material CMP-PY / PPy 1:5 is uniformly dispersed in the paraffin. The mass ratio of paraffin to the absorbing material is 85:15. When the thickness is mm, the maximum effective absorption bandwidth below -10 dB is 6.52 GHz, the frequency range is 11.34-17.86 GHz, and the minimum reflection loss of the absorbing material reaches -74.06 dB.

[0108] Comparative Example 1

[0109] Add 1000 mg of pyrrole to a 250 mL single-mouth bottle, inject 100 mL of 1 mol·L-1 ferric chloride solution into the reaction system, stir and react at room temperature for 4 h. Wash repeatedly with a large amount of water and ethanol, dry in a vacuum oven at 70°C, and obtain a black powdery composite absorber of conjugated microporous polymer and polypyrrole, which is named PPy, as shown in Table 5 below. Taking paraffin as the matrix, polypyrrole PPy is uniformly dispersed in the paraffin. The mass ratio of paraffin to absorbing material is 85:15. When the thickness is 2.1 mm, the maximum effective absorption bandwidth below -10 dB is 6 GHz, the frequency range is 11.45-17.45 GHz, and the minimum reflection loss of the absorbing material reaches -20 dB.

[0110] Results and Analysis

[0111] The present invention successfully synthesized a conjugated microporous polymer CMP-PY containing pyridine units, and successfully introduced polypyrrole into the conjugated microporous polymer micropores, obtaining two new nitrogen-doped conjugated microporous polymer-polypyrrole composite materials PY / PPy 1:5 and CMP-PY / PPy 1:3. Finally, the minimum reflection loss of PY / PPy 1:5 reached -70 dB, and the wave absorption characteristics were significantly enhanced. As the skeleton structure of polypyrrole, the conjugated microporous polymer can effectively regulate the aggregation state of polypyrrole. After polypyrrole and conjugated microporous polymer are composited, the impedance matching between the polypyrrole-conjugated microporous polymer composite material and electromagnetic waves can be significantly enhanced, so that it has a wider absorption frequency band, thereby improving the maximum wave absorption intensity of the nitrogen-doped conjugated microporous polymer absorbing material.

[0112] Structural Characterization of Conjugated Microporous Polymers

[0113] The solid samples were subjected to scanning electron microscopy, solid nuclear magnetic resonance carbon spectrum, and XPS photoelectron spectroscopy tests to verify the correctness of the obtained product structure.

[0114] Scanning electron microscopy: Figure 4 As shown in the figure, the material was treated with gold spraying and its microscopic state was observed using a scanning electron microscope. At a scale of 2 μm, the conjugated microporous polymer exists in the form of spheres. Most of these conjugated microporous polymer spheres are relatively complete, without gaps or other conditions, and without obvious interfaces like crystals, indicating that the polymer is in a network cross-linked state. The surface of the sphere is smooth and the material uniformity is good.

[0115] Solid-state NMR: Solid-state NMR of conjugated microporous polymers Figure 5 As shown, 148 ppm is CN / C=N bond, 141 ppm and 127 ppm are aromatic carbon, which proves that the conjugated microporous polymer is successfully prepared.

[0116] XPS photoelectron spectroscopy: Figure 6 As shown in the figure, by analyzing the total XPS photoelectron spectrum, it is known that nitrogen accounts for 8.34% and carbon accounts for 91.66%. The bonding state of carbon atoms in the material is further analyzed through the fine spectrum of carbon. By peak separation, carbon-nitrogen bonds and aromatic carbon can be seen. The photoelectron spectrum test shows the existence of carbon-nitrogen bonds and nitrogen elements in conjugated microporous polymerization, which further proves the successful synthesis of nitrogen-containing conjugated microporous polymers.

[0117] Characterization of basic physical and chemical properties of conjugated microporous polymer-polypyrrole composite microwave absorbing materials

[0118] The structure of the final absorbing material is further characterized.

[0119] Scanning electron microscopy: Figure 7As shown in the figure, the material was treated with gold spraying and its microscopic state was observed by scanning electron microscopy. The pyrrole monomer was absorbed into the micropores of the conjugated microporous polymer by vacuum distillation, and then the polypyrrole was oxidized and polymerized by ferric chloride. The polypyrrole was able to grow in the micropores of the conjugated microporous polymer, construct a conductive network, and form conductive conjugated microporous polymer microspheres with a diameter of about 400 nm. At the same time, some excess pyrrole molecules continued to grow on the surface of the microspheres, resulting in the appearance of tiny polypyrrole particles on the surface of the spheres. The surface particles in the figure are proof of the successful synthesis of polypyrrole, and the cracks on the surface of the spheres indicate that polypyrrole has been successfully introduced into the pores of the conjugated microporous polymer.

[0120] Infrared spectrum: Figure 8 As shown, after polypyrrole was introduced into CMP-TH, the infrared peaks of polypyrrole also appeared, indicating that polypyrrole was successfully synthesized.

[0121] Test of microwave absorption performance of conjugated microporous polymer absorbing materials

[0122] The above absorbers were filled into paraffin with a ratio of paraffin to absorber of 85:15, and made into concentric rings with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm, and a thickness of 2-5 mm. The rings were tested by a vector network analyzer using a coaxial method in the 2-18 GHz frequency band. Fig. 9 , 10 , 11, and 12 correspond to the comparison diagrams of CMP-PY / PPy 1:5, CMP-PY 1:3, polypyrrole, and the strongest absorption peak, respectively.

[0123] pass Figure 9-11 It can be seen that the minimum reflection loss of polypyrrole is no higher than -20 dB, and the wave absorption capacity of CMP-PY / PPy 1:3 is lower than that of pure polypyrrole at all thicknesses. When the thickness of CMP-PY / PPy 1:5 is 3.50 mm, the minimum reflection loss can reach -30 dB, showing excellent wave absorption performance. This result shows that by rationally optimizing the ratio of CMP-PY / PPy, the design strategy of inserting polypyrrole into pyridine conjugated microporous polymers can effectively improve the wave absorption performance of this type of material. The maximum values ​​of the wave absorption characteristics under each ratio were further compared, such as Fig.12As shown in the figure, the reflection loss diagrams of CMP-PY / PPy 1:5, CMP-PY / PPy 1:3, and PPy at 3.20 mm, 5.00 mm, and 2.08 mm, respectively. It can be seen that after optimization, the minimum reflection loss of CMP-TH / PPy1:5 reached -70 dB at a thickness of 3.20 mm, which is much higher than the wave absorption characteristics of pure polypyrrole. The above results show that the wave absorption performance of conjugated microporous polymer absorbers is not only highly controllable, but also proves that the development strategy of pyridine conjugated microporous polymer composite polypyrrole can significantly improve the wave absorption characteristics of such materials.

[0124] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A novel nitrogen-based conjugated microporous polymer absorbing material, characterized in that: The invention comprises an aza-conjugated microporous polymer containing pyridine units and polypyrrole. The conjugated microporous polymer is prepared by Suzuki coupling reaction of dibromopyridine monomers and borate monomers under the action of a palladium catalyst. The polypyrrole-aza-conjugated microporous polymer material with a network structure is obtained by confined polymerization of polypyrrole in the pores of the conjugated microporous polymer.

2. The novel nitrogen-doped conjugated microporous polymer absorbing material according to claim 1, characterized in that: The structure of the conjugated microporous polymer is shown in Formula 1: ………1.

3. The novel nitrogen-based conjugated microporous polymer absorbing material according to claim 1, characterized in that: The structure of the absorbing material is shown in Formula 2: ………2.

4. A method for preparing a novel nitrogen-based conjugated microporous polymer absorbing material, characterized in that: The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to any one of claims 1 to 3 specifically comprises the following steps: S1: Mix dibromopyridine monomer, borate monomer, catalyst and carbonate according to a set ratio and perform oxygen-free treatment; S2: adding organic solvent and water, the reaction temperature is 150°C and stirred, and the reaction time is 72h; S3: After the reaction is completed, the temperature is lowered to room temperature, and after purification, an azo-conjugated microporous polymer containing pyridine units is obtained, which is named CMP-PY. The reaction formula for preparing the conjugated microporous polymer is shown in Formula 3: …3； S4: mixing the conjugated microporous polymer and the pyrrole monomer according to a set ratio and evaporating under reduced pressure to obtain a solid-liquid mixture; S5: Add ferric chloride solution, stir and react at room temperature for 4 to 5 hours, and obtain the absorbing material after purification, named CMP-TH / PPy; the reaction formula for preparing the conjugated microporous polymer is shown in Formula 4: …4。 5. The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to claim 4, characterized in that: In step S1, the molar ratio of the dibromopyridine monomer to the borate ester monomer is 1.7:

1.

6. The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to claim 1, characterized in that: In step S1, the dibromopyridine monomer is one of 2,5-dibromopyridine, 2,6-dibromopyridine, and 3,5-dibromopyridine, and the borate monomer is one of 1,3,5-tris(4-phenylboronic acid pinacol ester)benzene, 4,4'-bis(phenylboronic acid pinacol ester)biphenyl, and 1,4-phenyldiboronic acid bispinacol ester.

7. The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to claim 1, characterized in that: In step S1, the catalyst is one of tetrakistriphenylphosphine palladium (Pd(PPh3)4), [1,1'-bis(diphenylphosphino)ferrocene]dichloropalladium (Pd(dppf)Cl2), Pd(OAc)2 (palladium acetate), and PdCl2 (palladium chloride).

8. The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to claim 1, characterized in that: In step S2, the volume ratio of the organic solvent to water is 19:

4.

9. The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to claim 1, characterized in that: In step S4, the mass ratio of the nitrogen-conjugated microporous polymer containing pyridine units to the pyrrole monomer is 1:(1-10).

10. The method for preparing the novel nitrogen-based conjugated microporous polymer absorbing material according to claim 1, characterized in that: In step S5, the concentration of the ferric chloride solution is 1 mol·L -1 .

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