Preparation method and application of PI / AGO composite wave-absorbing film

Abstract

The invention discloses a preparation method and application of a polyimide / aminated graphene oxide (PI / AGO) composite wave-absorbing film. The method comprises the following steps: preparing aminated graphene oxide (AGO) by grafting p-phenylenediamine to graphene oxide; the preparation method comprises the following steps: dispersing AGO in N, N-dimethylacetamide in an inert atmosphere, and carrying out low-temperature polycondensation on the N, N-dimethylacetamide, 4, 4 '-diaminodiphenyl ether and 3, 3', 4, 4 '-benzophenone tetracarboxylic dianhydride to prepare a polyamide acid / AGO solution; the composite film is obtained through film casting and stepped thermal imidization (150-300 DEG C gradient heating). The innovation lies in that AGO amino groups are bonded with polyimide monomers, nanoscale dispersion (the content is 1.6-2.8 wt%) is achieved, and the problems of high-temperature oxidation and interface defects of traditional filler are solved. The obtained film shows remarkable wave absorbing performance in a Ka wave band (26.5-40GHz), and is suitable for the fields of electromagnetic protection of high-frequency electronic equipment and radar stealth.

Description

Technical Field

[0001] The present invention belongs to the technical field of absorbing materials, and in particular relates to a preparation method and application of a PI / AGO composite absorbing film. Background Art

[0002] The rapid development and widespread application of electromagnetic waves have greatly promoted the advancement of communication networks, remote sensing, medical imaging, automobiles, radar systems, nondestructive testing, and numerous other emerging technologies. However, excessive electromagnetic waves lead to the accumulation of electromagnetic radiation in the environment, causing electromagnetic pollution. This pollution not only poses a potential threat to human health but also has the potential to disrupt ecological balance.

[0003] In this context, electromagnetic protection materials that can absorb or reflect electromagnetic waves to reduce radiation have become an important means of combating electromagnetic pollution. Absorbing materials, in particular, effectively prevent secondary pollution by absorbing electromagnetic waves into the material and dissipating them through methods such as heat, and have therefore become a research hotspot.

[0004] Polyimide (PI) offers unique advantages in the field of microwave-absorbing materials due to its excellent high-temperature resistance, high insulation, good mechanical properties, chemical corrosion resistance, and low dielectric constant. However, it should be noted that most polyimide films used as electromagnetic shielding materials rely primarily on their electromagnetic wave reflection properties to achieve shielding, which inevitably leads to secondary electromagnetic radiation pollution.

[0005] To address this issue, researchers have begun exploring the use of polyimide films as microwave absorbing materials. Currently, there are two main preparation methods: 1. Surface deposition / sputtering: For example, Andriyanti et al. used DC sputtering to deposit a gadolinium-doped cerium oxide-barium ferrite (GDC-BaFe2O4) thin film on a PI (Kapton) substrate to create a microwave absorbing film. The sample thickness was 70.5 μm at a sputtering time of 7.5 minutes, and the film achieved an RL of -39.6 dB at 10 GHz. min 2. Filler composite / blending method: For example, Zeng et al. prepared a multifunctional polyimide composite material doped with niobium pentoxide / carbon nanotube microspheres (NBCP). The results showed that when the volume filling amount of NBCP was 15%, the thickness of the composite material was 2.09 mm and its RL min The material exhibits excellent mechanical properties and a thermal insulation temperature difference of over 100°C in a 150°C thermal environment.

[0006] However, both mainstream methods have limitations: the sputtering method is expensive, has low material utilization and is prone to damage to the substrate; and the absorbing fillers (such as carbon materials) introduced by the composite thin film method are easily oxidized and fail at high temperatures, affecting long-term stability, and the interface defects between the filler and the substrate will reduce the flexibility and mechanical strength of the film.

[0007] Given that the research on the above-mentioned polyimide-based absorbing films is still immature, the present invention focuses on improving the absorbing performance of polyimide composite films, aiming to optimize existing methods or explore new approaches to address the above-mentioned limitations. Summary of the Invention

[0008] In view of this, the present invention provides a method for preparing a polyimide / aminated graphene oxide (PI / AGO) composite absorbing film. Through a chemical grafting method, the amino groups in p-phenylenediamine (PPDA) react with the oxygen-containing groups in graphene oxide (GO) to obtain aminated graphene oxide (AGO), and then composited with polyimide (PI) to obtain PI / AGO.

[0009] The method for preparing the PI / AGO thin film composite absorbing material of the present invention is characterized by comprising the following steps: 1) Preparation of AGO Graphene oxide is first dispersed in deionized water and ultrasonically treated, and then p-phenylenediamine is added. The mixture is stirred and reacted in an oil bath at 75-85°C for 10-15 hours. After the reaction is completed, the mixture is filtered, washed, and vacuum-dried to obtain amino-modified graphene oxide, denoted as AGO. The mass ratio of graphene oxide to p-phenylenediamine is 1:2-2:1. 2) Preparation of PI / AGO composite film First, under the protection of an inert atmosphere (argon or nitrogen), AGO is dispersed in N,N-dimethylacetamide and stirred evenly. After 4,4'-diaminodiphenyl ether is added to dissolve it, 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added in batches. Then, the mixture is reacted at a low temperature of 0-10°C for 3-6 hours and allowed to stand overnight to obtain a uniform mixed solution with an AGO content of 0.5-5.0 wt%, which is named PAA / AGO solution. Preferably, the mass content of AGO in the PAA / AGO solution is 1.6-2.8 wt%, and the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-benzophenone tetracarboxylic dianhydride is 1:1.01-1:1.05. The 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added in batches 4-6 times, with an interval of 5-15 minutes between each addition. Next, the PAA / AGO solution was coated to form a film. After solvent evaporation and preliminary imidization at 80-120°C, the temperature was programmed to 300°C in a tube furnace for complete imidization. The complete imidization procedure was: heating at 2°C / min, and keeping at 150°C, 200°C, 250°C, and 300°C for 1 hour each; a PI / AGO composite film was obtained.

[0010] The PI / AGO composite absorbing film of the present invention comprises AGO uniformly dispersed in a polyimide matrix with a content of 1.6 to 2.8 wt %. The film can be stacked to form an absorbing structure with a working thickness of 1.0 to 3.5 mm.

[0011] In the Ka band 26.5~40GHz frequency range, when the thickness is 2.5~3.5mm, the reflection loss RL min ≤-40 dB, effective absorption bandwidth EAB ≥ 2.5 GHz. When the AGO content is 2.4wt% and the thickness is 3.1mm, the RL min ≤-61.2dB, EAB≥4.4GHz.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses a chemical grafting method to react the amino groups in PPDA with the oxygen-containing groups in GO to obtain AGO, which is then composited with PI to obtain PI / AGO. SEM and FTIR images show that AGO is successfully composited into the PI film. The research results show that within the K band, the RL of PI / AGO-2.4 at 25.5 GHz min The RL of PI / AGO-2.4 at 3.1 mm and 30.5 GHz is -33.3 dB, and its corresponding EAB is 2.5 GHz. min The EAB of PI / AGO is -61.2 dB, and its corresponding EAB is 4.4 GHz. The amino groups in AGO react with BTDA through an acid-base reaction, so that the graphene is embedded in the PI polymer matrix. This significantly improves the interfacial compatibility between the inorganic and organic phases and enhances the dispersion of graphene. In addition, the PI / AGO sample has better absorption performance at higher frequencies, and with the increase of AGO content, the dielectric properties of the material improve, which makes PI / AGO have improved absorption performance. The thermal imidization temperature of 300 ° C gives the material a higher molecular structure integrity, which is important for maintaining the material's absorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1SEM images of (ab) PI surface, (cd) PI cross section, (ef) PI / AGO-1.6 surface, and (gh) PI / AGO-1.6 cross section.

[0014] Figure 2 FTIR spectra of AGO, PI, PI / AGO-300-1.6 and PI / AGO-400-1.6.

[0015] Figure 3 These are the Raman spectra of PI / AGO-200-1.6, PI / AGO-300-1.6, and PI / AGO-400-1.6.

[0016] Figure 4 XPS spectra of PI / AGO-300-1.6 and PI / AGO-400-1.6: (a) full spectrum, (b) C 1s, (c) N 1s, and (d) O 1s.

[0017] Figure 5 (a) Real part of the complex permittivity of PI / AGO in the K band, (b) Imaginary part of the complex permittivity in the K band, (c) Dielectric loss tangent in the K band, (d) Real part of the complex permittivity in the Ka band, (e) Real part of the complex permittivity in the Ka band, and (f) Dielectric loss tangent in the Ka band.

[0018] Figure 6 Cole-Cole curves of PI / AGO composite films with different AGO contents in the K band, including (a) PI / AGO-1.6, (b) PI / AGO-2.0, (c) PI / AGO-2.4, and (d) PI / AGO-2.8.

[0019] Figure 7 Cole-Cole curves of PI / AGO composite films with different AGO contents in the Ka band, including (a) PI / AGO-1.6, (b) PI / AGO-2.0, (c) PI / AGO-2.4, and (d) PI / AGO-2.8.

[0020] Figure 8 The reflection loss of PI / AGO composite films with different graphene contents in the K band varies with thickness; among them, (a) PI / AGO-1.6, (b) PI / AGO-2.0, (c) PI / AGO-2.4, and (d) PI / AGO-2.8.

[0021] Figure 9Reflection loss of PI / AGO composite films with different graphene contents in the Ka band: (a) PI / AGO-1.6, (b) PI / AGO-2.0, (c) PI / AGO-2.4, and (d) PI / AGO-2.8.

[0022] Figure 10 Impedance matching diagram of PI / AGO in (a) K band, (b) Ka band, (c) K band, and (d) Ka band. DETAILED DESCRIPTION

[0023] The present invention will be further explained below with reference to specific embodiments. Example

[0024] 1. Preparation of AGO 0.1 g of graphene oxide (GO) was added to 100 mL of deionized water, and 0.1 g of p-phenylenediamine (PPDA) was added to 10 mL of deionized water. The mixture was simultaneously sonicated for 1 h to obtain a GO dispersion and a PPDA solution. The GO dispersion was then transferred to a three-necked flask, heated to 80°C, and the PPDA solution was added. The mixture was then magnetically stirred in an 80°C oil bath for 12 h. After the reaction, the mixture was filtered and washed several times with deionized water. Finally, the black powder was dried in an oven at 80°C to obtain amino-modified graphene oxide powder, designated AGO.

[0025] 2. Preparation of PI / AGO composite film Taking PI / AGO-1.6 as an example, the preparation process of PI / AGO composite films with different AGO contents is introduced.

[0026] (1) Preparation of PAA / AGO solution: 0.0725 g of AGO was dispersed in 20.58 mL of DMAc for 3 h. 1.6642 g of 4-4'-diaminodiphenyl ether (ODA) was added under N2 atmosphere. After complete dissolution, 2.7863 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) was added in 5 portions. The molar ratio of ODA to BTDA was 1:1.02. The reaction was then continued in an ice bath at 0-5°C for 5 h and allowed to stand overnight. A uniform mixed solution with a solid content of 19% and an AGO content of 1.6 wt% was obtained, which was named PAA / AGO-1.6 solution. The remaining content formula is shown in Table 1 below.

[0027] Table 1 Formulations of polyamic acid solutions with different AGO contents (2) Preparation of PI / AGO composite film: The above PAA / AGO solution was coated with a wet film of 1.0 mm, and the solvent was evaporated at room temperature. After complete drying, the film was placed in an oven at 100°C for 1 hour for preliminary thermal imidization. After cooling naturally to room temperature, the film was demolded in deionized water and transferred to a tube furnace. Under an argon atmosphere, the temperature was programmed to 300°C for complete thermal imidization. The specific procedure was 150°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 300°C for 1 hour, with a heating rate of 2°C / min. After the tube furnace was cooled naturally to room temperature, it was taken out to obtain PI / AGO-1.6. Other samples were prepared in the same way.

[0028] The structural characterization and performance evaluation of the above-mentioned embodiment products are as follows: 1. Structural characterization (1) SEM test like Figure 1 As shown, the structural differences between the plane and cross section of PI and PI / AGO were compared by SEM. Figure 1 (ab) and Figure 1 (cd) It can be seen that the surface and cross section of the PI film are dense and smooth. Figure 1 (e-f) A small amount of protrusions on the edges of the sheets can be seen, and they are evenly dispersed. This is likely due to the introduction of amino groups into the polyimide, which improves the dispersion of AGO in the PI matrix. The abundant graphene sheet structures evident in Figure 1 (gh) confirm the successful preparation of the PI / AGO composite film.

[0029] (2) FTIR test Figure 2 The FTIR curves of AGO, PI, PI / AGO-300-1.6 and PI / AGO-400-1.6 are shown, where "-300" and "-400" represent the imidization temperature. AGO has a peak at 1608 cm -1 The absorption peak at 1361 cm -1 There is an obvious CN stretching vibration peak at 3463 cm, which confirms that the amino group is successfully grafted onto GO. -1 The absorption peak at 1774 cm represents the stretching vibration peak of the CN bond; -1 The absorption peak at 775 cm represents the C=O asymmetric stretching vibration peak; -1 The absorption peak at 1608 cm represents the bending vibration peak of the C=O bond and the deformation vibration peak of the imide ring; -1 The absorption peak at 1361 cm represents the C=C vibration peak of the aromatic carbon skeleton; and -1 The absorption peak at 1774 cm represents the CN stretching vibration peak. -1and 1731 cm -1 The C=O asymmetric stretching vibration and C=O symmetric stretching vibration at the position are both characteristic peaks of polyimide. Compared with the characteristic peak of polyamic acid (1660 cm -1 The carbonyl (CONH) absorption peak at 1550 cm -1 The C-NH absorption peak at 1361 cm indicates that the PI film treated at temperatures above 300°C has been completely imidized. The above analysis shows that the PI film was successfully prepared. Compared with PI, PI / AGO-300-1.6 and PI / AGO-400-1.6 have a C-NH absorption peak at 1361 cm -1 and 1608 cm -1 The intensities of the CN peak and C=C peak at π / 4 increase, indicating that AGO is successfully compounded into the PI film.

[0030] (3) Raman test Figure 3 The Raman spectra of PI / AGO-200-1.6, PI / AGO-300-1.6 and PI / AGO-400-1.6 are shown in Figure 1. -1 There are two obvious absorption peaks, corresponding to the D peak and the G peak. It is generally believed that the D peak represents the structural defects or disordered carbon produced in the material, while the G peak is caused by the sp 2 It is generally believed that the intensity ratio of D peak and G peak can be used to study the degree of graphitization of the material. As can be seen from the figure, as the imidization temperature increases from 200℃ to 400℃, I D :I G The value of α increased from 1.02 to 1.12 and then decreased to 1.11. The increase is due to the removal of the initial oxygen-containing groups, which creates new defects; the decrease is due to the rearrangement of the graphene carbon structure to repair the defects.

[0031] (4) XPS test To further investigate the surface composition and element valence of PI / AGO at 300℃ and 400℃, XPS tests were performed on PI / AGO-300-1.6 and PI / AGO-400-1.6. Figure 4 As shown in (a), both samples contain three elements: C, N, and O. Figure 4 In (b), PI / AGO-300-1.6 shows the characteristic peaks of C=C, CN, and C=O at 283.85 eV, 284.78 eV, and 286.88 eV, respectively. Figure 4 (c), the characteristic peak at 397.98 eV represents -C=N, the characteristic peak at 399.28 eV represents CN, and the characteristic peak at 401.08 eV represents -NR3+ The main forms of N in PI / AGO composite films are imide bonds (-CO-N-CO-) from PI molecular chains. -N= and -NR3 + The effective cyclodehydration of PAA can also be verified. Figure 2 The three characteristic peaks at 530.18 eV, 531.28 eV, and 532.48 eV in .4 (d) represent the CO bond, C=O bond, and OH bond, respectively.

[0032] When the temperature rises from 300℃ to 400℃, Figure 4 (b) The proportion of C=C bonds decreased from 83.1% to 81.0%. Figure 4 (d) The C=O bond content in the PI / AGO-400-1.6 sample is significantly reduced, with C=O bonds primarily present in the polyimide rings, and no significant OH bonds are observed. This suggests that the increase in temperature may be due to partial polyimide pyrolysis and main chain breakage.

[0033] , Absorption performance evaluation In addition to complex permittivity and complex permeability, a material's dissipative properties can also be evaluated using its dielectric loss tangent (tan δ =ε″ / ε′), a key indicator of electromagnetic-thermal energy conversion efficiency. To achieve efficient electromagnetic wave absorption, a sufficiently large loss tangent must be ensured. Absorbers with high dielectric loss can dissipate energy by converting more electromagnetic radiation energy into other forms of energy.

[0034] Figure 5 For PI / AGO-300 series samples in K-band and Ka-band 、 and The curve of value changing with frequency. Figure 5 (a) and Figure 5 (d) shows that all samples In the K-band range, there is an upward trend, and all All of them vary in the range of 3.75-7.5. Figure 5 (b) and Figure 5 In (e), PI / AGO-2.0 has high value, indicating that it may have a higher loss capacity for electromagnetic waves, and its maximum value is 2.94. and The change of the value shows a flat trend, which means that the speed of polarization inside the material cannot keep up with the rate of change of the electromagnetic field, resulting in polarization relaxation and energy loss. Figure 5 (c) and Figure 5 (f) shows that PI / AGO-2.8 The values ​​are greater than those of all other samples in both the K-band and Ka-band, indicating that it has the largest dielectric loss capability among all samples. A heterogeneous interface is formed between AGO and PI, thereby enhancing the interface polarization.

[0035] Debye relaxation theory is the polarization relaxation process exhibited by dielectric materials under the action of an external electric field. In heterogeneous media, the phenomenon of interface polarization relaxation is ubiquitous. The accumulation and non-uniform distribution of space charge at the interface of different phases can form a macroscopic electric moment, which continuously dissipates the energy of electromagnetic waves. The intensity of interface polarization is proportional to the difference in dielectric properties or conductivity between the two phases. This phenomenon is usually called the Maxwell-Wagner-Sillars effect. This effect is particularly significant in heterogeneous structures, manifested as the accumulation of charge at the interface and the formation of dipoles on the surface of particles or clusters. Especially in artificial nanostructures, due to the unique formation mechanism, the Maxwell-Wagner-Sillars effect is particularly prominent. By regulating the interface polarization relaxation process to optimize the impedance matching characteristics, it constitutes the core foundation of the design of excellent mixed-dimensional absorber materials. The kinetic process of dipole polarization and interface polarization relaxation follows the following control equations: (1) (2) Using formula (1) and formula (2), we can calculate ε' and ε" The relationship between them can be expressed by formula (3): (3) Where, is the frequency of the electromagnetic field, represents the static dielectric constant, is the high frequency limiting dielectric constant, represents the polarization relaxation time. The real part of the complex dielectric constant As the horizontal axis, the imaginary part Plotting the Cole-Cole semicircle curve with the vertical axis can be used to determine the dielectric loss properties of a material. Each semicircle in the Cole-Cole curve represents a dielectric relaxation process. The larger the radius of the semicircle, the greater the polarization loss in the material. If the curve contains multiple semicircles, it indicates that the material has undergone multiple dielectric relaxation processes.

[0036] Figure 6 Figure 2 shows the Cole-Cole curves of PI / AGO composite films with different AGO contents in the K band. It can be seen that the Cole-Cole curves of all samples have multiple semicircles, indicating that there are multiple polarization relaxation processes in the samples.

[0037] Figure 7Figure 2 shows the Cole-Cole curves of PI / AGO composite films at different AGO contents in the Ka band. Compared to the Cole-Cole curves in the K band, the semicircles of the Cole-Cole curves in the Ka band have larger radii, indicating a stronger polarization relaxation process.

[0038] Figure 8 The figure shows the change of reflection loss of PI / AGO composite film with different graphene contents in K band. Figure 8 It can be seen that the RL of PI / AGO-1.6 at 2.5 mm and 18 GHz min RL of PI / AGO-2.0 at 1.5 mm and 19.4 GHz is -10.7 dB. min The RL of PI / AGO-2.4 at 3.5 mm and 25.5 GHz is -24.2 dB, and its corresponding EAB is 4.45 GHz. min The RL of PI / AGO-2.8 at 1.75 mm and 18.3 GHz is -33.3 dB, and its corresponding EAB is 2.5 GHz. min is -25.3 dB, and the corresponding EAB is 3.63 GHz. At the same time, the RL at 1.5 mm and 21.41 GHz is min It is 18.7dB, and its corresponding EAB can reach 6.03GHz.

[0039] Figure 9 The reflection loss diagram of samples with different AGO contents in the Ka band varies with thickness. It can be seen that the RL of PI / AGO-1.6 at 3 mm and 36.7 GHz is min The RL of PI / AGO-2.0 at 1.18 mm and 26.5 GHz is -20.9 dB, and its corresponding EAB is 4.77 GHz. min The RL of PI / AGO-2.4 at 3.5 mm and 27.3 GHz is -18.6 dB, and its corresponding EAB is 3.5 GHz. min The RL at 3.1 mm and 30.5 GHz is -48.1 dB, and the corresponding EAB is 5.5 GHz. min The RL at 2.51 mm and 36.1 GHz is -61.2 dB, and the corresponding EAB is 4.4 GHz. min The RL of PI / AGO-1.6 at 33.2 GHz is -58.9 dB, and its corresponding EAB is 4.63 GHz. minThe value is -14.6 dB, and the EAB is 8 GHz. Compared with the reflection loss value in the K band, the RL of all samples in the Ka band is min Both have been improved, indicating that PI / AGO has better wave absorbing performance in the Ka band, and the PI film composited with AGO is more conducive to absorbing electromagnetic waves at high frequencies.

[0040] The impedance (Z) and electromagnetic wave attenuation ability of the absorbing material are both key factors in determining the absorbing performance of the material. Z can be calculated by formula (4), and the attenuation constant is It is one of the core parameters of the electromagnetic wave attenuation characteristics of the material, and its calculation formula is defined as follows: (4) Figure 10 The impedance matching diagram and attenuation constant diagram of PI / AGO in the K-band and Ka-band ranges are shown below. in The closer the value of / Z0| is to 1, the better the impedance matching performance of the material. Figure 10 (a, b) shows that PI / AGO-2.4 has the best impedance in the 18-26.5GHz and 26.5-40GHz frequency bands, with values ​​of 0.955 and 0.992 respectively. In contrast, at higher frequencies, it has better impedance performance, and more electromagnetic waves can enter the composite film and dissipate. Figure 8 and Figure 9 The reflection loss value results are consistent with .

Claims

1. A method for preparing a PI / AGO composite absorbing film, characterized in that: The following steps are involved: 1) Preparation of AGO First, graphene oxide was dispersed in deionized water and ultrasonically treated. Then, p-phenylenediamine was added and stirred in an oil bath at 75-85°C for 10-15 hours. After the reaction, the mixture was filtered, washed, and vacuum-dried to obtain amino-modified graphene oxide, denoted as AGO. 2) Preparation of PI / AGO composite film First, under an inert atmosphere, AGO was dispersed in N,N-dimethylacetamide and stirred evenly. 4,4'-diaminodiphenyl ether was added to dissolve it, and then 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added in batches. The mixture was then reacted at a low temperature of 0-10°C for 3-6 hours and allowed to stand overnight to obtain a uniform mixed solution with an AGO content of 0.5-5.0 wt%, named PAA / AGO solution. Next, the PAA / AGO solution was coated to form a film. After solvent evaporation and preliminary imidization at 80-120°C, the temperature was programmed to 300°C in a tube furnace for complete imidization to obtain a polyimide / amino-modified graphene oxide composite absorbing film, denoted as PI / AGO.

2. The method for preparing a PI / AGO composite absorbing film according to claim 1, wherein: In step 1), the mass ratio of graphene oxide to p-phenylenediamine is 1:2 to 2:

1.

3. The method for preparing a PI / AGO composite absorbing film according to claim 1, wherein: In step 2), the mass content of AGO in the PAA / AGO solution is 1.6-2.8 wt %, and the molar ratio of 4,4'-diaminodiphenyl ether to 3,3',4,4'-benzophenonetetracarboxylic dianhydride is 1:1.01-1:1.

05.

4. The method for preparing a PI / AGO composite absorbing film according to claim 1, characterized in that: In step 2), 3,3',4,4'-benzophenonetetracarboxylic dianhydride is added in batches 4 to 6 times, with an interval of 5 to 15 minutes between each addition.

5. The method for preparing a PI / AGO composite absorbing film according to claim 1, wherein: In step 2), the inert atmosphere is argon or nitrogen, and the complete imidization procedure is: heating at 2°C / min, and keeping at 150°C, 200°C, 250°C, and 300°C for 1 hour each.

6. A PI / AGO composite absorbing film, characterized in that: Prepared by the method of any one of claims 1-5, wherein AGO is uniformly dispersed in the polyimide matrix and has a content of 1.6-2.8 wt%.

7. Use of the PI / AGO composite absorbing film according to claim 6 in the fields of radar stealth, electromagnetic shielding or high-frequency electronic equipment protection.

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