Chemically grafted modified polyetherimide insulating composite material, and preparation method and application thereof

Abstract

The application discloses a chemically grafted modified polyetherimide insulating composite material and a preparation method and application thereof, and belongs to the technical field of polyimide-based composite insulating materials.The application aims to solve the technical problems that the existing polyimide-based composite insulating materials introduce inorganic fillers to improve the insulating performance, meanwhile, the mechanical performance is deteriorated, and the organic modification causes the phase separation phenomenon.The organic filler p-chlorostyrene is linked between the polymer matrix through a chemical bond, the phase separation phenomenon is perfectly avoided, new crystal phase structures are not introduced, and no significant crystallization behavior change is caused, the comprehensive performance of the polymer is significantly improved, excellent dielectric performance and insulating performance are achieved, and the application can be widely applied to advanced fields such as electrical, electronic and new energy vehicles.

Description

Technical Field

[0001] This invention belongs to the technical field of polyimide-based composite insulation materials, specifically relating to a chemically grafted modified polyetherimide insulation composite material, its preparation method, and its application. Background Technology

[0002] With the continuous advancement of new energy vehicle technology, trends towards electrification, intelligence, and high integration are emerging. The market share of pure electric and plug-in hybrid vehicles continues to increase, battery energy density and high-voltage platform technology are constantly improving, and electric drive systems are gradually developing towards multi-functionality and high power density. This not only places higher demands on the transportation efficiency and energy utilization of transportation systems, but also poses more stringent technical challenges to the performance, safety, and reliability of the core drive systems of transportation equipment.

[0003] As the core power unit of new energy vehicles, the drive motor has crucial strategic significance. Its efficiency level directly affects the vehicle's energy consumption and range, while power density and speed performance determine the vehicle's power performance and lightweight level. Because drive motors are developing towards higher power density, higher speed, and more compact and lightweight designs, the operating environment and voltage conditions of the motors are becoming increasingly stringent. This makes the requirements for the internal insulation materials of the motor particularly important. Especially under high voltage, the insulation material needs to have sufficient breakdown voltage to prevent current from penetrating the insulation layer, leading to short circuits or damage. At the same time, when the motor rotates at high speed, the electric field intensity may cause corona discharge, especially under high voltage, which may trigger partial discharge and damage the insulation material. Therefore, the insulation material of the drive motor not only needs to have a high breakdown voltage but also needs to have the ability to resist corona discharge to ensure the safety and stability of the motor under long-term high-efficiency operation.

[0004] Polyimide (PI) film, with its inherent high breakdown field strength, stable insulation over a wide temperature range, and excellent heat resistance, has always been the preferred material for critical components such as drive motor windings and slot insulation. However, with the continuous improvement of the operating environment and voltage conditions of drive motors, traditional polyimide materials can no longer withstand the insulation damage caused by high-frequency pulse voltages and corona discharge to the inter-turn insulation. To solve this problem, it is necessary to simultaneously improve the breakdown field strength and corona aging life of polyimide films. Breakdown field strength and corona aging life involve different physical mechanisms. While simply increasing the breakdown field strength can improve the material's ability to withstand transient overvoltages to some extent, if the corona aging performance is insufficient, the material will still undergo structural degradation and insulation failure due to partial discharge erosion under long-term high-frequency pulse stress. Conversely, improving only the corona life while ignoring the intrinsic breakdown strength will also make it difficult to meet the increasingly higher operating voltage requirements. Therefore, research on improving the insulation reliability of polyimide films under high-frequency and high-voltage conditions has shifted from optimizing single properties to synergistic enhancement of multiple properties. However, in traditional polyimide modification methods, the main problem with inorganic modification is the poor compatibility between inorganic fillers and the matrix, leading to a sharp deterioration in mechanical properties. Organic modification, on the other hand, cannot avoid phase separation between the matrix and fillers, resulting in increased current density. Thus, achieving a simultaneous improvement in the comprehensive performance of modified polyimide composites is crucial for the reliable operation of high-voltage, high-speed, and high-power-density drive motors. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of mechanical property degradation caused by the introduction of inorganic fillers to improve the insulation performance of existing polyimide-based composite insulation materials, and phase separation caused by organic modification. The invention provides a chemically grafted modified polyetherimide insulation composite material, its preparation method and application.

[0006] One objective of this invention is to provide a method for preparing a chemically grafted modified polyetherimide insulating composite material, the method comprising the following steps: Step 1: Add triaminopyrimidine and norborneol edical anhydride to N,N-dimethylacetamide solution. After reacting until the solution turns bright yellow and there is no precipitate, add 4,4'-diaminodiphenyl ether and stir under ultrasonic conditions for 20-50 min to obtain mixed solution a. Add bisphenol A type diether dianhydride to mixed solution a and stir until viscous to obtain mixed solution b. Step 2: Add p-chlorostyrene to mixed solution b and mix thoroughly to obtain mixed solution c. Vacuum the mixed solution c, then coat it onto the substrate. After curing and heat treatment, polyetherimide insulating composite material is obtained.

[0007] Further specifying, the 4,4'-diaminodiphenyl ether described in step 1 is purified by recrystallization in heated anhydrous ethanol before use.

[0008] Further specifying, the molar ratio of triaminopyrimidine to norborneol enediic anhydride in step 1 is 1:1.

[0009] Further specifying, in step 1, the amount of triaminopyrimidine accounts for 5 to 25% of the sum of the amounts of triaminopyrimidine and 4,4'-diaminodiphenyl ether.

[0010] Further specifying, the molar ratio of triaminopyrimidine to bisphenol A type diether dianhydride in step 1 is (0.5~2.5):10.1.

[0011] Further specifying, in step 1, the ratio of N,N-dimethylacetamide to triaminopyrimidine is 40 ml: (0.5~2.5) mmol.

[0012] Further specifying, in step 1, bisphenol A type diether dianhydride is added in portions, with each portion spaced 1 hour apart.

[0013] Further specifying, the molar ratio of p-chlorostyrene in step 2 to triaminopyrimidine in step 1 is 1:1.

[0014] Further specifying, in step 2, the mixed solution c is evacuated until no air bubbles are present in the colloid.

[0015] Further specified, in step 2, the curing temperature is 70-90℃, the time is 5-7 h, the heat treatment temperature is 150-250℃, the time is 1-2 h, and the heating rate is 20-40℃ per hour.

[0016] The second objective of this invention is to provide a polyetherimide insulating composite material with p-chloroaniline end-capped by the above method.

[0017] A third objective of this invention is to provide an application of the p-chloroaniline-terminated polyetherimide insulating composite material in the inter-turn insulation of high-voltage electrical appliances.

[0018] The significant advantages of this invention compared to existing technologies are: This invention links the organic filler, p-chlorostyrene, to the polymer matrix via chemical bonds, perfectly avoiding phase separation without introducing new crystal phase structures or causing significant changes in crystallization behavior, thus significantly improving the overall performance of the polymer. The polyetherimide insulating composite material prepared using this method exhibits excellent dielectric and insulating properties, with a breakdown strength as high as 793.8 kV / mm, maintaining a high level of 610.5 kV / mm even at 150℃, demonstrating excellent high-temperature electrical insulation stability. It can be widely applied in advanced fields such as electrical engineering, electronics, and new energy vehicles. Attached Figure Description

[0019] Figure 1 The image shows the scanning electron microscope (SEM) pattern of the pure polyetherimide insulating material prepared in Comparative Example 1. Figure 2 The image shows the scanning electron microscope (SEM) image of the polyetherimide insulating composite material prepared in Example 3. Figure 3 The image shows a scanning electron microscope image of the polyetherimide insulating composite material prepared in Example 5. Figure 4 FTIR spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5. Figure 5 XRD patterns of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5. Figure 6 XPS spectrum of pure polyetherimide prepared in Comparative Example 1; Figure 7 XPS spectrum of the polyetherimide insulating composite material prepared in Example 3; Figure 8 The dielectric spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 are shown; (a) is the dielectric constant, and (b) is the dielectric loss. Figure 9(a) shows the breakdown field strength spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 at room temperature. Figure 9(b) shows the breakdown field strength spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 at 100 °C. Figure 9(c) shows the breakdown field strength spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 at 150 °C. Figure 10(a) shows the leakage current spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composite materials with different grafting contents prepared in Examples 1-5 at room temperature. Figure 10(b) shows the leakage current spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 at 100 °C. Figure 10(c) shows the leakage current spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 at 150 °C. Figure 11Tensile spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different graft contents prepared in Examples 1-5; (a) at room temperature, (b) at 100 °C. Figure 12 The DMA spectra of pure polyetherimide prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 are shown; (a) represents modulus, and (b) represents loss. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0022] Example 1: A method for preparing a chemically grafted modified polyetherimide insulating composite material is carried out according to the following steps: Step 1: First, 4,4'-diaminodiphenyl ether was dissolved in anhydrous ethanol at 60 °C. After stirring for 30 min, it was placed in ice water to quickly precipitate crystals and obtain purified 4,4'-diaminodiphenyl ether. Then, 0.5 mmol of triaminopyrimidine and 0.5 mmol of norborneol ediol anhydride were added to 40 mL of N,N-dimethylacetamide solution. After reacting until the solution turned bright yellow and no precipitate was formed, 9.5 mmol of 4,4'-diaminodiphenyl ether was added. The mixture was stirred under sonication for 30 min to obtain mixed solution a. 10.1 mmol of bisphenol A type diether dianhydride was added to mixed solution a in 4 portions, with an interval of 1 h between each addition. After the addition was complete, the mixture was stirred until it became viscous to obtain mixed solution b. Step 2: Add 0.5 mmol of p-chlorostyrene to mixed solution b and mix thoroughly to obtain mixed solution c. Vacuum solution c is evacuated for 10 h and then coated onto a substrate. First, dry at 80°C for 6 h, then continue heating at a rate of 30°C per hour to 200°C and hold for 1.5 h. After that, peel off the film on the substrate to obtain a p-chloroaniline-terminated polyetherimide insulating composite material, named 0.5 CSAPI.

[0023] Example 2: This example differs from Example 1 in that: in step 1, the amount of triaminopyrimidine used is 1 mmol, and the amount of 4,4'-diaminodiphenyl ether used is 9 mmol; in step 2, the amount of p-chlorostyrene used is 1 mmol. The product is named 1.0 CSAPI. Other steps and parameters are the same as in Example 1.

[0024] Example 3: This example differs from Example 1 in that: in step 1, the amount of triaminopyrimidine used is 1.5 mmol, and the amount of 4,4'-diaminodiphenyl ether used is 8.5 mmol; in step 2, the amount of p-chlorostyrene used is 1.5 mmol. The product is named 1.5 CSAPI. Other steps and parameters are the same as in Example 1.

[0025] Example 4: This example differs from Example 1 in that: in step 1, the amount of triaminopyrimidine used is 2 mmol, and the amount of 4,4'-diaminodiphenyl ether used is 8 mmol; in step 2, the amount of p-chlorostyrene used is 2 mmol. The product is named 2.0 CSAPI. Other steps and parameters are the same as in Example 1.

[0026] Example 5: This example differs from Example 1 in that: in step 1, the amount of triaminopyrimidine used is 2.5 mmol, and the amount of 4,4'-diaminodiphenyl ether used is 7.5 mmol; in step 2, the amount of p-chlorostyrene used is 2.5 mmol. The product is named 2.5 CSAPI. Other steps and parameters are the same as in Example 1.

[0027] Comparative Example 1: Pure PEI First, 4,4'-diaminodiphenyl ether was dissolved in anhydrous ethanol at 60 °C, stirred for 30 min, and then placed in ice water to quickly precipitate crystals to obtain purified 4,4'-diaminodiphenyl ether. Then, 9.5 mmol of 4,4'-diaminodiphenyl ether and 10.1 mmol of bisphenol A diether dianhydride were added to 40 mL of N,N-dimethylacetamide solution and stirred until viscous to obtain a mixed solution. The mixed solution was vacuumed for 10 h and then coated onto a substrate. It was first dried at 80 °C for 6 h, and then heated to 200 °C at a rate of 30 °C per hour and held at that temperature for 1.5 h. The film on the substrate was then peeled off to obtain pure polyetherimide insulating material, named PEI.

[0028] Figure 1-3The images show scanning electron microscope (SEM) images of the insulating composite materials prepared in Comparative Example 1, Examples 3, and 5. As can be seen from the images, the cross-sections of all three samples exhibit relatively smooth and continuous morphology, with no obvious pores, cracks, or macroscopic phase separation observed. This indicates that the prepared films all possess good film-forming quality and structural integrity. The cross-sectional morphology exhibits the typical dense and uniform characteristics of polyimide materials, indicating that the grafting modification process did not disrupt the overall structural stability of the matrix.

[0029] Figure 4 To compare the FTIR spectra of the alcohol PEI prepared in Comparative Example 1 with the polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 of this invention, FTIR was used to characterize the PEI and CSAPI composite films in order to better understand their microstructure. The PEI sample was analyzed at 1775 cm⁻¹. -1 and 1715 cm -1 Distinct absorption peaks appear nearby, corresponding to the asymmetric and symmetric stretching vibrations of C=O in the imide ring, respectively; at 1375 cm⁻¹... -1 The characteristic peak at 725 cm⁻¹ is attributed to the CN stretching vibration in the imide ring. Furthermore, at 725 cm⁻¹... -1 The characteristic bending vibration peak of the imide ring can be observed nearby, indicating that the pure PEI film has a complete imide structure and the polyimide has been successfully imidized. For CSAPI films with different graft contents, their infrared spectra are generally consistent with those of PEI, and the position of the characteristic absorption peak of the imide ring does not shift significantly, indicating that the introduction of chlorostyrene does not destroy the polyimide backbone structure, and the composite system still maintains good chemical stability.

[0030] Figure 5 The figure shows the XRD patterns of pure PEI obtained in Comparative Example 1 and polyetherimide insulating composites with different grafting contents obtained in Examples 1-5 of this invention. PEI at 2... θThe diffraction patterns exhibit a wide, diffuse peak within the ≈15°~25° range, with no sharp peaks at higher angles. This indicates that PEI is predominantly amorphous, with only a certain degree of short-range ordered stacking. This aligns with the characteristic of polyimide segments being rigid and difficult to form long-range crystalline structures. For CSAPI films with different graft contents, the overall diffraction morphology remained consistent with PEI, showing wide, diffuse peaks rather than distinct crystalline peaks. This suggests that the grafting modification of chlorostyrene did not introduce a new crystalline phase structure or lead to significant changes in crystallization behavior; the composite system remained predominantly amorphous. As the graft content increased from 0.5 mmol to 2.5 mmol, the peak shape and position of the diffuse peaks changed only slightly, showing some differences in peak width and intensity. This reflects that the introduction of grafted segments may affect the stacking mode and local short-range order of polyimide molecular chains, but this effect is mainly reflected in the microscopic arrangement adjustment within the amorphous phase, rather than the formation of a new long-range ordered crystalline structure.

[0031] Figure 6 The XPS spectrum of pure PEI obtained in Comparative Example 1 clearly shows four different chemical environments of carbon atoms through peak fitting. The strongest peak at 284.8 eV is attributed to the numerous aromatic ring C-C bonds in the polymer molecular chain, as well as the aliphatic C-C bonds of the isopropylidene group (-C(CH3)2) in the BPADA monomer structure. The characteristic peak at approximately 286.2 eV is a composite peak, mainly corresponding to the ether carbon (COC) present in both BPADA and ODA monomer units, and also including the CN bond in the imine ring. The peak at 288.6 eV clearly corresponds to the carbonyl carbon (O=CN) in the imine ring, a characteristic signal of polyimide. In addition, the broad peak observed near approximately 291.5 eV is a characteristic peak of π-π stacking unique to aromatic rings. Furthermore, the analysis results of the O1s spectrum are in high agreement with the C1s spectrum. The O1s spectrum can be clearly resolved into two peaks: the main peak at approximately 532.1 eV belongs to the carbonyl oxygen (C=O) on the imine ring, while the shoulder peak at approximately 533.5 eV corresponds to the oxygen (COC) in the ether bond. Notably, since both BPADA and ODA monomers contain ether bonds, the COC peak exhibits a remarkably high intensity, perfectly consistent with the expected molecular structure. The N1s spectrum shows a symmetrical singlet at approximately 400.5 eV, which is clearly attributed to the nitrogen atom (Pyrrolie N) in the imine ring structure, rather than other nitrogen-containing species. The presence of this singlet indicates that the polyamic acid precursor in the polymer has undergone complete cyclization, forming a chemically homogeneous imine structure.

[0032] Figure 7The XPS spectra of the polyetherimide insulating composite material prepared in Example 3 of this invention are shown below. First, the C1s and O1s spectra of the graft copolymer maintain a high degree of similarity to the pure PEI matrix in overall profile, with the core characteristic peaks belonging to CC (284.8 eV), COC (286.2 eV), O=CN (288.6 eV), C=O (532.1 eV), and CO (533.5 eV) still present. This indicates that the grafting reaction process was mild and successfully preserved the basic skeletal structure of the polyimide backbone. In the N1s spectrum, compared to the only symmetrical Pyrrolie N single peak (400.5 eV) in the pure PEI matrix, the N1s spectrum of the graft copolymer exhibits an asymmetric fine structure. Its main peak is still located at 400.5 eV, belonging to the PEI backbone and the large number of imine ring N atoms (Pyrrolie N) on the newly formed connecting bridges. Crucially, a distinct shoulder peak appears at the low binding energy end of approximately 398.8 eV. This peak position is typical of sp² hybridized nitrogen atoms (C=NC) and clearly corresponds to the nitrogen atom on the pyrimidine ring in the triaminopyrimidine molecule introduced as a "chemical bridge." The appearance of this nitrogen signal in a new chemical environment is direct evidence that the triaminopyrimidine molecule has been successfully bonded to the polymer chain through a chemical reaction.

[0033] Figure 8 The dielectric spectra of pure PEI prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 of this invention are shown in Figure (a). As can be seen from Figure (a), the dielectric constant of all samples remains relatively stable in the low-frequency region, and shows a certain degree of decreasing trend with increasing frequency, exhibiting typical polymer dielectric response characteristics. This is mainly because under the action of a low-frequency electric field, the dipoles of the molecular chain segments can be fully oriented and polarized, thus contributing a higher dielectric constant; while under high-frequency conditions, the dipole orientation response gradually lags, the polarization ability weakens, and the dielectric constant decreases with increasing frequency. Figure (b) shows that the dielectric loss values ​​of all films are generally low, and show a trend of first decreasing and then increasing with frequency: in the low-to-mid-frequency region, the loss gradually decreases, mainly related to the reduction of dipole polarization loss; while in the higher frequency range, the dielectric loss rebounds, possibly related to the increased conductivity loss and enhanced interface polarization effect. The dielectric loss curves of different CSAPI films show basically the same trend, indicating that grafting modification did not cause a significant additional energy dissipation process.

[0034] Figure 9 shows the breakdown spectra of pure PEI prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 of this invention. As can be seen from Figure (a), the characteristic breakdown strength (Eb) of PEI at 25 °C is approximately 695.1 kV / mm. With the increase of grafting concentration, the breakdown strength of CASPI film shows a trend of first increasing and then decreasing. Among them, the Eb of 1.5 mmol CASPI increases to 793.8 kV / mm, which is about 14% higher than that of PEI, showing the best breakdown performance. When the grafting concentration is further increased to 2.5 mmol, the breakdown strength decreases, indicating that excessive grafting may introduce local structural inhomogeneity or interface defects, thereby weakening the electrical insulation performance. As shown in Figure (b), the breakdown strength of all samples decreased at 100 °C, but the CASPI system still showed a significant advantage. The Eb of 1.5 mmol CASPI reached 697.3 kV / mm, a more significant improvement compared to PEI (523.1 kV / mm). As shown in Figure (c), with further increases in temperature, the breakdown strength of PEI decreased to 462.5 kV / mm, while 1.5 mmol CASPI maintained a relatively high level of 610.5 kV / mm, demonstrating excellent high-temperature electrical insulation stability. Overall, the introduction of appropriate grafting structures can construct more deep-level traps within the polymer, enhancing the capture and confinement of charge carriers, while improving the interfacial bonding state and reducing local electric field distortion, thereby significantly improving the breakdown strength and high-temperature electrical insulation reliability of the material. 1.5 mmol was the optimal grafting concentration for this system, exhibiting the highest characteristic breakdown strength and good distribution stability under different temperature conditions, verifying the effectiveness of the molecular grafting strategy in improving the high-temperature, high-electric-field service performance of polyimide films.

[0035] Figure 10 shows the leakage current spectra of pure PEI prepared in Comparative Example 1 and polyetherimide insulating composites with different graft contents prepared in Examples 1-5 of this invention. At all test temperatures and electric field strengths, the leakage current density of all graft copolymers (CSAPI) was lower than that of pure PEI, indicating a significant reduction in conductivity loss. This suppression effect is particularly significant under high temperature and high field conditions. For example, at 150 °C and 125 kV / mm, the leakage current density of pure PEI reached as high as 2.0 × 10⁻⁶. -10 The leakage current density was A / mm², while the sample with a graft content of 1.5 mmol had a leakage current density of only 0.5 × 10⁻⁶. -10A / mm². This demonstrates that introducing functional side chains via covalent bonds can construct an efficient carrier suppression system. At all test temperatures, the leakage current density continuously decreased as the grafting content increased from 0.5 mmol to 1.5 mmol, reaching a minimum at 1.5 mmol. However, when the grafting content increased further, the leakage current density rebounded. This may be because while excessively high grafting density introduces more traps, it may also lead to excessively close average distances between traps, forming new conductive pathways. Furthermore, excessively high side chain density may also disrupt the orderly stacking of the main chain to some extent, introducing additional structural disorder.

[0036] Figure 11 The tensile spectra of pure PEI prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 of this invention are shown in Figure (a). As can be seen from Figure (a), at room temperature (25 °C), the mechanical properties of the composite film grafted with CSAPI are significantly enhanced compared with pure polyimide (tensile strength of 98 MPa). Its tensile strength initially increases and then decreases with increasing CSAPI content, reaching a peak of 135 MPa at a content of 1.5 mmol, which is approximately 38% higher than that of pure PI. However, when the content further increases to 2.5 mmol, the material properties deteriorate sharply, exhibiting obvious brittleness. As can be seen from Figure (b), this enhancement effect is more pronounced at high temperatures (100 °C). Although the strength of all samples decreases due to thermal softening, the tensile strength of the 1.5 mmol grafted film remains at 108 MPa, a value that even exceeds the strength of pure PI at room temperature. This fully demonstrates that the chemical grafting strategy significantly improves the thermal mechanical stability of the material.

[0037] Figure 12 The DMA spectra of pure PEI prepared in Comparative Example 1 and polyetherimide insulating composites with different grafting contents prepared in Examples 1-5 of this invention are shown. An appropriate amount of CSAPI side groups, introduced via covalent bonds, effectively restricts the segmental movement of the polymer backbone through its rigid aromatic structure, thereby macroscopically improving the material's stiffness. However, when the content increases to 2.5 mmol, the storage modulus drops sharply to approximately 11000 MPa, even lower than that of pure PEI. This may be because excessive grafting induces microphase separation or aggregation, forming structural defects that weaken the interaction between molecular chains. Figure (b) shows the loss factor curves of PEI and CSAPI matrix films as a function of temperature. The loss factor curves show that all samples exhibit a significant peak around 200–250 °C, corresponding to the glass transition temperature (Tg).

[0038] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A process for the preparation of a chemically grafted modified polyetherimide insulating composite material, characterized in that, The method described: Step 1: Add triaminopyrimidine and norborneol edical anhydride to N,N-dimethylacetamide solution. After reacting until the solution turns bright yellow and there is no precipitate, add 4,4'-diaminodiphenyl ether and stir under ultrasonic conditions for 20-50 min to obtain mixed solution a. Add bisphenol A type diether dianhydride to mixed solution a and stir until viscous to obtain mixed solution b. Step 2: Add p-chlorostyrene to mixed solution b and mix thoroughly to obtain mixed solution c. Vacuum the mixed solution c, then coat it onto the substrate. After curing and heat treatment, polyetherimide insulating composite material is obtained.

2. The method of claim 1, wherein, The 4,4'-diaminodiphenyl ether described in step 1 is purified by recrystallization in heated anhydrous ethanol before use.

3. The method of claim 1, wherein, In step 1, the molar ratio of triaminopyrimidine to norborneol enediic anhydride is 1:

1.

4. The method according to claim 1, characterized in that, In step 1, the amount of triaminopyrimidine accounts for 5-25% of the sum of the amounts of triaminopyrimidine and 4,4'-diaminodiphenyl ether, and the molar ratio of triaminopyrimidine to bisphenol A type diether dianhydride is (0.5-2.5):10.

1.

5. The method according to claim 1, characterized in that, In step 1, the ratio of N,N-dimethylacetamide to triaminopyrimidine is 40 mL: (0.5~2.5) mmol.

6. The method according to claim 1, characterized in that, In step 1, bisphenol A type diether dianhydride is added in portions, with each addition spaced 1 hour apart.

7. The method according to claim 1, characterized in that, In step 2, the molar ratio of p-chlorostyrene to triaminopyrimidine in step 1 is 1:

1.

8. The method according to claim 1, characterized in that, In step 2, the curing temperature is 70-90℃ and the time is 5-7h. The heat treatment temperature is 150-250℃ and the time is 1-2h. The heating rate is 20-40℃ per hour.

9. The p-chloroaniline-terminated polyetherimide insulating composite material obtained by the method of any one of claims 1-8.

10. The application of the p-chloroaniline-terminated polyetherimide insulating composite material of claim 9 in the inter-turn insulation of high-voltage electrical appliances.

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