A SiO2@hyperbranched polymer / polyimide composite film and its preparation method

Abstract

The present invention discloses a SiO2@hyperbranched polymer / polyimide composite film and a preparation method thereof. The composite film comprises SiO2@EHBP fillers and a polyimide matrix; the SiO2@EHBP fillers are obtained by modifying hollow SiO2 microspheres with an amino-silane coupling agent to obtain NH2-SiO2 and then grafting EHBP; the EHBP is an epoxy-terminated hyperbranched polyurethane obtained by modifying a hydroxyl-terminated hyperbranched polymer with epichlorohydrin. The SiO2 particles are modified with an amino-silane coupling agent to introduce an active amino group while forming a first layer of coating on the SiO2; then grafting with EHBP forms a second layer of coating. On the one hand, the epoxy group can chemically bond with the amino group on the surface of the SiO2 microspheres, and on the other hand, the SiO2 particles can be embedded in the voids of the hyperbranched polymer, thereby making the two-phase combination more compact. Finally, the SiO2@EHBP fillers are mixed with the polyimide substrate, thereby introducing more regular, uniform and closed pores into the substrate, and at the same time ensuring the dispersion of the inorganic material and the pores, improving the film-forming dielectric properties and tensile strength.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimide films, and particularly relates to a SiO2@hyperbranched polymer / polyimide composite film and a preparation method thereof. Background Art

[0002] Polyimide (PI), as a class of high-performance polymer materials with imide rings as the structural characteristics, has become a widely studied object in the microelectronics industry due to its excellent dielectric, thermodynamic, corrosion resistance and other properties. In order to obtain polyimide materials with lower dielectric constants, researchers have done a lot of work. The common methods include: 1) introducing substituents with lower molar polarizability, such as fluorine atoms, into the polymer matrix; 2) doping inorganic hybrid low-dielectric-constant fillers, such as polyhedral oligomeric silsesquioxane (POSS), silica, zeolite, etc.; for example, Chinese Patent CN201810160083.9 discloses a preparation method of a phenyl silsesquioxane / graphene oxide / polyimide three-phase composite film, which simultaneously introduces the hybrid material POSS and the inorganic filler graphene oxide into the base material polyimide to improve the overall dielectric properties and thermal properties of the composite material. In addition, Chinese Patent CN201310745175.0 discloses a low-dielectric-constant polymer / graphene fluoride composite material and a preparation method thereof, specifically discloses that graphene and its derivatives are heated and fluorinated to obtain graphene fluoride, and then mixed and cured in an epoxy resin or polyimide precursor colloidal solution to obtain the composite material; 3) introducing air holes into the polymer matrix.

[0003] In addition, there are also chemical modifications of the main chain and side chain of polyimide, introducing groups with rigid structures or fluorine atoms into its main chain, or grafting macromolecular groups such as hyperbranched groups on the side chain. Since they have lower dipole moments and molecular polarizabilities, they can effectively reduce the dielectric constant. However, it is difficult for non-porous dielectric materials to achieve the possibility of ultra-low dielectric constants. Therefore, it is usually expected to further reduce the dielectric constant by preparing porous dielectric materials. However, the introduction of holes often causes the mechanical properties of the material to decline, the airtightness to become worse, and the water absorption rate to increase, greatly damaging the mechanical strength of the material; and the demand for inorganic hybridization is usually large, which will lead to dispersion problems in the base material, and then affect the mechanical properties of the composite material, etc. Therefore, seeking new ideas that can reduce the dielectric constant of the material and maintain good mechanical properties, airtightness and low water absorption rate of the material is of crucial significance for promoting the exploration and research and development of a new generation of ultra-low dielectric constant dielectric materials.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The object of the present invention is to address the deficiencies in reducing the dielectric constant of polymer materials in the prior art, especially the problems caused by the introduction of inorganic fillers and pores, such as poor dispersion of the composite material, deteriorated mechanical properties, and increased water absorption rate, and to propose a SiO2@hyperbranched polymer / polyimide composite film and its preparation method.

[0006] On the one hand, the present invention provides a SiO2@hyperbranched polymer / polyimide composite film, and the composite film comprises SiO2@EHBP filler and a polyimide matrix;

[0007] The dosage of the SiO2@EHBP filler is 1 wt% - 20 wt% of the polyimide matrix;

[0008] Preferably, the dosage of the SiO2@EHBP filler is 8 wt% - 15 wt% of the polyimide acid matrix.

[0009] The polyimide matrix is obtained by polymerizing a dianhydride monomer and a diamine monomer, and the dosages of the dianhydride monomer and the diamine monomer are in a molar ratio of 1:1 - 2.

[0010] The dianhydride monomer is one or more of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA), or hexafluorodiacid anhydride (6FDA);

[0011] Preferably, the dianhydride monomer is one or more of 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) or hexafluorodiacid anhydride.

[0012] The diamine monomer is one or more of 2,2′-bis(trifluoromethyl)benzidine (TFMB), p-phenylenediamine (PPD), or 4,4′-diaminodiphenyl ether (ODA);

[0013] Preferably, the diamine monomer is one or more of 2,2′-bis(trifluoromethyl)benzidine (TFMB) or 4,4′-diaminodiphenyl ether.

[0014] The SiO2@EHBP filler is obtained by amino modification of hollow SiO2 nanoparticle microspheres and then graft modification with EHBP.

[0015] The average particle size of the hollow SiO2 nanoparticle microspheres is 50 - 100 nm, the purity is ≥99.9 wt%, the specific surface area is about 45.5 m 2 / g, and the wall thickness is 5 - 15 nm;

[0016] Further, the amino-functionalized SiO2 nanoparticles are obtained by modifying silica particles with an amino-silane coupling agent to obtain amino-functionalized hollow silica microspheres (NH2-SiO2).

[0017] The amino-silane coupling agent includes one or more of (3-aminopropyl)triethoxysilane (KH-550), aminopropylmethyldiethoxysilane, and N-(2-aminoethyl-3-aminopropyl)trimethoxysilane.

[0018] The hyperbranched polymer is a hyperbranched polyurethane with terminal epoxy groups, and its structural general formula is as follows:

[0019]

[0020] Among them, D is a branched unit, L is a linear unit, and T is a terminal unit;

[0021] Further, D≥1, L≥1, and T≥1;

[0022] Preferably, at least one of R1 and R2 is The other is -OH.

[0023] Further, the hyperbranched polyurethane with terminal epoxy groups is obtained by modifying the hyperbranched polymer with terminal hydroxyl groups with epichlorohydrin; further, the hyperbranched polyurethane with terminal epoxy groups is specifically obtained by the following method: First, using diethanolamine (DEA) and methyl acrylate (MA) as raw materials, an AB2 monomer, namely methyl N,N-dihydroxyethyl-3-aminopropionate, is synthesized through a Michael addition reaction, and then using TMP as the reaction center core, a hyperbranched polymer with terminal hydroxyl groups is synthesized by the "quasi-one-step method", and the molar ratio of TMP to the AB2 monomer is 1:3-21; finally, the hyperbranched polymer with terminal hydroxyl groups is modified with epichlorohydrin to obtain a hyperbranched polymer with terminal epoxy groups, and the molar ratio of epichlorohydrin to the hyperbranched polymer with terminal hydroxyl groups is 10-30:1.

[0024] On the other hand, the present invention provides a method for preparing a SiO2@hyperbranched polymer / polyimide composite film, and its preparation process includes the following steps:

[0025] Step 1: Preparation of amino-functionalized hollow silica microspheres

[0026] Modify silica microspheres with an amino-silane coupling agent to prepare amino-functionalized hollow silica microspheres.

[0027] The specific implementation steps are as follows: Add a mixed solution of silane coupling agent, deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:4) into a flask and mix them in the flask. Stir at 60 °C for 1 h, then add SiO2 particles into the mixed solution and continue stirring for 5 h (by mass, the dosage of the silane coupling agent is 1% - 3% of the SiO2 particles). Filter and dry to obtain amino-modified SiO2 nanoparticles (SiO2-NH2).

[0028] Step 2: Preparation of hyperbranched polymer EHBP

[0029] S1: Preparation of hyperbranched polymer with terminal hydroxyl groups

[0030] Using DEA and MA as raw materials, synthesize methyl N,N-dihydroxyethyl-3-aminopropionate monomer through Michael addition reaction. The crude monomer is extracted with ether and vacuum filtered to obtain a colorless transparent oily substance. Then, using TMP as the reaction center core and methyl N,N-dihydroxyethyl-3-aminopropionate as the AB2 monomer, synthesize the hyperbranched polymer with terminal hydroxyl groups through the "quasi-one-step method"; dissolve the obtained yellow viscous liquid in acetone, then reprecipitate with dichloromethane and extract with ether to obtain the hyperbranched polymer with terminal hydroxyl groups; the specific implementation steps are as follows: Add DEA and anhydrous methanol into a reactor, stir well at room temperature until DEA is fully dispersed in methanol, and slowly dropwise add MA under nitrogen protection, maintaining the dropping rate at 45 - 60 drops per minute; among them, the dosages of DEA and MA are in a molar ratio of 1:1.5 - 2; after the dropping is completed, maintain the system temperature at 35 °C and react for 4 h, then rotary evaporate at 50 °C to remove formaldehyde and unreacted MA, add anhydrous ether and extract 3 times, and then rotary evaporate to obtain a colorless transparent oily AB2 monomer; add trimethylolpropane (TMP) and p-toluenesulfonic acid (p-TSA) with a mass fraction of 2% (calculated based on the total mass of AB2 monomer and TMP) into the reactor, stir at 110 °C to melt and mix the two, then slowly dropwise add the AB2 monomer, and after the dropping is completed, stir and react at 120 °C for 5 h, and then rotary evaporate the mixed solution at 100 °C for about 1 h until there are no bubbles and the reaction terminates. Repeatedly purify the above liquid multiple times, extract and retain the upper clear liquid and rotary evaporate to obtain the hyperbranched polymer with terminal hydroxyl groups. Among them, the dosages of TMP and AB2 monomer are in a molar ratio of 1:3 - 21.

[0031] S2: Preparation of hyperbranched polymer with terminal epoxy groups (EHBP)

[0032] Modify the hyperbranched polymer with terminal hydroxyl groups (HBP) using epichlorohydrin to obtain the hyperbranched polymer with terminal epoxy groups;

[0033] The specific implementation steps are as follows: Dissolve the above-prepared HBP in N,N-dimethylformamide (DMF), add boron trifluoride diethyl ether as a catalyst (the dosage of the catalyst is 0.5-2% of HBP by mass), and drop epichlorohydrin (ECH) at a rate of 20-35 drops per minute during stirring. The molar ratio of epichlorohydrin to HBP is 10-30:1. After the reaction system is heated to 65 °C, keep it for 2 h, and then rotary evaporate the unreacted ECH and DMF at 100 °C; then transfer the mixed solution to a reactor and slowly drop a sodium hydroxide aqueous solution with a mass concentration of 25% (sodium hydroxide is 2 / 3 times the amount of substance of epichlorohydrin) at a dropping rate of 40-45 drops per minute. After the dropping is completed, heat it to 80 °C and react for 3 h, and then rotary evaporate the water at 90 °C. Filter and centrifuge the product after rotary evaporation to obtain a clear viscous liquid (EHBP).

[0034] Step 3: Preparation of SiO2@hyperbranched polymer / polyimide composite film

[0035] S1: Preparation of end-epoxy hyperbranched polymer modified nano-silica (SiO2@EHBP) filler. Using the blending method, add the above-prepared epoxy-group-containing hyperbranched polymer to a reactor, and add amino-functionalized nano-silica at a ratio (the dosage of amino-functionalized nano-silica is 10%-20% of the hyperbranched polymer by mass) under stirring to make it blend evenly with the hyperbranched polymer to obtain epoxy hyperbranched polymer grafted hollow nano-silica microspheres (SiO2@EHBP). The blending reaction time is 2-3 h.

[0036] S2: Preparation of polyamic acid solution (PAA)

[0037] Prepare a polyamic acid solution by reacting dianhydride and diamine monomers;

[0038] The specific implementation steps are as follows: Before the reaction starts, vacuum dry the diamine monomer at 40-50 °C for 12 h, and vacuum dry the dianhydride monomer at 100-110 °C for 24 h. In a nitrogen atmosphere: Add the dianhydride monomer and the diamine monomer to a three-necked flask equipped with a mechanical stirrer, a constant-temperature low-temperature bath, and a thermometer. Among them, the dosages of the dianhydride monomer and the diamine monomer are in a molar ratio of 1:1-2; stir at 25-30 °C, add anhydrous DMAC to dissolve, and end the reaction after reacting for 12 h after complete dissolution. After degassing, obtain a PAA solution.

[0039] S3: Preparation of SiO2@EHBP / polyimide composite film

[0040] Add the SiO2@EHBP filler obtained in Step S1 to the polyamic acid solution. After stirring well, add a catalyst and a dehydrating agent to the polyamic acid, and react at 25-30 °C for 15-20 h to obtain the SiO2@EHBP / PI slurry, controlling the solid content to be 18%-22%;

[0041] The dosage of the SiO2@EHBP filler is 1 wt% - 20 wt% of the polyimide matrix (based on the total amount of diamine and dianhydride monomers);

[0042] Preferably, the dosage of the SiO2@EHBP filler is 8 wt% - 15 wt% of the polyimide matrix;

[0043] Preferably, the molar ratio of the addition amount of the catalyst to the diamine is 0.2 - 0.5:1, and the molar ratio of the addition amount of the dehydrating agent to the diamine is 5 - 7:1;

[0044] The catalyst is one or more of triethylamine, pyridine, and N-ethylpiperidine;

[0045] The dehydrating agent is one or more of acetic anhydride and propionic anhydride;

[0046] Finally, coat the obtained SiO2@EHBP / PI slurry and bake it at 80 - 250 °C for 30 - 75 min in an N2 environment to obtain a film with a thickness of 50 - 100 μm.

[0047] The beneficial effects of this application include:

[0048] (1) The introduction of the hollow silica inorganic material brings in a regular, uniform, and closed pore structure, reducing the dielectric constant of the composite material. At the same time, the double-layer coated hollow structure significantly reduces the hygroscopicity of the inorganic material (silica) itself and the pores;

[0049] (2) Silica is an inorganic nano-filler, and its introduction significantly improves the toughening effect of the polymer matrix. At the same time, the nano-microspheres double-layer coated with an amino-silane coupling agent layer and a hyperbranched polymer active layer have a significant reduction in the interaction force between particles due to the steric hindrance formed by the polymer chains on the surface of the microspheres, reducing the agglomeration between particles, forming good dispersion in the polymer substrate, and improving the mechanical properties of the composite material;

[0050] (3) Hyperbranched polymers have a highly branched three-dimensional spherical structure and a large number of end groups. Compared with the corresponding linear molecules, they have small molecular size, a large number of short branched chains, weak intermolecular interactions, and low viscosity. Secondly, there are numerous functional groups on the surface of hyperbranched polymers, resulting in a very large end-capping functionality. These active groups have very high reactivity. The introduction of the terminal epoxy group hyperbranched polymer in the present invention, on the one hand, the epoxy group combines with the amino group on the surface of the hollow nanospheres to enhance the binding between the two; on the other hand, it reacts with the active groups (such as carboxyl groups) on the polymer substrate (polyamic acid), enhancing the binding stability between the nanoparticles and the substrate. Further, the branched chains on the hyperbranched polymer and the polymer substrate are intertwined and interpenetrated to form a stable network structure, enhancing the toughness and mechanical properties of the overall material;

[0051] (4) The diamine and dianhydride monomers selected in the present invention contain a large number of benzene ring structures and planar structures, which can help ensure the insulation performance of the film. With the incorporation of F atoms, it will provide high hydrophobicity; the specific 4,4′-(4,4′-isopropyl diphenoxy) bis(phthalic anhydride) has a soft molecular chain and an ether bond therein, which can enhance the flexibility of the molecular chain and improve the film-forming mechanical properties.

[0052] In summary, the SiO2@hyperbranched polymer / polyimide composite film prepared by the present invention is expected to be applied in the fields of aerospace, electronics, and microelectronics. Description of the Drawings

[0053] Figure 1 Schematic diagram for the preparation of a low dielectric constant polyimide composite film (SiO2@EHBP / PI). Detailed Embodiments

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0055] General Embodiment

[0056] A SiO2@hyperbranched polymer / polyimide composite film, the composite film includes SiO2@EHBP filler and a polyimide matrix, and its preparation schematic diagram is as shown in the appendix; specifically, the preparation steps are as follows: Figure 1 shown; specifically, the preparation steps are as follows:

[0057] Step 1: Preparation of amino-functionalized hollow silica microspheres

[0058] Modify the silica microspheres with an amino-silane coupling agent to prepare amino-functionalized hollow silica microspheres;

[0059] The specific implementation steps are as follows: Add a mixed solution of silane coupling agent, deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:4) into a flask and mix them in the flask. Stir at 60 °C for 1 h, and then add SiO2

[0060] particles into the mixed solution and continue to stir for 5 h (by mass, the dosage of the silane coupling agent is 1% - 3% of the SiO2 particles). Filter and dry to obtain amino-modified SiO2 nanoparticles (SiO2-NH2).

[0061] Step 2: Preparation of hyperbranched polymer EHBP

[0062] S1: Preparation of hyperbranched polymer with terminal hydroxyl groups

[0063] Using DEA and MA as raw materials, synthesize N,N-dihydroxyethyl-3-aminopropionic acid methyl ester monomer through Michael addition reaction. The crude monomer is extracted with ether and vacuum filtered to obtain a colorless transparent oily substance. Then, using TMP as the reaction center core and N,N-dihydroxyethyl-3-aminopropionic acid methyl ester as the AB2 monomer, synthesize the hyperbranched polymer with terminal hydroxyl groups through the "quasi-one-step method"; dissolve the obtained yellow viscous liquid in acetone, and then reprecipitate with dichloromethane and extract with ether to obtain the hyperbranched polymer with terminal hydroxyl groups; the specific implementation steps are as follows: Add DEA and anhydrous methanol into a reactor, stir well at room temperature until DEA is fully dispersed in methanol, and slowly dropwise add MA under nitrogen protection, maintaining the dropping rate at 45 - 60 drops / minute; among them, the dosages of DEA and MA are in a molar ratio of 1:1.5 - 2; after the dropping is completed, maintain the system temperature at 35 °C and react for 4 h, then rotary evaporate at 50 °C to remove formaldehyde and unreacted MA, add anhydrous ether and extract 3 times, and then rotary evaporate to obtain a colorless transparent oily AB2 monomer; add trimethylolpropane (TMP) and p-toluenesulfonic acid (p-TSA) with a mass fraction of 2% (calculated based on the total mass of AB2 monomer and TMP) into the reactor, stir at 110 °C to make them melt and mix, and then slowly dropwise add the AB2 monomer. After the dropping is completed, stir and react at 120 °C for 5 h, and then rotary evaporate the mixture at 100 °C for about 1 h until there are no bubbles and the reaction terminates. Purify the above liquid repeatedly for many times, extract and retain the upper clear liquid and rotary evaporate to obtain the hyperbranched polymer with terminal hydroxyl groups, where the molar ratio of TMP to AB2 monomer is 1:3 - 21.

[0064] S2: Preparation of hyperbranched polymer with terminal epoxy groups (EHBP)

[0065] Modify the hyperbranched polymer with terminal hydroxyl groups (HBP) using epichlorohydrin to obtain the hyperbranched polymer with terminal epoxy groups;

[0066] The specific implementation steps are as follows: Dissolve the above-prepared HBP in N,N-dimethylformamide (DMF), add boron trifluoride diethyl ether as a catalyst (the dosage of the catalyst is 0.5-2% of HBP by mass), and dropwise add epichlorohydrin (ECH) at a rate of 20-35 drops per minute during stirring. The molar ratio of epichlorohydrin to HBP is 10-30:1. After the reaction system is heated to 65 °C, it is maintained for 2 h, and then the unreacted ECH and DMF are removed by rotary evaporation at 100 °C; then the mixed solution is transferred to a reactor and a sodium hydroxide aqueous solution with a mass concentration of 25% (sodium hydroxide is 2 / 3 times the amount of substance of epichlorohydrin) is slowly added dropwise at a dropping rate of 40-45 drops per minute. After the addition is completed, the temperature is raised to 80 °C and the reaction is carried out for 3 h, and then the water is removed by rotary evaporation at 90 °C. The product after rotary evaporation is filtered and centrifuged to obtain a clear viscous liquid (EHBP).

[0067] Step 3: Preparation of SiO2@hyperbranched polymer / polyimide composite film

[0068] S1: Preparation of end-epoxy hyperbranched polymer modified nano-silica (SiO2@EHBP) microsphere filler. Using the blending method, add the above-prepared epoxy-group-containing hyperbranched polymer to a reactor, and add amino-functionalized nano-silica at a ratio (the dosage of amino-functionalized nano-silica is 10%-20% of the hyperbranched polymer by mass) under stirring to make it blend evenly with the hyperbranched polymer to obtain epoxy hyperbranched polymer grafted hollow nano-silica microspheres (SiO2@EHBP). The blending reaction time is 2-3 h.

[0069] S2: Preparation of polyamic acid solution (PAA)

[0070] Prepare a polyamic acid solution by reacting dianhydride and diamine monomers;

[0071] The specific implementation steps are as follows: Before the reaction starts, vacuum-dry the diamine monomer at 40-50 °C for 12 h, and vacuum-dry the dianhydride monomer at 100-110 °C for 24 h. In a nitrogen atmosphere, add the dianhydride monomer and the diamine monomer to a three-necked flask equipped with mechanical stirring, a constant-temperature low-temperature bath, and a thermometer. Among them, the dosages of the dianhydride monomer and the diamine monomer are in a molar ratio of 1:1-2; stir at 25-30 °C, add anhydrous DMAC to dissolve, and after complete dissolution, react for 12 h and then end the reaction. After degassing, a PAA solution is obtained.

[0072] S3: Preparation of SiO2@EHBP / polyimide composite film

[0073] Add the SiO2@EHBP microspheres obtained in Step S1 to the polyamic acid solution. After stirring well, add a catalyst and a dehydrating agent to the polyamic acid, and react at 25-30 °C for 15-20 h to obtain the SiO2@EHBP / PI slurry, controlling the solid content to be 18%-22%. Finally, coat the obtained SiO2@EHBP / PI slurry and bake it in an N2 environment at 80-250 °C for 30-75 min to obtain a film with a thickness of 50-100 μm.

[0074] Example 1

[0075] A SiO2@EHBP / PI composite film, the composite film includes SiO2@EHBP filler and a polyimide matrix, and its preparation steps are as follows:

[0076] Step 1: Preparation of amino-functionalized silica microspheres

[0077] Add 0.2 g of silane coupling agent KH560, 100 ml of a mixed solution of deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:4) to a flask, mix well, stir at 60 °C for 1 h, then add 10 g of SiO2 powder to the mixed solution and continue to stir for 5 h, filter and dry to obtain SiO2-NH2.

[0078] Step 2: Preparation of epoxy-terminated hyperbranched polymer

[0079] S1: Preparation of hydroxyl-terminated hyperbranched polymer

[0080] Add 105 g (1 mol) of DEA and 10 mL of anhydrous methanol to a reactor, stir well at room temperature until DEA is fully dispersed in methanol, slowly dropwise add 129 g (1.5 mol) of MA under nitrogen protection, and keep the dropping rate at 45-60 drops per minute. After the dropping is completed, maintain the system temperature at 35 °C and react for 4 h, then rotary evaporate to remove formaldehyde and unreacted MA at 50 °C, extract with anhydrous ether 3 times and then rotary evaporate to obtain a colorless and transparent oily AB2 monomer;

[0081] Add 134 g (1.0 mol) of TMP and 2% (calculated based on the total mass of AB2 monomer and TMP) of p-TSA to the reactor, stir at 110 °C to melt and mix the two, then slowly dropwise add 1719 g (9.0 mol) of AB2 monomer. After the dropping is completed, stir and react at 120 °C for 5 h, and then rotary evaporate the mixed solution at 100 °C for about 1 h until there are no bubbles and the reaction stops. Repeatedly purify the above liquid multiple times, extract and keep the upper clear liquid and rotary evaporate to obtain HBP.

[0082] S2: Preparation of epoxy-terminated hyperbranched polymer

[0083] 0.5 mol of the HBP prepared above was dissolved in 1.0 mol of DMF, 1.5 g of boron trifluoride ether was added as a catalyst, 10 mol of ECH was added dropwise at a rate of 20 to 35 drops / min while stirring, the reaction system was heated to 65°C and kept reacting for 2 h, and then the unreacted ECH and DMF were removed by rotary evaporation at 100°C; the mixed solution was then transferred to a reactor and slowly dripped with a sodium hydroxide aqueous solution having a mass concentration of 25% (the amount of sodium hydroxide was 6 mol) at a dripping speed of 40 to 45 drops / min. After the addition was completed, the temperature was raised to 80°C and reacted for 3 h, and then the water was removed by rotary evaporation at 90°C. The product after rotary evaporation was filtered and centrifuged to obtain a clear viscous liquid (EHBP).

[0084] Step 3: Preparation of SiO2@EHBP / polyimide low dielectric constant composite film

[0085] S1: Preparation of epoxy-terminated hyperbranched polymer grafted nano-silica (SiO2@EHBP) microspheres: The epoxy-terminated hyperbranched polymer prepared above is added into a reactor, and amino-treated nano-silica (15% by mass) is added under stirring to make it blend evenly with the hyperbranched polymer. The blending reaction time is 2.5 h to obtain SiO2@EHBP microspheres.

[0086] S2: Preparation of polyimide acid solution

[0087] Before the reaction, the diamine monomer was vacuum dried at 40-50° C. for 12 h, and the dianhydride monomer was vacuum dried at 100-110° C. for 24 h. In a nitrogen atmosphere, TFMB (32 g, 0.1 mol) and BPADA (52 g, 0.1 mol) were added to a three-necked flask with mechanical stirring, a constant temperature low-temperature bath, a thermometer and a constant pressure dropping funnel, and stirred at 25-30° C., and 336 mL of anhydrous DMAC (solid content 20%) was added to dissolve. After complete dissolution, the reaction was terminated at 25-30° C. for 12 h, and the PAA solution was obtained after degassing.

[0088] S3: Preparation of SiO2@hyperbranched polymer / polyimide composite films

[0089] After adding 1wt% SiO2@EHBP to the PAA solution and stirring thoroughly for reaction, a catalyst and a dehydrating agent are added to the polyamic acid, and the mixture is reacted at 25-30°C for 15-20h to obtain SiO2@EHBP / PI slurry. Finally, the obtained SiO2@EHBP / PI slurry is coated and baked at 80-250°C for 30-75min in a N2 environment to obtain a thin film with a thickness of 50μm, which is recorded as SiO2@EHBP / PI(TB)-1%.

[0090] Example 2

[0091] Adjust the dosage of SiO2@EHBP in Step S3 of Example 1 to 5 wt%, and keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(TB)-5%.

[0092] Example 3

[0093] Adjust the dosage of SiO2@EHBP in Step S3 of Example 1 to 8 wt%, and keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(TB)-8%.

[0094] Example 4

[0095] Adjust the dosage of SiO2@EHBP in Step S3 of Example 1 to 11 wt%, and keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(TB)-11%.

[0096] Example 5

[0097] Adjust the dosage of SiO2@EHBP in Step S3 of Example 1 to 14 wt%, and keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(TB)-14%.

[0098] Example 6

[0099] Adjust the dosage of SiO2@EHBP in Step S3 of Example 1 to 20 wt%, and keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(TB)-20%.

[0100] Example 7

[0101] According to the operation steps of Example 4, adjust the diamine monomer to PPD (10.8 g, 0.1 mol) and the dianhydride monomer to BPDA (29.4 g, 0.1 mol) in Step S2 of Step Three, and synchronously adjust the dosages of the solvent, catalyst and dehydrating agent. Keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(PB)-11%.

[0102] Example 8

[0103] According to the operation steps of Example 4, adjust the diamine monomer to ODA (20.0 g, 0.1 mol) and the dianhydride monomer to 6FDA (44.4 g, 0.1 mol) in Step S2 of Step Three, and synchronously adjust the dosages of the solvent, catalyst and dehydrating agent. Keep the remaining steps unchanged. The obtained polyimide film is denoted as SiO2@EHBP / PI(OF)-11%.

[0104] Example 9

[0105] According to the operation steps of Example 4, adjust the dosages of diamine and dianhydride monomers in Step S2 to TFMB (64 g, 0.2 mol) and BPADA (52 g, 0.2 mol), and synchronously adjust the dosages of solvent, catalyst, and dehydrating agent, denoted as SiO2@EHBP / PI(TB’)-11%.

[0106] Comparative Example 1

[0107] An EHBP / PI composite film, the composite film includes EHBP filler and polyimide matrix, and its preparation steps are as follows:

[0108] Step 1: Preparation of epoxy-terminated hyperbranched polymer

[0109] S1: Preparation of hydroxyl-terminated hyperbranched polymer

[0110] Add 105 g (1 mol) of DEA and 10 mL of anhydrous methanol into a reactor, stir well at room temperature until DEA is fully dispersed in methanol, and slowly dropwise add 129 g (1.5 mol) of MA under nitrogen protection, keeping the dropping rate at 45 - 60 drops per minute. After the dropping is completed, maintain the system temperature at 35 °C and react for 4 h, then rotary evaporate to remove formaldehyde and unreacted MA at 50 °C, extract with anhydrous ether 3 times and then rotary evaporate to obtain a colorless transparent oily AB2 monomer; add 134 g (1.0 mol) of TMP and p-TSA with a mass fraction of 2% (based on the total mass of AB2 monomer and TMP) into the reactor, stir at 110 °C to melt and mix the two, and then slowly dropwise add 1719 g (9.0 mol) of AB2 monomer. After the dropping is completed, stir and react at 120 °C for 5 h, and then rotary evaporate the mixed solution at 100 °C for about 1 h until no bubbles are present and the reaction is terminated. Purify the above liquid repeatedly for multiple times, extract and retain the upper clear liquid and rotary evaporate to obtain HBP.

[0111] S2: Preparation of epoxy-terminated hyperbranched polymer

[0112] Take 0.5 mol of the above-prepared HBP and dissolve it in 1.0 mol of DMF, add 1.5 g of boron trifluoride etherate as a catalyst, and dropwise add 10 mol of ECH at a rate of 20 - 35 drops per minute during stirring. After the reaction system is heated to 65 °C, keep reacting for 2 h and then rotary evaporate to remove unreacted ECH and DMF at 80 °C and 100 °C respectively; then transfer the mixed solution to a reactor and slowly dropwise add a sodium hydroxide aqueous solution with a mass concentration of 25% (the amount of sodium hydroxide is 6 mol)), with a dropping rate of 40 - 45 drops per minute. After the dropping is completed, raise the temperature to 80 °C and react for 3 h, and then rotary evaporate to remove water at 90 °C. Filter and centrifuge the product after rotary evaporation to obtain a clear viscous liquid (EHBP).

[0113] Step 2: Preparation of EHBP / Polyimide Low Dielectric Constant Composite Film

[0114] S1: Preparation of Polyamic Acid Solution

[0115] Before the reaction starts, vacuum dry the diamine monomer at 40 - 50 °C for 12 h, and vacuum dry the dianhydride monomer at 100 - 110 °C for 24 h. In a nitrogen atmosphere: Add TFMB (32 g, 0.1 mol) and BPADA (52 g, 0.1 mol) into a three-necked flask equipped with a mechanical stirrer, a constant-temperature low-temperature bath, a thermometer, and a constant-pressure dropping funnel. Stir at 25 - 30 °C, add 336 mL of anhydrous DMAC (solid content 20%) to dissolve. After complete dissolution, react at 25 - 30 °C for 12 h and then end the reaction. After degassing, obtain the PAA solution.

[0116] S2: Preparation of Hyperbranched Polymer / Polyimide Composite Film

[0117] Add 8 wt% of EHBP to the PAA solution and stir well. Then add a catalyst and a dehydrating agent to the polyamic acid.

[0118] React at 25 - 30 °C for 15 - 20 h to obtain the EHBP / PI slurry.

[0119] Finally, coat the obtained EHBP / PI slurry and bake it at 80 - 250 °C for 30 - 75 min in an N2 environment to obtain a film with a thickness of 50 μm, denoted as EHBP / PI(TB)-8%.

[0120] Comparative Example 2

[0121] According to the operation steps of Comparative Example 1, adjust the dosage of EHBP to 11%, and keep the other steps unchanged. The obtained polyimide film is denoted as EHBP / PI(TB)-11%.

[0122] Comparative Example 3

[0123] A SiO2 / PI composite film, the composite film includes SiO2 filler and a polyimide matrix, and its preparation steps are as follows:

[0124] Step 1: Preparation of Amino-functionalized Silica Microspheres

[0125] Add 0.2 g of silane coupling agent KH560, 100 ml of a mixed solution of deionized water and ethanol (the volume ratio of deionized water to ethanol is 1:4) into a flask, mix evenly, stir at 60 °C for 1 h. Then add 10 g of SiO2 powder into the mixed solution and continue to stir for 5 h. Filter and dry to obtain NH2-SiO2.

[0126] Step 2: Preparation of SiO2 / PI Composite Film

[0127] S1: Preparation of polyamic acid solution

[0128] Before the reaction starts, vacuum dry the diamine monomer at 40 - 50 °C for 12 h, and vacuum dry the dianhydride monomer at 100 - 110 °C for 24 h. In a nitrogen atmosphere: Add TFMB (32 g, 0.1 mol) and BPADA (52 g, 0.1 mol) into a three-necked flask equipped with mechanical stirring, constant-temperature low-temperature bath, thermometer and constant-pressure dropping funnel, stir at 25 - 30 °C, add 336 mL of anhydrous DMAC (solid content 20%) to dissolve. After complete dissolution, react at 25 - 30 °C for 12 h and then end the reaction. After degassing, obtain the PAA solution.

[0129] S2: Preparation of SiO2 / polyimide composite film

[0130] Add 8 wt% of NH2-SiO2 particles into the PAA solution and stir well. Then add a catalyst and a dehydrating agent to the polyamic acid, and react at 25 - 30 °C for 15 - 20 h to obtain the SiO2 / PI slurry;

[0131] Finally, coat the obtained SiO2 / PI slurry, and bake it at 80 - 250 °C for 30 - 75 min in an N2 environment to obtain a film with a thickness of 50 μm, denoted as SiO2 / PI(TB)-8%.

[0132] Comparative example 4

[0133] According to the operation steps of comparative example 3, adjust the dosage of SiO2-NH2 particles to 11%, and keep the other steps unchanged. The obtained polyimide film is denoted as SiO2 / PI(TB)-11%.

[0134] Comparative example 5

[0135] The preparation steps of a PI film are as follows:

[0136] Before the reaction starts, vacuum dry the diamine monomer at 40 - 50 °C for 12 h, and vacuum dry the dianhydride monomer at 100 - 110 °C for 24 h. In a nitrogen atmosphere: Add TFMB (32 g, 0.1 mol) and BPADA (52 g, 0.1 mol) into a three-necked flask equipped with mechanical stirring, constant-temperature low-temperature bath, thermometer and constant-pressure dropping funnel, stir at room temperature, add 336 mL of anhydrous DMAC (solid content 20%) to dissolve. After complete dissolution, react at 25 - 30 °C for 12 h and then end the reaction. After degassing, obtain the PAA solution. Add a catalyst and a dehydrating agent to the polyamic acid solution, and react at 25 - 30 °C for 15 - 20 h to obtain the PI slurry;

[0137] Finally, the obtained PI slurry was coated and baked at 80 - 250 °C for 30 - 75 min in an N2 environment to obtain a film with a thickness of 50 μm, denoted as PI(TB).

[0138] The component ratios of the composite films in Examples 1 - 9 and Comparative Examples 1 - 5 are shown in Table 1.

[0139] Table 1 Summary of component ratios of the composite films in Examples 1 - 9 and Comparative Examples 1 - 5

[0140]

[0141] The properties of the composite films in Examples 1 - 9 and Comparative Examples 1 - 5 were tested, and the results are shown in Table 2.

[0142] Tensile strength and elongation at break: The tensile strength and elongation at break were detected using an electronic universal testing machine. Each group of samples was measured 5 times, and the results were averaged.

[0143] Dielectric constant (D k ) and dissipation factor (D f ): The samples to be tested were dried at 60 °C for 6 h to remove the moisture in the samples. The relative humidity during testing was less than 40%. Then, the D k / D f value of the samples to be tested was measured using a precision impedance analyzer (model Agilent 4294A).

[0144] Table 2 Summary of performance characterizations of the composite films in Examples 1 - 9 and Comparative Examples 1 - 5

[0145] Group Composite film <![CDATA[D k > <![CDATA[D f > Tensile strength (MPa) Elongation at break % Example 1 <![CDATA[SiO2@EHBP / PI(TB)-1%]]> 3.10 0.0427 132.5 26.9 Example 2 <![CDATA[SiO2@EHBP / PI(TB)-5%]]> 2.95 0.0418 133.9 26.5 Example 3 <![CDATA[SiO2@EHBP / PI(TB)-8%]]> 2.80 0.0392 140.6 26.2 Example 4 <![CDATA[SiO2@EHBP / PI(TB)-11%]]> 2.55 0.0348 137.1 25.8 Example 5 <![CDATA[SiO2@EHBP / PI(TB)-14%]]> 2.32 0.0321 151.4 23.1 Example 6 <![CDATA[SiO2@EHBP / PI(TB)-20%]]> 2.13 0.0319 132.3 21.7 Example 7 <![CDATA[SiO2@EHBP / PI(PB)-11%]]> 2.76 0.0395 132.9 24.1 Example 8 <![CDATA[SiO2@EHBP / PI(OF)-11%]]> 2.64 0.0358 149.5 24.6 Example 9 <![CDATA[SiO2@EHBP / PI(TB’)-11%]]> 2.51 0.0338 148.1 25.6 Comparative Example 1 EHBP / PI(TB)-8% 3.16 0.0447 138.6 25.8 Comparative Example 2 EHBP / PI(TB)-11% 3.15 0.0439 144.2 24.7 Comparative Example 3 <![CDATA[SiO2 / PI(TB)-8%]]> 2.92 0.0396 139.8 24.4 Comparative Example 4 <![CDATA[SiO2 / PI(TB)-11%]]> 2.66 0.0388 141.9 23.5 Comparative Example 5 PI(TB) 3.25 0.0455 128.2 26.4

[0146] As shown in Table 1, by comparing Examples 1 - 6, it can be found that the addition of an appropriate amount of (SiO2@EHBP) microspheres can reduce the dielectric constant of the composite material and greatly improve the mechanical properties of the modified system. However, when the amount of SiO2@EHBP is too large, the mechanical properties of the modified system deteriorate. In particular, with the increase in the addition amount of the hollow microspheres, there is a trend of decreasing elongation at break. This is because although the hollow microsphere particles were hyperbranched treated before filling the PI material, the hardness and modulus of the hollow microspheres are much higher than those of PI, and the bonding strength between PI and the rigid microspheres is not high enough. During stretching, interface fracture and microcracks and other defects are likely to occur, resulting in a decrease in the toughness of the composite material. On the other hand, silica is an inorganic nano - filler. The uniform dispersion of an appropriate amount of nano - particles in the substrate is likely to produce a stress concentration effect, generating microcracks, i.e., crazes, between the particles and the matrix. At the same time, plastic deformation occurs between the particles and the matrix, absorbing more impact energy and improving the toughening effect. However, if the amount used is too much, the microcracks are likely to develop into macroscopic cracks, resulting in a decline in performance.

[0147] Comparing Example 1 with Examples 7-9, it can be found that by selecting diamine and dianhydride monomers containing a large number of benzene ring structures and planar structures, and cooperating with monomers containing F atoms, such as a specific 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) monomer, the molecular chain itself is soft and has ether bonds therein, which can enhance the flexibility of the molecular chain and improve the mechanical properties of the film formation.

[0148] Comparing Comparative Examples 1-2, Comparative Example 5, Example 3, and Example 4, it can be found that the introduction of EHBP can improve the dielectric and mechanical properties of the composite material, especially the mechanical properties of the material. This may be because the hyperbranched polymer has a small molecular size, a large number of short branched chains, small intermolecular interaction forces, and low viscosity; secondly, there are many functional groups on the surface; the introduction of EHBP can react with active groups (such as carboxyl groups) on the polymer substrate (polyamic acid) to enhance the binding stability. Further, the branched chains on the hyperbranched polymer and the polymer substrate are intertwined to form a stable network structure, enhancing the overall toughness of the material.

[0149] Comparing Comparative Examples 3-4, Comparative Example 5, Example 3, and Example 4, it can be found that the introduction of hollow microspheres can significantly improve the dielectric properties of the composite material. Since silica is an inorganic nano-filler with a low dielectric constant, and its introduction brings a regular, uniform, and closed pore structure, the dielectric constant of the composite material is reduced.

[0150] In summary, it can be found that by modifying silica with an amino-silane coupling agent, an active group amino is introduced while forming the first layer of coating on silica; secondly, a hyperbranched polymer with terminal epoxy groups is used for the second layer of coating. On the one hand, the epoxy groups can chemically bond with the amino groups on the surface of the silica microspheres, and on the other hand, the silica can be embedded in the voids of the hyperbranched polymer, thereby making the two-phase combination more compact. Finally, the double-coated silica microspheres are mixed with the polyimide substrate, thereby introducing more regular, uniform, and closed pores into the substrate, and at the same time ensuring the dispersibility of the inorganic material and the pores. Finally, a SiO2@hyperbranched polymer / polyimide composite film is obtained, which has certain improvements in dielectric properties and tensile strength.

Claims

1. A SiO2@hyperbranched polymer / polyimide composite film, characterized in that, The composite film comprises SiO2@EHBP filler and a polyimide matrix; the dosage of the SiO2@EHBP filler is 14 wt% of the polyimide matrix; The SiO2@EHBP filler is obtained by grafting modification of NH2-SiO2 particles which are obtained by modifying hollow SiO2 nanoparticles with an amino silane coupling agent; The EHBP is a hyperbranched polymer with terminal epoxy groups, and the hyperbranched polymer with terminal epoxy groups is obtained by modifying a hyperbranched polymer with terminal hydroxyl groups with epichlorohydrin. The structural general formula is as follows: where D≥1, L≥1, T≥1; at least one of R1 and R2 is the other is -OH; The polyimide matrix is obtained by polymerizing a dianhydride monomer and a diamine monomer. The dosages of the dianhydride monomer and the diamine monomer are in a molar ratio of 1:1 to 2; the diamine monomer is one or more of 2,2'-bis(trifluoromethyl)benzidine or p-phenylenediamine.

2. The SiO2@hyperbranched polymer / polyimide composite film according to claim 1, wherein The dianhydride monomer is one or more of 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) or hexafluorodiacid dianhydride.

3. The SiO2@hyperbranched polymer / polyimide composite film according to claim 2, characterized in that, The average particle size of the hollow SiO2 nanoparticle microspheres is 50-100 nm, the purity is ≥99.9 wt%, the specific surface area is 45.5 m 2 / g, and the wall thickness is 5-15 nm.

4. The SiO2@hyperbranched polymer / polyimide composite film according to claim 3, characterized in that, The amino-functionalized silane coupling agent comprises one or more of (3-aminopropyl)triethoxysilane, aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

5. A preparation method of the SiO2@hyperbranched polymer / polyimide composite film according to any one of claims 1 to 4, and the preparation process comprises the following steps: Step 1, preparation of amino-functionalized hollow silica microspheres: modifying silica microspheres with an amino silane coupling agent to prepare NH2-SiO2 particle microspheres; Step 2, preparation of the hyperbranched polymer EHBP: S1: Preparation of HBP: Using DEA and MA as raw materials, synthesizing N,N-dihydroxyethyl-3-aminopropionate methyl ester monomer through Michael addition reaction. The crude monomer is extracted with ether and vacuum filtered; then using TMP as the reaction center core and N,N-dihydroxyethyl-3-aminopropionate methyl ester as the AB2 monomer, synthesizing the crude hyperbranched polymer with terminal hydroxyl groups through the "quasi-one-step method"; dissolving the obtained crude product in acetone, then reprecipitating with dichloromethane and extracting with ether to obtain HBP; S2: Preparation of EHBP: Modifying HBP with epichlorohydrin to obtain EHBP; Step 3, preparation of the SiO2@EHBP / polyimide composite film: S1: Preparation of the SiO2@EHBP filler: Using the blending method, adding the EHBP prepared in Step 2 into a reactor, adding NH2-SiO2 particles under stirring. By mass, the dosage of the NH2-SiO2 particles is 10% to 20% of the hyperbranched polymer, and making it blend evenly with the hyperbranched polymer to obtain SiO2@EHBP. The blending reaction time is 2 to 3 h; S2: Preparation of PAA: Preparing PAA by reacting a dianhydride and a diamine monomer; S3: Preparation of SiO2@hyperbranched polymer / polyimide composite film: Add the SiO2@EHBP filler obtained in step S1 of step three into the PAA solution. After stirring evenly, add a catalyst and a dehydrating agent, and react at 25-30 °C for 15-20 h to obtain SiO2@EHBP / PI slurry; finally, coat the obtained SiO2@EHBP / PI slurry and bake it at 80-250 °C for 30-75 min in an N2 environment to obtain the film.

6. The preparation method according to claim 5, characterized in that, The specific implementation steps of the said step one are as follows: Add a mixed solution of a silane coupling agent, deionized water and ethanol into a flask, and the volume ratio of deionized water to ethanol is 1:4; mix in the flask and stir at 60 °C for 1 h, then add SiO2 particles into the mixed solution and continue to stir for 5 h; by mass, the dosage of the silane coupling agent is 1%-3% of the SiO2 particles, and filter and dry to obtain NH2-SiO2 particles.

7. The preparation method according to claim 5, characterized in that, The specific implementation steps of the said step S1 of step two are as follows: Add DEA and anhydrous methanol into a reactor, and stir well at room temperature until DEA is fully dispersed in methanol. Slowly dropwise add MA under nitrogen protection, and keep the dropping rate at 45-60 drops / minute; among them, the dosages of DEA and MA are in a molar ratio of 1:1.5-2; after dropping, maintain the system temperature at 35 °C and react for 4 h, then rotary evaporate to remove formaldehyde and unreacted MA at 50 °C, add anhydrous ether for extraction 3 times and then rotary evaporate to obtain a colorless transparent oily AB2 monomer; subsequently, add trimethylolpropane and 2 wt% p-toluenesulfonic acid into the reactor. The dosage of p-toluenesulfonic acid is based on the total mass of AB2 monomer and TMP. Stir at 110 °C to melt and mix the two, then slowly dropwise add the AB2 monomer. After dropping, stir and react at 120 °C for 5 h, and then rotary evaporate the mixed solution at 100 °C for about 1 h until there are no bubbles and the reaction terminates; extract the above liquid and keep the upper clear liquid and rotary evaporate to obtain HBP; the dosages of TMP and AB2 monomer are in a molar ratio of 1:3-21.

8. The preparation method according to claim 5, characterized in that, The specific implementation steps of the said step S2 of step two are as follows: Take the HBP prepared in step S1 of step two and dissolve it in N,N-dimethylformamide, and add boron trifluoride diethyl etherate as a catalyst; by mass, the dosage of the catalyst is 0.5%-2% of HBP; when stirring, dropwise add epichlorohydrin at a rate of 20-35 drops / minute, and the molar ratio of epichlorohydrin to HBP is 10-30:1; raise the temperature of the reaction system to 65 °C and keep it for 2 h, then rotary evaporate at 100 °C to remove unreacted ECH and DMF; then transfer the mixed solution to a reactor and dropwise add a 25% sodium hydroxide aqueous solution. The sodium hydroxide is 2 / 3 times the amount of substance of epichlorohydrin, and the dropping rate is 40-45 drops / minute. After dropping, raise the temperature to 80 °C and react for 3 h, then rotary evaporate at 90 °C to remove water; filter and centrifuge to obtain EHBP.

9. The preparation method according to claim 5, characterized in that, The specific implementation steps of the third step S2 are as follows: Before the reaction starts, vacuum-dry the diamine monomer at 40 - 50 °C for 12 h, and vacuum-dry the dianhydride monomer at 100 - 110 °C for 24 h; in a nitrogen atmosphere: add the dianhydride monomer and the diamine monomer into a three-necked flask equipped with a mechanical stirrer, a constant-temperature low-temperature bath, and a thermometer. Among them, the dosages of the dianhydride monomer and the diamine monomer are in a molar ratio of 1:1 - 2; stir at 25 - 30 °C, add anhydrous DMAC to dissolve, and react for 12 h after complete dissolution, and degas to obtain a PAA solution.

10. The preparation method according to claim 5, characterized in that, The molar ratio of the addition amount of the catalyst to the diamine is 0.2 - 0.5:1, and the molar ratio of the addition amount of the dehydrating agent to the diamine is 5 - 7:1; the catalyst is one or more of triethylamine, pyridine, and N-ethylpiperidine; the dehydrating agent is one or more of acetic anhydride and propionic anhydride.

11. The preparation method according to claim 10, characterized in that, The solid content of the SiO2@EHBP / PI slurry is 18% - 22%; the thickness of the film is 50 - 100 μm.

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