Low-dielectric fluorine-containing silane modified polyimide and application thereof

Abstract

The invention discloses low-dielectric fluorine-containing silane modified polyimide and an application thereof. The structural formula of the low-dielectric fluorine-containing silane modified polyimide is # imgabs0 #; r1 is a fluorine-containing silane group; r2 is an aromatic anhydride group; aR is an aromatic group; and Ar'and Ar ''are one of phenoxy benzene groups or fluorine-containing biphenyl groups. The preparation method comprises the following steps: dissolving a hydroxyfluorene diamine compound, ether-containing polyamine and fluorine-containing polyamine in a polar organic solvent in an inert atmosphere, and then adding dianhydride and an end-capping reagent for condensation polymerization to obtain polyamide acid; the preparation method comprises the following steps: mixing polyamide acid, a water-carrying agent and fluorine-containing silane, and carrying out imidization reaction to obtain the low-dielectric fluorine-containing silane modified polyimide. The fluorine-containing silane polyimide prepared by the invention has a large-volume fluorenyl structure, flexible ether bonds, a silane structure and fluorine atoms with relatively high electronegativity, so that the prepared fluorine-containing silane polyimide has relatively low dielectric properties, and the processability of the polyimide and the solubility of the polyimide in various organic solvents are also improved.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a low-dielectric fluorine-containing silane-modified polyimide and application thereof. Background Art

[0002] In recent years, with the rapid development of high-frequency communication technology, low dielectric constant materials have attracted much attention as one of the important supporting materials in this field. Polyimide (PI) is a polymer with excellent thermal stability, outstanding mechanical properties, low dielectric constant, solvent resistance and other superior properties. It is widely used in aerospace, microelectronics industry and other fields. However, the dielectric properties of traditional polyimide materials still need to be improved, especially in the high-frequency band, the dielectric properties decrease significantly, which limits its application in high-frequency communication. Therefore, the preparation of polyimide materials with lower dielectric constants has become one of the research hotspots in recent years, which has a profound impact on improving high-frequency communication technology and expanding its application range.

[0003] The main factors affecting the dielectric constant of materials include molecular polarizability, applied electric field frequency, material density and temperature, etc. At present, there are two main methods to reduce the dielectric constant of PI. One method is to introduce low-polarizability substituents to reduce the polarizability of dipoles in molecules, such as trifluoromethyl, alicyclic structure, large steric hindrance substituents, asymmetric structures, and rigid non-planar large conjugated structures. Patent application number 201911423721.2 discloses a low-dielectric fluorinated polyimide composite film and a preparation method thereof; 9,9-bis[4-(4-amino-3-trifluoromethylphenoxy)phenyl]fluorene and dianhydride monomers are added to the dispersion of cage-type polysilsesquioxane, and in-situ polymerization is performed to obtain a low-dielectric fluorinated polyimide. The material has a large volume of fluorene-based structure and silane structure and fluorine atoms with strong electronegativity, which makes the preparation of fluorinated polyimide have low dielectric properties, but the dielectric constant of the material at 1MHz is 2.23, and the frequency unit of high-frequency communication is generally GHz. The polyimide with a dielectric constant of 2.23 at 1MHz obviously cannot meet the requirements of high-frequency communication. The patent with application number CN201610656823.9 discloses a crystalline copolymer polyimide resin with low melt viscosity and easy melt processing and its application. The material is prepared by polycondensation reaction of aromatic dianhydride monomer, aromatic diamine monomer and end-capping agent. Although the material has a flexible ether bond, it can only improve the processing performance, and the dielectric properties are not good, which cannot meet the requirements of high-frequency communication. Patent application number 201810600971.8 discloses an ultra-low expansion fluorinated polyimide film and its preparation method and application. The introduction of fluorine atoms or fluorinated groups can ensure the heat resistance and thermal dimensional stability of the polyimide film. This material is only suitable for the flexible optoelectronic field and is not suitable for high-frequency communication. Therefore, a low-dielectric fluorinated silane-modified polyimide is needed, with a dielectric constant low enough to meet the requirements of high-frequency communication, good flexibility, low melt viscosity, and improved processability. Summary of the invention

[0004] In view of the above-mentioned prior art, the purpose of the present invention is to provide a low dielectric fluorinated silane modified polyimide and its application. The fluorinated silane polyimide prepared by the present invention has a bulky fluorene structure, a flexible ether bond, a silane structure and a fluorine atom with strong electronegativity, so that the prepared fluorinated silane polyimide has lower dielectric properties, and also improves the processing performance of the polyimide and its solubility in various organic solvents.

[0005] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect of the present invention, a low dielectric fluorinated silane-modified polyimide is provided, and the structural formula of the low dielectric fluorinated silane-modified polyimide is as follows: ; Among them, R 1is a fluorine-containing silane group; R 2 is an aromatic anhydride group; AR is a fluorinated or non-fluorinated biphenyl group, or a phenoxybenzene group; Ar' is a phenoxybenzene group or a fluorinated biphenyl group; Ar'' is a fluorinated biphenyl group or a phenoxybenzene group; m, n, q are all integers greater than 1.

[0006] Preferably, when Ar' is a phenoxybenzene group, Ar'' is a fluorinated biphenyl group; when Ar' is a fluorinated biphenyl group, Ar'' is a phenoxybenzene group.

[0007] Preferably, the R 1 is selected from a triethoxyfluorosilane group, a trifluoropropanetrimethoxysilane group, a triethoxy(perfluorooctyl)silane group, a trimethoxy(pentafluorophenyl)silane group or a triethoxy(pentafluorophenyl)silane group; said R 2 is phenylacetylene phthalic anhydride; the AR is , , or ; Ar' and Ar'' are selected from , , or ; When Ar' is or When Ar'' is or ; When Ar' is or When Ar'' is or .

[0008] A second aspect of the present invention provides a method for preparing a low dielectric fluorinated silane-modified polyimide, comprising the following steps: (1) In an inert atmosphere, a hydroxyfluorene diamine compound, an ether-containing polyamine, and a fluorine-containing polyamine are dissolved in a polar organic solvent, and then a dianhydride and a capping agent are added to carry out a polycondensation reaction to obtain a polyamic acid; (2) The polyamic acid, the water-carrying agent and the fluorinated silane are mixed and subjected to an imidization reaction to obtain a low dielectric fluorinated silane-modified polyimide.

[0009] Preferably, in step (1), the inert atmosphere is nitrogen.

[0010] Preferably, in step (1), the hydroxyfluorene diamine compound is 9,9-bis(3-amino-4-hydroxyphenyl)fluorene; the ether-containing polyamine is an aromatic ether-containing diamine; the fluorine-containing polyamine is an aromatic fluorine-containing diamine; the polar organic solvent is selected from N-methylpyrrolidone, N,N'-dimethylformamide or N,N'-dimethylacetamide; the dianhydride is an aromatic dianhydride; and the end-capping agent is phenylacetylene phthalic anhydride.

[0011] Preferably, the aromatic dianhydride is selected from 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride or 3,4'-oxydiphthalic anhydride; the aromatic ether-containing diamine is 1,3-bis(3-aminophenoxy)benzene or 3,3'-oxydiphenylamine; the aromatic fluorine-containing diamine is selected from 2,2-bis(trifluoromethyl)diaminobiphenyl or 2,2-bis(4-aminophenyl)hexafluoropropane.

[0012] Preferably, in step (1), the molar ratio of the hydroxyfluorene diamine compound, the ether-containing polyamine, the fluorine-containing polyamine, the dianhydride and the end-capping agent is m:n:q:(m+n+q):2(m+n+q); the temperature of the polycondensation reaction is 20-50°C, and the time of the polycondensation reaction is 12-24 h.

[0013] More preferably, the temperature of the polycondensation reaction is 0-25° C., and the time of the polycondensation reaction is 5-20 h.

[0014] Preferably, in step (2), the water-carrying agent is xylene or toluene; and the fluorine-containing silane is selected from triethoxyfluorosilane, trifluoropropanetrimethoxysilane, triethoxy(perfluorooctyl)silane, trimethoxy(pentafluorophenyl)silane or triethoxy(pentafluorophenyl)silane.

[0015] Preferably, in step (2), the molar ratio of the polyamic acid, the water-carrying agent and the fluorinated silane is 1:2-5:2-5; the temperature of the imidization reaction is 120-250° C., and the time of the imidization reaction is 10-12 h.

[0016] More preferably, the temperature of the imidization reaction is 140-220° C. and the duration of the imidization reaction is 4-12 h.

[0017] The third aspect of the present invention provides the use of low dielectric fluorinated silane modified polyimide in at least one of the following 1) to 4): 1) Preparation of polyimide films for high-frequency communications; 2) Improve the solubility of polyimide in organic solvents; 3) Improve the processability of polyimide; 4) Improve the low dielectric properties of polyimide films.

[0018] In a fourth aspect of the present invention, a polyimide film is provided, wherein the polyimide film has good low dielectric properties at high frequencies, for example, a polyimide film with a thickness of 60 to 70 μm has a dielectric constant of less than 4.0 F / m and a dielectric loss of less than 0.04 at a frequency of 20 GHz.

[0019] Preferably, the curing temperature of the polyimide film prepared by the polyimide is: The temperature of the first stage is preferably 150-170°C, more preferably 160°C, and the time is preferably 1-3 h, more preferably 2 h; the temperature of the second stage is preferably 270-290°C, more preferably 280°C, and the time is preferably 0.5-1.5 h, more preferably 1 h; the temperature of the third stage is preferably 330-350°C, more preferably 340°C, and the time is preferably 0.4-0.6 h, more preferably 0.5 h; the temperature of the fourth stage is preferably 370-390°C, more preferably 380°C, and the time is preferably 1-3 h, more preferably 2 h.

[0020] Beneficial effects of the present invention: (1) The preparation method of the present invention is simple and easy to implement, has a short synthetic route, and is suitable for industrial mass production.

[0021] (2) The fluorine-containing silane polyimide prepared by the present invention has a bulky fluorene structure, a flexible ether bond, a silane structure and fluorine atoms with strong electronegativity, so that the prepared fluorine-containing silane polyimide has lower dielectric properties and also improves the processing performance of the polyimide.

[0022] (3) The fluorinated silane-modified polyimide prepared by the present invention is oxidized in DMAC, DMF, NMP, DMSO, THF and CHCl 3 It has good solubility in organic solvents such as polyimide, and the polyimide film prepared using the polyimide has good low dielectric properties, and is expected to be used in high-frequency communication technology in aerospace and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : Infrared spectrum of the polyimide prepared in Example 1. DETAILED DESCRIPTION

[0024] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0025] As introduced in the background technology section, the dielectric properties of traditional polyimide materials still need to be improved, especially in the high-frequency band, where the dielectric properties decrease significantly, limiting their application in high-frequency communications. Improving high-frequency communication technology and expanding its application range have a very far-reaching impact.

[0026] Based on this, the purpose of the present invention is to provide a low dielectric fluorine-containing silane modified polyimide and its application. The fluorine-containing silane polyimide prepared by the present invention has a large volume fluorene group structure and a silane structure and a fluorine atom with strong electronegativity. Large volume structures such as fluorene groups have characteristics such as high free volume. The polyimide resin constructed by adjusting its proportion in the molecular chain will inevitably affect the stacking degree of the polyimide molecular chain, thereby producing different dielectric loss properties. At the same time, the fluorine atom has a strong electronegativity, and its binding to the extranuclear electrons is strong, the atomic radius is small, and the self-polarization rate is low. The content of fluorine atoms will also have an important influence on the intensity of the polarization effect of the polyimide molecular chain. At the same time, the fluorine-containing silane polyimide provided by the present invention has a flexible ether bond and the presence of the silane structure increases the free volume and flexibility of the polymer molecular chain, so that the processability (macroscopic solution viscosity, melt viscosity) of the polyimide is good. After phenylacetylene phthalic anhydride is used as an end-capping agent for end-capping, the alkynyl groups can be further cross-linked to improve the thermodynamic properties of the polyimide. Therefore, the polyimide film prepared by using the polyimide of the present invention can ensure good low dielectric constant performance in the field of high-frequency communication while having the characteristics of high processability; and the fluorinated silane polyimide is resistant to fluorine in DMAC, DMF, NMP, DMSO, THF and CHCl 3 It has good solubility in organic solvents.

[0027] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0028] The test materials used in the examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels.

[0029] Example 1 (1) Preparation of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene: 6.0g of 9,9-bis(4-hydroxyphenyl)fluorene was placed in a 250mL three-necked reaction bottle, and then 30mL of acetone was added and stirred to dissolve. Then the reaction device was placed in an ice-water bath, and 6.0g of concentrated nitric acid was slowly added through a constant pressure funnel within 30min and stirred for 12h. Then 30mL of deionized water was added to the reaction solution, and a yellow powder was gradually precipitated. The powder was filtered out by a suction filtration device, washed with ethanol 3 to 4 times, and dried under vacuum to finally obtain 4.5g of the nitrated compound intermediate. In a 250mL three-necked flask equipped with a mechanical stirring device, add 4.5g of the nitro compound intermediate synthesized above and 30mL of ethanol, stir at room temperature for half an hour under the protection of nitrogen, then add 0.5g of palladium / carbon (10wt%) and 30mL of hydrazine hydrate to the solution through a constant pressure dropping funnel within 2h, use a microwave with a frequency of 2GHz to heat up to 60℃ at a heating rate of 10℃ / min, and react the system for 12h. After the reaction is completed, filter and remove palladium / carbon while hot, then drop deionized water into the solution to precipitate a white solid, and after suction filtration and vacuum drying at 100℃, 3.1g of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene is obtained.

[0030] (2) Preparation of polyamic acid: In a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.1 mol of 1,3-bis(3-aminophenoxy)benzene was added to 100 mL of N-methylpyrrolidone (NMP). After it was completely dissolved, 0.05 mol of 2,2-bis(trifluoromethyl)diaminobiphenyl and 0.05 mol of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene prepared in step (1) were added. After it was completely dissolved, 0.2 mol of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride and 0.4 mol of phenylacetylene anhydride were added. The mixture was stirred at room temperature for 24 h to form a viscous polyamic acid.

[0031] (3) Preparation of fluorinated silane polyimide: 1.0 mol xylene and 0.6 mol trifluoropropane trimethoxysilane were added to the polyamic acid system prepared in step (2), and the system was heated to 140°C. The xylene and water were azeotropically carried out to promote the imidization reaction of the system to proceed in the forward direction. After 4 hours of sufficient water carrying, the heating was stopped. The solution was slowly poured into 500 mL of deionized water for precipitation with continuous stirring. The obtained precipitate was washed by boiling ethanol 3-5 times, and then dried in a vacuum oven at 100°C for 10 hours to obtain 46.35 g of the target polyimide polymer PI-1, whose structure is shown in Formula I: ; Among them, AR is , Ar' is , Ar'' is .

[0032] The specific structural formula is: The polyimide PI-1 prepared in Example 1 was subjected to infrared testing. The test results are as follows: Figure 1 As shown by Figure 1 It can be seen that the structure of the polyimide prepared by the present invention is consistent with expectations.

[0033] Example 2 (1) The preparation of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene was carried out in the same manner as step (1) of Example 1.

[0034] (2) Preparation of polyamic acid: In a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.1 mol of 1,3-bis(3-aminophenoxy)benzene was added to 100 mL of N,N-dimethylacetamide. After it was completely dissolved, 0.05 mol of 2,2-bis(4-aminophenyl)hexafluoropropane and 0.05 mol of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene prepared in step (1) were added. After it was completely dissolved, 0.2 mol of 2,3,3',4'-biphenyltetracarboxylic dianhydride and 0.4 mol of phenylacetylene anhydride were added. The mixture was stirred and reacted at room temperature for 24 h to form a viscous polyamic acid.

[0035] (3) Preparation of fluorinated silane polyimide: Add 1.0 mol toluene and 0.6 mol trifluoropropane trimethoxysilane to the polyamic acid system prepared in step (2), heat to 140°C, and use xylene and water to azeotropically carry out water to promote the thermal imidization reaction of the system to proceed in the forward direction. After 4 hours of sufficient water carrying, stop heating. Slowly pour the solution into 500 mL deionized water for precipitation with continuous stirring. After the obtained precipitate is washed by boiling with ethanol 3-5 times, it is dried in a vacuum oven at 100°C for 10 hours. 46.56 g of the target polyimide polymer PI-2 is obtained, and its structure is shown in Formula I of Example 1, wherein, AR is , Ar' is , Ar'' is : The specific structural formula is: Example 3 (1) The preparation of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene was carried out in the same manner as step (1) of Example 1.

[0036] (2) Preparation of polyamic acid: In a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.1 mol of 3,3'-oxydiphenylamine was added to 100 mL of N,N-dimethylacetamide. After it was completely dissolved, 0.05 mol of 2,2-bis(trifluoromethyl)diaminobiphenyl and 0.05 mol of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene prepared in step (1) were added. After it was completely dissolved, 0.2 mol of 2,3,3',4'-biphenyltetracarboxylic dianhydride and 0.4 mol of phenylacetylene anhydride were added. The mixture was stirred and reacted at room temperature for 24 h to form a viscous polyamic acid.

[0037] (3) Preparation of fluorinated silane polyimide: Add 1.0 mol xylene and 0.6 mol trifluoropropane trimethoxysilane to the polyamic acid system prepared in step (2), heat the system to 140°C, and use xylene and water to azeotropically carry out water to promote the thermal imidization reaction of the system to proceed in the forward direction. After 4 hours of sufficient water carrying, stop heating. Slowly pour the solution into 500 mL deionized water for precipitation while stirring continuously. After the obtained precipitate is washed by boiling in ethanol 3-5 times, it is dried in a vacuum oven at 100°C for 10 hours. 44.87 g of the target polyimide polymer PI-3 is obtained, and its structure is shown in Formula I of Example 1, wherein, AR is , Ar' is , Ar'' is : The specific structural formula is: Example 4 (1) The preparation of 9,9-bis(3-amino-4-hydroxyphenyl)fluorene was carried out in the same manner as step (1) of Example 1.

[0038] (2) Preparation of polyamic acid: In a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.1 mol 3,3'-oxydiphenylamine was added to 100 mL N-methylpyrrolidone. After it was completely dissolved, 0.05 mol 2,2-bis(4-aminophenyl)hexafluoropropane and 0.05 mol 9,9-bis(3-amino-4-hydroxyphenyl)fluorene prepared in step (1) were added. After it was completely dissolved, 0.2 mol 2,3,3',4'-biphenyltetracarboxylic acid dianhydride and 0.4 mol phenylacetylene anhydride were added. The mixture was stirred and reacted at room temperature for 24 h to form a viscous polyamic acid.

[0039] (3) Preparation of fluorinated silane polyimide: Add 1.0 mol toluene and 0.6 mol trifluoropropane trimethoxysilane to the polyamic acid system prepared in step (2), heat the system to 140°C, and use xylene and water to azeotropically carry out water to promote the thermal imidization reaction of the system to proceed in the forward direction. After 4 hours of sufficient water carrying, stop heating. Slowly pour the solution into 500 mL deionized water for precipitation while stirring continuously. After the obtained precipitate is washed by boiling in ethanol 3-5 times, it is dried in a vacuum oven at 100°C for 10 hours. 45.10 g of the target polyimide polymer PI-4 is obtained, and its structure is shown in Formula I of Example 1, wherein, AR is , Ar' is , Ar'' is : The specific structural formula is: Comparative Example 1 The difference from Example 1 is that in step (2), in a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.1 mol 9,9-bis(3-amino-4-hydroxyphenyl)fluorene is added to 100 mL of N-methylpyrrolidone (NMP), and after it is completely dissolved, 0.1 mol 2,3,3',4'-biphenyltetracarboxylic dianhydride and 0.2 mol phenylacetylene phthalic anhydride are added, and the reaction is stirred at room temperature for 24 h to form a viscous polyamic acid.

[0040] Finally, the polyimide polymer PI-5 was prepared, and its structural formula is shown below: .

[0041] Comparative Example 2 The difference from Example 1 is that in step (2), in a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.1 mol 1,3-bis(3-aminophenoxy)benzene is added to 100 mL of N-methylpyrrolidone (NMP), and after it is completely dissolved, 0.05 mol 9,9-bis(3-amino-4-hydroxyphenyl)fluorene is added, and after it is completely dissolved, 0.15 mol 2,3,3',4'-biphenyltetracarboxylic dianhydride and 0.3 mol phenylacetylene anhydride are added, and the reaction is stirred at room temperature for 24 h to form a viscous polyamic acid.

[0042] Finally, the polyimide polymer PI-6 was prepared, and its structural formula is shown below: Comparative Example 3 The difference from Example 1 is that in step (2), in a 500 mL three-necked flask equipped with a nitrogen inlet and outlet, a magnetic stirrer, a thermometer, and a condenser, under the protection of nitrogen, 0.05 mol 2,2-bis(trifluoromethyl)diaminobiphenyl and 0.05 mol 9,9-bis(3-amino-4-hydroxyphenyl)fluorene are added to 100 mL of N-methylpyrrolidone (NMP), and after they are completely dissolved, 0.1 mol 2,3,3',4'-biphenyltetracarboxylic acid dianhydride and 0.2 mol phenylacetylene phthalic anhydride are added, and the reaction is stirred at room temperature for 24 h to form a viscous polyamic acid.

[0043] Finally, the polyimide polymer PI-7 was prepared, and its structural formula is shown below: .

[0044] Comparative Example 4 The difference from Example 1 is that in step (3), trifluoropropane trimethoxysilane is not added. The polyimide polymer PI-8 finally prepared has the following structural formula: Test example: performance test 1. Solubility test The solubility of the polyimide prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was tested by dissolving the polyimide in DMAC, DMF, NMP, DMSO, THF and CHCl 3 The concentration of polyimide in different solvents is 10 mg / mL. The solubility of polyimide in different solvents is tested, ++: completely dissolved at room temperature; +: completely dissolved by heating; +-: partially dissolved; --: insoluble by heating. The test results are shown in Table 1.

[0045] Table 1 Solubility of polyimide It can be seen from the test results in Table 1 that the polyimide prepared in Examples 1 to 4 has better solubility than Comparative Examples 1 to 4. The polyimide structure provided by the present invention introduces a bulky fluorene structure, an ether bond, and a fluorinated silane structure, so that the polyimide prepared by the present invention exhibits good solubility in most polar solvents.

[0046] 2. Dielectric properties test The dielectric properties of the polyimide films prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were tested. The test method was as follows: a molding machine was used to mold the polyimide into a circular sheet with uniform thickness. During the test, a layer of circular silver with a diameter of 22 mm was sprayed on both sides of the circular sheet as a test electrode. A broadband dielectric impedance spectrometer was used to characterize the dielectric constant of the composite foam at different porosities. The voltage amplitude was 1.0 V, the DC potential was 0.4 V, and the frequency scanning range was 1 to 10° Hz. The test results are shown in Table 2.

[0047] Table 2 Dielectric properties of polyimide film at 20 GHz As shown in Table 2, compared with Comparative Examples 1 to 4, the polyimide prepared in Examples 1 to 4 has better low dielectric properties after being prepared into polyimide films. This is because the fluorine-containing silane polyimide provided by the present invention has a large volume fluorene structure and a silane structure and a fluorine atom with strong electronegativity, so that the prepared fluorine-containing silane polyimide has lower dielectric properties.

[0048] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A low dielectric fluorinated silane modified polyimide, characterized in that: The structural formula of the low dielectric fluorinated silane modified polyimide is as follows: ； Among them, R1 is a fluorine-containing silane group; R2 is an aromatic anhydride group; AR is a fluorine-containing or non-fluorine-containing biphenyl group, or a phenoxybenzene group; Ar' is a phenoxybenzene group or a fluorine-containing biphenyl group; Ar'' is a fluorine-containing biphenyl group or a phenoxybenzene group; m, n, and q are all integers greater than 1.

2. The low dielectric fluorinated silane modified polyimide according to claim 1, characterized in that: When Ar' is a phenoxybenzene group, Ar'' is a fluorinated biphenyl group; when Ar' is a fluorinated biphenyl group, Ar'' is a phenoxybenzene group.

3. The low dielectric fluorinated silane modified polyimide according to claim 2, characterized in that: The R1 is selected from a triethoxyfluorosilane group, a trifluoropropane trimethoxysilane group, a triethoxy (perfluorooctyl) silane group, a trimethoxy (pentafluorophenyl) silane group or a triethoxy (pentafluorophenyl) silane group; the R2 is phenylacetylene phthalic anhydride; the AR is , , or ; Ar' and Ar'' are selected from , , or ; When Ar' is or When Ar'' is or ; When Ar' is or When Ar'' is or .

4. The method for preparing the low dielectric fluorinated silane modified polyimide according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) In an inert atmosphere, a hydroxyfluorene diamine compound, an ether-containing polyamine, and a fluorine-containing polyamine are dissolved in a polar organic solvent, and then a dianhydride and a capping agent are added to carry out a polycondensation reaction to obtain a polyamic acid; (2) The polyamic acid, the water-carrying agent and the fluorinated silane are mixed and subjected to an imidization reaction to obtain a low dielectric fluorinated silane-modified polyimide.

5. The preparation method according to claim 4, characterized in that: In step (1), the hydroxyfluorene diamine compound is 9,9-bis(3-amino-4-hydroxyphenyl)fluorene; the ether-containing polyamine is an aromatic ether-containing diamine; the fluorine-containing polyamine is an aromatic fluorine-containing diamine; the polar organic solvent is selected from N-methylpyrrolidone, N,N'-dimethylformamide or N,N'-dimethylacetamide; the dianhydride is an aromatic dianhydride; and the end-capping agent is phenylacetylene phthalic anhydride.

6. The preparation method according to claim 5, characterized in that: The aromatic dianhydride is selected from 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride or 3,4'-oxydiphthalic anhydride; the aromatic ether-containing diamine is 1,3-bis(3-aminophenoxy)benzene or 3,3'-oxydiphenylamine; the aromatic fluorine-containing diamine is selected from 2,2-bis(trifluoromethyl)diaminobiphenyl or 2,2-bis(4-aminophenyl)hexafluoropropane.

7. The preparation method according to claim 4, characterized in that: In step (1), the molar ratio of the hydroxyfluorene diamine compound, the ether-containing polyamine, the fluorine-containing polyamine, the dianhydride and the end-capping agent is m:n:q:(m+n+q):2(m+n+q); the temperature of the polycondensation reaction is 20-50°C, and the time of the polycondensation reaction is 12-24 h.

8. The preparation method according to claim 4, characterized in that: In step (2), the water-carrying agent is xylene or toluene; the fluorine-containing silane is selected from triethoxyfluorosilane, trifluoropropanetrimethoxysilane, triethoxy(perfluorooctyl)silane, trimethoxy(pentafluorophenyl)silane or triethoxy(pentafluorophenyl)silane.

9. The preparation method according to claim 4, characterized in that: In step (2), the molar ratio of the polyamic acid, the water-carrying agent and the fluorinated silane is 1:2-5:2-5; the temperature of the imidization reaction is 120-250° C., and the time of the imidization reaction is 10-12 h.

10. Use of the low dielectric fluorinated silane modified polyimide according to any one of claims 1 to 3 in at least one of the following 1) to 4): 1) Preparation of polyimide films for high-frequency communications; 2) Improve the solubility of polyimide in organic solvents; 3) Improve the processability of polyimide; 4) Improve the low dielectric properties of polyimide films.

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