Method for synthesizing fluorinated polyimide film by using water-alcohol cosolvent

Abstract

The invention relates to the technical field of polymer synthesis, in particular to a method for synthesizing a fluorinated polyimide film through a water-alcohol cosolvent. The method comprises the following steps: in a water-alcohol cosolvent, forming a reaction system from a fluorine-containing aryl diamine monomer and a fluorine-containing aryl dianhydride monomer under the catalytic action of a pyridine compound, and then carrying out nucleophilic reaction to obtain a fluorine-containing polyamide acid solution; coating a mold with the fluorine-containing polyamide acid solution, carrying out solid-phase polymerization-thermal imidization reaction, and demolding to obtain a fluorinated polyimide film; the FPI film is synthesized by adopting a water-alcohol cosolvent of water, normal propyl alcohol and isopropyl alcohol, the solubility of a fluorinated monomer is improved by the water-alcohol cosolvent, the reduction of the surface tension of the cosolvent is crucial for improving the solubility of the monomer and promoting the interaction of the monomer, the polymerization process is accelerated, and the yield of the film is increased. And the obtained FPI film has higher molecular weight, mechanical property and light transmittance.

Description

Technical Field

[0001] The invention relates to the technical field of polymer synthesis, and in particular to a method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent. Background Art

[0002] Polyimide (PI) is an aromatic heterocyclic polymer material with imide ring repeating units in the main chain of the molecule. It has excellent high temperature resistance, low temperature resistance, electrical insulation, mechanical, optical, aging resistance, radiation resistance and solvent resistance. It is mainly used in plastics, fibers and films, aerospace, automotive industry, electronic and electrical industry, gas separation membranes and high-performance electronic packaging materials. Fluorinated polyimide (FPI) is a versatile material with a wide range of uses. Due to its excellent physical properties, including high optical transparency and low dielectric constant, it is widely used in various applications such as displays and transparent films.

[0003] FPI, like other polyimides, is traditionally synthesized by forming a precursor polyamic acid (PAA) in an organic solvent and then performing imidization. Commonly used solvents for this process include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF), which are aprotic polar solvents. However, these solvents are harmful to the environment and toxic. In addition, PAA is prone to rapid hydrolysis, resulting in insufficient storage stability.

[0004] To overcome the environmental and health issues caused by organic solvents in traditional polyimide synthesis methods and to improve the stability of precursors, researchers are exploring hydrothermal polymerization as a more environmentally friendly alternative. This method avoids the use of harmful organic solvents and additional chemicals or catalysts by dispersing diamines and dianhydrides in water to form monomer salts. Compared with the traditional two-step method, aqueous phase polymerization simplifies the synthesis process and helps to produce poly(amic acid) salts (PAAS) with better storage stability. However, this method also has its limitations and is mainly applicable to monomers with good water solubility. For monomers containing fluorine groups or with limited solubility in water, aqueous system polymerization may not be the best choice. Therefore, it is of great significance to develop an environmentally friendly and low-cost method for synthesizing fluorinated polyimides using water-alcohol co-solvents. Summary of the invention

[0005] In order to solve the above technical problems, a method for synthesizing a fluorinated polyimide film using a water-alcohol cosolvent is provided. The method of the invention can directly obtain an FPI film, and the synthesized FPI has a higher molecular weight, excellent mechanical properties, and high film transparency.

[0006] In order to achieve the above objectives, the present invention is implemented by the following technical solutions:

[0007] A method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent comprises the following steps:

[0008] In the presence of a water-alcohol co-solvent, a fluorine-containing aromatic diamine monomer and a fluorine-containing aromatic dianhydride monomer are reacted under the catalytic action of a pyridine compound to form a reaction system, and then a nucleophilic reaction is performed to obtain a fluorine-containing polyamic acid solution;

[0009] The fluorinated polyamic acid solution is coated on the mold, and then solid phase polymerization-thermal imidization reaction is carried out, and the fluorinated polyimide film is obtained after demoulding.

[0010] Furthermore, the water-alcohol co-solvent is a mixed solvent consisting of water, n-propanol and isopropanol, in which the mass proportion of water is 10%-40%, the mass proportion of n-propanol is 10%-80%, and the mass proportion of isopropanol is 10%-80%.

[0011] Preferably, in the mixed solvent, water accounts for 20%-40% by mass, n-propanol accounts for 30%-40% by mass, and isopropanol accounts for 30%-40% by mass.

[0012] Preferably, water, n-propanol and isopropanol are in equal mass ratios in the mixed solvent.

[0013] Furthermore, the fluorine-containing aromatic diamine monomer is selected from one or more of 2,2'-bis(trifluoromethyl)benzidine (TFMB), 4,4'-(hexafluoroisopropylene)diphenylamine (6FDA-DAM), 2,2'-bis(4-aminophenoxyphenyl)hexafluoropropane (BAPF), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (p-6FAPB), and 1,1-bis(4-aminophenyl)-1(-3',5'-bistrifluoromethyl)phenyl-2,2,2-trifluoroethane (9FDA).

[0014] Furthermore, the fluorine-containing aromatic dianhydride monomer is selected from one or more of 4,4'-(2-trifluoromethyl)biphenyl dianhydride (BTFB) and 4,4'-(hexafluoroisopropylene)diphthalic anhydride (6FDA).

[0015] Furthermore, the pyridine compound is selected from one or more of 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (PPY), and 4-piperidinylpyridine (PPP).

[0016] Furthermore, the molar ratio of the fluorine-containing aromatic diamine monomer, the fluorine-containing aromatic dianhydride monomer and the pyridine compound is 1:1:1.8-2.2; and the mass percentage of the reaction system is 15%-30%.

[0017] Furthermore, the process of obtaining the fluorinated polyamic acid solution is carried out under a protective atmosphere and under stirring, and the stirring speed is within the range of 200-500 rpm;

[0018] The order of adding materials is: firstly place the fluorinated aromatic diamine monomer in a reaction container, dissolve the pyridine compound in the water-alcohol co-solvent and then mix it with the fluorinated aromatic diamine monomer, stir at room temperature for 20-60 minutes, then add the fluorinated aromatic dianhydride monomer, and carry out nucleophilic reaction at 60-70°C for 1-4 hours.

[0019] Furthermore, the solid phase polymerization-thermal imidization reaction is carried out in a vacuum oven, and the process parameters are: heating from room temperature to a first temperature of 28-45° C. at a heating rate of 1-3° C. / min, and keeping at the first temperature for 2 hours;

[0020] Maintaining a heating rate of 1-3°C / min, heating from the first temperature to a second temperature of 60-80°C, and baking at the second temperature for 3 hours;

[0021] Heating from the second temperature to a third temperature of 140-160° C. at a heating rate of 4-10° C. / min, and baking at the third temperature for 3 hours;

[0022] Maintaining a heating rate of 4-10°C / min, heating from the third temperature to a fourth temperature of 180-220°C, and baking at the fourth temperature for 40 minutes;

[0023] Maintaining a heating rate of 4-10°C / min, heating from the fourth temperature to 230-280°C, and baking at the fourth temperature for 40 minutes;

[0024] The temperature is raised from the fourth temperature to a fifth temperature of 300-350° C. at a heating rate of 4-10° C. / min, and the mixture is kept at the fifth temperature for 30 minutes.

[0025] Preferably, the process parameters of the solid phase polymerization-thermal imidization reaction are: heating from room temperature to 30°C at a heating rate of 1-3°C / min, and keeping at 30°C for 2h;

[0026] Maintain a heating rate of 1-3°C / min from 30°C to 70°C, and bake at 70°C for 3 hours;

[0027] Heating rate: 4-10℃ / min from 70℃ to 150℃, and keeping at 150℃ for 3h;

[0028] Maintain a heating rate of 4-10°C / min from 150°C to 200°C, and bake at 200°C for 40 minutes;

[0029] Maintain a heating rate of 4-10°C / min from 200°C to 250°C, and bake at 250°C for 40 minutes;

[0030] Maintain a heating rate of 4-10°C / min from 250°C to 320°C, and bake at 320°C for 30 minutes.

[0031] Beneficial technical effects:

[0032] Since fluorine-based materials themselves have high surface tension, this hinders their dissolution in water. In order to overcome this limitation, the present invention uses water, n-propanol and isopropanol as water-alcohol co-solvents, which can effectively reduce the surface tension of the solvent and increase the solubility of the fluorine-containing monomer in the water-containing solvent, which makes it possible to synthesize the fluorine-based monomer that was previously difficult to dissolve in water; the present invention uses water, n-propanol and isopropanol as water-alcohol co-solvents, avoids the use of high-boiling point solvents, reduces the use and discharge of organic solvents, reduces pollution to the environment, and has high environmental protection; the method for synthesizing FPI using water-alcohol co-solvents does not require a high-temperature and high-pressure reactor, saves energy consumption and equipment investment, reduces production costs, and is suitable for large-scale batch production; the present invention uses water, n-propanol and isopropanol as water-alcohol co-solvents to first perform a nucleophilic reaction to obtain a polyfluorinated poly (amic acid) salt (FPAAS) precursor, which exhibits strong hydrolysis stability and improves the quality and performance stability of the product; then, by directly performing a solid-state polymerization-thermal imidization process on the FPAAS precursor solution, a high-molecular-weight FPI film can be directly obtained, and the obtained FPI film exhibits high transparency and strong tensile strength;

[0033] The method of the present invention has the advantages of simple production process, no need for fine control of molecular weight, low reaction temperature, low reaction energy consumption, short reaction time, easy operation and control; the present invention effectively solves the environmental problems associated with traditional organic solvents and provides a sustainable alternative for FPI production; the method of the present invention has the advantages of simple FPI synthesis and no need for fine control of molecular weight, while complying with environmental protection principles, which makes it different from traditional organic synthesis methods. In addition, the special properties of FPI indicate that it has broad potential in engineering applications. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Unless otherwise specifically stated, the numerical value set forth in these embodiments does not limit the scope of the present invention. The technology and method known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology and method should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0036] In addition, it should be noted that the use of terms such as "first" and "second" to limit the temperature of process parameters is only to facilitate the distinction between the temperatures in each step. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0037] The experimental methods in the following examples without specifying specific conditions are usually measured in accordance with national standards; if there is no corresponding national standard, the method is carried out in accordance with the general standard requirements or general methods.

[0038] Discussion Example

[0039] In this case, the surface tension of a solvent mixed with water and an alcohol was tested. The surface tension of the water-alcohol solution was measured using a surface tension meter from Shanghai Hengping Instrument Factory at a test temperature of 25°C. The results are shown in Table 1 below.

[0040] Table 1 Effect of alcohol content on solvent surface tension

[0041]

[0042]

[0043] As can be seen from Table 1, the surface tensions of water and the mixed solvents of four alcohols are different. The results show that after water and alcohol are combined, the surface tension decreases significantly with the increase of alcohol content. The decreases of IPA and PrOH are the largest. The present invention uses IPA and PrOH together to dissolve two fluorinated monomers, which can be quickly dissolved at a nucleophilic reaction temperature of 60-70°C, which can improve the solubility of the fluorinated monomers. The reduction of surface tension is crucial to improving the solubility of fluorinated monomers and promoting the interaction between fluorinated monomers.

[0044] Example 1

[0045] A method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent comprises the following steps:

[0046] Water, PrOH and IPA are mixed in a mass ratio of 1:1:1 to form a water-alcohol co-solvent (i.e., the composition of the water-alcohol co-solvent is 100wt%: PrOH accounts for 33.3%, IPA accounts for 33.3%, and water accounts for 33.4%);

[0047] Synthesis of FPAA precursor: Under a nitrogen atmosphere, TFMB (CAS No. 341-58-2, 20.8150 g, 0.065 mol) was placed in a reaction vessel, and DMAP (15.3168 g, 0.1254 mol) was dissolved in 215 mL of a water-alcohol co-solvent and mixed with TFMB in a reaction vessel, and stirred continuously at room temperature for 40 min; then 6FDA (CAS No. 1107-00-2, 28.8800 g, 0.065 mol) was added to form a reaction system, and a nucleophilic reaction was carried out at 70°C for 1 h to obtain a 20 wt% oligomeric fluorinated polyamic acid solution (FPAAS) solution.

[0048] FPI film synthesis: the above-obtained oligomeric FPAAS solution was coated on the mold and placed in a vacuum oven for solid phase polymerization-thermal imidization reaction. The process parameters were: heating from room temperature to 30°C at a heating rate of 2°C / min, and keeping at 30°C for 2h; heating from 30°C to 70°C at a heating rate of 2°C / min, and keeping at 70°C for 3h; heating from 70°C to 150°C at a heating rate of 5°C / min, and keeping at 150°C for 3h; heating from 150°C to 200°C at a heating rate of 5°C / min, and keeping at 200°C for 40min; heating from 200°C to 250°C at a heating rate of 5°C / min, and keeping at 250°C for 40min; heating from 250°C to 320°C at a heating rate of 5°C / min, and keeping at 320°C for 30min;

[0049] After demoulding, a fluorinated polyimide (FPI) film was obtained.

[0050] Example 2

[0051] A method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent comprises the following steps:

[0052] Water, PrOH and IPA are mixed to form a water-alcohol co-solvent, wherein the composition of the water-alcohol co-solvent is 100 wt %: PrOH accounts for 40%, IPA accounts for 40%, and water accounts for 20%;

[0053] Synthesis of FPAA precursor: TFMB (CAS No. 341-58-2,

[0054] At the same time, DMAP (12.0724 g, 0.0988 mol) was dissolved in 215 mL of water-alcohol co-solvent and mixed with TFMB in the reaction container, and stirred at room temperature for 40 min; then 6FDA (CAS No. 1107-00-2, 23.1050 g, 0.052 mol) was added to form a reaction system, and a nucleophilic reaction was carried out at 60 ° C for 4 h to obtain a 15 wt% oligomeric fluorinated polyamic acid solution (FPAAS) solution.

[0055] FPI film synthesis: the above-obtained oligomeric FPAAS solution was coated on the mold and placed in a vacuum oven for solid phase polymerization-thermal imidization reaction. The process parameters were: heating from room temperature to 30°C at a heating rate of 2°C / min, and keeping at 30°C for 2h; heating from 30°C to 70°C at a heating rate of 2°C / min, and keeping at 70°C for 3h; heating from 70°C to 160°C at a heating rate of 8°C / min, and keeping at 160°C for 3h; heating from 160°C to 210°C at a heating rate of 8°C / min, and keeping at 210°C for 40min; heating from 210°C to 260°C at a heating rate of 8°C / min, and keeping at 260°C for 40min; heating from 260°C to 320°C at a heating rate of 8°C / min, and keeping at 320°C for 30min;

[0056] After demoulding, a fluorinated polyimide (FPI) film was obtained.

[0057] Example 3

[0058] A method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent comprises the following steps:

[0059] Water, PrOH and IPA are mixed to form a water-alcohol co-solvent, wherein the composition of the water-alcohol co-solvent is 100 wt %: PrOH accounts for 40%, IPA accounts for 40%, and water accounts for 20%;

[0060] Synthesis of FPAA precursor: Under a nitrogen atmosphere, TFMB (CAS No. 341-58-2, 26.8750 g, 0.0839 mol) was placed in a reaction vessel, and DMAP (19.7977 g, 0.1611 mol) was dissolved in 215 mL of a water-alcohol co-solvent and mixed with TFMB in a reaction vessel, and stirred at room temperature for 40 min; then 6FDA (CAS No. 1107-00-2, 37.2719 g, 0.0839 mol) was added to form a reaction system, and a nucleophilic reaction was carried out at 65 ° C for 3 h to obtain a 25 wt% oligomeric fluorinated polyamic acid solution (FPAAS) solution.

[0061] FPI film synthesis: the above-obtained oligomeric FPAAS solution was coated on the mold and placed in a vacuum oven for solid phase polymerization-thermal imidization reaction. The process parameters were: heating from room temperature to 30°C at a heating rate of 2°C / min, and keeping at 30°C for 2h; heating from 30°C to 70°C at a heating rate of 2°C / min, and keeping at 70°C for 3h; heating from 70°C to 150°C at a heating rate of 5°C / min, and keeping at 150°C for 3h; heating from 150°C to 200°C at a heating rate of 5°C / min, and keeping at 200°C for 40min; heating from 200°C to 250°C at a heating rate of 5°C / min, and keeping at 250°C for 40min; heating from 250°C to 320°C at a heating rate of 5°C / min, and keeping at 320°C for 30min;

[0062] After demoulding, a fluorinated polyimide (FPI) film was obtained.

[0063] Comparative Example 1

[0064] The preparation process of this case is the same as that of Example 1, except that the co-solvent is water and isopropanol in an equal mass ratio.

[0065] Comparative Example 2

[0066] The preparation process of this case is the same as that of Example 1, except that the co-solvent is composed of water and n-propanol in an equal mass ratio.

[0067] Comparative Example 3

[0068] The preparation process of this case is the same as that of Example 1, except that anhydrous ethanol is used as the solvent.

[0069] Comparative Example 4

[0070] The preparation process of this case is the same as that of Example 1, except that DMF is used as the solvent.

[0071] Test Case

[0072] The molecular weights of the FPAAS and FPI prepared in the above cases were tested, and the results are shown in Table 2.

[0073] Table 2 Molecular weight of FPAAS and FPI obtained in each case

[0074]

[0075] As can be seen from Table 2, the number average molecular weight of the precursor oligomeric FPAAS ranges from 890.45 to 1356.52 g / mol. Compared with polyimides prepared from general organic solvents that have analytical limitations due to insolubility and infusibility, the FPI prepared by the present invention is soluble due to its fluorine group, and the degree of polymerization of the ready-made polymer by subsequent solid phase polymerization-thermal imidization reaction can be quantified by measuring the change in molecular weight after the oligomeric FPAAS is converted into FPI at high temperature. According to the GPC analysis of FPI, the present invention first synthesizes an oligomeric FPAAS precursor, and the molecular weight of the polymer chain is significantly increased with the subsequent solid phase polymerization-thermal imidization reaction, and has a higher polymer molecular weight than PI synthesized by conventional organic solvents.

[0076] The mechanical properties and light transmittance of the FPI prepared in the above cases were tested. The results are shown in Table 3.

[0077] Table 3 Mechanical properties of FPI films in each case

[0078]

[0079] As can be seen from Table 4, the physical properties of FPI synthesized in different solvents are different. The present invention uses water, n-propanol, and isopropanol as water-alcohol cosolvents to first synthesize an oligomeric FPAAS precursor, and then directly forms an FPI film by solid-state polymerization-thermal imidization. The obtained FPI film has a higher molecular weight, mechanical properties, and light transmittance than the conventional FPI film obtained by the synthesis method of Comparative Example 4.

[0080] The present invention adopts a water-alcohol co-solvent of water, n-propanol and isopropanol to synthesize an FPI film. The water-alcohol co-solvent improves the solubility of the fluorinated monomer. The reduction of the surface tension of the co-solvent is crucial to improving the solubility of the monomer and promoting the interaction between the monomers, so that the polymerization process is accelerated. The obtained FPI film has a higher molecular weight, mechanical properties and light transmittance.

[0081] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for synthesizing a fluorinated polyimide film using a water-alcohol cosolvent, characterized in that: The steps include: In the presence of a water-alcohol co-solvent, a fluorine-containing aromatic diamine monomer and a fluorine-containing aromatic dianhydride monomer are reacted under the catalytic action of a pyridine compound to form a reaction system, and then a nucleophilic reaction is performed to obtain a fluorine-containing polyamic acid solution; The fluorinated polyamic acid solution is coated on the mold, and then solid phase polymerization-thermal imidization reaction is carried out, and the fluorinated polyimide film is obtained after demoulding.

2. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to claim 1, characterized in that: The water-alcohol co-solvent is a mixed solvent consisting of water, n-propanol and isopropanol, wherein the mass proportion of water in the mixed solvent is 10%-40%, the mass proportion of n-propanol is 10%-80%, and the mass proportion of isopropanol is 10%-80%.

3. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to claim 2, characterized in that: The mass proportion of water in the mixed solvent is 20%-40%, the mass proportion of n-propanol is 30%-40%, and the mass proportion of isopropanol is 30%-40%.

4. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to any one of claims 1 to 3, characterized in that: The fluorine-containing aromatic diamine monomer is selected from one or more of 2,2'-bis(trifluoromethyl)benzidine, 4,4'-(hexafluoroisopropylene)diphenylamine, 2,2'-bis(4-aminophenoxyphenyl)hexafluoropropane, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, and 1,1-bis(4-aminophenyl)-1(-3',5'-bistrifluoromethyl)phenyl-2,2,2-trifluoroethane.

5. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to any one of claims 1 to 3, characterized in that: The fluorine-containing aromatic dianhydride monomer is selected from one or more of 4,4'-(2-trifluoromethyl)biphenyl dianhydride and 4,4'-(hexafluoroisopropylene)diphthalic anhydride.

6. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to any one of claims 1 to 3, characterized in that: The pyridine compound is selected from one or more of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine and 4-piperidinylpyridine.

7. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to any one of claims 1 to 3, characterized in that: The molar ratio of the fluorine-containing aromatic diamine monomer, the fluorine-containing aromatic dianhydride monomer and the pyridine compound is 1:1:1.8-2.2; and the mass percentage of the reaction system is 15%-30%.

8. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to any one of claims 1 to 3, characterized in that: The process of obtaining the fluorinated polyamic acid solution is carried out under a protective atmosphere and under stirring, and the stirring speed is within the range of 200-500 rpm; The order of adding materials is: firstly place the fluorinated aromatic diamine monomer in a reaction container, dissolve the pyridine compound in the water-alcohol co-solvent and then mix it with the fluorinated aromatic diamine monomer, stir at room temperature for 20-60 minutes, then add the fluorinated aromatic dianhydride monomer, and carry out nucleophilic reaction at 60-70°C for 1-4 hours.

9. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to any one of claims 1 to 3, characterized in that: The solid phase polymerization-thermal imidization reaction is carried out in a vacuum oven, and the process parameters are: The temperature is raised from room temperature to a first temperature of 28-45°C at a heating rate of 1-3°C / min, and then kept at the first temperature for 2 hours; Maintaining a heating rate of 1-3°C / min, heating from the first temperature to a second temperature of 60-80°C, and baking at the second temperature for 3 hours; Heating from the second temperature to a third temperature of 140-160° C. at a heating rate of 4-10° C. / min, and baking at the third temperature for 3 hours; Maintaining a heating rate of 4-10°C / min, heating from the third temperature to a fourth temperature of 180-220°C, and baking at the fourth temperature for 40 minutes; Maintaining a heating rate of 4-10°C / min, heating from the fourth temperature to 230-280°C, and baking at the fourth temperature for 40 minutes; The temperature is raised from the fourth temperature to a fifth temperature of 300-350° C. at a heating rate of 4-10° C. / min, and the mixture is kept at the fifth temperature for 30 minutes.

10. The method for synthesizing a fluorinated polyimide film using a water-alcohol co-solvent according to claim 9, characterized in that: The process parameters of the solid phase polymerization-thermal imidization reaction are: The temperature was raised from room temperature to 30°C at a rate of 1-3°C / min, and then kept at 30°C for 2h; Maintain a heating rate of 1-3°C / min from 30°C to 70°C, and bake at 70°C for 3 hours; Heating rate: 4-10℃ / min from 70℃ to 150℃, and keeping at 150℃ for 3h; Maintain a heating rate of 4-10°C / min from 150°C to 200°C, and bake at 200°C for 40 minutes; Maintain a heating rate of 4-10°C / min from 200°C to 250°C, and bake at 250°C for 40 minutes; Maintain a heating rate of 4-10°C / min from 250°C to 320°C, and bake at 320°C for 30 minutes.

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