A terminal boronic acid crosslinked fluoropolyamide-imide film, and a preparation method and application thereof
By reacting diacyl chlorides with fluorinated diamines containing fluorine and imide structures with fluorinated diamines and end-capping with 3-aminophenylboronic acid, fluorinated polyimide films with end groups of boric acid were prepared. This method solved the problems of complex preparation process and poor performance of polyimide films, and achieved films with low coefficient of thermal expansion, high transparency and excellent mechanical properties, which are suitable for optical devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIAMEN UNIV
- Filing Date
- 2025-02-21
- Publication Date
- 2026-08-04
AI Technical Summary
Existing polyimide films are complex and difficult to control in their preparation process, and are prone to warping and misalignment when combined with inorganic/metallic materials, making it difficult to balance transparency and mechanical properties.
A fluorinated polyamide-imide oligomer with phenylboronic acid end groups was prepared by reacting a diacyl chloride with a fluorinated diamine with a fluorinated imide structure and end-capping with 3-aminophenylboronic acid. Subsequently, a high-temperature heat treatment was performed to form a fluorinated polyamide-imide film with end-boronic acid crosslinking.
The polymerization process has been simplified, and the film has a low coefficient of thermal expansion, high tensile strength and high transparency, and is reprocessable, making it suitable as a transparent layer material for optical devices.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer materials technology, specifically to a boric acid-terminated crosslinked fluorinated polyamide imide film, its preparation method, and its application. Background Technology
[0002] As display technology advances towards flexibility and foldability, high-performance transparent polymer films are showing great potential as alternatives to rigid glass substrates and cover materials. Polyimide films have attracted significant attention due to their excellent thermal, mechanical, and stability properties. However, traditional polyimides exhibit a golden-yellow color due to the presence of charge transfer complexes between and within polymer chains, severely limiting their application in the optoelectronic display field.
[0003] To improve the light transmittance of polyimide films, three main strategies are employed: first, introducing highly electronegative fluorine atoms to suppress charge transfer; second, introducing large side groups or twisted structures to increase interchain spacing and achieve simplified conjugation; and third, introducing alicyclic structures to reduce π electrons. These three methods effectively achieve the transparency of polyimides. However, in practical applications, besides high transparency, transparent polyimides also require a low linear coefficient of thermal expansion to avoid warping, misalignment, and debonding caused by mismatched coefficients of thermal expansion when composited with other inorganic / metallic materials during the manufacturing process. Furthermore, these three strategies often weaken the mechanical properties and thermal dimensional stability of transparent polyimides.
[0004] Polyamide-imides, in addition to possessing the five-membered nitrogen heterocyclic structure of polyimides, also contain amide bonds. The introduction of amide bonds facilitates the formation of hydrogen bonds between molecular chains, effectively enhancing the mechanical properties of the polymer and reducing its coefficient of thermal expansion. Currently, the preparation methods of polyamide-imides can be divided into three categories: 1) polycondensation of diamines / dianhydrides containing amide groups; 2) co-condensation of diamines and dianhydride monomers with diacid chloride monomers; and 3) dehydration polycondensation of diamines with diacids containing imide structures. To ensure excellent thermal and mechanical properties, the molecular weight of polyamide-imides needs to be sufficiently large. All three methods involve condensation reactions. According to polymer polymerization theory, to ensure high molecular weight, the purity of the monomers involved in the polymerization and the accuracy of the molar ratio of each monomer must be strictly controlled. Simultaneously, small molecules such as water must be removed promptly under high temperature and pressure during the reaction. These limitations make the control of the polymerization process exceptionally complex and difficult to scale up.
[0005] Therefore, there is a need to develop a transparent polyamide-imide film that has an easier polymerization process, excellent mechanical properties, and a low coefficient of thermal expansion. Summary of the Invention
[0006] This invention addresses the challenges of complex and difficult-to-control polymerization processes in the preparation of transparent polyamide-imides with high mechanical properties and low coefficient of thermal expansion in existing technologies. It provides a boric acid-crosslinked fluorinated polyamide-imide film and its preparation method. This method not only avoids the problems of strict control of monomer feed ratio in polymerization and reduced solubility and high system viscosity caused by high polymer molecular weight, but also produces films with low coefficient of thermal expansion, high tensile strength, and transparency.
[0007] The present invention provides a boric acid-terminated crosslinked fluorinated polyamide imide, the synthesis process of which involves reacting a fluorinated diacyl chloride with a fluorinated diamine to obtain a acyl chloride-terminated fluorinated polyamide imide oligomer, which is then reacted with 3-aminophenylboronic acid to prepare a phenylboronic acid-terminated fluorinated polyamide imide oligomer, and finally dehydration condensation through high-temperature heat treatment to form a boric acid-terminated crosslinked fluorinated polyamide imide.
[0008] This invention also provides a method for preparing a boric acid-terminated crosslinked fluorinated polyamide imide film, comprising the following steps:
[0009] (1) Under nitrogen atmosphere, fluorinated diamine is dissolved in an anhydrous organic solvent, and fluorinated diacyl chloride with amide structure is added under ice bath to form acyl chloride-terminated fluorinated polyamide imide. 3-aminophenylboronic acid is added and the reaction continues to form fluorinated polyamide imide with phenylboronic acid end group. A precipitant is added to the reaction solution to precipitate the resin, and the resin is obtained after washing and drying.
[0010] (2) The resin is dissolved in an anhydrous organic solvent to form a solution. After forming a film using a film-forming process, the film is dehydrated and condensed by heat treatment to form a boric acid-crosslinked fluorinated polyamide imide film.
[0011] Optionally, the fluorinated diamine has at least one of the following structural formulas or a combination of the following structures:
[0012]
[0013] Optionally, the diacyl chloride containing a fluorinated imide structure has at least one of the following structural formulas or a combination of the following structures:
[0014]
[0015] Optionally, the preparation method of the diacyl chloride containing a fluorinated imide structure is as follows: ... Trimeric trioxide was added to acetic acid and refluxed at 115°C for 24 h. The reaction solution was then added to a large amount of ethanol or methanol, the precipitate was collected, and dried under vacuum to obtain a diacid monomer containing an imide structure. The diacid monomer containing an imide structure was then reacted with sulfoxide at 80°C for 4 h, and excess sulfoxide was removed by rotary evaporation to obtain a diacyl chloride monomer containing an imide structure.
[0016] Optionally, the molar ratio of the fluorinated diamine to the diacyl chloride with a fluorinated imide structure is 0.8-0.9:1.
[0017] Optionally, the organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and cyclopentanone.
[0018] Optionally, the molar ratio of 3-aminophenylboronic acid to diacyl chloride containing a fluorine-containing imide structure is 0.4-0.8:1.
[0019] Optionally, the heat treatment includes programmed temperature drying and post-programmed temperature drying. The programmed temperature drying includes the following steps: 50℃-60℃ / 1-2h, 80℃-90℃ / 1-2h, 120℃-130℃ / 1-2h, 150℃-160℃ / 1-2h; the post-programmed temperature drying includes the following steps: 180℃-190℃ / 1-2h, 210℃-220℃ / 1-2h, 250℃-260℃ / 1-2h, to ensure complete solvent removal and boric acid crosslinking.
[0020] Optionally, the precipitant includes ethanol, water, methanol, etc.
[0021] Optionally, the film-forming process includes coating, drying, heat treatment, etc.
[0022] Furthermore, the preparation method comprises the following steps:
[0023] (1) Under nitrogen atmosphere, fluorinated diamine is dissolved in anhydrous organic solvent by stirring. Fluorinated diacyl chloride with fluorinated imide structure is added in batches under ice bath. After the addition is complete, the reaction is carried out in an ice bath for 2-4 hours, and then at room temperature for 4-12 hours. 3-aminophenylboronic acid is added and the reaction is continued at room temperature for 12-24 hours to form fluorinated polyamide imide with phenylboronic acid end group. The solid content is controlled at 10-20% during the reaction. After the reaction is complete, it is slowly poured into a mixed solvent of ethanol and water under vigorous stirring to precipitate a white fibrous resin, which is then dried under vacuum.
[0024] (2) Dissolve the dried resin in an anhydrous organic solvent to prepare a solution with a solid content of 10-20 wt%; then pour it onto a substrate, coat it with a doctor blade, and then dry it by programmed temperature rise. Finally, in a vacuum oven, continue to raise the temperature again to completely remove the solvent and crosslink it. Finally, after it cools down to room temperature naturally, it is taken out to obtain a boric acid-terminated crosslinked fluorinated polyamide imide film.
[0025] The thickness of the prepared films ranged from 20 to 50 μm.
[0026] The obtained terminal boric acid crosslinked fluorinated polyamide imide film may optionally have the following structure:
[0027]
[0028] R1 is a residue of the diacyl chloride with the above-mentioned fluorinated imide structure, and R2 is a residue of the above-mentioned fluorinated diamine.
[0029] The synthetic route for the above-mentioned terminal boric acid crosslinked fluorinated polyamide imide is as follows:
[0030]
[0031] R1 can be selected as R2 can be selected as
[0032] The above-mentioned terminal boric acid crosslinked fluorinated polyamide imide film is used as a transparent layer material for optical devices, including but not limited to display devices, photodetectors, etc.
[0033] Compared with the prior art, the present invention has the following beneficial effects:
[0034] (1) In this invention, the preparation process of fluorinated polyamide imide is prepared by reacting diacyl chloride with fluorinated diamine with fluorinated imide structure. The polymerization conditions are mild, and the polymerization of the two is not equimolar. Instead, end-capping treatment is performed by adding 3-aminophenylboronic acid, which avoids the problem of reduced solubility and poor flowability caused by high molecular weight.
[0035] (2) This invention ensures transparency by introducing fluorine-containing groups, enhances the inter-chain forces by introducing amide structures through polymerization reaction, reduces the coefficient of thermal expansion, and avoids the impact of low molecular weight on the mechanical properties of the film by end-capping with 3-aminophenylboronic acid and then thermal crosslinking.
[0036] (3) The present invention uses phenylboronic acid for end capping and reheat crosslinking, which avoids the problem of system gelation and difficult polymerization and film formation caused by the introduction of traditional multifunctional monomers. At the same time, due to the dynamic nature of boric acid ester bonds, the crosslinked fluorinated polyamide imide film also has the ability to be reprocessed.
[0037] (4) The fluorinated polyamide imide of the present invention has high transparency, low thermal expansion and good mechanical properties, and is suitable for use as a transparent layer material in optical devices.
[0038] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description
[0039] Figure 1 The thermal expansion curve of the end-borate crosslinked fluorinated polyamide imide film prepared in Example 1 is shown below.
[0040] Figure 2 The stress-strain curve of the end-borate crosslinked fluorinated polyamide imide film prepared in Example 1;
[0041] Figure 3 Visible light transmittance curve of the end-borate crosslinked fluorinated polyamide imide film prepared in Example 1;
[0042] Figure 4 This is a schematic diagram of the reprocessing of the end-borate crosslinked fluorinated polyamide imide film prepared in Example 1. Detailed Implementation
[0043] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.
[0044] Example 1
[0045] The preparation method of 2,2'-(2,2'-bis(trifluoromethyl)-[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dioxoisoindoline-5-acyl chloride) is as follows: 10 mmol of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl and 20 mmol of trimellitic anhydride were added to 60 mL of glacial acetic acid and refluxed at 115 °C for 24 hours. After the system temperature cooled to room temperature, it was poured into ethanol, the precipitate was collected, filtered, and repeatedly washed three times with ethanol. Finally, it was dried in a vacuum oven at 150 °C for 24 hours.
[0046] Under nitrogen atmosphere, 0.8 mmol of 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was added to a thoroughly dried three-necked flask, followed by 9 mL of anhydrous DMAc. The mixture was magnetically stirred to dissolve the precipitate. After placing the flask in an ice bath for 20 min, 1 mmol of 2,2'-(2,2'-bis(trifluoromethyl)-[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dioxoisoindoline-5-acyl chloride) was added in several portions to ensure uniform reaction. After the addition was complete, the mixture was reacted in an ice bath for 2 h, followed by a reaction at room temperature for 4 h. Then, 0.4 mmol of 3-aminophenylboronic acid was added, and the reaction was continued at room temperature for 12 h. After the reaction was complete, the precipitate was slowly poured into a 1:1 mixture of ethanol and water under vigorous stirring, precipitating a white fibrous resin, which was then dried at 100 °C for 24 h.
[0047] The dried resin was dissolved in DMAc to prepare a 10 wt% solution. This solution was then slowly poured onto a flat glass plate and coated into a film at a height of 1000 mm. The film was then dried at a temperature increased by 50°C for 2 hours, 80°C for 1 hour, 120°C for 1 hour, and 150°C for 1 hour. Afterward, it was transferred to a vacuum oven preheated to 150°C and dried at 180°C for 1 hour, 210°C for 1 hour, and 250°C for 1 hour to completely remove the solvent and crosslink the material. Finally, after allowing it to cool naturally to room temperature, the resulting boric acid-terminated crosslinked fluorinated polyamide-imide film sample was obtained.
[0048] Example 2
[0049] Under nitrogen atmosphere, 0.8 mmol of 2,2-bis(4-aminophenyl)hexafluoropropane was added to a thoroughly dried three-necked flask, followed by 9 mL of anhydrous DMAc. The mixture was magnetically stirred to dissolve the precipitate. After placing the flask in an ice bath for 20 min, 1 mmol of 2,2'-(2,2'-bis(trifluoromethyl)-[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dioxoisoindoline-5-acyl chloride) was added in several portions to ensure uniform reaction. After the addition was complete, the mixture was reacted in an ice bath for 2 h, followed by a reaction at room temperature for 4 h. Then, 0.4 mmol of 3-aminophenylboronic acid was added, and the reaction was continued at room temperature for 12 h. After the reaction was complete, the precipitate was slowly poured into a 1:1 mixture of ethanol and water under vigorous stirring, precipitating a white fibrous resin, which was then dried at 100 °C for 24 h.
[0050] The dried resin was dissolved in DMAc to prepare a 10 wt% solution. This solution was then slowly poured onto a flat glass plate and coated into a film at a height of 1000 mm. The film was then dried at a temperature increased by 50°C for 2 hours, 80°C for 1 hour, 120°C for 1 hour, and 150°C for 1 hour. Afterward, it was transferred to a vacuum oven preheated to 150°C and dried at 180°C for 1 hour, 210°C for 1 hour, and 250°C for 1 hour to completely remove the solvent and crosslink the material. Finally, after allowing it to cool naturally to room temperature, the resulting boric acid-terminated crosslinked fluorinated polyamide-imide film sample was obtained.
[0051] Example 3
[0052] The preparation method of ((perfluoropropane-2,2-diyl)bis(4,1-phenyl))bis(1,3-dioxoisoindoline-5-acyl chloride) is as follows: 10 mmol of 2,2-bis(4-aminophenyl)hexafluoropropane and 20 mmol of trimellitic anhydride were added to 60 mL of glacial acetic acid and refluxed at 115 °C for 24 hours. After the system temperature cooled to room temperature, it was poured into ethanol, the precipitate was collected, filtered, and repeatedly washed three times with ethanol. Finally, it was dried in a vacuum oven at 150 °C for 24 hours.
[0053] Under nitrogen atmosphere, 0.8 mmol of 2,2-bis(4-aminophenyl)hexafluoropropane was added to a thoroughly dried three-necked flask, followed by 9 mL of anhydrous DMAc. The mixture was magnetically stirred to dissolve the DMAc. After placing the flask in an ice bath for 20 min, 1 mmol of 2,2'-((perfluoropropane-2,2-diyl)bis(4,1-phenyl))bis(1,3-dioxoisoindoline-5-acyl chloride) was added in several portions to ensure uniform reaction. After the addition was complete, the mixture was reacted in an ice bath for 2 h, followed by a reaction at room temperature for 4 h. Then, 0.4 mmol of 3-aminophenylboronic acid was added, and the reaction was continued at room temperature for 12 h. After the reaction was complete, the precipitate was slowly poured into a 1:1 mixture of ethanol and water under vigorous stirring, precipitating a white fibrous resin, which was then dried at 100 °C for 24 h.
[0054] The dried resin was dissolved in DMAc to prepare a 10 wt% solution. This solution was then slowly poured onto a flat glass plate and coated into a film at a height of 1000 mm. The film was then dried at a temperature increased by 50°C for 2 hours, 80°C for 1 hour, 120°C for 1 hour, and 150°C for 1 hour. Afterward, it was transferred to a vacuum oven preheated to 150°C and dried at 180°C for 1 hour, 210°C for 1 hour, and 250°C for 1 hour to completely remove the solvent and crosslink the material. Finally, after allowing it to cool naturally to room temperature, the resulting boric acid-terminated crosslinked fluorinated polyamide-imide film sample was obtained.
[0055] Example 4
[0056] Under nitrogen atmosphere, 0.8 mmol of 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was added to a thoroughly dried three-necked flask, followed by 9 mL of anhydrous DMAc. The mixture was magnetically stirred to dissolve the DMAc. After placing the flask in an ice bath for 20 min, 1 mmol of 2,2'-((perfluoropropane-2,2-diyl)bis(4,1-phenyl))bis(1,3-dioxoisoindoline-5-acyl chloride) was added in several portions to ensure uniform reaction. After the addition was complete, the mixture was reacted in an ice bath for 2 h, followed by a reaction at room temperature for 4 h. Then, 0.4 mmol of 3-aminophenylboronic acid was added, and the reaction was continued at room temperature for 12 h. After the reaction was complete, the precipitate was slowly poured into a 1:1 mixture of ethanol and water under vigorous stirring, precipitating a white fibrous resin, which was then dried at 100 °C for 24 h.
[0057] The dried resin was dissolved in DMAc to prepare a 10 wt% solution. This solution was then slowly poured onto a flat glass plate and coated into a film at a height of 1000 mm. The film was then dried at a temperature increased by 50°C for 2 hours, 80°C for 1 hour, 120°C for 1 hour, and 150°C for 1 hour. Afterward, it was transferred to a vacuum oven preheated to 150°C and dried at 180°C for 1 hour, 210°C for 1 hour, and 250°C for 1 hour to completely remove the solvent and crosslink the material. Finally, after allowing it to cool naturally to room temperature, the resulting boric acid-terminated crosslinked fluorinated polyamide-imide film sample was obtained.
[0058] Example 5
[0059] Under nitrogen atmosphere, 0.9 mmol of 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl was added to a thoroughly dried three-necked flask, followed by 9 mL of anhydrous DMAc. The mixture was magnetically stirred to dissolve the DMAc. After placing the flask in an ice bath for 20 min, 1 mmol of 2,2'-((perfluoropropane-2,2-diyl)bis(4,1-phenyl))bis(1,3-dioxoisoindoline-5-acyl chloride) was added in several portions to ensure uniform reaction. After the addition was complete, the mixture was reacted in an ice bath for 2 h, followed by a reaction at room temperature for 4 h. Then, 0.4 mmol of 3-aminophenylboronic acid was added, and the reaction was continued at room temperature for 12 h. After the reaction was complete, the precipitate was slowly poured into a 1:1 mixture of ethanol and water under vigorous stirring, precipitating a white fibrous resin, which was then dried at 100 °C for 24 h.
[0060] The dried resin was dissolved in DMAc to prepare a 10 wt% solution. This solution was then slowly poured onto a flat glass plate and coated into a film at a height of 1000 mm. The film was then dried at a temperature increased by 50°C for 2 hours, 80°C for 1 hour, 120°C for 1 hour, and 150°C for 1 hour. Afterward, it was transferred to a vacuum oven preheated to 150°C and dried at 180°C for 1 hour, 210°C for 1 hour, and 250°C for 1 hour to completely remove the solvent and crosslink the material. Finally, after allowing it to cool naturally to room temperature, the resulting boric acid-terminated crosslinked fluorinated polyamide-imide film sample was obtained.
[0061] Table 1. Main properties of the fluorinated polyamide-imide films prepared in Examples 1-5
[0062] serial number Coefficient of thermal expansion (ppm / K) Tensile strength (MPa) <![CDATA[T 550 (%)]]> Example 1 9.6 195 85 Example 2 10.3 201 84 Example 3 10.5 198 85 Example 4 11.3 193 84 Example 5 12.4 178 87
[0063] The coefficient of thermal expansion (CTE) of the thin film was determined using a static mechanical analyzer (TMA) under a nitrogen atmosphere, with a test temperature range of 50-250°C. The CTE curve of the boric acid-terminated crosslinked fluorinated polyamide-imide film of Example 1 is shown below. Figure 1 As shown in Table 1, the coefficient of thermal expansion is 9.6 ppm / K.
[0064] The tensile properties of the film were tested according to the national standard GB / T1040.3-2006, using a universal testing machine. At least five groups of samples were tested, and the average value was taken. The stress-strain curve of the boric acid-terminated crosslinked fluorinated polyamide-imide film in Example 1 is shown below. Figure 2 As shown.
[0065] The transmittance of the thin film was measured using a UV-Vis spectrometer. 550 The transmittance at 550 nm is the transmittance of a film with a thickness of approximately 20 μm. The visible light transmittance curve of the end-borate crosslinked fluorinated polyamide-imide film of Example 1 is shown below. Figure 3 As shown.
[0066] The end-borate crosslinked fluorinated polyamide imide films prepared in Examples 1-5 have a coefficient of thermal expansion of <12.5 ppm / K, with a minimum of 9.6 ppm / K, and a tensile strength of >175 MPa, with a maximum exceeding 200 MPa. 550 With a purity of 84% or higher, it possesses excellent overall performance.
[0067] like Figure 4 As shown, the end-borate crosslinked fluorinated polyamide-imide film of Example 1 was redissolved and completely dissolved in anhydrous DMAc at room temperature to prepare a fluorinated polyamide-imide solution, which could be recoated, showing excellent reprocessing performance.
[0068] As shown in Table 1, the end-borate crosslinked fluorinated polyamide-imide film obtained in this invention exhibits high light transmittance, a low linear coefficient of thermal expansion, and excellent mechanical properties. Therefore, the end-borate crosslinked fluorinated polyamide-imide film of this invention is suitable for use as a transparent layer material in optical devices, including but not limited to display devices and photodetectors.
[0069] The above embodiments are only used to further illustrate the present invention of a boric acid-crosslinked fluorinated polyamide imide film, its preparation method and application. However, the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.
Claims
1. A method for preparing a boric acid-terminated crosslinked fluorinated polyamide imide film, characterized in that, Includes the following steps: (1) Under nitrogen atmosphere, fluorinated diamine is dissolved in an anhydrous organic solvent, and fluorinated diacyl chloride with an imide structure is added in batches under ice bath conditions. The reaction is carried out in an ice bath for 2-4 hours, and then at room temperature for 4-12 hours to form acyl chloride-terminated fluorinated polyamide-imide oligomers. 3-aminophenylboronic acid is added, and the reaction is continued at room temperature for 12-24 hours to form fluorinated polyamide-imide oligomers with phenylboronic acid end groups. The solid content of the reaction solution is controlled to be 10-20% during the reaction. A precipitant is added to the reaction solution for precipitation, and the resin is obtained after washing and drying. The molar ratio of fluorinated diamine to fluorinated diacyl chloride with an imide structure is 0.8-0.9:1, and the molar ratio of 3-aminophenylboronic acid to fluorinated diacyl chloride with an imide structure is 0.4-0.8:
1. The fluorinated diacyl chloride with an imide structure includes , At least one of them; (2) The resin is dissolved in an anhydrous organic solvent to form a solution. After forming a film using a film-forming process, the film is dehydrated and condensed by heat treatment to form a terminal boric acid crosslinked fluorinated polyamide imide film. The maximum temperature of the heat treatment is 250℃-260℃.
2. The method for preparing a boric acid-terminated crosslinked fluorinated polyamide imide film according to claim 1, characterized in that: The fluorinated diamine includes , At least one of them.
3. The method for preparing a boric acid-terminated crosslinked fluorinated polyamide imide film according to claim 1, characterized in that: In step (2), the heat treatment includes programmed temperature drying and post-programmed temperature drying. The programmed temperature drying includes the following steps: 50℃-60℃ / 1-2h, 80℃-90℃ / 1-2h, 120℃-130℃ / 1-2h, 150℃-160℃ / 1-2h; the post-programmed temperature drying includes the following steps: 180℃-190℃ / 1-2h, 210℃-220℃ / 1-2h, 250℃-260℃ / 1-2h.
4. A boric acid-terminated crosslinked fluorinated polyamide imide film, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 3.
5. The terminal boric acid crosslinked fluorinated polyamide imide film according to claim 4, characterized in that: The terminal boric acid crosslinked fluorinated polyamide imide has the following structure: ， Wherein, R1 is a residue of the fluorinated imide diacyl chloride, and R2 is a residue of the fluorinated diamine.
6. The application of the end-borate crosslinked fluorinated polyamide imide film according to claim 4 or 5 as a transparent layer material for optical devices.