A 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, a polyimide, a polymer film, and a method for preparing them.

Abstract

This invention discloses a 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, a polyimide, a polymer film, and a preparation method thereof. This invention utilizes a modified monomer with two active amino groups and a benzocyclobutenyl group that can be directly crosslinked by heat as a diamine monomer for polymerization, thereby introducing the benzocyclobutenyl group into the side chain of the polymer molecule. The four-membered ring of benzocyclobutenene undergoes ring-opening crosslinking at high temperature to form an eight-membered ring structure. No low-molecular-weight byproducts are released during curing, and no catalyst or initiator is required during the curing process, thus preventing the introduction of other heteroatoms. The resulting polymer film exhibits excellent heat resistance and dielectric properties, showing broad application prospects in the field of soluble, easily processed, and low-water-absorption resins.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, a polyimide, a polymer film, and a method for preparing them. Background Technology

[0002] Aromatic diamine monomers are key monomers for preparing high-performance polymers such as polyimide and polyamide. Therefore, the structure of aromatic diamine monomers has an important influence on the thermal stability, mechanical properties and media resistance of the materials.

[0003] To meet the demands of materials used in high-temperature and extreme environments, heat resistance is a critical requirement. For example, heat-fixed polyimides are typically obtained by reacting end-group crosslinkable groups such as cyano, maleimide, norbornene, and phenylethynyl groups. After crosslinking, their molecules possess a stable three-dimensional crosslinked network structure, resulting in excellent heat resistance and long-term use at high temperatures. If crosslinkable groups are introduced onto the side groups or side chains of linear polyimides, the excellent solubility of the linear polymer before crosslinking allows for solution processing to prepare thin film materials. Subsequent crosslinking further enhances the material's heat resistance and resistance to various media, expanding its application areas.

[0004] Benzocyclobutene (BCB) functional groups can undergo photo- or thermal crosslinking, exhibiting a wide processing window and excellent processing capabilities. Furthermore, BCB does not release low-molecular-weight byproducts during curing, and the curing process does not require the addition of catalysts or initiators, thus avoiding the introduction of other heteroatoms. Simultaneously, the BCB structure contains only carbon and hydrogen atoms, resulting in crosslinked polymers with good thermal stability, excellent dielectric properties, and low hygroscopicity. However, incorporating the BCB structure into aromatic diamine molecules to prepare diamine monomers presents significant challenges, and no existing technologies have reported this.

[0005] Patent application number WO2023182377 discloses a method for preparing high molecular weight triarylamine compounds, which synthesizes a monoamine intermediate containing benzocyclobutene, as shown in Formula II, via a 4-bromobenzocyclobutene coupling reaction, and then prepares organic light-emitting materials. In addition, researchers have designed and synthesized imides with a benzocyclobutene (BCB) structure, as shown in Formula III, and synthesized benzocyclobutene-terminated liquid crystal polyester imides via solution condensation copolymerization. However, while monoamine monomers can be used for end-capping, they cannot be introduced into the polymer side chains.

[0006] Therefore, there is an urgent need to develop a diamine monomer containing a benzocyclobutene structure, which can introduce the benzocyclobutene structure into the polymer side chain, thereby improving the heat resistance of the polymer.

[0007] Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, polyimide, polymer film, and preparation method. The novel diamine monomer containing a benzocyclobutene directly thermally crosslinkable structure of this invention can introduce the benzocyclobutene structure into the molecular side chain through copolymerization. By utilizing the crosslinking regulation of this structure at high temperature, molecular motion is suppressed, and a polyimide with excellent heat resistance and dielectric properties is obtained.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A 5(4-benzocyclobutenyl)-1,3-phenylenediamine compound having the structure shown in formula (I):

[0011]

[0012] This invention also discloses a method for preparing the above-mentioned 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, comprising the following steps:

[0013] (1) 1-Bromo-3,5-dinitrobenzene and a reducing agent were mixed and reacted to obtain intermediate S-1;

[0014] (2) The intermediate S-1 and the amino protecting agent were dissolved in a protic solvent for amino protection to obtain intermediate S-2;

[0015] (3) The intermediate S-2 was dissolved in a solvent and mixed with arylboronic acid, and then Suzuki cross-coupling was carried out under the action of palladium catalyst to obtain intermediate S-3.

[0016] (4) After dissolving the intermediate S-3 in a solvent, the protecting group is removed under the action of a protic acid to obtain the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound;

[0017]

[0018] Optionally, in step (1), the reducing agent includes iron powder, zinc powder or Pd / C; the reaction temperature is 80℃~90℃; the reaction time is 3h~5h; and the mass ratio of 1-bromo-3,5-dinitrobenzene to the reducing agent is 1~1.5:6~8.

[0019] Optionally, the purification method in step (1) is filtration and / or extraction.

[0020] Optionally, in step (2), the amino protecting agent is di-tert-butyl dicarbonate; the protic solvent is anhydrous ethanol; the reaction temperature is room temperature; the reaction time is 12h to 24h; and the mass ratio of intermediate S-1 to di-tert-butyl dicarbonate is 1:2.

[0021] Optionally, the purification method in step (2) is dichloromethane column chromatography.

[0022] Optionally, in step (3), the arylboronic acid is benzocyclobutene-4-boronic acid; the palladium catalyst is tetrakis(triphenylphosphine)palladium; the solvent includes one or more of toluene, ethanol, and water; the base includes one or two of sodium carbonate, cesium carbonate, and potassium carbonate; the reaction temperature is 100℃~120℃; the reaction time is 12h~24h; and the mass ratio of intermediate S-2, benzocyclobutene-4-boronic acid, and tetrakis(triphenylphosphine)palladium is 1:1.2:0.1.

[0023] Optionally, the purification method in step (3) is column chromatography separation.

[0024] Optionally, in step (4), the protic acid includes trifluoroacetic acid or hydrochloric acid; the solvent includes dichloromethane or ethyl acetate; the reaction temperature is room temperature; the reaction time is 12h to 24h; and the mass-volume ratio of the protic acid to intermediate S-2 is 1 to 1.5: 4 to 5.

[0025] The present invention also discloses a polyimide, wherein the raw materials of the polyimide include a dianhydride monomer, a diamine monomer one, and a diamine monomer two; the diamine monomer two is the above-mentioned 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, or the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound prepared by the above-mentioned preparation method.

[0026] Optionally, the molar ratio of the dianhydride monomer, the first diamine monomer, and the second diamine monomer is 10:(7-6):(3-4).

[0027] Optionally, the dianhydride monomer is a bisphenol A type diether dianhydride; the diamine monomer is m-phenylenediamine.

[0028] The present invention also discloses a method for preparing polyimide as described above, comprising the following steps: copolymerizing dianhydride monomer with diamine monomer one and diamine monomer two in an organic solvent, followed by an imidization reaction of dehydration cyclization, and then successively undergoing precipitation, washing, Soxhlet extraction, drying and high-temperature curing to obtain the polyimide.

[0029] Optionally, the organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0030] Optionally, the copolymerization reaction temperature is 15℃~30℃; the copolymerization reaction time is 12h~24h.

[0031] Optionally, the reaction temperature for the dehydration cyclization imidization is 15℃~30℃; the reaction time for the dehydration cyclization imidization is 24h~36h.

[0032] Optionally, the precipitant used for precipitation may include methanol and / or ethanol.

[0033] Optionally, the Soxhlet extraction may use methanol and / or ethanol as the extraction agent.

[0034] Optionally, the Soxhlet extraction temperature is 110℃~140℃; the Soxhlet extraction time is 24h~48h.

[0035] Optionally, the high-temperature curing temperature is 220℃~260℃; the high-temperature curing time is 7h.

[0036] The present invention also discloses a polymer film, wherein the polymer film is the polyimide described above or the polyimide prepared by the above preparation method.

[0037] Optionally, the preparation method of the polymer film includes the following steps: dissolving the polyimide in an organic solvent, casting it into a film, removing the organic solvent by gradient heating, and curing it at high temperature to obtain the polymer film.

[0038] Optionally, the organic solvent includes one or more of m-cresol, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0039] Optionally, the mass concentration of the organic solution containing polyimide is 10% to 15%.

[0040] Optionally, the melting temperature is 100℃~120℃.

[0041] Optionally, the gradient heating includes heating at 60°C for 12 hours, followed by heating at 80°C, 100°C, 120°C, 150°C, 180°C and 200°C for 2 hours in sequence.

[0042] Optionally, the high-temperature curing includes heating at 220°C for 2 hours, at 240°C for 3 hours, and at 260°C for 2 hours in sequence.

[0043] Optionally, the thickness of the polymer film is 60–80 μm.

[0044] Implementing the embodiments of the present invention will have the following beneficial effects:

[0045] This invention utilizes a modified monomer with two active amino groups and a benzocyclobutene group that can be directly crosslinked by heating. This monomer can be used as a diamine monomer for polymerization, thereby introducing the benzocyclobutene group into the side chain of the polymer molecule. The four-membered ring of benzocyclobutene undergoes ring-opening crosslinking at high temperature to form an eight-membered ring structure. No low-molecular-weight byproducts are released during curing, and no catalyst or initiator is required during the curing process, thus avoiding the introduction of other heteroatoms. The resulting polymer film has excellent heat resistance and dielectric properties, and has broad application prospects in the field of soluble, easily processed, and low-water-absorption target resins.

[0046] The novel diamine monomer containing a benzocyclobutene-containing, directly thermally crosslinkable structure proposed in this invention requires simple raw material components, and the synthesis process involves mild, simple, and easily controllable reaction conditions, making it environmentally friendly. Through precise process control, the prepared product is easily purified, contains few impurities, and has a high yield, thus making it suitable for large-scale industrial production. Attached Figure Description

[0047] Figure 1 The image shows the 1H NMR spectrum of intermediate S-1 in this embodiment of the invention.

[0048] Figure 2 The image shows the 1H NMR spectrum of intermediate S-2 from Example 1 of this invention.

[0049] Figure 3 The image shows the 1H NMR spectrum of intermediate S-3 in Example 1 of this invention.

[0050] Figure 4 The image shows the 1H NMR spectrum of the diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine of Example 1 of this invention.

[0051] Figure 5 The Fourier transform infrared (FT-IR) spectra of polyimide PI-BP2 and diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB) in Example 3 of this invention are shown. Detailed Implementation

[0052] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0053] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0054] Example 1

[0055] First, zinc powder (8.3 g) and water (80 ml) were added to a three-necked flask and stirred rapidly. The pH was adjusted to 5 with acetic acid, and the mixture was evacuated under vacuum and purged with nitrogen three times. The mixture was then heated to 80°C and reacted for 1 hour to activate the zinc powder. After cooling, 1-bromo-3,5-dinitrobenzene (3.7 g) and ethanol (150 ml) were added, and the mixture was heated to 80°C and reacted for another 3 hours. Potassium hydroxide was added, and the pH was adjusted to neutral. The mixture was filtered while hot, and the solvent was removed under reduced pressure. The mixture was extracted and separated, dried over anhydrous magnesium sulfate, and the solvent was evaporated to dryness to obtain orange powder S-1,5-bromo-1,3-phenylenediamine, with a yield of 90%.

[0056] 4.0 g of 5-bromo-1,3-phenylenediamine and 10.26 g of ditert-butyl dicarbonate were dissolved in 30 mL of anhydrous ethanol and reacted with stirring at room temperature for 24 h. The reaction was then stopped, and the solvent was removed by rotary evaporation. The mixture was purified by silica gel chromatography, and the solvent was removed under reduced pressure to give a yellow solid S-2 in 90% yield.

[0057] The monomer benzocyclobutene-4-boronic acid (2.13 g), intermediate S-2 (4.64 g), and cesium carbonate (8.6 g) were added to a three-necked flask. The catalyst tetraphenylphosphine palladium (1.38 g) was then added, followed by toluene, ethanol, and an aqueous solution. The mixture was evacuated under nitrogen three times and heated to reflux at 110 °C for 24 hours. The reaction was then stopped, and the solution turned yellow. After cooling to room temperature, the reaction mixture was extracted, washed three times with water, dried over anhydrous magnesium sulfate, filtered, and the solvent was removed under reduced pressure. Purification was performed by silica gel chromatography to give a yellow solid S-3 in 75% yield.

[0058] Intermediate S-3 (7.4 g) was placed in a three-necked flask, and dichloromethane (50 ml) was added and stirred to dissolve. Trifluoroacetic acid (20 ml) was slowly added dropwise, and the mixture was stirred at room temperature for 4 hours. Sodium hydroxide was added to adjust the pH to neutral. The mixture was washed three times with water, dried, and the solvent was removed under reduced pressure. The mixture was then purified by chromatography on silica gel to obtain a reddish-gray powder with a yield of 80%.

[0059] in, Figures 1-4 The image shows the 1H NMR spectrum of the compound obtained in Example 1 of this invention.

[0060] Example 2

[0061] Under nitrogen protection, 1.0622 g (2 mmol) of bisphenol A type diether dianhydride (BPADA), 0.1946 g (1.4 mmol) of m-phenylenediamine (MXDA), 0.1326 g (0.6 mmol) of the diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB) prepared in Example 1, and 10 ml of N-methylpyrrolidone were added to a 50 mL reaction flask. The mixture was stirred at 25 °C for 24 h, and 0.64 ml of acetic anhydride and 0.64 ml of pyridine were slowly added. The reaction was carried out at room temperature for 24 h to complete imidization. The reaction solution was added dropwise to excess methanol to precipitate the precipitate. The precipitate was filtered, washed three times with methanol, and extracted with ethanol at 120 °C for 24 h using Soxhlet extraction. The precipitate was then dried under vacuum to obtain polyimide PI-BP1, which was a pale yellow fibrous solid.

[0062] 0.1 g of PI-BP1 powder was weighed and added to 2 ml of m-cresol, then heated to 100 °C to dissolve completely, yielding a yellow solution. The resulting solution was coated onto a 60*60 mm, 3 mm thick glass plate, and the solvent was removed by heating at the following intervals: 60 °C -12 h, 80 °C -2 h, 100 °C -2 h, 120 °C -2 h, 150 °C -2 h, 180 °C -2 h, and 200 °C -2 h. After cooling to room temperature, the film was demolded to obtain a PI-BP1 film.

[0063] Weigh 0.1g of PI-BP1 powder and add it to 2ml of m-cresol. Heat to 100℃ to dissolve completely, obtaining a yellow solution. Coat the resulting solution onto a 60*60mm, 3mm thick glass plate. Remove the solvent by heating at 60℃-12h, 80℃-2h, 100℃-2h, 120℃-2h, 150℃-2h, 180℃-2h, and 200℃-2h. Then, cure the film by heating at 220℃-2h, 240℃-3h, and 260℃-2h. After cooling to room temperature, demold to obtain a p-PI-BP1 film.

[0064] Example 3

[0065] The only difference between this embodiment and Example 2 is that the feed was changed to 1.0622 g (2 mmol) of bisphenol A type diether dianhydride (BPADA), 0.1668 g (1.2 mmol) of m-phenylenediamine (MXDA), 0.1768 g (0.8 mmol) of the diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB) prepared in Example 1, and 10 ml of N-methylpyrrolidone, which were added to a 50 mL reaction flask. Other conditions remained unchanged, and polyimide PI-BP2 was obtained, which was a pale yellow fibrous solid.

[0066] Weigh 0.1 g of PI-BP2 powder, prepare a solution according to Example 2, and coat it to obtain PI-BP2 film and p-PI-BP2 film sequentially. Figure 5 The Fourier transform infrared spectra of PI-BP2 and MPDA-BCB obtained in Example 3 of the present invention are shown.

[0067] The reaction formulas in Examples 2 and 3 are shown in Formula IV:

[0068]

[0069] Comparative Example 1:

[0070] The only difference between this comparative example and Example 2 is that MPDA-BCB was not added, and the amount of m-phenylenediamine added was adjusted to 2 mmol to prepare polyimide PI-BP0, which is a white fibrous solid.

[0071] 0.1 g of PI-BP0 powder was weighed and added to 2 ml of m-cresol. The solution was heated to 100°C to dissolve completely, yielding a colorless solution. The resulting solution was coated onto a 60*60 mm, 3 mm thick glass plate. The solvent was removed by heating at the following intervals: 60°C-12 h, 80°C-2 h, 100°C-2 h, 120°C-2 h, 150°C-2 h, 180°C-2 h, and 200°C-2 h. After cooling to room temperature, the film was demolded to obtain the PI-BP0 film.

[0072] The reaction formula in Comparative Example 1 is shown in Formula V:

[0073]

[0074] The structures of Examples 1-3 and Comparative Example 1 were characterized by nuclear magnetic resonance and infrared absorption spectroscopy, which verified that the structure of the product met expectations. The thin film was prepared using the products of Examples 2-3 and Comparative Example 1.

[0075] Heat resistance test

[0076] The heat resistance of the PI resins obtained in Examples 2-3 and Comparative Example 1 was evaluated using DSC and DMA, and the test results are shown in Table 1.

[0077] Table 1. DSC and DMA data of polyimide before and after crosslinking

[0078]

[0079] Note: a is tested by DSC, b is tested by DMA.

[0080] As can be seen from the data in Table 1, the heat resistance of Examples 2-3 is better than that of Comparative Example 1, which does not contain modified monomers. In particular, when the modified diamine monomer in Example 3 is added to 40%, the glass transition temperature of the modified polyimide increases from 169°C to 233°C.

[0081] With increasing proportions of crosslinkable modified monomers, the glass transition temperature of crosslinked polyimides shows an upward trend. This may be attributed to the increased crosslinking degree after benzocyclobutene ring-opening, leading to decreased intermolecular spacing, increased molecular chain entanglement, and restricted movement of polyimide molecular chain segments. This results in a higher temperature requirement for molecular chain movement, macroscopically manifesting as a gradual increase in glass transition temperature and a significant improvement in heat resistance.

[0082] In summary, this invention utilizes the synthesized diamine monomer 5-(4-benzocyclobutenyl)-1,3-phenylenediamine (MPDA-BCB) and copolymerizes it with diamine and dianhydride monomers. Benzocyclobutenyl groups are introduced into the polyimide side chains through copolymerization. The crosslinking regulation of the benzocyclobutenyl structure suppresses molecular motion, resulting in a polyimide with excellent overall performance. The heat resistance of polymer films made from the polyimide prepared by this invention is effectively improved. Furthermore, the preparation of the monomers involved in this invention is highly reproducible and can meet the practical needs of synthesizing polyimides, polyamides, and other polymers.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound, characterized in that, It has the structure shown in equation (I): 。 2. A method for preparing the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound as described in claim 1, characterized in that, Includes the following steps: (1) 1-Bromo-3,5-dinitrobenzene and a reducing agent are mixed and reacted to obtain intermediate S-1; (2) The intermediate S-1 and the amino protecting agent are dissolved in a protic solvent for amino protection to obtain intermediate S-2; (3) The intermediate S-2 was dissolved in a solvent and mixed with arylboronic acid, and then Suzuki cross-coupling was carried out under the action of palladium catalyst to obtain intermediate S-3; (4) After dissolving the intermediate S-3 in a solvent, the protecting group is removed under the action of a protic acid to obtain the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound; 。 3. The preparation method according to claim 2, characterized in that, In step (1), the reducing agent includes iron powder, zinc powder or Pd / C; the reaction temperature is 80℃~90℃; the reaction time is 3h~5h; the mass ratio of 1-bromo-3,5-dinitrobenzene to reducing agent is 1~1.5:6~8; In step (2), the amino protecting agent is di-tert-butyl dicarbonate; the protic solvent is anhydrous ethanol; the reaction temperature is room temperature; the reaction time is 12h~24h; and the mass ratio of intermediate S-1 to di-tert-butyl dicarbonate is 1:

2. In step (3), the arylboronic acid is benzocyclobutene-4-boronic acid; the palladium catalyst is tetrakis(triphenylphosphine)palladium; the solvent includes one or more of toluene, ethanol, and water; the base includes one or two of sodium carbonate, cesium carbonate, and potassium carbonate; the reaction temperature is 100℃~120℃; the reaction time is 12h~24h; and the mass ratio of intermediate S-2, benzocyclobutene-4-boronic acid, and tetrakis(triphenylphosphine)palladium is 1:1.2:0.

1. In step (4), the protic acid includes trifluoroacetic acid or hydrochloric acid; the solvent includes dichloromethane or ethyl acetate; the reaction temperature is room temperature; the reaction time is 12h~24h; and the mass-volume ratio of the protic acid to intermediate S-3 is 1~1.5:4~5.

4. A polyimide, characterized in that, The raw materials for the polyimide include dianhydride monomer, diamine monomer one, and diamine monomer two; The diamine monomer 2 is the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound according to claim 1, or the 5-(4-benzocyclobutenyl)-1,3-phenylenediamine compound prepared by the preparation method according to any one of claims 2-3; The dianhydride monomer is a bisphenol A type diether dianhydride; The diamine monomer is m-phenylenediamine; The mass ratio of the dianhydride monomer, the first diamine monomer, and the second diamine monomer is 10:(7~6):(3~4). The method for preparing the polyimide includes the following steps: The polyimide was obtained by copolymerizing dianhydride monomer with diamine monomer I and diamine monomer II in an organic solvent, followed by an imidization reaction of dehydration cyclization, and then by precipitation, washing, Soxhlet extraction, drying and high-temperature curing. The organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The copolymerization reaction temperature is 15℃~30℃; the copolymerization reaction time is 12h~24h; The reaction temperature for the dehydration cyclization imidization is 15℃~30℃; the reaction time for the dehydration cyclization imidization is 24h~36h. The precipitant used for precipitation includes methanol and / or ethanol; The Soxhlet extraction uses methanol and / or ethanol as the extraction solvent; The Soxhlet extraction temperature is 110℃~140℃; the Soxhlet extraction time is 24h~48h. The high-temperature curing temperature is 220℃~260℃; the high-temperature curing time is 7h.

5. A polymer film, characterized in that, The polymer film is the polyimide according to claim 4; the method for preparing the polymer film includes the following steps: The polyimide is dissolved in an organic solvent and cast into a film. The organic solvent is removed by gradient heating and then cured at high temperature to obtain the polymer film.

6. The polymer film according to claim 5, characterized in that, The organic solvent includes one or more of m-cresol, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The melting temperature is 100℃~120℃; The gradient heating includes heating at 60°C for 12 hours, followed by heating at 80°C, 100°C, 120°C, 150°C, 180°C and 200°C for 2 hours in sequence. The high-temperature curing includes heating at 220°C for 2 hours, at 240°C for 3 hours, and at 260°C for 2 hours in sequence; The thickness of the polymer film is 60-80 μm.

Images