Highly transparent polyimide film containing a benzonorbornene structure and method for producing the same

Abstract

The application discloses a high-transparency polyimide film containing a benzonorbornene structure and a preparation method of the film, and has a structural formula: the film is prepared by copolymerization of ether bond dianhydride monomers or ester bond dianhydride monomers containing a benzonorbornene structure, a diamine monomer containing a benzonorbornene and a pyridine structure and an aromatic diamine monomer. The film has good optical transparency and low moisture absorption, and also guarantees mechanical properties and thermal properties. The method is easy to operate and control, has few technological processes, and has low raw material and production costs.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a highly transparent polyimide film and its preparation method. Background Technology

[0002] Traditional aromatic polyimide materials exhibit strong charge-transfer complex (CTC) effects both intramolecularly and interchainly due to the presence of strong electron donors (diamines) and electron acceptors (dianhydrides). This CTC effect results in strong absorption of visible light, leading to their deep color. This characteristic of traditional polyimide materials severely limits their application in fields such as optoelectronics. Therefore, improving the light transmittance of polyimide materials while maintaining their high heat resistance and dimensional stability has become a current research hotspot.

[0003] Introducing alicyclic structures into the polyimide structure is beneficial for improving the transmittance of polyimide films. For example, in the literature (Polymer Chemistry, 2017, 8(39): 6165-6172.), the naphthalene-containing alicyclic dianhydride monomer 2R,5R,7S,10S-naphthalenetetracarboxylic acid dianhydride (HNTDA) was polymerized with ODA, 1,4-bis(4-aminophenoxy)benzene (1,4,4′-APB), BAPB, and MBCHA in a one-step process. The resulting PI film exhibited good transparency and heat resistance. This dianhydride, by introducing alicyclic structures, can be used to prepare high-temperature resistant, colorless, and transparent polyimide films. This is mainly because the alicyclic structure can disrupt the conjugated structure on the polyimide chain segments, reduce the interaction forces between molecular chains, increase the free volume between chains, and reduce the formation of CTC, thereby improving the transmittance of polyimide while maintaining good heat resistance. The introduction of strongly electronegative fluorine groups is also beneficial for improving the transmittance of polyimide films. As described in the literature (European Polymer Journal, 2013, 49(11):3657-3672.), dianhydride monomers TA-TFMB and TA-TFBP with trifluoromethyl side groups were designed and synthesized. These monomers were then condensed and polymerized with the diamine monomer TFMB, and chemical imidization was performed to prepare a high-temperature resistant transparent polyimide film with a low coefficient of thermal expansion. This dianhydride, by introducing a strongly electronegative group, reduces the stacking of polyimide molecular chains, increases the free volume between chains, reduces intramolecular and intermolecular charge transfer interactions, and improves the light transmittance of polyimide. Simultaneously, the pyridine ring, as a rigid aromatic heterocycle, can improve the thermal stability and mechanical properties of the polymer when introduced into the polyimide backbone. The molar refractive index of the pyridine ring is greater than that of the benzene ring; therefore, polyimides containing aromatic pyridine rings have better light transmittance and can soften the color of polyimide films. By directly introducing norbornene onto the benzene ring, dianhydride and diamine monomers with a benzonorbornene structure are obtained. Due to the non-planar bicyclic configuration of norbornene, these monomers have become an important monomer for the preparation of high-transmittance polyimide films. Summary of the Invention

[0004] To address the issue of low optical transmittance of polyimide without compromising its thermodynamic properties, this invention proposes a method for preparing highly transparent polyimide films.

[0005] This invention is achieved through the following technical solution.

[0006] This invention uses ester-bonded dianhydride monomers or ether-bonded dianhydride monomers containing benzonorbornene structures as raw materials to copolymerize with diamine monomers containing benzonorbornene and pyridine structures as well as aromatic diamine monomers to prepare a series of highly transparent polyimide films containing benzonorbornene structures.

[0007] The present invention discloses a highly transparent polyimide film containing a benzonorbornene structure, the main chain of which contains ether or ester bonds and pyridine heterocycles. One side of the ether or ester bond is attached to the para position of the benzene ring in the benzonorbornene structure, and the other side is attached to the benzene ring or pyridine ring in the aromatic structure. Its structural formula is as follows:

[0008]

[0009] -X- indicates an ether bond; or an ester bond.

[0010] 0 <y<1。

[0011] n represents the degree of aggregation, which is an integer, n>0.

[0012] R represents H; CH3; CF3.

[0013] -Ar- represents an aromatic ring, and its structural formula is:

[0014]

[0015] The polyimide film containing a benzonorbornene structure prepared by this invention features the following main chain structure characteristics: ether or ester bonds serve as connecting groups, ensuring the flexibility of the molecular chain; the aromatic benzene ring and pyridine heterocyclic structure ensure the rigidity of the molecular chain; the norbornene bicyclic structure as side groups disrupts the regular stacking between macromolecules, increases the free volume between chain segments, retains a certain degree of polymer solubility, reduces the dielectric constant of the material, and the bicyclic structure possesses highly polar sp... 2 The cis double bond configuration ensures a certain degree of stacking between macromolecules, improving the thermal properties of the polymer. At the same time, the high-temperature reduction of the borneol double bond can cause cross-linking, enhancing the thermal and mechanical properties of the material.

[0016] The polyimide film with a benzonorbornene structure in its main chain prepared by this invention has excellent optical transmittance, thermal properties and mechanical properties, and the synthesis process is simple and low cost.

[0017] The present invention discloses a method for preparing a highly transparent polyimide film containing benzonorbornene, comprising the following steps:

[0018] Under nitrogen protection, diamine monomers containing benzonorbornene and pyridine structures, as well as aromatic diamine monomers, are dissolved in anhydrous organic solvents. After complete dissolution, equimolar amounts of ether-bonded dianhydrides or ester-bonded dianhydrides containing benzonorbornene structures are added in batches. The reaction system is then reacted at 0–20°C for 12 hours to obtain a polyamic acid solution with a solid content of 6–20 wt%. The polyamic acid solution is then cast into a film to obtain a polyamic acid wet film. The polyimide wet film is then placed in an oven and set... The polyimide wet film was subjected to thermal imidization treatment at a temperature of 60–90°C for 5–8 hours to increase its solid content to 65–70%. The temperature was then increased in an oven according to a programmed heating sequence to obtain a polyimide film. The heating sequence was as follows: holding at 100°C for 30 minutes, then increasing to 150°C and holding for 30 minutes; then increasing to 200°C and holding for 30 minutes; then increasing to 250°C and holding for 1 hour; and finally increasing to 280°C and holding for 30 minutes. After cooling, the film was peeled off from the glass substrate to obtain a polyimide film with a benzonorbornene structure in its main chain.

[0019] The ether-bonded dianhydride monomer containing a benzonorbornene structure described in this invention has the following structural formula:

[0020]

[0021] Its name is 3,6-bis(ether-triphenylamine)benzonorbornene, also known as 1,4-dihydro-1,4-mannaphthyl-5,8-bis(ether-1,3-dihydroisobenzofuran-5-anhydride).

[0022] The ester-bonded dianhydride monomer containing the benzonorbornene structure has the following structural formula:

[0023]

[0024] Its name is 3,6-bis(ester-trimethylbenzene tricarboxylic anhydride)benzonorbornene, also known as 1,4-dihydro-1,4-mannaphthyl-5,8-bis(ester-1,3-dihydroisobenzofuran-5-anhydride).

[0025] The diamine monomer containing benzonorbornene and pyridine structures described in this invention has the following structural formula:

[0026]

[0027] When R is H, the diamine monomer containing benzonorbornene and pyridine structures is 3,6-bis(5-aminopyridyl-2-oxy)benzonorbornene, also known as 1,4-dihydro-1,4-methylnaphthalene-5,8-bis(oxy-4-amino-2-pyridine).

[0028] When R is CH3, the diamine monomer containing benzonorbornene and pyridine structures is 3,6-bis(3-methyl-5-aminopyridyl-2-oxy)benzonorbornene, also known as 1,4-dihydro-1,4-methylnaphthalene-5,8-bis(oxy-6-methyl-4-amino-2-pyridine).

[0029] When R is CF3, the diamine monomer containing benzonorbornene and pyridine is 3,6-bis(3-trifluoromethyl-5-aminopyridyl-2-oxy)benzonorbornene, also known as 1,4-dihydro-1,4-methylnaphthalene-5,8-bis(oxy-6-trifluoromethyl-4-amino-2-pyridine).

[0030] The aromatic diamine monomers described in this invention are: 1,4-diaminobenzene, 2-methyl-1,4-diaminobenzene, 2-trifluoromethyl-1,4-diaminobenzene, 1,3-diaminobenzene, 5-methyl-1,3-diaminobenzene, 5-trifluoromethyl-1,3-diaminobenzene, 2,5-diaminopyridine, 3-methyl-2,5-diaminopyridine, 3-trifluoromethyl-2,5-diaminopyridine, 3,5-diaminopyridine, 4,4'-diaminodiphenyl sulfone, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-diamino-2,2 One of the following: '-dimethylbiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethyl)biphenyl, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-bis(trifluoromethyl)diphenylmethane, 4,4'-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)benzene, 4,4'-diaminodiphenyl ether, and 4,4'-bis(4-aminophenoxy)biphenyl.

[0031] The molar ratio of the diamine monomer containing benzonorbornene and pyridine structures to the aromatic diamine monomer described in this invention is y:(1-y), 0 <y<1。

[0032] The anhydrous organic solvent described in this invention is one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.

[0033] The beneficial effects of this invention are as follows: The method for preparing a highly transparent polyimide film with a main chain containing a benzonorbornene structure proposed in this invention has a simple preparation process, low production cost, and high yield. Furthermore, the raw materials are inexpensive and readily available, and the reaction conditions are easy to control, exhibiting excellent reproducibility. The main chain structure of the polyimide film proposed in this invention is composed of ether or ester bonds linked to aromatic benzene rings or pyridine heterocycles. This ensures excellent heat resistance while reducing the formation of intramolecular and intermolecular charge-transfer complexes in the polyimide, thereby improving the optical transmittance of the polyimide film. It is a high-performance polyimide material with broad application prospects. Attached Figure Description

[0034] Figure 1 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 1 of the present invention.

[0035] Figure 2 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 2 of the present invention.

[0036] Figure 3 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 3 of the present invention.

[0037] Figure 4 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 4 of the present invention.

[0038] Figure 5 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 5 of the present invention.

[0039] Figure 6 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 6 of the present invention.

[0040] Figure 7 This is the UV-Vis spectrum of the polyimide film prepared in Example 7 of the present invention.

[0041] Figure 8 This is the UV-Vis spectrum of the polyimide film prepared in Example 8 of the present invention.

[0042] Figure 9 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 9 of the present invention.

[0043] Figure 10 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 10 of the present invention.

[0044] Figure 11 This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 11 of the present invention.

[0045] Figure 12This is the ultraviolet-visible spectrum of the polyimide film prepared in Example 12 of the present invention.

[0046] Figure 13 The infrared spectrum of the ether-bonded dianhydride monomer containing a benzonorbornene structure in the main chain of this invention is shown.

[0047] Figure 14 The infrared spectrum of the ester bond dianhydride monomer containing a benzonorbornene structure in the main chain of this invention is shown. Detailed Implementation

[0048] The present invention will be further illustrated by the following embodiments.

[0049] Example 1.

[0050] Under nitrogen protection, 1 mmol (0.358 g) of 3,6-bis(5-aminopyridyl-2-oxy)benzonorbornene and 1 mmol (0.208 g) of the diamine monomer 4,4'-diaminodiphenyl ether were dissolved in 14.6 mL of N,N-dimethylacetamide. After complete dissolution, 2 mmol (0.932 g) of the dianhydride monomer 3,6-bis(etheryl-trimethylbenzene tricarboxylic anhydride)benzonorbornene was added to the reaction system, maintaining the solid content of the system at approximately 10%. The reaction system was heated to 20 °C. The reaction was carried out at ℃ for 12 hours to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 80℃ for 6 hours, then heated to 100℃ and held for 30 minutes, then heated to 150℃ and held for 30 minutes; then heated to 200℃ and held for 30 minutes; then heated to 250℃ and held for 1 hour; then heated to 280℃ and held for 30 minutes. After cooling, the film was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0051] Example 2.

[0052] Under nitrogen protection, 1.2 mmol (0.593 g) of diamine monomer 3,6-bis(3-trifluoromethyl-5-aminopyridinyl-2-oxy)benzonorbornene and 0.8 mmol (0.086 g) of diamine monomer 1,4-diaminobenzene were dissolved in 10 mL of N,N-dimethylacetamide. After complete dissolution, 2 mmol (0.932 g) of dianhydride monomer 3,6-bis(ether-trimethylbenzene tricarboxylic anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at 15%. The reaction system was reacted at 0 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0053] Example 3.

[0054] Under nitrogen protection, 0.7 mmol (0.251 g) of 3,6-bis(5-aminopyridyl-2-oxy)benzonorbornene and 1.3 mmol (0.197 g) of the diamine monomer 2,5-diaminopyridine were dissolved in 10 mL of N,N-dimethylformamide. After complete dissolution, 2 mmol (0.932 g) of the dianhydride monomer 3,6-bis(etheryl-trimethylbenzene tricarboxylic anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at about 10%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 60°C for 6 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0055] Example 4.

[0056] Under nitrogen protection, 0.8 mmol (0.309 g) of diamine monomer 3,6-bis(3-methyl-5-aminopyridinyl-2-oxy)benzonorbornene and 1.2 mmol (0.384 g) of diamine monomer 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl were dissolved in 12.03 mL of N-methylpyrrolidone. After complete dissolution, 2 mmol (0.932 g) of dianhydride monomer 3,6-bis(ether-triphenylamine anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at 15%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0057] Example 5.

[0058] Under nitrogen protection, 1 mmol (0.494 g) of diamine monomer 3,6-bis(3-trifluoromethyl-5-aminopyridinyl-2-oxy)benzonorbornene and 1 mmol (0.334 g) of diamine monomer 2,2'-bis(4-aminophenyl)hexafluoropropane were dissolved in 10.5 mL of N,N-dimethylformamide. After complete dissolution, 2 mmol (0.932 g) of dianhydride monomer 3,6-bis(ether-triphenylamine anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at 15%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide homopolymer film.

[0059] Example 6.

[0060] Under nitrogen protection, 1 mmol (0.494 g) of diamine monomer 3,6-bis(3-trifluoromethyl-5-aminopyridinyl-2-oxy)benzonorbornene and 1 mmol (0.108 g) of diamine monomer 1,4-diaminobenzene were dissolved in 15.6 mL of N,N-dimethylacetamide. After complete dissolution, 2 mmol (1.044 g) of dianhydride monomer 3,6-bis(ester-trimethylbenzenetrihydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at about 10%. The reaction system was reacted at 0 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0061] Example 7.

[0062] Under nitrogen protection, 1.8 mmol (0.644 g) of 3,6-bis(5-aminopyridinyl-2-oxy)benzonorbornene and 0.2 mmol (0.042 g) of diamine monomer 4,4'-diaminodiphenyl ether were dissolved in 6.6 mL of N-methylpyrrolidone. After complete dissolution, 2 mmol (1.044 g) of dianhydride monomer 3,6-bis(ester-trimethylbenzenetrihydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at about 20%. The reaction system was reacted at 20 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 80°C for 6 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0063] Example 8.

[0064] Under nitrogen protection, 0.1 mmol (0.036 g) of 3,6-bis(5-aminopyridinyl-2-oxy)benzonorbornene and 1.9 mmol (0.471 g) of diamine monomer 4,4'-diaminodiphenyl sulfone were dissolved in 5.0 mL of N,N-dimethylformamide. After complete dissolution, 2 mmol (1.044 g) of dianhydride monomer 3,6-bis(ester-trimethylbenzenetricarboxylic anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at 18%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 60°C for 4 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0065] Example 9.

[0066] Under nitrogen protection, 0.4 mmol (0.143 g) of 3,6-bis(5-aminopyridyl-2-oxy)benzonorbornene and 1.6 mmol (0.512 g) of the diamine monomer 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 20.4 mL of N,N-dimethylformamide. After complete dissolution, 2 mmol (1.044 g) of the dianhydride monomer 3,6-bis(ester-trimethylbenzenetricarboxylic anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at about 8%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0067] Example 10.

[0068] Under nitrogen protection, 1.6 mmol (0.618 g) of diamine monomer 3,6-bis(3-methyl-5-aminopyridinyl-2-oxy)benzonorbornene and 0.4 mmol (0.267 g) of diamine monomer 2,2'-bis(4-aminophenyl)hexafluoropropane were dissolved in 10.5 mL of N-methylpyrrolidone. After complete dissolution, 2 mmol (1.044 g) of dianhydride monomer 3,6-bis(ester-trimethylbenzenetricarboxylic anhydride)benzonorbornene dianhydride monomer was added to the reaction system to maintain the solid content of the system at about 15%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast into a film to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0069] Example 11.

[0070] Under nitrogen protection, 0.2 mmol (0.072 g) of 3,6-bis(5-aminopyridinyl-2-oxy)benzonorbornene and 1.8 mmol (0.446 g) of diamine monomer 4,4'-diaminodiphenyl sulfone were dissolved in 8.0 mL of N,N-dimethylformamide. After complete dissolution, 2 mmol (0.923 g) of dianhydride monomer 3,6-bis(ether-trimethylbenzene tricarboxylic anhydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at about 20%. The reaction system was reacted at 10 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 60°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0071] Example 12.

[0072] Under nitrogen protection, 1.9 mmol (0.734 g) of diamine monomer 3,6-bis(3-methyl-5-aminopyridinyl-2-oxy)benzonorbornene and 1 mmol (0.011 g) of diamine monomer 1,4-diaminobenzene were dissolved in 30 mL of N,N-dimethylacetoamide. After complete dissolution, 2 mmol (1.044 g) of dianhydride monomer 3,6-bis(ester-trimethylbenzenetrihydride)benzonorbornene was added to the reaction system to maintain the solid content of the system at about 6.0%. The reaction system was reacted at 0 °C for 12 h to obtain a polyamic acid solution with a certain viscosity. The polyamic acid solution was then cast to obtain a polyamic acid wet film. The wet film was kept at 70°C for 5 hours, then heated to 100°C and held for 30 minutes, then heated to 150°C and held for 30 minutes; then heated to 200°C and held for 30 minutes; then heated to 250°C and held for 1 hour; then heated to 280°C and held for 30 minutes. After cooling, it was placed in boiling water to peel it off from the glass substrate, thus obtaining the polyimide film.

[0073] The optical properties of the polyimide film were tested, and the test results are shown in Table 1.

[0074]

[0075] The polyimide film was subjected to thermal performance testing, and the test results are shown in Table 2.

[0076]

[0077] The polyimide film was subjected to mechanical and moisture absorption property tests, and the test results are shown in Table 3.

[0078]

[0079] In summary, this invention proposes a series of methods for preparing highly transparent polyimide films. The structural feature is an asymmetric, non-coplanar structure of benzonorbornene in the main chain, with aromatic ether or ester bonds as linking groups, which increases solubility, improves optical transmittance, and ensures mechanical and thermal properties. The preparation methods of this invention are easy to operate and control, have fewer process steps, and lower raw material and production costs, making them suitable for industrial production. The resulting polyimide films exhibit excellent performance and have broad application prospects.

[0080] The above embodiments are described in detail with reference to the accompanying drawings, and preferred embodiments of the present invention are described in detail. Various modifications or changes made to the above embodiments by those skilled in the art, without departing from the essence of the present invention, all fall within the protection scope of the present invention.

Claims

1. A highly transparent polyimide film containing benzonorbornene, characterized in that... Containing ether or ester bonds and pyridine heterocycles, wherein one side of the ether or ester bond is attached to the para position of the benzene ring in the benzonorbornene structure, and the other side is attached to the benzene ring or pyridine ring in the aromatic structure, its structural formula is: -X- indicates an ether bond; or an ester bond; 0<y<1； n represents the degree of aggregation, which is an integer, n>0; R represents one of H, CH3, or CF3; -Ar- represents an aromatic ring, and its structural formula is one of the following:

2. The method for preparing a highly transparent polyimide film containing benzo[a]norbornene structure according to claim 1, characterized in that: Includes the following steps: Under nitrogen protection, diamine monomers containing benzonorbornene and pyridine structures, and aromatic diamine monomers are dissolved in an anhydrous organic solvent. After complete dissolution, equimolar amounts of ether-bonded dianhydrides or ester-bonded dianhydrides containing benzonorbornene structures are added in batches. The reaction system is reacted at 0–20°C for 12 h to obtain a polyamic acid solution with a solid content of 6–20 wt%. The polyamic acid solution is then cast into a film to obtain a polyamic acid wet film. The polyimide wet film is then placed in an oven at a temperature of 60–90°C for 5–8 h to increase its solid content to 65–70%. The oven is then heated according to a temperature program to perform thermal imidization treatment on the polyimide wet film to obtain a polyimide film. The heating program is as follows: hold at 100℃ for 30 minutes, then heat to 150℃ and hold for 30 minutes; then heat to 200℃ and hold for 30 minutes; then heat to 250℃ and hold for 1 hour. Raise the temperature to 280℃ and hold for 30 minutes.

3. The method for preparing a highly transparent polyimide film containing benzonorbornene according to claim 2, characterized in that: The diamine monomer containing benzonorbornene and pyridine structures has the following structural formula: In the formula, R represents one of H, CH3 or CF3.

4. The method for preparing a highly transparent polyimide film containing benzonorbornene according to claim 2, characterized in that: The aromatic diamine monomers are: 1,4-diaminobenzene, 2-methyl-1,4-diaminobenzene, 2-trifluoromethyl-1,4-diaminobenzene, 1,3-diaminobenzene, 5-methyl-1,3-diaminobenzene, 5-trifluoromethyl-1,3-diaminobenzene, 2,5-diaminopyridine, 3-methyl-2,5-diaminopyridine, 3-trifluoromethyl-2,5-diaminopyridine, 3,5-diaminopyridine, 4,4'-diaminodiphenyl sulfone, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4 One of 4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3'-bis(trifluoromethyl)biphenyl, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-bis(4-aminophenoxy)benzene, 4,4'-bis(3-aminophenoxy)benzene, 4,4'-diaminodiphenyl ether, or 4,4'-bis(4-aminophenoxy)biphenyl; The ratio of the diamine monomer containing benzonorbornene and pyridine structures to the aromatic diamine monomer is y:(1-y), 0 <y<1。 5. The method for preparing a highly transparent polyimide film containing benzonorbornene according to claim 2, characterized in that: The anhydrous organic solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.

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