Copolyimide with thermal stability, preparation method thereof and copolyimide film

Abstract

The invention discloses copolyimide with thermal stability, a preparation method thereof and a copolyimide film, and a naphthalene ring structure is introduced into a main chain structure of polyimide, so that the obtained copolyimide has high heat resistance and mechanical properties; meanwhile, due to the single-bond structure in the binaphthyl anhydride monomer, the solubility of the polymer is improved, a traditional two-step polymerization method can be changed into a one-step method, the method is simple, complex equipment is not needed, the process condition is mild and easy to control, the yield is high, and industrial popularization and application are easy.

Description

Technical Field

[0001] The present invention relates to the technical field of polyimides, and more particularly to a copolymerized polyimide with thermal stability, a preparation method thereof, and a copolymerized polyimide film. Background Art

[0002] Polyimide materials are a type of material with excellent comprehensive performance, with advantages such as good thermal stability, excellent mechanical properties, good dimensional stability, excellent chemical stability, high breakdown voltage, low dielectric constant, high flame retardancy, and low expansion coefficient. They are a type of polymer containing imide rings on their main chain. They are widely used as special coatings, films, fibers and composite materials in electronics, aerospace, industrial separation, optoelectronic displays and mechanical components.

[0003] Polyimides are primarily synthesized from dianhydrides and diamines. There are many different types of dianhydrides and diamines, and different combinations can yield polyimides with varying properties. Synthesis methods are primarily categorized into one-step and two-step methods.

[0004] The two-step process is typically used to prepare polyimides insoluble in organic solvents. The first step involves low-temperature polycondensation of dianhydride and diamine in a polar solvent, such as DMF, DMAC, NMP, or a THE / methanol mixture, to obtain a soluble polyamic acid. The second step involves heating to approximately 300°C after film formation or spinning to dehydrate and achieve imidization, yielding the polyimide. For soluble polyimides, acetic anhydride and a tertiary amine catalyst can be added to the polyamic acid to initiate imidization, yielding a polyimide solution or powder.

[0005] The one-step method involves directly heating and polycondensing diamine and dianhydride in a high-boiling-point solvent to produce polyimide. The reaction also proceeds through the formation of a polyamidoamine acid intermediate, followed by imidization to produce polyimide. Based on the reaction mechanism, the key step in the one-step polymerization is still imidization. Numerous studies have shown that acidic catalysts can accelerate the imidization reaction. A fundamental prerequisite for the one-step method is that the polyimide can be dissolved in the solvent used for polymerization. However, due to the rigid heterocyclic structure of polyimides, they are generally insoluble in common organic solvents. Consequently, there are relatively few solvents available for the one-step synthesis, with m-cresol and p-chlorophenol being commonly used. Both solvents are phenolic compounds, viscous liquids at room temperature, with boiling points exceeding 200°C. Polymerization reactions are generally carried out at these high temperatures to ensure the dissolution of the polyimide and promote the imidization reaction.

[0006] Kapton (polyimide film) is a high-performance polymer material developed by DuPont. It is known for its excellent heat resistance, mechanical strength, chemical stability and dielectric properties. It is widely used in aerospace, flexible circuits, high-temperature insulation and other fields. The preparation of traditional Kapton usually relies on a two-step process, namely, first, a soluble polyamic acid (PAA) precursor solution is generated by condensation of dianhydride and diamine monomers, and then an insoluble polyimide film is formed by high-temperature dehydration and imidization. This method uses organic solvents, which is not only complex and energy-intensive, but also the final product is difficult to dissolve in conventional solvents due to its highly conjugated rigid molecular structure, making the film difficult to reprocess or recycle. At the same time, the modification schemes in the existing technology that introduce flexible segments or reduce the degree of imidization to improve solubility are often accompanied by a significant deterioration of thermal stability (such as glass transition temperature and thermal decomposition temperature), limiting its application in high-temperature scenarios. In addition, traditional polyimides rely on polar solvents during the synthesis process (such as PAA needs to be soluble in highly polar solvents) and PAA acid is extremely unstable, which increases the difficulty of storage and also increases the environmental and cost burden.

[0007] Therefore, there is an urgent need to develop a new polyimide material system that has good solubility, high thermal performance and simplified process. Summary of the Invention

[0008] The object of the present invention is to overcome the above-mentioned defects of the prior art and provide a copolymer polyimide with thermal stability, a preparation method thereof, and a copolymer polyimide film. By introducing a naphthalene ring structure into the main chain structure of the polyimide, the resulting copolymer polyimide not only has high heat resistance, but also improves the solubility of the polymer due to the single bond structure in the dinaphthyl anhydride monomer, and can also be converted from a traditional two-step polymerization process to a one-step process.

[0009] To achieve the above object, the technical solution of the present invention is as follows: A thermally stable copolymer polyimide comprising a repeating structural unit shown in the following formula: .

[0010] The present invention also discloses a method for preparing the thermally stable copolymerized polyimide. The copolymerized polyimide is prepared by condensation copolymerization using a dianhydride compound and an aromatic diamine compound as raw materials.

[0011] Optionally, the preparation method includes the following steps: adding the dianhydride compound and the aromatic diamine compound into a solvent and mixing them, adding an alkaline catalyst to the obtained reaction solution for heating reaction, and obtaining the copolymerized polyimide through post-treatment.

[0012] Optionally, the molar volume ratio of the aromatic diamine compound to the solvent is 5 mmol: (6-35) mL.

[0013] Optionally, the molar ratio of the alkaline catalyst to the aromatic diamine compound is (0.5-1.5):5.

[0014] Optionally, the molar ratio of the dianhydride compound to the aromatic diamine compound is 1:1.

[0015] Optionally, the dianhydride compound is 4,4',5,5'-binaphthyltetracarboxylic dianhydride (BNTDA) and pyromellitic anhydride (PMDA).

[0016] Optionally, the aromatic diamine compound is 4,4'-diaminodiphenyl ether (ODA).

[0017] Optionally, the structural formula of 4,4',5,5'-binaphthyltetracarboxylic dianhydride (BNTDA) is: .

[0018] Optionally, the structural formula of pyromellitic anhydride (PMDA) is: .

[0019] Optionally, the structural formula of 4,4'-diaminodiphenyl ether (ODA) is: .

[0020] Optionally, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the copolymerized polyimide is 40% to 90%.

[0021] Optionally, the solvent is selected from at least one of phenol solvents, sulfone solvents, ketone solvents and amide solvents with a boiling point higher than 150° C., preferably m-methylphenol.

[0022] Optionally, the alkaline catalyst includes at least one of carbonates, bicarbonates, hydroxides, alkali metal salts of alcohols, metal hydrides, pyridine, quinolines, and organic amine compounds, preferably one or more of quinolines and organic amines, more preferably isoquinoline and / or triethylamine.

[0023] Optionally, the temperature of the heating reaction is 170°C to 230°C, preferably 180°C to 220°C, and more preferably 190°C to 210°C.

[0024] Optionally, the heating reaction time is 10h~20h.

[0025] Optionally, the post-treatment specifically includes: cooling the polymer solution obtained after the heating reaction to room temperature, adding methanol and stirring, and then washing, purifying, filtering and drying in sequence.

[0026] Optionally, the washing time is 1h~4h.

[0027] The present invention also discloses a copolymerized polyimide film with thermal stability. The copolymerized polyimide film is prepared by the following steps: dissolving the copolymerized polyimide described above in m-cresol, coating the film after complete dissolution, and then curing the film by heating to obtain the copolymerized polyimide film.

[0028] Optionally, the heating curing specifically includes: first heating to 60°C~80°C and drying for 1h~2h, then heating to 150°C~160°C and drying for 1h~2h, continuing to heating to 350°C~360°C and drying for 0.5h~1h, and then heating to 400°C and drying for 0.5h~1h.

[0029] Optionally, the film-forming coating method is a casting method.

[0030] The implementation of the present invention will have the following beneficial effects: The present invention provides a naphthalene ring-containing acid anhydride, prepared by a one-step polymerization of a dianhydride compound and an aromatic diamine compound. The use of a naphthalene ring-containing dianhydride monomer for polycondensation enhances the rigidity of the polymerization system and maintains thermal stability. Furthermore, the single-bond structure of the binaphthyl anhydride improves the solubility of the entire system. Furthermore, the present invention utilizes the naphthalene ring-containing acid anhydride as a comonomer, resulting in a film having both excellent heat resistance and mechanical properties, while also improving the solubility of conventional Kapton film. Compared to conventional two-step methods, the present method is simple, does not require complex equipment, offers mild process conditions, is easily controllable, and offers high yields, making it readily applicable in industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 DMA graphs of the copolymerized polyimides prepared in Examples 2, 4 and 5 of the present invention and Comparative Example 1.

[0032] Figure 2 3 is the thermogravimetric diagram of the copolymerized polyimide prepared in Examples 2, 4 and 5 of the present invention and Comparative Example 1.

[0033] Figure 3 It is a comparison diagram of the dissolution of the polyimide obtained in Example 1 of the present invention and the commercial Kapton dissolved in m-cresol, as well as a diagram of the film formation after the re-dissolution of Example 1. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0035] In the polyimide copolymer of the present invention, the polyimide is obtained by polycondensing 4,4',5,5'-binaphthyltetracarboxylic dianhydride, pyromellitic anhydride and 4,4'-diaminodiphenyl ether. The process of preparing the polyimide copolymer is listed in detail below.

[0036] Example 1 A polyimide copolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether was used as the diamine monomer, 0.654 g (3 mmol) of pyromellitic anhydride, and 0.788 g (2 mmol) of 4,4',5,5'-binaphthyltetracarboxylic dianhydride were used as the dianhydride monomer. 0.1 ml (approximately 1 mmol) of isoquinoline was added to the reaction system and dissolved in 10 mL of m-cresol (m-cretol). Stirring continued until complete dissolution. The mixture was heated to 80°C in a dry Schlenk reaction tube and stirred for 3 hours. The temperature was then raised to 190°C and stirred for 10 hours. After the reaction, the reaction solution was cooled to room temperature and the polymer solution was slowly poured into 200 ml of methanol to obtain a flocculent product. The product was dissolved in chloroform and then poured into methanol for precipitation. This process was repeated three times for purification and finally dried under vacuum for 12 hours.

[0037] The polyimide copolymer of this embodiment includes repeating structural units shown in the following formula: ; Among them, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the polyimide copolymer is 40%.

[0038] A polyimide copolymer film, the preparation method of which comprises: dissolving the polyimide polymer prepared in this embodiment in m-cresol to obtain a solution with a solid content of 6.25%, laying a film by a casting method after complete dissolution, gradually heating to 60°C and drying for 2 hours, drying at 150°C for 2 hours, continuing to heat to 350°C and drying for 1 hour, and then heating to 400°C and drying for 0.5 hours, with a thickness of 40 μm.

[0039] Example 2 A polyimide copolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether was used as the diamine monomer, 0.545 g (2.5 mmol) of pyromellitic anhydride, and 0.985 g (2.5 mmol) of 4,4',5,5'-binaphthyltetracarboxylic dianhydride were used as the dianhydride monomer. 0.1 ml (approximately 1 mmol) of isoquinoline was added to the reaction system and dissolved in 10 mL of m-cresol (m-cretol). Stirring continued until complete dissolution. The mixture was heated to 80°C in a dry Schlenk reaction tube and stirred for 3 hours. The temperature was then raised to 190°C and stirred for 10 hours. After the reaction, the reaction solution was cooled to room temperature and the polymer solution was slowly poured into 200 ml of methanol to obtain a flocculent product. The product was dissolved in chloroform and then poured into methanol for precipitation. This process was repeated three times for purification and finally dried under vacuum for 12 hours.

[0040] The polyimide copolymer of this embodiment includes repeating structural units shown in the following formula: ; Among them, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the polyimide copolymer is 50%.

[0041] A polyimide copolymer film was prepared according to the preparation method described in Example 1 to obtain a film having a thickness of 40 μm. The relevant performance test results of the film are shown in Table 1. Example 3 A polyimide copolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether was used as the diamine monomer, 0.436 g (2 mmol) of pyromellitic anhydride, and 1.183 g (3 mmol) of 4,4',5,5'-binaphthyltetracarboxylic dianhydride were used as the dianhydride monomer. 0.1 ml (approximately 1 mmol) of isoquinoline was added to the reaction system and dissolved in 10 mL of m-cresol (m-cretol). Stirring continued until complete dissolution. The mixture was heated to 80°C in a dry Schlenk reaction tube and stirred for 3 hours. The temperature was then raised to 190°C and stirred for 10 hours. After the reaction, the reaction solution was cooled to room temperature and the polymer solution was slowly poured into 200 ml of methanol to obtain a flocculent product. The product was dissolved in chloroform and then poured into methanol for precipitation. This process was repeated three times for purification and finally dried under vacuum for 12 hours.

[0042] The polyimide copolymer of this embodiment includes repeating structural units shown in the following formula: ; Among them, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the polyimide copolymer is 60%.

[0043] A polyimide copolymer film was prepared according to the preparation method described in Example 1 to obtain a film having a thickness of 40 μm. The relevant performance test results of the film are shown in Table 1.

[0044] Example 4 A polyimide copolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether was used as the diamine monomer, 0.327 g (1.5 mmol) of pyromellitic anhydride, and 1.379 g (3.5 mmol) of 4,4',5,5'-binaphthyltetracarboxylic dianhydride were used as the dianhydride monomer. 0.1 ml (approximately 1 mmol) of isoquinoline was added to the reaction system and dissolved in 10 mL of m-cresol (m-cretol). Stirring continued until complete dissolution. The mixture was heated to 80°C in a dry Schlenk reaction tube and stirred for 3 hours. The temperature was then raised to 190°C and stirred for 10 hours. After the reaction, the reaction solution was cooled to room temperature and the polymer solution was slowly poured into 200 ml of methanol to obtain a flocculent product. The product was dissolved in chloroform and then poured into methanol for precipitation. This process was repeated three times for purification and finally dried under vacuum for 12 hours.

[0045] The polyimide copolymer of this embodiment includes repeating structural units shown in the following formula: ; Among them, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the polyimide copolymer is 70%.

[0046] A polyimide copolymer film was prepared according to the preparation method described in Example 1 to obtain a film having a thickness of 40 μm. The relevant performance test results of the film are shown in Table 1.

[0047] Example 5 A polyimide copolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether was used as the diamine monomer, 0.218 g (1 mmol) of pyromellitic anhydride, and 1.576 g (4 mmol) of 4,4',5,5'-binaphthyltetracarboxylic dianhydride were used as the dianhydride monomer. 0.1 ml (approximately 1 mmol) of isoquinoline was added to the reaction system and dissolved in 10 mL of m-cresol (m-cretol). Stirring continued until complete dissolution. The mixture was heated to 80°C in a dry Schlenk reaction tube and stirred for 3 hours. The temperature was then raised to 190°C and stirred for 10 hours. After the reaction, the reaction solution was cooled to room temperature and the polymer solution was slowly poured into 200 ml of methanol to obtain a flocculent product. The product was dissolved in chloroform and then poured into methanol for precipitation. This process was repeated three times for purification and finally dried under vacuum for 12 hours.

[0048] The polyimide copolymer of this embodiment includes repeating structural units shown in the following formula: ; Among them, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the polyimide copolymer is 80%.

[0049] A polyimide copolymer film was prepared according to the preparation method described in Example 1 to obtain a film having a thickness of 40 μm. The relevant performance test results of the film are shown in Table 1.

[0050] Example 6 A polyimide copolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether was used as the diamine monomer, 0.109 g (0.5 mmol) of pyromellitic anhydride, and 1.773 g (4.5 mmol) of 4,4',5,5'-binaphthyltetracarboxylic dianhydride were used as the dianhydride monomer. 0.1 ml (approximately 1 mmol) of isoquinoline was added to the reaction system and dissolved in 10 mL of m-cresol (m-cretol). Stirring continued until complete dissolution. The mixture was heated to 80°C in a dry Schlenk reaction tube and stirred for 3 hours. The temperature was then raised to 190°C and stirred for 10 hours. After the reaction, the reaction solution was cooled to room temperature and the polymer solution was slowly poured into 200 ml of methanol to obtain a flocculent product. The product was dissolved in chloroform and then poured into methanol for precipitation. This process was repeated three times for purification and finally dried under vacuum for 12 hours.

[0051] The polyimide copolymer of this embodiment includes repeating structural units shown in the following formula: ; Among them, the copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the polyimide copolymer is 90%.

[0052] A polyimide copolymer film is prepared according to the preparation method described in Example 1 to obtain a film with a thickness of 40 μm. The relevant performance test results of the film are shown in Table 1 Comparative Example 1 A polyimide homopolymer, the preparation method of which comprises: Under a nitrogen atmosphere, 1 g (5 mmol) of 4,4'-diaminodiphenyl ether as a diamine monomer was dissolved in 10 mL of DMAC and stirred until completely dissolved. 1.09 g (5 mmol) of pyromellitic anhydride was added, and the mixture was heated to 60°C and stirred for 3 h to obtain a homogeneous solution with a solid content of 17 wt%, which was a polyimide homopolymer.

[0053] A polyimide copolymer film was prepared according to the preparation method described in Example 1 to obtain a film having a thickness of 40 μm. The relevant performance test results of the film are shown in Table 1.

[0054] Test Case 1. The intrinsic viscosity (η) of the PI film was measured using an Ubbelohde viscometer (capillary inner diameter, 1.07 mm) in a 30°C constant-temperature water bath. The solvent was m-cresol, and the solution concentration was 0.5 dL / g. The dynamic mechanical properties of the PI film were tested using a dynamic mechanical analyzer (DMA) at a test frequency of 1 Hz, a temperature range of 40–400°C, a heating rate of 10°C / min, and a film sample size of 5 × 40 mm. The thermal stability of the PI film was analyzed using a thermogravimetric analyzer (TGA) in an N2 atmosphere, a temperature range of 40–800°C, and a heating rate of 20°C / min.

[0055] The thermal performance test results of the copolymerized polyimide prepared in Examples 1-6 and the Kapton prepared in Comparative Example 1 are shown in Table 1 below. Figure 1 、 Figure 2 see.

[0056] Table 1 Thermal performance test results

[0057] According to Table 1 and Figure 1 The results show that the Kapton of Comparative Example 1 is insoluble in m-cresol, while the polyimide series copolymers prepared in the present invention are soluble in m-cresol; in addition, the glass transition temperature of the polyimide series copolymers prepared in the present invention is not lower than that of Comparative Example 1, but is higher. The thermal decomposition temperature is an important parameter to characterize the thermal stability of polymers. Figure 2 The test data shows that the 5% thermal weight loss temperature (T5%) of the copolymerized polyimide in N2 atmosphere is 500~550℃, which is almost unchanged compared with the thermal decomposition temperature of the Kapton system, indicating that the synthesized copolymerized polyimide has excellent thermal stability.

[0058] 2. Solubility test method: 10 mg of PI film prepared in Examples 1-6 and Comparative Example 1 was placed in a test tube containing 1 mL of solvent, and its dissolution was observed at room temperature or under heating conditions, and the results shown in Table 2 were obtained.

[0059] Table 2 Solubility test results

[0060] As shown in Table 2, the copolymerized polyimide prepared in the present invention is more soluble in H2SO4 and m-Cresol organic solvents than Kapton. This is primarily due to the single bonds in the polymer molecular chain structure, and the introduction of BNTDA disrupts the distribution and regularity of the original system's PI molecular backbone, resulting in a looser polymer structure. This indicates that the Kapton system after BNTDA copolymerization improves its solubility in m-cresol without compromising thermal performance. Furthermore, traditional Kapton films, due to their poor solubility, can only be prepared through a two-step reaction. The PAA acid obtained through this two-step reaction is highly unstable and difficult to store. Copolymerization improves the preparation process, allowing the traditional two-step process to be converted to a one-step process.

[0061] 3. By Figure 3 It can be seen from the dissolution comparison diagram of Example 1 and Comparative Example 1 after being dissolved in m-cresol respectively, that the solubility of Example 1 in m-cresol is significantly better than that of Comparative Example 1, and Figure 3 It also shows that Example 1 can form a film after being dissolved again, which shows its reproducibility.

[0062] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A thermally stable copolymer polyimide, characterized in that: The copolymerized polyimide comprises a repeating structural unit shown in the following formula: 。 2. A method for preparing a thermally stable copolymerized polyimide according to claim 1, characterized in that: The copolymerized polyimide is prepared by condensation copolymerization using dianhydride compounds and aromatic diamine compounds as raw materials.

3. The preparation method according to claim 2, characterized in that The preparation method comprises the following steps: The dianhydride compound and the aromatic diamine compound are added to a solvent and mixed, a basic catalyst is added to the obtained reaction solution to carry out heating reaction, and the copolymerized polyimide is obtained through post-treatment.

4. The preparation method according to claim 3, characterized in that The molar volume ratio of the aromatic diamine compound to the solvent is 5 mmol: (6-35) mL; The molar ratio of the alkaline catalyst to the aromatic diamine compound is (0.5-1.5):5; The molar ratio of the dianhydride compound to the aromatic diamine compound is 1:

1.

5. The preparation method according to claim 3, characterized in that The dianhydride compounds are 4,4',5,5'-binaphthyltetracarboxylic dianhydride and pyromellitic anhydride; The aromatic diamine compound is 4,4'-diaminodiphenyl ether.

6. The preparation method according to claim 5, characterized in that The copolymerization ratio of 4,4',5,5'-binaphthyltetracarboxylic dianhydride in the copolymerized polyimide is 40% to 90%.

7. The preparation method according to claim 3, characterized in that The solvent is selected from at least one of phenolic solvents, sulfone solvents, ketone solvents and amide solvents having a boiling point higher than 150°C; The alkaline catalyst includes at least one of carbonate, bicarbonate, hydroxide, alkali metal salt of alcohol, metal hydride, pyridine, quinoline, and organic amine compounds; The temperature of the heating reaction is 170° C. to 230° C., and the time of the heating reaction is 10 h to 20 h.

8. The preparation method according to claim 3, characterized in that The post-treatment specifically includes: cooling the polymer solution obtained after the heating reaction to room temperature, adding methanol and stirring, and then washing, purifying, filtering and drying in sequence.

9. A thermally stable copolymerized polyimide film, characterized in that: The copolymerized polyimide film is prepared by the following steps: The copolymerized polyimide according to claim 1 is dissolved in m-cresol, coated to form a film after the dissolution is complete, and then heated and cured to obtain the copolymerized polyimide film.

10. The thermally stable copolymerized polyimide film according to claim 9, wherein The heating curing specifically includes: first heating to 60°C~80°C and drying for 1h~2h, then heating to 150°C~160°C and drying for 1h~2h, continuing to heating to 350°C~360°C and drying for 0.5h~1h, and then heating to 400°C and drying for 0.5h~1h.

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