A polyamide-imide polymer, its preparation method and application

Abstract

This invention relates to the field of polymer materials technology, and more particularly to a polyamide-imide polymer, its preparation method, and its applications. This invention uses a polyamide-imide polymer having the structure shown in Formula I to prepare a polyamide-imide film. The polyamide-imide polymer uses 2,2'-di(trifluoromethyl)diaminobiphenyl as a diamine monomer and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] as an anhydride monomer, which is copolymerized with terephthaloyl chloride in different proportions and 2,2'-di(trifluoromethyl)diaminobiphenyl to obtain the polyamide-imide polymer, and then to prepare the polyamide-imide film. The PAI film prepared by this invention has high visible light transmittance, low coefficient of thermal expansion and mechanical properties, and good solubility in most organic solvents, making it easy to process and showing broad application prospects in the optoelectronic field.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyamide-imide polymer, its preparation method and application. Background Technology

[0002] In recent years, the requirements for polymer optical films in the modern optoelectronic field have become increasingly stringent. Compared to the fragility and heavy weight of traditional inorganic glass substrates, colorless and transparent polyimide (CPI) films, as substrate materials, are widely used in the manufacture of optoelectronic devices such as touch screens, flexible displays, and flexible printed circuit boards due to their good heat resistance and dimensional stability under high-temperature conditions, as well as their excellent optical and mechanical properties. The superior properties of polyimide largely stem from the strong charge transfer (CT) interaction between dianhydride and diamine monomers. This interaction also causes polyimide to strongly absorb visible light, resulting in a yellow to dark brown color. Traditionally, the color of polyimide films has significantly limited their use in the optoelectronic field; therefore, improving the optical properties of polyimide films has become a hot topic. Furthermore, in electronic devices, polymer substrates experience significant thermal expansion / contraction at high temperatures, leading to serious problems such as misalignment and adhesion failure of micro-components. Therefore, improving the dimensional stability of polymers is also crucial.

[0003] Currently, the most direct way to improve dimensional stability is to reduce the coefficient of thermal expansion. However, it is difficult to simultaneously obtain both excellent optical transmittance and a low coefficient of thermal expansion. In other words, improving the thermal stability of the polymer often reduces the optical performance of the film. Therefore, obtaining colorless and transparent polyimide films with a low coefficient of thermal expansion and certain mechanical properties remains a research hotspot for those skilled in the art.

[0004] In summary, in the fields of microelectronics and optoelectronics, improving traditional polyimide films, increasing optical transmittance, reducing the coefficient of thermal expansion, and researching and preparing high-temperature resistant, high-strength, colorless, and transparent polyimide film products are urgent needs. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a polyamide-imide polymer, its preparation method and application. The polyamide-imide film prepared by the polyamide-imide polymer provided by the present invention has good optical transmittance while maintaining a low coefficient of thermal expansion and superior mechanical properties.

[0006] This invention provides a polyamide-imide polymer having the structure shown in Formula I;

[0007]

[0008] In Equation I, x and y are both integers, 25≤x≤500, and 50≤y≤750.

[0009] This invention also provides a method for preparing a polyamide-imide polymer, comprising the following steps:

[0010] A) Under a protective atmosphere, 2,2'-bis(trifluoromethyl)diaminobenzidine monomer, aprotic polar solvent and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were mixed to obtain the first mixture.

[0011] B) Mix the first mixture with terephthaloyl chloride in an ice-water bath and react at room temperature;

[0012] C) Mix the system after the reaction in step B), the dehydration catalyst, and the imidizing agent to carry out a chemical imidization reaction;

[0013] D) Mix the system after the reaction in step C) with a precipitant to precipitate, and obtain a polyamide-imide polymer with the structure shown in Formula I;

[0014]

[0015] In Equation I, x and y are both integers, 25≤x≤500, and 50≤y≤750.

[0016] Preferably, the molar ratio of 2,2'-bis(trifluoromethyl)diaminobenzidinediamine monomer, 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer and terephthaloyl chloride is 1:0.1 to 1:0 to 0.9; and the molar amount of terephthaloyl chloride is not 0.

[0017] Preferably, the aprotic polar solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide;

[0018] The protective gas is nitrogen.

[0019] Preferably, in step B), the reaction time is 10 to 14 hours.

[0020] Preferably, the dehydration catalyst comprises at least one of acetic anhydride, propionic anhydride, benzoic anhydride, and trifluoroacetic anhydride; the imidizing agent comprises at least one of pyridine, methylpyridine, quinoline, and isoquinoline.

[0021] The molar ratio of the dehydration catalyst, the imidizing agent, and the 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer is 3-9:3-9:0.5-1.5.

[0022] Preferably, in step C), the chemical imidization reaction is carried out at room temperature for 10–14 hours.

[0023] Preferably, in step D), the precipitant includes at least one of methanol, ethanol, isopropanol, and water.

[0024] The present invention also provides a polyamide-imide film, which is prepared from the polyamide-imide polymer described above or the polyamide-imide polymer prepared by the preparation method described above.

[0025] This invention also provides a method for preparing a polyamide-imide film, comprising the following steps:

[0026] The casting solution is uniformly coated onto the substrate. After removing the solvent, the film is removed and dried to obtain a polyamide-imide film.

[0027] The casting solution is obtained by mixing a polyamide-imide polymer and a proton-polar solvent;

[0028] The polyamide-imide polymer is the polyamide-imide polymer described above or the polyamide-imide polymer prepared by the preparation method described above.

[0029] Preferably, the aprotic polar solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide;

[0030] The solid content of the casting solution is 5% to 20%;

[0031] The method for removing the solvent is to remove it by heating.

[0032] The heating method includes:

[0033] First, raise the temperature to 50-80℃ and hold for 6-8 hours, then raise the temperature to 100-120℃ and hold for 1-2 hours, then raise the temperature to 150-170℃ and hold for 1-2 hours, then raise the temperature to 200-220℃ and hold for 1-2 hours, and finally raise the temperature to 250-270℃ and hold for 1-2 hours.

[0034] This invention utilizes a polyamide-imide polymer having the structure shown in Formula I to prepare a polyamide-imide film. The polyamide-imide polymer uses 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) as the diamine monomer and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] (BzDA) as the anhydride monomer. These monomers are copolymerized with terephthaloyl chloride (TPC) and TFMB in different proportions to prepare the polyamide-imide polymer (PAI), which is then used to prepare the polyamide-imide film. The PAI film prepared by this invention exhibits high visible light transmittance, with a transmittance of over 85% at 400 nm, and excellent dimensional stability (CTE value as low as 23 ppm K). -1 It possesses good mechanical properties and excellent solubility in most organic solvents, making it easy to process and suitable for a wide range of applications in the optoelectronic field. Attached Figure Description

[0035] Figure 1 The above is the 1H NMR spectrum of the polyamide-imide polymer of Example 1 of this invention;

[0036] Figure 2 Thermogravimetric curves of the polyamide-imide polymers in Examples 1-3 of this invention are shown.

[0037] Figure 3 This is a dynamic thermomechanical analysis curve of the polyamide-imide polymer of Example 1 of the present invention;

[0038] Figure 4 The visible light optical transmittance properties of the polyamide-imide polymers in Examples 1-3 of this invention are shown. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] This invention provides a polyamide-imide polymer having the structure shown in Formula I;

[0041]

[0042] In Equation I, x and y are both integers, 25≤x≤500, and 50≤y≤750.

[0043] In some embodiments of the present invention, the range of x is 25≤x≤250, 50≤x≤500, or 75≤x≤750.

[0044] In some embodiments of the present invention, the range of y is 75≤y≤750, 50≤y≤500, or 25≤y≤250.

[0045] In some embodiments of the present invention, the weight-average molecular weight of the polyamide-imide polymer is 10,000 to 1,000,000; specifically, it is 50,000 to 575,000, such as 50,000 to 500,000, 55,000 to 550,000, or 57,500 to 575,000.

[0046] The present invention also provides a method for preparing the polyamide-imide polymer described above, comprising the following steps:

[0047] A) Under a protective atmosphere, 2,2'-bis(trifluoromethyl)diaminobenzidine monomer, aprotic polar solvent and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were mixed to obtain the first mixture.

[0048] B) Mix the first mixture with terephthaloyl chloride in an ice-water bath and react at room temperature;

[0049] C) Mix the system after the reaction in step B), the dehydration catalyst, and the imidizing agent to carry out a chemical imidization reaction;

[0050] D) Mix the system after the reaction in step C) with a precipitant to precipitate and obtain a polyamide-imide polymer.

[0051] In step A):

[0052] Under a protective atmosphere, 2,2'-bis(trifluoromethyl)diaminobenzidine monomer, aprotic polar solvent, and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were mixed to obtain a first mixture.

[0053] Specifically, including:

[0054] Under a protective atmosphere, 2,2'-bis(trifluoromethyl)diaminobenzidine monomer and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were sequentially dissolved in an aprotic polar solvent to obtain a first mixture.

[0055] In some embodiments of the present invention, the protective gas is nitrogen.

[0056] In some embodiments of the present invention, the molar ratio of 2,2'-bis(trifluoromethyl)diaminobiphenyldiamine monomer and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer is 1:0.1 to 1, for example 1:0.25, 1:0.5 or 1:0.75.

[0057] In some embodiments of the present invention, the aprotic polar solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide. The total amount of the 2,2'-bis(trifluoromethyl)diaminobiphenyldiamine monomer and the 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer in a ratio of 2-4 mmol:3-5 mL to the amount of the aprotic polar solvent, for example, 2.5 mmol:4 mL, 3 mmol:4 mL, or 3.5 mmol:4 mL.

[0058] In some embodiments of the invention, the dissolution is carried out at room temperature. The dissolution is carried out under stirring conditions.

[0059] In step B):

[0060] The first mixture was mixed with terephthaloyl chloride in an ice-water bath and the reaction was carried out at room temperature.

[0061] Specifically, including:

[0062] Terephthaloyl chloride was dissolved in the first mixture in an ice-water bath and the reaction was carried out at room temperature.

[0063] In some embodiments of the present invention, the molar ratio of 2,2'-bis(trifluoromethyl)diaminobiphenyldiamine monomer, 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer and terephthaloyl chloride is 1:0.1 to 1:0 to 0.9, for example 1:0.25:0.75, 1:0.5:0.5 or 1:0.75:0.25; and the molar amount of terephthaloyl chloride is not 0.

[0064] In some embodiments of the invention, the dissolution is carried out under stirring conditions.

[0065] In some embodiments of the present invention, the reaction time is 10 to 14 hours, for example, 12 hours. The reaction is carried out under stirring conditions.

[0066] In step C):

[0067] The system after step B), the dehydration catalyst, and the imidizing agent are mixed to carry out a chemical imidization reaction.

[0068] In some embodiments of the present invention, the dehydration catalyst includes at least one of acetic anhydride, propionic anhydride, benzoic anhydride, and trifluoroacetic anhydride; the imidizing agent includes at least one of pyridine, methylpyridine, quinoline, and isoquinoline.

[0069] The molar ratio of the dehydration catalyst, the imidizing agent, and the 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer is 3-9:3-9:0.5-1.5; for example, 3:9:0.5, 6:6:1, or 9:3:1.5.

[0070] The chemical imidization reaction is carried out at room temperature for 10–14 hours, for example, 12 hours. The chemical imidization reaction is conducted under stirring.

[0071] In step D):

[0072] The system after the reaction in step C) is mixed with a precipitant to precipitate, thereby obtaining a polyamide-imide polymer.

[0073] Specifically, including:

[0074] The system after the reaction in step C) is slowly poured into a precipitant to precipitate, thus obtaining a polyamide-imide polymer.

[0075] In some embodiments of the invention, the slow pouring rate is 0.005 to 0.02 mL / s, for example, 0.01 mL / s.

[0076] In some embodiments of the present invention, the precipitant includes at least one of methanol, ethanol, isopropanol, and water.

[0077] After sedimentation, a white flocculent precipitate was obtained.

[0078] In some embodiments of the present invention, after precipitation, the process further includes:

[0079] The precipitate is washed, filtered, and dried.

[0080] The washing process can involve repeated agitation and washing, specifically, repeated agitation and washing three times.

[0081] The drying process is vacuum drying, with a temperature of 120°C and a time of 8–12 hours.

[0082] The present invention also provides a polyamide-imide film, which is prepared from the polyamide-imide polymer described above or the polyamide-imide polymer prepared by the preparation method described above.

[0083] The present invention also provides a method for preparing the polyamide-imide film described above, comprising the following steps:

[0084] The casting solution is uniformly coated onto the substrate. After removing the solvent, the film is removed and dried to obtain a polyamide-imide film.

[0085] The casting solution is obtained by mixing a polyamide-imide polymer and an aprotic polar solvent.

[0086] In some embodiments of the present invention, the aprotic polar solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide.

[0087] In some embodiments of the present invention, the solid content of the casting solution is 5% to 20%, for example, 5%.

[0088] The substrate can be a clean glass plate.

[0089] The present invention does not impose any special restrictions on the coating method, but prefers the casting method.

[0090] One method to remove the solvent is to heat it in a vacuum oven.

[0091] In some embodiments of the present invention, the heating method includes:

[0092] First, raise the temperature to 50-80℃ and hold for 6-8 hours, then raise the temperature to 100-120℃ and hold for 1-2 hours, then raise the temperature to 150-170℃ and hold for 1-2 hours, then raise the temperature to 200-220℃ and hold for 1-2 hours, and finally raise the temperature to 250-270℃ and hold for 1-2 hours.

[0093] After removing the solvent, the process also includes cooling to room temperature.

[0094] Before demolding and drying, the process also includes immersing the substrate in water.

[0095] The obtained polyamide-imide film is a colorless and transparent polyamide-imide film.

[0096] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0097] Beneficial effects:

[0098] (1) The polyamide-imide film prepared in this invention uses a fluorinated diamine monomer. The introduction of fluorinated groups increases the inter-chain spacing, reduces intermolecular forces, and increases the free volume of the polymer. Furthermore, fluorine atoms can disrupt the regularity of the molecular chains, increasing their flexibility and thus greatly improving the solubility of the polyamide-imide. It can dissolve in N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide, thereby improving the processing performance of the product. Moreover, fluorine atoms have strong electronegativity, which can inhibit the formation of charge-transfer complexes (CTC), thereby increasing the optical transmittance of the film and reducing its yellowness value. The visible light transmittance is approximately 85%–90%.

[0099] (2) The polyamide-imide film prepared by the present invention uses an alicyclic structure acid anhydride monomer. The introduction of the alicyclic structure can destroy the conjugated structure on the original aromatic polyimide chain segment, reduce the intermolecular forces, thereby inhibiting the formation of CTC, improving the optical transmittance of the film, and increasing the molecular chain spacing, which also helps to improve the solubility of polyamide-imide.

[0100] (3) The polyamide-imide film prepared in this invention uses terephthaloyl chloride as a comonomer. Because the main chain formed by its polymerization with diamine monomer has a rigid linear structure and contains amide structure, the polyamide-imide film has high heat resistance, with a glass transition temperature of 350-370℃, and a low coefficient of thermal expansion, with a CTE value as low as 23ppm K. -1 Therefore, the soluble, colorless, transparent polyamide-imide film with low thermal expansion coefficient prepared by this invention has excellent comprehensive properties and has good application prospects in high-tech fields such as microelectronics and optoelectronics.

[0101] To further illustrate the present invention, the following detailed description of a polyamide-imide polymer, its preparation method, and its application, in conjunction with embodiments, is provided by the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0102] Comparative Example 1

[0103] The polyamide-imide polymer has the structure shown in formula (1);

[0104]

[0105] In formula (1), n ​​is an integer, 50≤n≤500; the weight-average molecular weight of the polyamide-imide polymer shown in formula (1) is 30000~300000.

[0106] 1) Preparation of polyamide-imide polymer with the structure shown in formula (1):

[0107] 1-1) Under a nitrogen atmosphere, 0.6405 g (2 mmol) of 2,2'-bis(trifluoromethyl)diaminobenzidinediamine monomer and 0.8129 g (2 mmol) of 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were sequentially dissolved in 4 mL of N,N-dimethylacetamide at room temperature by stirring to obtain the first mixture;

[0108] 1-2) The first mixture, acetic anhydride (1.2251 g, 12 mmol), and pyridine (0.9492 g, 12 mmol) were mixed and subjected to a chemical imidization reaction at room temperature for 12 h; the chemical imidization reaction was carried out under stirring.

[0109] 1-3) The system after the reaction in step 1-2) was slowly poured into ethanol (300 mL) at a rate of 0.01 mL / s to precipitate, and a white flocculent precipitate was obtained. The precipitate was stirred and washed three times, filtered, and vacuum dried at 120 °C for 10 h to obtain the polyamide-imide polymer with the structure shown in formula (1).

[0110] 2) Preparation of polyamide-imide films:

[0111] The polyamide-imide polymer with the structure shown in formula (1) was dissolved uniformly in N,N-dimethylacetamide to prepare a casting solution with a solid content of 5%. The casting solution was uniformly coated onto a clean glass plate using a casting method. The solvent was removed by heating in a vacuum oven according to the following procedure: 80℃ / 6h, 100℃ / 1h, 150℃ / 1h, 200℃ / 1h, 250℃ / 1h. After cooling to room temperature, the glass plate was immersed in water, the film was removed and dried to obtain a polyamide-imide film with a thickness of 30μm.

[0112] Example 1

[0113] The polyamide-imide polymer has the structure shown in Formula I;

[0114] Where x and y are both integers, 25≤x≤250, 75≤y≤750; the weight-average molecular weight of the polyamide-imide polymer is 50,000 to 500,000.

[0115] 1) Preparation of the polyamide-imide polymer:

[0116] 1-1) Under a nitrogen atmosphere, 0.6405 g (2 mmol) of 2,2'-bis(trifluoromethyl)diaminobenzidinediamine monomer and 0.2032 g (0.5 mmol) of 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were sequentially dissolved in 4 mL of N,N-dimethylacetamide at room temperature by stirring to obtain the first mixture;

[0117] 1-2) Terephthaloyl chloride (0.3045 g, 1.5 mmol) was dissolved in the first mixture in an ice-water bath and stirred at room temperature for 12 h.

[0118] 1-3) The system after the reaction in step 1-2), acetic anhydride (0.3063 g, 3 mmol) and pyridine (0.7119 g, 9 mmol) were mixed and subjected to a chemical imidization reaction at room temperature for 12 h; the chemical imidization reaction was carried out under stirring.

[0119] 1-4) The system after the reaction in step 1-3) was poured into ethanol (300 mL) at a rate of 0.01 mL / s to precipitate, and a white flocculent precipitate was obtained. The precipitate was stirred and washed three times, filtered, and vacuum dried at 120 °C for 10 h to obtain the polyamide-imide polymer with the structure shown in formula (2).

[0120] Figure 1 This is the 1H NMR spectrum of the polyamide-imide polymer of Example 1 of the present invention.

[0121] Figure 2 The images show the thermogravimetric curves of the polyamide-imide polymers used in Examples 1-3 of this invention. Figure 2 It can be seen that as the content of terephthaloyl chloride decreases, the thermal decomposition temperature of polyamide-imide polymers becomes lower and lower.

[0122] Figure 3 This is a dynamic thermomechanical analysis curve of the polyamide-imide polymer of Example 1 of the present invention. From... Figure 3 It is known that the polyamide-imide polymer prepared by this invention has a high glass transition temperature, which can reach 367°C.

[0123] Figure 4 This is a visible light optical transmittance diagram of the polyamide-imide polymers of Examples 1-3 of the present invention. From... Figure 4 It can be seen that as the content of 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer increases, the transmittance of polyamide-imide polymer at 400 nm becomes higher and higher.

[0124] 2) Preparation of polyamide-imide films:

[0125] The polyamide-imide polymer with the structure shown in formula (2) was dissolved uniformly in N,N-dimethylacetamide to prepare a casting solution with a solid content of 5%. The casting solution was uniformly coated onto a clean glass plate using a casting method. The solvent was removed by heating in a vacuum oven according to the following procedure: 80℃ / 6h, 100℃ / 1h, 150℃ / 1h, 200℃ / 1h, 250℃ / 1h. After cooling to room temperature, the glass plate was immersed in water, the film was removed and dried to obtain a polyamide-imide film with a thickness of 30μm.

[0126] Example 2

[0127] The polyamide-imide polymer has the structure shown in Formula I;

[0128] Where x and y are both integers, 50≤x≤500, 50≤y≤500; the weight-average molecular weight of the polyamide-imide polymer is 55000~550000.

[0129] 1) Preparation of the polyamide-imide polymer:

[0130] 1-1) Under a nitrogen atmosphere, 0.6405 g (2 mmol) of 2,2'-bis(trifluoromethyl)diaminobenzidinediamine monomer and 0.4064 g (1 mmol) of 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were sequentially dissolved in 4 mL of N,N-dimethylacetamide at room temperature by stirring to obtain the first mixture;

[0131] 1-2) Terephthaloyl chloride (0.2030 g, 1 mmol) was dissolved in the first mixture in an ice-water bath and stirred at room temperature for 12 h.

[0132] 1-3) The system after the reaction in step 1-2), acetic anhydride (0.6126 g, 6 mmol) and pyridine (0.4746 g, 6 mmol) were mixed and subjected to a chemical imidization reaction at room temperature for 12 h; the chemical imidization reaction was carried out under stirring.

[0133] 1-4) The system after the reaction in step 1-3) was poured into ethanol (300 mL) at a rate of 0.01 mL / s to precipitate, and a white flocculent precipitate was obtained. The precipitate was stirred and washed three times, filtered, and vacuum dried at 120 °C for 10 h to obtain the polyamide-imide polymer with the structure shown in formula (3).

[0134] 2) Preparation of polyamide-imide films:

[0135] The polyamide-imide polymer with the structure shown in formula (3) was dissolved uniformly in N,N-dimethylacetamide to prepare a casting solution with a solid content of 5%. The casting solution was uniformly coated onto a clean glass plate using a casting method. The solvent was removed by heating in a vacuum oven according to the following procedure: 80℃ / 6h, 100℃ / 1h, 150℃ / 1h, 200℃ / 1h, 250℃ / 1h. After cooling to room temperature, the glass plate was immersed in water, the film was removed and dried to obtain a polyamide-imide film with a thickness of 30μm.

[0136] Example 3

[0137] The polyamide-imide polymer has the structure shown in Formula I;

[0138] Where x and y are both integers, 75≤x≤750, 25≤y≤250; the weight-average molecular weight of the polyamide-imide polymer is 57500~575000.

[0139] 1) Preparation of the polyamide-imide polymer:

[0140] 1-1) Under a nitrogen atmosphere, 0.6405 g (2 mmol) of 2,2'-bis(trifluoromethyl)diaminobenzidinediamine monomer and 0.6096 g (1.5 mmol) of 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were sequentially dissolved in 4 mL of N,N-dimethylacetamide at room temperature by stirring to obtain the first mixture;

[0141] 1-2) Dissolve terephthaloyl chloride (0.1015 g, 0.5 mmol) in the first mixture in an ice-water bath and stir the mixture at room temperature for 12 h.

[0142] 1-3) The system after the reaction in step 1-2), acetic anhydride (0.9189 g, 9 mmol) and pyridine (0.2373 g, 3 mmol) were mixed and subjected to a chemical imidization reaction at room temperature for 12 h; the chemical imidization reaction was carried out under stirring.

[0143] 1-4) The system after the reaction in step 1-3) was poured into ethanol (300 mL) at a rate of 0.01 mL / s to precipitate, and a white flocculent precipitate was obtained. The precipitate was stirred and washed three times, filtered, and vacuum dried at 120 °C for 10 h to obtain the polyamide-imide polymer with the structure shown in formula (4).

[0144] 2) Preparation of polyamide-imide films:

[0145] The polyamide-imide polymer with the structure shown in formula (4) was dissolved uniformly in N,N-dimethylacetamide to prepare a casting solution with a solid content of 5%. The casting solution was uniformly coated onto a clean glass plate using a casting method. The solvent was removed by heating in a vacuum oven according to the following procedure: 80℃ / 6h, 100℃ / 1h, 150℃ / 1h, 200℃ / 1h, 250℃ / 1h. After cooling to room temperature, the glass plate was immersed in water, the film was removed and dried to obtain a polyamide-imide film with a thickness of 30μm.

[0146] Comparative Example 2

[0147] The polyamide-imide polymer has the structure shown in formula (2);

[0148]

[0149] In formula (2), n is an integer, 50≤n≤500; the weight-average molecular weight of the polyamide-imide polymer is 25000~250000.

[0150] 1) Preparation of the polyamide-imide polymer:

[0151] 1-1) Under a nitrogen atmosphere, 0.6405 g (2 mmol) of 2,2'-bis(trifluoromethyl)diaminobenzidinediamine monomer was dissolved in 4 mL of N,N-dimethylacetamide by stirring at room temperature to obtain the first mixture;

[0152] 1-2) Terephthaloyl chloride (0.4060 g, 2 mmol) was dissolved in the first mixture in an ice-water bath and stirred at room temperature for 12 h.

[0153] 1-3) The system after the reaction in step 1-2), acetic anhydride (1.2252 g, 12 mmol) and pyridine (0.9492 g, 12 mmol) were mixed and subjected to a chemical imidization reaction at room temperature for 12 h; the chemical imidization reaction was carried out under stirring.

[0154] 1-4) The system after the reaction in step 1-3) was poured into ethanol (300 mL) at a rate of 0.01 mL / s to precipitate, and a white flocculent precipitate was obtained. The precipitate was stirred and washed three times, filtered, and vacuum dried at 120 °C for 10 h to obtain the polyamide-imide polymer with the structure shown in formula (5).

[0155] 2) Preparation of polyamide-imide films:

[0156] The polyamide-imide polymer with the structure shown in formula (5) was dissolved uniformly in N,N-dimethylacetamide to prepare a casting solution with a solid content of 5%. The casting solution was uniformly coated onto a clean glass plate using a casting method. The solvent was removed by heating in a vacuum oven according to the following procedure: 80℃ / 6h, 100℃ / 1h, 150℃ / 1h, 200℃ / 1h, 250℃ / 1h. After cooling to room temperature, the glass plate was immersed in water, the film was removed and dried to obtain a polyamide-imide film with a thickness of 30μm.

[0157] The optical properties, heat resistance and mechanical properties of the polyamide-imide films obtained in Comparative Examples 1-2 and Examples 1-3 were tested, and the results are shown in Table 1.

[0158] Table 1. Performance test results of the polyamide-imide films obtained in Comparative Examples 1-2 and Examples 1-3

[0159]

[0160] As shown in Table 1, the colorless and transparent polyamide-imide film prepared by this invention has good heat resistance and optical properties. Specifically, the glass transition temperature (Tg) of the film is between 350 and 370°C, the transmittance at 400 nm is above 85%, the cut-off wavelength (λcut-off) is below 355 nm, the yellowness value is maintained between 1.7 and 1.85, and the coefficient of thermal expansion (CTE) can reach as low as 23 ppm K. -1 .

[0161] Compared with Comparative Example 1, the colorless and transparent polyamide-imide films prepared in Examples 1-3 showed significant improvements in heat resistance, glass transition temperature, dimensional stability, and mechanical properties. This demonstrates that after introducing terephthaloyl chloride monomer, the rigidity of the polyamide-imide film prepared in this invention gradually increases with the increase of terephthaloyl chloride content, and the mechanical properties are also improved. Furthermore, the coefficient of thermal expansion of the film is greatly reduced, and the CTE value decreases significantly. In addition, as can be seen from Comparative Example 2 and Examples 1-3, the film prepared by polymerization using anhydride monomers with a 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] alicyclic structure has significantly improved optical properties. This demonstrates that the introduction of the alicyclic structure can disrupt the conjugated structure on the original aromatic polyimide chain segments, reduce intermolecular forces, thereby inhibiting the formation of CTC and improving the optical transmittance of the film.

[0162] The solubility of the polyamide-imide films obtained in Comparative Examples 1-2 and Examples 1-3 was tested, and the results are shown in Table 2.

[0163] Table 2. Solubility test results of polyamide-imide films obtained in Comparative Examples 1-2 and Examples 1-3

[0164] m-Cresol DMAc NMP DMF <![CDATA[CHCl3]]> Comparative Example 1 + + + + - Example 1 + + + + - Example 2 + + + + - Example 3 + + + + - Comparative Example 2 + + + + -

[0165] As shown in Table 2, the colorless and transparent polyamide-imide film prepared by the present invention has good solubility and can be dissolved in most aprotic polar organic solvents, and has good processability.

[0166] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A polyamide-imide polymer having the structure shown in Formula I; In Equation I, x and y are both integers, 25≤x≤500, and 50≤y≤750.

2. A method for preparing a polyamide-imide polymer, comprising the following steps: A) Under a protective atmosphere, 2,2'-bis(trifluoromethyl)diaminobenzidine monomer, aprotic polar solvent and 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer were mixed to obtain the first mixture. B) Mix the first mixture with terephthaloyl chloride in an ice-water bath and react at room temperature; C) Mix the system after the reaction in step B), the dehydration catalyst, and the imidizing agent to carry out a chemical imidization reaction; D) Mix the system after the reaction in step C) with a precipitant to precipitate, and obtain a polyamide-imide polymer with the structure shown in Formula I; In Equation I, x and y are both integers, 25≤x≤500, and 50≤y≤750.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 2,2'-bis(trifluoromethyl)diaminobenzidine monomer, 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer and terephthaloyl chloride is 1:0.1 to 1:0 to 0.9; and the molar amount of terephthaloyl chloride is not 0.

4. The preparation method according to claim 2, characterized in that, The aprotic polar solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide; The protective gas is nitrogen.

5. The preparation method according to claim 2, characterized in that, In step B), the reaction time is 10 to 14 hours.

6. The preparation method according to claim 2, characterized in that, The dehydration catalyst includes at least one of acetic anhydride, propionic anhydride, benzoic anhydride, and trifluoroacetic anhydride; the imidizing agent includes at least one of pyridine, methylpyridine, quinoline, and isoquinoline. The molar ratio of the dehydration catalyst, the imidizing agent, and the 5,5'-(1,4-phenylene)bis[hexahydro-4,7-methanolisobenzofuran-1,3-dione] anhydride monomer is 3-9:3-9:0.5-1.

5.

7. The preparation method according to claim 2, characterized in that, In step C), the chemical imidization reaction is carried out at room temperature for 10–14 hours.

8. The preparation method according to claim 2, characterized in that, In step D), the precipitant includes at least one of methanol, ethanol, isopropanol, and water.

9. A polyamide-imide film, wherein the polyamide-imide film is prepared from the polyamide-imide polymer of claim 1 or the polyamide-imide polymer prepared by any one of claims 2 to 8.

10. A method for preparing a polyamide-imide film, comprising the following steps: The casting solution is uniformly coated onto the substrate. After removing the solvent, the film is removed and dried to obtain a polyamide-imide film. The casting solution is obtained by mixing a polyamide-imide polymer and a proton-polar solvent; The polyamide-imide polymer is the polyamide-imide polymer according to claim 1 or the polyamide-imide polymer prepared by any one of claims 2 to 8.

11. The preparation method according to claim 10, characterized in that, The aprotic polar solvent includes N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, m-cresol, or dimethyl sulfoxide; The solid content of the casting solution is 5% to 20%; The method for removing the solvent is to remove it by heating. The heating method includes: First, raise the temperature to 50-80℃ and hold for 6-8 hours, then raise the temperature to 100-120℃ and hold for 1-2 hours, then raise the temperature to 150-170℃ and hold for 1-2 hours, then raise the temperature to 200-220℃ and hold for 1-2 hours, and finally raise the temperature to 250-270℃ and hold for 1-2 hours.

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