Process for preparing polyamic acid and polyamic acid

Abstract

The application discloses a polyamide acid preparation method and polyamide acid, and belongs to the high polymer material. The polyamide acid preparation method comprises the following steps: mixing a diamine monomer with a first solvent to form a first raw material solution in a water-free environment; adding a dianhydride monomer and a second solvent into the first raw material solution to obtain a second raw material solution at a temperature of 0-15 DEG C; and heating the second raw material solution to 15-50 DEG C to perform a reaction, and obtaining the polyamide acid after the reaction is completed. The molar ratio of the dianhydride monomer and the diamine monomer is 1:0.93-1.07. The raw material ratio and the preparation steps are improved in the embodiment of the application, the problems of wide polyamide acid molecular weight distribution, large viscosity and molecular weight fluctuation can be effectively improved, and the storage stability of the polyamide acid is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and particularly to a method for preparing polyamic acid and polyamic acid itself. Background Technology

[0002] Polyimide is a polymer with excellent comprehensive properties, including high temperature resistance, low temperature resistance, radiation resistance, mechanical properties, and dielectric properties. It is widely used in electronics, aerospace, machinery, military industry, and civilian materials.

[0003] The performance of polyimide materials is directly related to the quality of their precursor, polyamic acid, which is usually prepared by reacting dianhydride monomers and diamine monomers in an aprotic polar solvent at low temperature.

[0004] However, polyamic acids currently known to exist have problems such as a wide molecular weight distribution and large fluctuations in viscosity and molecular weight, resulting in poor storage stability. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing polyamic acid and polyamic acid, which can solve the above-mentioned technical problems.

[0006] Specifically, the following technical solutions are included:

[0007] On the one hand, a method for preparing polyamic acid is provided, the method comprising:

[0008] In an anhydrous environment, diamine monomers are mixed with a first solvent to form a first feed solution;

[0009] At a temperature of 0℃~15℃, a dianhydride monomer and a second solvent are added to the first raw material solution to obtain a second raw material solution;

[0010] The second raw material solution is heated to 15°C to 50°C for reaction. After the reaction is completed, the polyamic acid is obtained.

[0011] The molar ratio of the dianhydride monomer to the diamine monomer is 1:0.93 to 1.07.

[0012] In some possible implementations, the dianhydride monomer and the second solvent are added to the first feed solution at a temperature of less than or equal to 5°C to obtain the second feed solution.

[0013] In some possible implementations, the diamine monomer is added in batches by a reduction method, and after each addition of the diamine monomer, a predetermined amount of the first solvent is added for dissolution.

[0014] In some possible implementations, the dianhydride monomer is added in batches by a reduction method, and after each addition of the dianhydride monomer, a predetermined amount of the second solvent is added for dissolution.

[0015] In some possible implementations, the anhydrous environment is achieved by introducing nitrogen gas into the reaction system.

[0016] In some possible implementations, the chemical structural formula of the dianhydride monomer is shown below:

[0017]

[0018] Wherein, A includes at least one of a substituted or unsubstituted benzene ring or a heterocycle;

[0019] The chemical structural formula of the diamine monomer is shown below:

[0020]

[0021] Each of R1 independently includes at least one of a substituted or unsubstituted benzene ring or heterocycle.

[0022] On the other hand, a polyamic acid is provided, which is prepared by any of the methods described above.

[0023] In some possible implementations, the chemical structural formula of the polyamic acid is shown below:

[0024]

[0025] A and R1 each independently include at least one of a substituted or unsubstituted benzene ring or a heterocycle;

[0026] Wherein, when A and R1 each independently comprise a substituted or unsubstituted benzene ring, the amide group and carboxyl group are respectively connected to the carbon atom located at the para positivity on the benzene ring;

[0027] as well as,

[0028] When A and R1 each independently include two or more connected benzene rings, the position of the carbon atom connected to the current benzene ring and the adjacent benzene ring is taken as position 1.

[0029] For A, the amide group and the carboxyl group are respectively connected to any two adjacent carbon atoms at positions 2, 3, and 4 of the current benzene ring;

[0030] For R, the amide group is attached to any one of the carbon atoms at positions 2, 3, or 4 of the benzene ring.

[0031] In some possible implementations, the intrinsic viscosity of the polyamic acid is 1 dL / g to 1.5 dL / g.

[0032] In some possible implementations, the polyamic acid has a weight-average molecular weight of 80w to 120w and a molecular weight distribution index of 1 to 3.

[0033] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0034] The method for preparing polyamic acid provided in this invention controls the feeding temperature of the dianhydride monomers at 0°C to 15°C and the reaction temperature of the diamine monomers and dianhydride monomers at 15°C to 50°C, which is higher than the feeding temperature. This specific temperature control operation provides at least the following advantages for the preparation of polyamic acid: it enhances the reactivity of the diamine monomers and dianhydride monomers, making the reaction more complete and thorough, thus controlling the problem of an excessively wide molecular weight distribution of polyamic acid, i.e., it helps to reduce the molecular weight distribution index of polyamic acid, and also helps to obtain a higher reaction rate. Simultaneously, maintaining a molar ratio of dianhydride monomers to diamine monomers of 1:0.93 to 1.07 ensures that one of the dianhydride monomers and diamine monomers reacts as completely as possible while reducing the residue of the other, which helps to reduce viscosity and molecular weight fluctuations in polyamic acid. As can be seen, by improving the feeding temperature and reaction temperature (low-temperature feeding and high-temperature reaction) and controlling the raw material ratio, the embodiments of the present invention can effectively improve the problems of wide molecular weight distribution and large viscosity and molecular weight fluctuation of polyamic acid, thereby effectively improving the storage stability of polyamic acid. Attached Figure Description

[0035] Figure 1 The infrared spectrum of the polyamic acid prepared in Example 1 is provided as an embodiment of the present invention. Detailed Implementation

[0036] To make the technical solutions and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0037] On one hand, embodiments of the present invention provide a method for preparing polyamic acid, the method comprising:

[0038] Step 1: In an anhydrous environment, the diamine monomer is mixed with the first solvent to form the first raw material solution.

[0039] Step 2: At a temperature of 0℃ to 15℃, add dianhydride monomers and a second solvent to the first raw material solution to obtain the second raw material solution.

[0040] Step 3: Heat the second raw material liquid to 15℃~50℃ for reaction. After the reaction is complete, polyamic acid is obtained.

[0041] It should be noted that, before the reaction, the second raw material liquid is heated, which means that the reaction temperature of the second raw material liquid is greater than the feeding temperature of the second raw material liquid. That is, the special feature of this embodiment of the invention is low temperature feeding + high temperature reaction.

[0042] The molar ratio of dianhydride monomers to diamine monomers is 1:0.93 to 1.07, for example, including but not limited to: 1:0.93, 1:0.94, 1:0.95, 1:0.96, 1:0.97, 1:0.98, 1:0.99, 1:1, 1:1.02, 1:1.03, 1:1.04, 1:1.05, etc.

[0043] The method for preparing polyamic acid provided in this invention controls the feeding temperature of the dianhydride monomers at 0°C to 15°C and the reaction temperature of the diamine monomers and dianhydride monomers at 15°C to 50°C, which is higher than the feeding temperature. This specific temperature control operation provides at least the following advantages for the preparation of polyamic acid: it enhances the reactivity of the diamine monomers and dianhydride monomers, making the reaction more complete and thorough, thus controlling the problem of an excessively wide molecular weight distribution of polyamic acid, i.e., it helps to reduce the molecular weight distribution index of polyamic acid, and also helps to obtain a higher reaction rate. Simultaneously, maintaining a molar ratio of dianhydride monomers to diamine monomers of 1:0.93 to 1.07 ensures that one of the dianhydride monomers and diamine monomers reacts as completely as possible while reducing the residue of the other, which helps to reduce viscosity and molecular weight fluctuations in polyamic acid. As can be seen, by improving the feeding temperature and reaction temperature (low-temperature feeding and high-temperature reaction) and controlling the raw material ratio, the embodiments of the present invention can effectively improve the problems of wide molecular weight distribution and large viscosity and molecular weight fluctuation of polyamic acid, thereby effectively improving the storage stability of polyamic acid.

[0044] The following are exemplary descriptions of each step involved in the preparation method of this polyamic acid:

[0045] For step 1, in an anhydrous environment, the diamine monomer is mixed with the first solvent to form the first raw material liquid.

[0046] In some examples, a reaction vessel is provided, which is cleaned with a cleaning solvent such as acetone, and then dried in an oven (e.g., at a temperature of 60°C to 80°C for 1 to 2 hours).

[0047] Then, nitrogen gas is introduced into the cleaned reaction vessel for 10 to 120 minutes, with the nitrogen flow rate controlled at 0.1 L / min to 1.0 L / min, for example, 0.7 L / min to 1.0 L / min. This creates an anhydrous environment inside the reaction vessel to prevent moisture from interfering with the subsequent reaction process. This is because the presence of moisture can cause the hydrolysis of dianhydride monomers, affecting the polymerization reaction between dianhydride monomers and diamine monomers.

[0048] Further, the nitrogen flow rate is adjusted to 0.1 L / min to 0.8 L / min, and diamine monomers and the first solvent are added to the reaction vessel. The nitrogen flow rate is appropriately reduced to prevent the first solvent from being dispersed.

[0049] For example, the first solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and dimethyl sulfoxide.

[0050] In some examples, diamine monomers are added in batches using a reduction method, with a predetermined amount of the first solvent added after each addition for dissolution. By using the reduction method to add diamine monomers, errors in the amount of diamine and dianhydride monomers can be reduced, thereby achieving precise control over the ratio of diamine and dianhydride monomers.

[0051] Correspondingly, the first solvent is also added in batches by a reduction method, with each addition of the first solvent being an equal part of the batch, such as 1 / 4, 1 / 3, 1 / 2, etc.

[0052] Once the diamine monomer and the first solvent are mixed evenly by stirring, the first raw material solution is formed.

[0053] For step 2, at a temperature of 0℃ to 15℃, dianhydride monomers and a second solvent are added to the first raw material solution to obtain the second raw material solution.

[0054] In some examples, a dianhydride monomer and a second solvent are added to a first feed solution at a temperature of 5°C or less to obtain a second feed solution. Studies have found that controlling the temperature at which the dianhydride monomer is added to be 5°C or less can significantly improve the problem of an excessively wide molecular weight distribution index in polyamic acid.

[0055] For example, the reaction vessel containing the first raw material liquid can be placed in an ice bath to control the temperature of the first raw material liquid between 0°C and 5°C, for example, below 0°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, etc.

[0056] Then, at 0℃~5℃, dianhydride monomers and a second solvent are added to the reaction vessel and stirred until homogeneous to obtain a low-temperature, homogeneous second raw material solution.

[0057] In some examples, after the feed is fully added, the ice bath can be maintained for a certain period of time, such as 30 to 60 minutes, so that the temperature of the second feed liquid is always kept below or equal to 5°C. This setting helps to enhance the activity of the reactants in the subsequent polymerization reaction, making the polymerization reaction more complete and ultimately reducing the viscosity of polyamic acid and improving its molecular weight fluctuation.

[0058] For example, the second solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and dimethyl sulfoxide. Further, the second solvent may be the same as the first solvent.

[0059] In some examples, dianhydride monomers are added in batches using a decreasing method, with a predetermined amount of a second solvent added after each addition for dissolution. By using this decreasing method, errors in the feed amount can be reduced, allowing for precise control of the feed ratio of diamine and dianhydride monomers. Correspondingly, the second solvent is also added in batches using a decreasing method, with each addition being an equal portion of the added batch, such as 1 / 4, 1 / 3, 1 / 2, etc.

[0060] For step 3, the second raw material liquid is heated to 15℃~50℃ to carry out the reaction. After the reaction is completed, polyamic acid is obtained.

[0061] After the second raw material liquid is stirred evenly, the ice bath can be removed, and an oil bath can be used to heat the reaction vessel to 15℃~50℃, and the reaction can be carried out under stirring conditions.

[0062] Furthermore, the reaction temperature is set to 25℃~50℃, for example, the reaction temperature includes but is not limited to 20℃, 25℃, 28℃, 30℃, 32℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 47℃, etc., so that the reaction between the diamine and the dianhydride is more complete and thorough, thereby preparing polyamic acid.

[0063] The reaction time can be controlled to be more than 8 hours, for example, 8 to 24 hours. After the reaction is completed, the air bubbles in the product system are removed by depressurization to prevent them from affecting the viscosity test of polyamic acid, and then the polyamic acid can be discharged.

[0064] The preparation method of polyamic acid provided in this invention, wherein the chemical structural formulas of the dianhydride monomers involved are as follows:

[0065]

[0066] Wherein, the A group includes at least one of the substituted or unsubstituted benzene rings or heterocycles, that is, the A group may include (1) one or more benzene rings, (2) one or more heterocycles, and (3) both benzene rings and hybridizations, and the number of benzene rings and hybridizations may be one or more.

[0067] When there are multiple benzene rings in group A, or multiple heterocycles, or multiple benzene rings and heterocycles, benzene rings can be connected to each other, or heterocycles can be connected to each other, or benzene rings can be connected to each other through fusion, non-fusion (chemical bonding), or a combination of fusion and non-fusion.

[0068] The aforementioned non-fused methods include single-bond connections and connections through at least one atom, such as C, O, sulfone, or carbonyl groups.

[0069] The chemical structural formulas of the above-mentioned diamine monomers can be found below:

[0070]

[0071] Wherein, the R1 group is substituted or unsubstituted with at least one of the benzene rings or heterocycles, that is, the R1 group may include (1) one or more benzene rings, (2) one or more heterocycles, and (3) both benzene rings and hybridization, and the number of benzene rings and hybridization can be one or more. When the number of benzene rings in the R1 group is multiple, or the number of heterocycles is multiple, or the number of benzene rings and heterocycles is multiple, the benzene rings and benzene rings, or heterocycles and heterocycles can be connected by fusion, non-fusion, or a combination of fusion and non-fusion. For the above non-fusion, it includes connection by single bond, or connection by at least one atom, such as C, O, sulfone, or carbonyl.

[0072] In some examples, when the benzene ring and heterocycle contain substituents, the substituents include at least one of halogen, methyl, and trifluoromethyl (CF3).

[0073] For example, the chemical structural formula of group A can be as follows:

[0074]

[0075]

[0076]

[0077] For example, the chemical structure of the R1 group can be as follows:

[0078]

[0079]

[0080]

[0081] Another method, according to embodiments of the present invention, is a polyamic acid prepared by any of the polyamic acid preparation methods described above.

[0082] The polyamic acid provided in this invention, based on the above preparation method, has a narrower molecular weight distribution, significantly improved viscosity and molecular weight fluctuations, and thus achieves excellent storage stability.

[0083] In some examples, the chemical structural formula of this polyamic acid is shown below:

[0084]

[0085] In this configuration, A and R1 each independently include at least one substituted or unsubstituted benzene ring or heterocycle. When there are multiple benzene rings in A and R1, or multiple heterocycles, or multiple benzene rings and heterocycles, the benzene rings can be connected to each other, or the heterocycles can be connected to each other, or the two can be combined in a fused manner. For the aforementioned non-fused manner, this includes connection by a single bond, or connection by at least one atom, such as a C, O, sulfone, or carbonyl group.

[0086] In some examples, when the benzene ring and heterocycle contain substituents, the substituents include at least one of halogens, methyl groups, and trifluoromethyl (CF3). All of these types of substituents allow polyamic acid to retain the aforementioned advantages.

[0087] In some examples, when A and R1 each independently comprise a substituted or unsubstituted benzene ring, the amide group and carboxyl group are respectively attached to carbon atoms at symmetrical substitution positions on the benzene ring. In other words, the amide group and carboxyl group are distributed at symmetrical substitution positions on the benzene ring.

[0088] In some examples, when A and R1 each independently comprise two or more connected benzene rings, the position of the carbon atom in the current benzene ring connected to an adjacent benzene ring is designated as position 1. For A, the amide group and carboxyl group are connected to any two adjacent carbon atoms at positions 2, 3, and 4 of the current benzene ring, respectively; for R, the amide group is connected to any carbon atom at positions 2, 3, and 4 of the benzene ring in which it resides, and the benzene ring in this case is the one to which the amide group is connected.

[0089] For example, the chemical structure of group A can be shown below, where * represents the binding site of group A with the amide group ~CONH~, and *` represents the binding site of group A with the carboxyl group:

[0090]

[0091]

[0092]

[0093] For example, the chemical structure of the R1 group can be as follows, where * indicates the binding site between the R1 group and the amide group ~CONH~:

[0094]

[0095]

[0096]

[0097] In some examples, the intrinsic viscosity of the polyamic acid provided in the embodiments of the present invention is 1 dL / g to 1.5 dL / g, for example, 1 dL / g, 1.1 dL / g, 1.2 dL / g, 1.3 dL / g, 1.4 dL / g, 1.5 dL / g, etc. The intrinsic viscosity of the polyamic acid within the above range not only gives it sufficient modulus, elongation at break, and mechanical properties, but also makes the polyamic acid have good flowability.

[0098] Studies have found that when the weight-average molecular weight of polyamic acid is low, there may be incomplete reaction, and its mechanical properties, such as elongation at break and modulus, may not meet the requirements. When the weight-average molecular weight of polyamic acid is too high, it may result in poor flowability.

[0099] When the molecular weight distribution index of polyamic acid is too wide, there may be unreacted raw materials or chain segments. This will not only have an adverse effect on the storage stability of polyamic acid, but the increase in the proportion of these small molecular segments will also cause the fluctuation range of the molecular weight and viscosity of polyamic acid to increase, which in turn will cause large fluctuations in the mechanical properties of polyimide such as modulus and elongation at break.

[0100] To overcome the above-mentioned technical problems, the polyamic acid provided in the embodiments of the present invention has a weight-average molecular weight of 80w to 120w, such as 80w, 85w, 90w, 95w, 100w, 105w, 110w, 115w, 120w, etc., and a molecular weight distribution index of 1 to 3. The weight-average molecular weight and molecular weight distribution index of the polyamic acid are within the above range, so that it has both excellent mechanical properties and flowability.

[0101] The polyamic acid provided in this invention can be used to prepare polyimide resins with excellent comprehensive properties, and is suitable for fields such as optical fiber coating, flexible electronics, aerospace, mechanical materials, and photoresist materials.

[0102] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0103] Example 1

[0104] Example 1 provides a polyamic acid, which is prepared by the following method:

[0105] A reaction vessel was provided and cleaned with acetone, then dried in an oven at 80°C for 2 hours. Nitrogen gas was then introduced into the cleaned reaction vessel for 60 minutes at a flow rate of 1.0 L / min to create an anhydrous environment. The nitrogen flow rate was then adjusted to 0.5 L / min, and 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, stirring thoroughly until the 4,4'-diaminodiphenyl ether was completely dissolved to form the first feedstock solution.

[0106] The reaction vessel containing the first raw material solution was placed in an ice bath to maintain its temperature below 5°C. Biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, and the mixture was stirred thoroughly to obtain a low-temperature, homogeneous second raw material solution. The molar ratio of biphenyltetracarboxylic dianhydride to 4,4'-diaminodiphenyl ether was 1:1.045. After complete addition, the reaction vessel was kept in the ice bath for another 40 minutes.

[0107] Remove the ice bath and use an oil bath to heat the reaction vessel to 30°C for the reaction. Increase the stirring speed and, under stirring conditions, allow 4,4'-diaminodiphenyl ether to react with biphenyltetracarboxylic dianhydride for 18 hours. After the reaction is complete, remove air bubbles under reduced pressure to obtain polyamic acid.

[0108] Figure 1 The infrared spectrum of the polyamic acid prepared in Example 1 is shown below. Figure 1 It can be seen that 4,4'-diaminodiphenyl ether reacted fully and effectively with biphenyltetracarboxylic dianhydride.

[0109] Example 2

[0110] Example 2 provides a polyamic acid, which is prepared by the following method:

[0111] A reaction vessel was provided and cleaned with acetone, then dried in an oven at 80°C for 2 hours. Nitrogen gas was then introduced into the cleaned reaction vessel for 60 minutes at a flow rate of 1.0 L / min to create an anhydrous environment. The nitrogen flow rate was then adjusted to 0.5 L / min, and 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, stirring thoroughly until the 4,4'-diaminodiphenyl ether was completely dissolved to form the first feedstock solution.

[0112] The reaction vessel containing the first raw material solution was placed in an ice bath to maintain its temperature below 5°C. Biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, and the mixture was stirred thoroughly to obtain a low-temperature, homogeneous second raw material solution. The molar ratio of biphenyltetracarboxylic dianhydride to 4,4'-diaminodiphenyl ether was 1:1.05. After complete addition, the reaction vessel was kept in the ice bath for another 40 minutes.

[0113] Remove the ice bath and use an oil bath to heat the reaction vessel to 35°C for the reaction. Increase the stirring speed and, under stirring conditions, allow 4,4'-diaminodiphenyl ether to react with biphenyltetracarboxylic dianhydride for 18 hours. After the reaction is complete, remove air bubbles under reduced pressure to obtain polyamic acid.

[0114] Example 3

[0115] Example 3 provides a polyamic acid, which is prepared by the following method:

[0116] A reaction vessel was provided and cleaned with acetone, then dried in an oven at 80°C for 2 hours. Nitrogen gas was then introduced into the cleaned reaction vessel for 60 minutes at a flow rate of 1.0 L / min to create an anhydrous environment. The nitrogen flow rate was then adjusted to 0.5 L / min, and 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, stirring thoroughly until the 4,4'-diaminodiphenyl ether was completely dissolved to form the first feedstock solution.

[0117] The reaction vessel containing the first raw material solution was placed in an ice bath to maintain its temperature below 5°C. Then, biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, and the mixture was stirred until homogeneous, resulting in a low-temperature, homogeneous second raw material solution. The molar ratio of biphenyltetracarboxylic dianhydride to 4,4'-diaminodiphenyl ether was 1:0.97. After complete addition, the reaction vessel was kept in the ice bath for another 40 minutes.

[0118] Remove the ice bath and use an oil bath to heat the reaction vessel to 40°C for the reaction. Increase the stirring speed and, under stirring conditions, allow the biphenyl tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether to react for 20 hours. After the reaction is complete, remove the bubbles under reduced pressure to obtain polyamic acid.

[0119] Example 4

[0120] Example 4 provides a polyamic acid, which is prepared by the following method:

[0121] A reaction vessel was provided and cleaned with acetone, then dried in an oven at 80°C for 2 hours. Nitrogen gas was then introduced into the cleaned reaction vessel for 60 minutes at a flow rate of 1.0 L / min to create an anhydrous environment. The nitrogen flow rate was then adjusted to 0.5 L / min, and 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, stirring thoroughly until the 4,4'-diaminodiphenyl ether was completely dissolved to form the first feedstock solution.

[0122] The reaction vessel containing the first raw material solution was placed in an ice bath to maintain its temperature below 5°C. Then, pyromellitic dianhydride and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, and the mixture was stirred thoroughly to obtain a low-temperature, homogeneous second raw material solution. The molar ratio of pyromellitic dianhydride to 4,4'-diaminodiphenyl ether was 1:1.045. After complete addition, the reaction vessel was kept in the ice bath for another 40 minutes.

[0123] Remove the ice bath and use an oil bath to heat the reaction vessel to 40°C for the reaction. Increase the stirring speed and, under stirring conditions, allow the biphenyl tetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether to react for 20 hours. After the reaction is complete, remove the bubbles under reduced pressure to obtain polyamic acid.

[0124] Comparative Example 1

[0125] A reaction vessel was provided and cleaned with acetone, then dried in an oven at 80°C for 2 hours. Nitrogen gas was then introduced into the cleaned reaction vessel for 60 minutes, with the nitrogen flow rate controlled at 1.0, creating an anhydrous environment inside the vessel. The nitrogen flow rate was then adjusted to 0.5, and 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide were added to the reaction vessel in one step. The mixture was stirred until the 4,4'-diaminodiphenyl ether was completely dissolved, forming the first feedstock solution.

[0126] Then, biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method at 40°C, and stirred until homogeneous to obtain the second feed solution. The molar ratio of biphenyltetracarboxylic dianhydride to 4,4'-diaminodiphenyl ether was 1:1.1, and the reaction was carried out at 40°C for 18 hours. After the reaction was complete, bubbles were removed under reduced pressure to obtain polyamic acid.

[0127] Comparative Example 2

[0128] A reaction vessel was provided and cleaned with acetone, then dried in an oven at 80°C for 2 hours. Nitrogen gas was then introduced into the cleaned reaction vessel for 60 minutes, with the nitrogen flow rate controlled at 1.0, creating an anhydrous environment inside the vessel. The nitrogen flow rate was then adjusted to 0.5, and 4,4'-diaminodiphenyl ether and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method, stirring thoroughly until the 4,4'-diaminodiphenyl ether was completely dissolved to form the first feedstock solution.

[0129] Then, biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide were added to the reaction vessel in batches using a decreasing method at room temperature (above 15°C and less than or equal to 25°C), and stirred until homogeneous to obtain the second feed solution. The molar ratio of biphenyltetracarboxylic dianhydride to 4,4'-diaminodiphenyl ether was 1:1.045, and the reaction was carried out at 30°C for 18 hours. After the reaction was complete, bubbles were removed under reduced pressure to obtain polyamic acid.

[0130] Test case

[0131] The properties of the polyamic acids provided in Examples 1 to 4, and Comparative Examples 1 to 2, were measured using test examples, as detailed below:

[0132] (1) The viscosity of polyimide acid was determined by the Grignard tube method, and the intrinsic viscosity was further calculated based on the viscosity.

[0133] (2) The weight-average molecular weight and molecular weight distribution of polyamic acid were determined by gel permeation chromatography.

[0134] (3) Mix polyamic acid with N,N-dimethylacetamide (the mass concentration of polyamic acid is 20%) to obtain the sample to be tested, and then measure the apparent viscosity of the sample to be tested using a rotational viscometer.

[0135] (4) Place the above-mentioned test samples in different time periods, and then use a rotational viscometer to test the apparent viscosity at different time periods in order to track storage stability.

[0136] (5) Curing polyamic acid into a film to form a polyimide film sample, and using a universal tensile testing machine to test the modulus and elongation at break of the polyimide film sample.

[0137] The polyimide film samples were prepared as follows: Polyamic acid was slowly poured onto the top of a tinplate, and a film scraper was used to slowly and uniformly scrape the polyamic acid into a film. The film was then placed in an oven at 150°C for 5-10 minutes to remove the solvent. Imidization treatment was then performed in a muffle furnace (150°C for 1 hour, 250°C for 1 hour, 350°C for 1 hour, and 400°C for 1 hour). During imidization, nitrogen gas was slowly introduced, with the nitrogen level maintained at 0.5-1 liters, thus obtaining the polyimide film. The polyimide film was then cut into 5cm wide strips using a scalpel at a defect-free location to obtain the polyimide film samples.

[0138] The characteristic parameters of the polyamic acid provided in Examples 1 to 4, and Comparative Examples 1 to 2 are shown in Table 1:

[0139] Table 1

[0140]

[0141] Table 2 shows some characteristic parameters of the polyamic acid provided in Example 1 and Comparative Examples 1-2 during multiple batch synthesis. Here, "multiple batches" refers to multiple preparation processes performed according to the same preparation method.

[0142] Table 2

[0143]

[0144] The apparent viscosity and mechanical properties of the polyamic acid provided in Example 1 and Comparative Example 2 after being left for different time periods are shown in Tables 3 and 4, respectively.

[0145] Table 3

[0146]

[0147] Table 4

[0148]

[0149] As shown in Tables 1 to 4, compared with Comparative Example 1, the molecular weight distribution index of polyamic acid in Example 1 was reduced, and the modulus and elongation at break were significantly improved. The intrinsic viscosity, molecular weight and molecular weight distribution fluctuations were also smaller.

[0150] Compared to Comparative Example 2, the polyamic acid in Example 1 exhibits a significantly reduced molecular weight distribution index, and its intrinsic viscosity, molecular weight, and molecular weight distribution fluctuations are significantly reduced. Moreover, after 150 days of storage, the polyamic acid in Comparative Example 2 shows a decrease rate of over 20% in its intrinsic viscosity, modulus, and elongation at break, far exceeding that of the polyamic acid in Example 1. Therefore, the polyamic acid provided in Example 1 demonstrates superior storage stability.

[0151] The above description is merely for the purpose of enabling those skilled in the art to understand the technical solutions of the present invention, and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing polyamic acid, characterized in that, The method for preparing the polyamic acid includes: In an anhydrous environment, diamine monomers are mixed with a first solvent to form a first feed solution; The reaction vessel containing the first raw material solution was placed in an ice bath. At a temperature of 0°C to 5°C, a dianhydride monomer and a second solvent were added to the first raw material solution to obtain the second raw material solution. After the addition was complete, the ice bath was maintained so that the temperature of the second raw material solution was always kept below 5°C. The second raw material solution is heated to 15°C~50°C for reaction. After the reaction is completed, the polyamic acid is obtained. The molar ratio of the dianhydride monomer to the diamine monomer is 1:0.93~1.

07.

2. The method for preparing polyamic acid according to claim 1, characterized in that, The diamine monomer is added in batches by a reduction method, and after each addition of the diamine monomer, a set amount of the first solvent is added for dissolution.

3. The method for preparing polyamic acid according to claim 1, characterized in that, The dianhydride monomers are added in batches using a reduction method, and after each addition of the dianhydride monomers, a set amount of the second solvent is added for dissolution.

4. The method for preparing polyamic acid according to claim 1, characterized in that, The anhydrous environment is achieved by introducing nitrogen gas into the reaction system.

5. The method for preparing polyamic acid according to any one of claims 1 to 4, characterized in that, The chemical structural formula of the dianhydride monomer is shown below: ； Wherein, A includes at least one of a substituted or unsubstituted benzene ring or a heterocycle; The chemical structural formula of the diamine monomer is shown below: ； Each of R1 independently includes at least one of a substituted or unsubstituted benzene ring or heterocycle.

6. The method for preparing polyamic acid according to claim 5, characterized in that, The chemical structural formula of the polyamic acid is shown below: ； A and R1 each independently include at least one of a substituted or unsubstituted benzene ring or a heterocycle; Wherein, when A and R1 each independently comprise a substituted or unsubstituted benzene ring, the amide group and carboxyl group are respectively connected to the carbon atom located at the para positivity on the benzene ring; as well as, When A and R1 each independently include two or more connected benzene rings, the position of the carbon atom connected to the current benzene ring and the adjacent benzene ring is taken as position 1. For A, the amide group and the carboxyl group are respectively connected to any two adjacent carbon atoms at positions 2, 3, and 4 of the current benzene ring; For R, the amide group is attached to any one of the carbon atoms at positions 2, 3, or 4 of the benzene ring.

7. The method for preparing polyamic acid according to claim 6, characterized in that, The intrinsic viscosity of the polyamic acid is 1 dL / g to 1.5 dL / g.

8. The method for preparing polyamic acid according to claim 6, characterized in that, The polyamic acid has a weight-average molecular weight of 80w to 120w and a molecular weight distribution index of 1 to 3.

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