Functional polyamide acid slurry and preparation method thereof

Abstract

The invention provides functional polyamide acid slurry and a preparation method thereof. The preparation method of the functional polyamide acid slurry comprises the following steps: mixing a solvent, polyphosphoric acid and diamine, adding dianhydride, and reacting to obtain the functional polyamide acid slurry, wherein at least one of diamine and dianhydride contains an aromatic heterocyclic structure. The functional polyamide acid slurry provided by the invention is prepared by the preparation method. According to the preparation method, the contradictory relationship among the solid content, the viscosity and the surface tension can be balanced, and the functional polyamide acid slurry with good stability and film-forming property is prepared.

Description

Technical Field

[0001] This invention belongs to the field of polyimide synthesis technology, and specifically relates to a functional polyamic acid slurry and its preparation method. Background Technology

[0002] Polyimide is a heterocyclic polymer (R-CO-NH-CO-R') containing imide groups in its molecular structure. It possesses excellent mechanical properties, resistance to high and low temperatures, acid and alkali resistance, and biocompatibility, and is widely used in electronics, aerospace, and flexible displays in the form of films, fibers, and composite materials. Polyimide is typically prepared via a two-step process: first, an ammonium slurry is obtained by polymerizing an aromatic dianhydride and a diamine in an aprotic polar solvent; then, the slurry undergoes dehydration and cyclization via thermal or chemical methods to obtain the final polyimide. Therefore, the properties of the ammonium slurry determine the quality of the final product.

[0003] When applied in spraying, casting, and spinning, the solid content and kinetic viscosity of polyamic acid slurries are crucial factors affecting processability. Polyamic acid molecules readily form numerous hydrogen bonds within and between molecular chains, and the ionization of carboxylic acid groups enhances the polyelectrolyte effect. Therefore, slurries with high solid content typically have very high kinetic viscosity, sometimes even leading to gelation. Reducing the solid content can lower the kinetic viscosity to some extent, but this increases solvent consumption and production costs, reducing production efficiency. Current methods to address the poor flowability of slurries with high solid content mainly include: controlling the water content of the reaction system (CN101558102A), introducing esterification products of acid anhydrides as comonomers (CN106589371A), adding polysiloxane-based (CN104292459A) thickeners, and using ammonium carboxylate surfactants (CN112409612A, CN111808285A). However, these methods may suffer from poor controllability, complex operation, and high additive content.

[0004] Furthermore, although polyimide products come in various forms, thin films account for the largest share (over 80%), being the earliest commercialized and most widely used product form. The performance of the polyamic acid slurry is a key factor affecting the film-forming properties of polyimide on a substrate. The lower the surface tension of the slurry, the smaller the contact angle on the substrate, the better the wetting effect, and the better the film-forming properties. Most polyamic acid slurries have a surface tension of 50-65 mN / m, which is mainly controlled by adding low surface tension solvents and surfactants. This approach has drawbacks such as poor environmental friendliness, complex composition and processes, difficulty in controlling overall performance, and increased costs. The solid content of the polyamic acid slurry is one of the indicators for film-forming properties. The lower the solid content and the higher the solvent content, the lower the surface tension of the polyamic acid. However, polyamic acid slurries with excessively low solid content can also lead to poor polyimide film-forming properties, thus affecting the thermal and mechanical properties of the polyimide film. Conversely, slurries with high solid content have high viscosity, which also affects film formation and processing.

[0005] CN117164853A discloses a method for preparing low-viscosity polyamic acid slurry and polyimide products. The method involves reacting a monocarboxylic anhydride with the amino groups in a portion of a diamine monomer to generate a monoamino amide, which then reacts with a dianhydride. This results in the polyamic acid molecular chain having amide and anhydride groups at its end groups, thus controlling the molecular chain length and ultimately regulating the viscosity of the polyamic acid slurry. During the subsequent imidization process, the terminal amide and anhydride groups react, further increasing the polyimide molecular chain length and molecular weight, thereby improving the performance of the polyimide product. Simultaneously, the generated monocarboxylic anhydride volatilizes and is eliminated at high temperatures. However, the reaction efficiency between the monoamino amide and the dianhydride is reduced, the product has poor controllability, and the high viscosity problem of the system at high solids content is not fundamentally solved.

[0006] CN115974067A discloses a pyridine ring-modified polyimide high thermal conductivity graphite film and its preparation method. This pyridine ring-modified polyimide high thermal conductivity graphite film is prepared from diamine and dianhydride; the diamine contains all or part of a pyridine structure, and the dianhydride contains all or part of a pyridine structure, and at least one raw material contains a pyridine structure. By introducing an appropriate amount of pyridine structure into the PI backbone to form an intrinsic PI resin, the pyridine structure has a self-catalytic effect, which is beneficial for forming a planar PI framework, further inducing the graphite film to form an ordered, well-defined, and highly crystalline layered structure, improving the thermal conductivity of the graphite film, and simultaneously reducing the carbonization and graphitization temperature, which is beneficial for reducing energy consumption and saving energy. Although this technology obtains PI through a two-step method, the process does not involve the design and control of the molecular weight and viscosity of the intermediate PAA slurry, while the slurry properties directly affect various aspects of the film product's properties.

[0007] CN112500570A discloses a flexible display device and a polyamic acid varnish and polyimide film for displays. The flexible display device includes a flexible substrate and a display unit. The flexible substrate includes a polyimide film formed from a polyamic acid varnish. The polyamic acid varnish includes a polar organic solvent and polyamic acid, and the surface tension of the polyamic acid varnish is 30-50 mN / m. This polyamic acid varnish has good wetting properties with the glass substrate, is easy to process into a film, and the formed PI film has a low coefficient of thermal expansion, making it suitable for flexible displays. Although this technology obtains PI through a two-step method, the process does not involve the viscosity design and control of the intermediate PAA slurry, and the amount of end-capping agent used is large.

[0008] CN105461926A discloses an environmentally friendly stable polyamic acid solution and its preparation method. The method involves taking a tertiary amine, an aromatic primary amine, a directional dianhydride, an aromatic diamine, and water. The weighed tertiary amine is divided into two portions, A and B. Under certain conditions, water and the aromatic primary amine are added to a three-necked flask. Tertiary amine A and the aromatic diamine are then added to the three-necked flask for reaction. The reaction solution is heated, and the aromatic dianhydride is added and stirred. The temperature of the reaction solution is then lowered, and tertiary amine B is added and stirred. The reaction solution is then cooled and allowed to stand to obtain a polyamic acid solution. This technology uses many additives and involves complex operating steps.

[0009] CN108929438A discloses a method for preparing polyamic acid and a method for preparing polyimide from polyamic acid. An aromatic diamine, an aromatic diacid anhydride, and a dispersant are added to one or more solvents selected from aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ethers, and esters. The mixture is heated and kept at a constant temperature under the action of a catalyst to carry out a polycondensation reaction, generating a suspension containing solid polyamic acid. The catalyst is selected from one or more of tripolyphosphate, tributyl phosphate, triphenyl phosphite, polyphosphoric acid, and ω-aminohexanoic acid, and the mass of the catalyst is 0.5-1.8 wt% of the sum of the masses of the aromatic diamine and the aromatic diacid anhydride. The dispersant includes one or more of triethylhexylphosphonic acid, 1-methylpentanol, hydroxypropyl cellulose, and glucon. This technology requires a catalyst, has complex operating steps, and does not address the adjustment and optimization of the polyamic acid solution viscosity.

[0010] Therefore, how to balance the contradictory relationship between solid content, viscosity, and surface tension, and how to obtain polyamic acid slurry with excellent performance and simple system has become one of the urgent problems to be solved in this field. Summary of the Invention

[0011] To address the aforementioned technical problems, the present invention aims to provide a functional polyamic acid slurry and a polyimide film, as well as a method for preparing the same. The present invention balances the contradictory relationships between solid content, viscosity, and surface tension, enabling the preparation of a functional polyamic acid slurry with good stability and film-forming properties.

[0012] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a functional polyamic acid slurry, comprising the following steps:

[0013] (I) Mix the solvent, polyphosphoric acid and diamine to obtain a mixed system;

[0014] (II) Add the dianhydride to the mixture obtained in step (I) to obtain a reaction system, and after the reaction system reacts, the functional polyamic acid slurry is obtained;

[0015] The diamine may or may not contain an aromatic heterocyclic structure, the dianhydride may or may not contain an aromatic heterocyclic structure, and at least one of the diamine and the dianhydride contains an aromatic heterocyclic structure.

[0016] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, based on the amount of solvent used being 100% by mass, the amount of polyphosphoric acid added is 0.2-1% by mass.

[0017] In the above-described method for preparing functional polyamic acid slurry, preferably, the solvent comprises an aprotic polar solvent. More preferably, the solvent comprises one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0018] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the aromatic heterocyclic structure includes one or a combination of several of pyridine, pyrazine, furan, imidazole and oxazole.

[0019] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the diamine includes one or a combination of several of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,6-diaminopyridine, 2,5-furandimethylamine, 2-(3-aminophenyl)-5-aminobenzimidazole and 2-(4-aminophenyl)-5-aminobenzoxazole.

[0020] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the dianhydride includes one or a combination of several of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,6-bis(3,3',4,4'-diphenylanhydroxy)pyrazine.

[0021] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the molar ratio of the diamine and the dianhydride is 1:(0.995-1.005).

[0022] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the total mass of the diamine and the dianhydride accounts for 10-30% of the total mass of the reaction system.

[0023] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the system temperature in steps (I) and (II) is -15 to 30°C.

[0024] In the above-mentioned method for preparing functional polyamic acid slurry, preferably, the reaction time in step (II) is 1-8 hours.

[0025] A second aspect of the present invention provides a functional polyamic acid slurry, which is prepared by the above-described method for preparing functional polyamic acid slurry.

[0026] This invention provides a functional polyamic acid slurry and its preparation method. This invention overcomes the problem in existing technologies where high solids content leads to high kinetic viscosity, resulting in poor film-forming properties and processability of polyimide films. This invention balances the contradictory relationships between solids content, viscosity, and surface tension, achieving both high solids content and high viscosity while maintaining low surface tension in the polyamic acid slurry. Furthermore, this invention reduces the viscosity of the slurry and improves its storage stability. Therefore, this invention can prepare a functional polyamic acid slurry with high solids content, low kinetic viscosity, good stability, and good film-forming properties. Moreover, the polyamic acid slurry of this invention has advantages such as a relatively simple system, low additive content, simple preparation process, and high controllability.

[0027] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0028] 1. The functional polyamic acid slurry of the present invention exhibits improved film-forming properties. The aromatic heterocyclic structure in the monomer raw material of the present invention contains nitrogen and / or oxygen atoms. The present invention unexpectedly discovered that these heteroatoms can reduce the surface tension of the slurry and improve film-forming stability. Furthermore, the aromatic heterocyclic structure can enhance the electron transfer effect within and between molecular chains, thereby improving the thermal properties of polyamic acid.

[0029] 2. The functional polyamic acid slurry of the present invention exhibits reduced kinetic viscosity. The present invention creatively incorporates polyphosphoric acid into the reaction system. Polyphosphoric acid undergoes a hydrolysis reaction with water in the system, generating free hydrogen ions that weaken the hydrogen bonding between and within polyamic acid molecules, thus shielding the polyelectrolyte effect of polyamic acid and significantly reducing the kinetic viscosity of the system. Simultaneously, the aromatic heterocyclic structure contained in the monomer raw materials of the present invention can induce a planar molecular weight configuration, reducing intra- and inter-chain entanglement, which is beneficial for reducing the slurry viscosity. Therefore, the present invention achieves the effect of reducing the kinetic viscosity of the slurry through the synergistic effect of polyphosphoric acid and monomer raw materials containing aromatic heterocyclic structures.

[0030] 3. The functional polyamic acid slurry of the present invention exhibits improved storage stability. The polyphosphoric acid added to the reaction system in this invention can undergo a hydrolysis reaction with water in the system, maintaining a low water content, slowing down the degradation of polyamic acid, and improving the stability of the slurry. Attached Figure Description

[0031] Figure 1 The graph shows the intrinsic viscosity of the functional polyamic acid slurry in Example 2 as a function of time. Detailed Implementation

[0032] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0033] According to a specific embodiment of the present invention, a first aspect of the present invention provides a method for preparing a functional polyamic acid slurry, which includes the following steps:

[0034] (I) Mix the solvent, polyphosphoric acid and diamine to obtain a mixed system;

[0035] (II) Add the dianhydride to the mixture obtained in step (I) to obtain a reaction system, and after the reaction system reacts, the functional polyamic acid slurry is obtained;

[0036] The diamine may or may not contain an aromatic heterocyclic structure, the dianhydride may or may not contain an aromatic heterocyclic structure, and at least one of the diamine and the dianhydride contains an aromatic heterocyclic structure.

[0037] In some embodiments, the amount of polyphosphoric acid added is 0.2-1% by mass, based on a solvent dosage of 100% by mass.

[0038] In some embodiments, the solvent comprises an aprotic polar solvent. Preferably, the solvent comprises one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0039] In some embodiments, the aromatic heterocyclic structure includes one or a combination of several of pyridine, pyrazine, furan, imidazole, and oxazole.

[0040] In some embodiments, the diamine includes one or a combination of several of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,6-diaminopyridine, 2,5-furandimethylamine, 2-(3-aminophenyl)-5-aminobenzimidazole, and 2-(4-aminophenyl)-5-aminobenzoxazole.

[0041] In some embodiments, the dianhydride includes one or a combination of several of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,6-bis(3,3',4,4'-diphenylanhydroxy)pyrazine.

[0042] Those skilled in the art will understand that at least one of the diamine and dianhydride raw materials of the present invention needs to contain an aromatic heterocyclic structure. Therefore, when selecting the diamine and dianhydride from the specific substances described above, it is necessary to avoid simultaneously selecting a diamine and a dianhydride that do not contain an aromatic heterocyclic structure. Both the diamine and dianhydride described above can be obtained commercially or prepared by methods in the prior art. For example, 2,6-bis(3,3',4,4'-diphenylanhydroxy)pyrazine can be prepared according to the method disclosed in CN108822092A.

[0043] In some embodiments, the molar ratio of the diamine to the dianhydride is 1:(0.995-1.005).

[0044] In some embodiments, the total mass of the diamine and the dianhydride accounts for 10-30% of the total mass of the reaction system. The reaction system is a combination of the solvent, polyphosphoric acid, diamine, and dianhydride of the present invention.

[0045] In some embodiments, the dianhydride in step (II) is added to the mixed solution obtained in step (I) either all at once or in batches. When added in batches, it can be added in three or more separate additions.

[0046] In some embodiments, the system temperature in steps (I) and (II) is -15 to 30°C, preferably -5 to 20°C.

[0047] In some embodiments, the reaction time in step (II) is 1-8 hours, preferably 2-5 hours.

[0048] According to a specific embodiment of the present invention, a second aspect of the present invention provides a functional polyamic acid slurry, which is prepared by the above-described method for preparing functional polyamic acid slurry.

[0049] In some embodiments, the solid content of the functional polyamic acid slurry is 10-30 wt%.

[0050] In some embodiments, the surface tension of the functional polyamic acid slurry is 31-42 mN / m.

[0051] In some embodiments, the intrinsic viscosity of the functional polyamic acid slurry is 1.78-3.22 dL / g.

[0052] In some embodiments, the kinetic viscosity of the functional polyamic acid slurry is 6200-36200 centipoise.

[0053] The technical solutions of the present invention are illustrated in detail below through embodiments and comparative examples. However, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the key points of the present invention.

[0054] The test methods used in the examples and comparative examples are as follows.

[0055] (1) Solid content

[0056] The solid content is calculated using the following formula:

[0057] Solid content (%) = solid mass (g) / total mass (g) × 100%.

[0058] (2) Film-forming properties

[0059] The surface tension was measured at room temperature using the Du Nouy ring method and a Kruss K100 surface tension meter.

[0060] (3) Intrinsic viscosity

[0061] Take an appropriate amount of polyamic acid slurry and dilute it with the solvent used to prepare the slurry to obtain a concentration of 2 mg / mL. -1 The polyamic acid solution was tested using a Hangzhou Zhuoxiang HCT-6 series automatic viscometer. The test conditions were as follows: test temperature was 25℃, and the Ubbelohde viscometer tube diameter was 0.58mm.

[0062] (4) Kinetic viscosity

[0063] The test was conducted using an Anton Paar ViscoQC 300 contact rotational viscometer. The test conditions were as follows: running time of 40 minutes, rotation speed of 20-100 rpm, rotor model L1, and test temperature of 25℃.

[0064] (5) Stability

[0065] The intrinsic viscosity of the polyamic acid slurry was tested periodically (once upon completion of preparation; once every day for a total of three tests; then once every three days for a total of two tests; and then once every five days thereafter. The slurry was stored at 0°C) to examine the degree and rate of decrease in its intrinsic viscosity. In this invention, the storage time examined is the time elapsed when the intrinsic viscosity decreases by 15%.

[0066] Example 1

[0067] 98.7000 g of N,N-dimethylformamide and 0.1975 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 2.2792 g (21.08 mmol) of p-phenylenediamine. After stirring and dissolving, 8.6850 g (21.08 mmol) of 2,6-bis(3,3',4,4'-diphenyl anhydride oxy)pyrazine was added. The mixture was stirred at -15 °C for 1 hour to obtain a functional polyamic acid slurry with a solid content of 10 wt%, a surface tension of 35 mN / m, an intrinsic viscosity of 1.78 dL / g, a kinetic viscosity of 6200 centipoise, and a shelf life of 12 days.

[0068] Example 2

[0069] 36.0666 g of N,N-dimethylformamide and 0.1803 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 2.3251 g (18.43 mmol) of 2,5-furandimethylamine. After stirring and dissolving, 4.0396 g (18.52 mmol) of pyromellitic dianhydride was added. The mixture was stirred at -10 °C for 2 hours to obtain a functional polyamic acid slurry with a solid content of 15 wt%, a surface tension of 31 mN / m, an intrinsic viscosity of 2.08 dL / g, a kinetic viscosity of 8600 centipoise, and a shelf life of 17 days. Figure 1 This is a graph showing the change in intrinsic viscosity of the functional polyamic acid slurry of this embodiment over time.

[0070] Example 3

[0071] 41.5068 g of N,N-dimethylacetamide and 0.3321 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 2.8177 g (25.82 mmol) of 2,6-diaminopyridine. After stirring and dissolving, 7.5590 g (25.69 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added to the system in three equal portions in three batches. The mixture was stirred at 0°C for 4 hours to obtain a functional polyamic acid slurry with a solid content of 20 wt%, a surface tension of 35 mN / m, an intrinsic viscosity of 2.28 dL / g, a kinetic viscosity of 23200 centipoise, and a shelf life of 19 days.

[0072] Example 4

[0073] 74.6369 g of N-methylpyrrolidone and 0.7464 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 5.7747 g (25.75 mmol) of 2-(3-aminophenyl)-5-aminobenzimidazole. After stirring and dissolving, 10.6090 g (25.75 mmol) of 2,6-bis(3,3',4,4'-diphenyl anhydride oxy)pyrazine was added. The mixture was stirred at 5°C for 5 hours to obtain a functional polyamic acid slurry with a solid content of 18 wt%, a surface tension of 40 mN / m, an intrinsic viscosity of 2.32 dL / g, a kinetic viscosity of 21500 centipoise, and a shelf life of 22 days.

[0074] Example 5

[0075] 69.18 g of N-methylpyrrolidone and 0.3459 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 7.1652 g (31.81 mmol) of 2-(4-aminophenyl)-5-aminobenzoxazole. After stirring and dissolving, 10.1298 g (31.65 mmol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride was added to the system in four equal portions in four batches. The mixture was stirred at 10 °C for 6 hours to obtain a functional polyamic acid slurry with a solid content of 20 wt%, a surface tension of 38 mN / m, an intrinsic viscosity of 2.78 dL / g, a kinetic viscosity of 23100 centipoise, and a shelf life of 22 days.

[0076] Example 6

[0077] 97.7588 g of dimethyl sulfoxide and 0.7205 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 6.8239 g (62.53 mmol) of 2,6-diaminopyridine. After stirring and dissolving, 25.7624 g (62.53 mmol) of 2,6-bis(3,3',4,4'-diphenyl anhydride oxy)pyrazine was added. The mixture was stirred at 20 °C for 7 hours to obtain a functional polyamic acid slurry with a solid content of 25 wt%, a surface tension of 42 mN / m, an intrinsic viscosity of 3.08 dL / g, a kinetic viscosity of 34500 centipoise, and a shelf life of 24 days.

[0078] Example 7

[0079] 20.8082 g of N-methylpyrrolidone and 0.05202 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 3.2576 g (25.82 mmol) of 2,5-furandimethylamine. After stirring and dissolving, 5.6602 g (25.95 mmol) of pyromellitic dianhydride was added to the system in three equal portions in three batches. The mixture was stirred at 30 °C for 8 hours to obtain a functional polyamic acid slurry with a solid content of 30 wt%, a surface tension of 40 mN / m, an intrinsic viscosity of 3.22 dL / g, a kinetic viscosity of 36200 centipoise, and a shelf life of 19 days.

[0080] Comparative Example 1

[0081] This comparative example is basically the same as Example 2, except that: no polyphosphoric acid is added in this comparative example, the solid content of the resulting polyamic acid slurry is 15wt%, the surface tension is 36mN / m, the intrinsic viscosity is 2.36dL / g, the kinetic viscosity is 13600 centipoise, and the storage time is 9 days.

[0082] Comparative Example 2

[0083] This comparative example is compared with Example 3.

[0084] 41.5068 g of N,N-dimethylacetamide and 0.3321 g of polyphosphoric acid (Maclean's reagent, content (H3PO4) ≥ 105%) were added to a three-necked flask, followed by 5.1702 g (25.82 mmol) of 4,4'-diaminodiphenyl ether. After stirring and dissolving, 7.5590 g (25.69 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride was added to the system in three equal portions in three batches. The mixture was stirred at 0°C for 4 hours to obtain a polyamic acid slurry with a solid content of 20 wt%, a surface tension of 55 mN / m, an intrinsic viscosity of 2.31 dL / g, a kinetic viscosity of 23500 centipoise, and a shelf life of 17 days.

[0085] Comparative Example 3

[0086] Referring to the preparation method of polyamic acid slurry for DuPont's Kapton series films, using N,N-dimethylacetamide as a solvent, diaminodiphenyl ether and pyromellitic dianhydride were reacted at 10°C for 10 hours in the presence of the solvent. When the molar ratio of diaminodiphenyl ether to pyromellitic dianhydride was 1:1 and the solid content of the polyamic acid slurry was 20wt%, the kinetic viscosity of the obtained polyamic acid slurry was 870,000 centipoise.

[0087] As can be seen from the data of the above examples and comparative examples, the present invention, by using monomer raw materials containing aromatic heterocyclic structures and adding polyphosphoric acid to the reaction system, prepares functional polyamic acid slurries with improved film-forming properties, reduced kinetic viscosity, and improved storage stability. In contrast, the polyamic acid slurries prepared in Comparative Examples 1-3, which either did not add polyphosphoric acid, did not use monomer raw materials containing aromatic heterocyclic structures, or neither added polyphosphoric acid nor used monomer raw materials containing aromatic heterocyclic structures, exhibited higher surface tension, higher kinetic viscosity, and shorter shelf life compared to the examples.

Claims

1. A method for preparing a functional polyamic acid slurry, comprising the following steps: (I) Mix the solvent, polyphosphoric acid and diamine to obtain a mixed system; (II) Add the dianhydride to the mixture obtained in step (I) to obtain a reaction system, and after the reaction system reacts, the functional polyamic acid slurry is obtained; The diamine may or may not contain an aromatic heterocyclic structure, the dianhydride may or may not contain an aromatic heterocyclic structure, and at least one of the diamine and the dianhydride contains an aromatic heterocyclic structure.

2. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, Based on a solvent usage of 100% by mass, the amount of polyphosphoric acid added is 0.2-1% by mass.

3. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The solvent includes aprotic polar solvents.

4. The method for preparing the functional polyamic acid slurry according to claim 3, wherein, The solvent includes one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

5. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The aromatic heterocyclic structure includes one or a combination of several of pyridine, pyrazine, furan, imidazole and oxazole.

6. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The diamine includes one or a combination of several of p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,6-diaminopyridine, 2,5-furandimethylamine, 2-(3-aminophenyl)-5-aminobenzimidazole, and 2-(4-aminophenyl)-5-aminobenzoxazole.

7. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The dianhydride includes one or a combination of several of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,6-bis(3,3',4,4'-diphenylanhydroxy)pyrazine.

8. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The molar ratio of the diamine to the dianhydride is 1:(0.995-1.005).

9. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The total mass of the diamine and the dianhydride accounts for 10-30% of the total mass of the reaction system.

10. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The system temperature in steps (I) and (II) is -15 to 30°C.

11. The method for preparing the functional polyamic acid slurry according to claim 1, wherein, The reaction time in step (II) is 1-8 hours.

12. A functional polyamic acid slurry, which is prepared by the method of preparing the functional polyamic acid slurry according to any one of claims 1-11.

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