CN114085378B

CN114085378B - Polyamide acid solution and preparation method thereof, polyimide film and preparation method and application thereof

Info

Publication number: CN114085378B
Application number: CN202111356070.7A
Authority: CN
Inventors: 马晓宇; 赵贺; 杨天宇; 张求学; 吕庆龙
Original assignee: Jilin Optical and Electronic Materials Co Ltd
Current assignee: Jilin Optical and Electronic Materials Co Ltd
Priority date: 2021-11-16
Filing date: 2021-11-16
Publication date: 2023-08-18
Anticipated expiration: 2041-11-16
Also published as: CN114085378A

Abstract

The invention relates to the technical field of high polymer materials, and particularly discloses a polyamic acid solution which comprises a first compound, a second compound and an ionic liquid, wherein the chemical structural formulas of the first compound and the second compound are limited, and the specific composition of the ionic liquid is limited; also disclosed is a polyimide film prepared from the polyamic acid solution; the preparation method comprises the steps of coating a polyamic acid solution on a substrate, drying, and then controlling the temperature to rise for curing, so that the polyimide film has low linear expansion Coefficient (CTE), low birefringence and excellent heat resistance; also disclosed is the use of polyimide films in displays, touch panels or solar cell substrates.

Description

Polyamide acid solution and preparation method thereof, polyimide film and preparation method and application thereof

Technical Field

The invention relates to the technical field of high polymer materials, in particular to a polyamic acid solution and a preparation method thereof, a polyimide film and a preparation method and application thereof.

Background

Aromatic polyimide has excellent physical and chemical properties, such as mechanical properties, heat resistance and dielectric properties, so that the aromatic polyimide has wide application in the fields of aerospace, semiconductor industry, electronic industry and the like. With the development of the display industry, polyimide film materials are being actively promoted to replace ITO glass, and the polyimide film materials endow the display with flexibility and light weight, and can be continuously produced by adopting a winding process so as to reduce the production cost. However, aromatic polyimide exhibits a tan color due to intramolecular conjugation and formation of a charge transfer complex, and thus, the optical formation of a polyimide film is poor.

Currently, researchers have proposed many methods to improve the optical properties of polyimide, and colorless transparent polyimide films are obtained by polymerization in ionic liquids. As disclosed in the patent publication No. CN 105492496B, a method of preparing a polyimide film having excellent thermal properties and being transparent by introducing fluorine atoms into the molecule to inhibit the formation of intramolecular conjugation and charge transfer complexes; in the patent publication No. 107531902A, a dianhydride monomer and a 1, 3-bis (4-aminophenoxy) phenylenediamine monomer are copolymerized to obtain a polyimide resin which is colorless and transparent while improving heat resistance and mechanical properties. In the invention patent with publication number of CN105367795, dianhydride and diamine are polymerized in ionic liquid to cure polyimide at low temperature to avoid Wen Bianhuang, so as to obtain colorless transparent polyimide film. The invention patent with publication number of CN112175184A is to introduce ionic liquid into aliphatic polyimide to reduce the conjugated electron cloud density and cut off conjugation, so as to improve the transparency of the film and prepare the flexible polyimide film with high transparency and low chromaticity. However, the birefringence of the polyimide film disclosed above is generally poor, and when light passes through a film having a large birefringence, problems such as incorrect color display, blurred color, or reduced viewing angle may occur, which often limit the application of polyimide materials.

Therefore, the polyimide film with excellent heat resistance and mechanical property, the preparation method and the application thereof are technical problems which are needed to be solved by the technicians in the field.

Disclosure of Invention

In view of this, the present invention provides a polyamic acid solution and a method for producing the same, and also discloses a polyimide film obtained by thermally curing the above polyamic acid solution, which has a low coefficient of linear expansion (CTE), a low birefringence and excellent heat resistance.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

a polyamic acid solution comprising a first compound, a second compound and an ionic liquid; the chemical structural formula of the compound I is shown in the formula I:

the chemical structural formula of the compound II is shown as a formula II:

in the formula I and the formula II, X is an alicyclic or aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4; y is an alicyclic or aromatic 2-valent diamine residue with the carbon number more than or equal to 4; n is an integer of 50 to 300; m is an integer of 50 to 300;

z has the chemical structural formula III:

wherein R in the formula III is olefin with 2-18 carbon atoms, alkylsilyl with 1-10 carbon atoms, alkoxy with 1-8 carbon atoms, cycloalkoxy with 3-8 carbon atoms, alkali metal ion, ammonium ion, imidazolium ion or pyridinium ion;

The ionic liquid is one or more of 1-butyl-3-methylimidazole trifluoroacetate, chlorinated 1-hydroxyethyl-3-methylimidazole and chlorinated 1-butyl-3-methylimidazole.

Preferably, in the polyimide solution, the total content of the compound I in which X is an aromatic 4-valent tetracarboxylic dianhydride residue having not less than 4 carbon atoms and Y is an aromatic 2-valent diamine residue having not less than 4 carbon atoms and the compound II in which X is an aromatic 4-valent tetracarboxylic dianhydride residue having not less than 4 carbon atoms and Y is an aromatic 2-valent diamine residue having not less than 4 carbon atoms is more than 50mol% relative to the compound I and the compound II.

Preferably, in the polyimide solution, the total content of the compound I in which X is an aromatic 4-valent tetracarboxylic dianhydride residue having not less than 4 carbon atoms and Y is an aromatic 2-valent diamine residue having not less than 4 carbon atoms and the compound II in which X is an aromatic 4-valent tetracarboxylic dianhydride residue having not less than 4 carbon atoms and Y is an aromatic 2-valent diamine residue having not less than 4 carbon atoms is more than 80mol% relative to the compound I and the compound II.

Preferably, in the polyimide solution, the total content of the compound I in which X is an aromatic 4-valent tetracarboxylic dianhydride residue having not less than 4 carbon atoms and Y is an aromatic 2-valent diamine residue having not less than 4 carbon atoms and the compound II in which X is an aromatic 4-valent tetracarboxylic dianhydride residue having not less than 4 carbon atoms and Y is an aromatic 2-valent diamine residue having not less than 4 carbon atoms is more than 90mol% relative to the compound I and the compound II.

Preferably, the chemical structural formula of X is formula iv:

wherein A in the formula IV is any one of direct bond, ether bond, methylene, ester bond, ketone bond, amide bond, dimethylsilylene, alkylene with 1-6 carbon atoms and aromatic group with less than 12 carbon atoms, R ₁ Is any one of hydrogen atom, aromatic group with carbon number less than 12, alkyl with carbon number of 1-3, halogen and hydroxy, R ₂ Is any one of a hydrogen atom, an aromatic group having a carbon number of less than 12, an alkyl group having a carbon number of 1 to 3, a halogen, and a hydroxyl group, and p is an integer of 0 to 3.

Preferably, A is a direct bond and R is ₁ Is a hydrogen atom, R is ₂ Is a hydrogen atom, and p is 1; the polyimide film thus produced can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

Preferably, the X is a residue of a 4-valent tetracarboxylic dianhydride, which may be phenyltetracarboxylic acid, 2,3,5, 6-pyridinetetracarboxylic acid, 3',4' -biphenyltetracarboxylic acid, 2, 3',4' -biphenyltetracarboxylic acid, 2', 3' -biphenyltetracarboxylic acid; 3,3',4' -benzophenone tetracarboxylic acid, 2', 3' -benzophenone tetracarboxylic acid, 3,4' -oxybisphthalic anhydride, 1, 4-bis (trifluoromethyl) -2,3,5, 6-benzene tetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) sulfone, bis (3, 4-dicarboxyphenyl) ether, 1,4,5, 8-naphthalene tetracarboxylic dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 3,4,9, the monomer may be used in combination of two or more of 10-perylene tetracarboxylic dianhydride, bis (3, 4-dicarboxyphenyl) sulfide dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) propane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) propane dianhydride, p-phenylene-bistrimellitate dianhydride, p-ethylene-bistrimellitate dianhydride, ethylene glycol bistrimellitate anhydride, 4' - (4, 4' -isopropyldiphenoxy) bis (phthalic anhydride), 3',4' -triphenyl bisether tetracarboxylic dianhydride, 4- (2, 5-dioxotetrahydrofuran-3-yl) -1,2,3, 4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride, 1,6,7, 12-tetra-tert-butylphenoxy-3, 4,9, 10-tetracarboxylic acid dianhydride, and the like.

Preferably, the chemical structural formula of Y is formula v:

wherein B in formula V is any one of direct bond, ether bond, methylene, ester bond, ketone bond, amide bond, dimethylsilylene, alkylene having 1 to 6 carbon atoms, and aromatic group having 12 or less carbon atoms, R ₃ Is any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; r is R ₄ Is any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; q is an integer of 0 to 3.

Preferably, B is a direct bond, R is ₃ Is a hydrogen atom, R is ₄ Is a hydrogen atom, and p is 1; the polyimide film thus produced can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

Preferably, Y is a 2-valent diamine residue, the 2-valent diamine may be m-phenylenediamine, p-phenylenediamine, 3, 5-diaminobenzoic acid, 1, 5-naphthalenediamine, 2, 6-naphthalenediamine, 9, 10-anthracenediamine, 2, 7-diaminofluorene, 4 '-diaminobenzanilide, 3,4' -diaminodiphenyl ether, 2, 4-diaminofluorobenzene, 2, 5-diaminofluorobenzene 2, 4-diaminotoluene, and 2-methyl-1, 4-phenylenediamine, 2, 5-diaminobenzotrifluoride, 3, 5-diaminobenzotrifluoride, 2, 3-diaminopyridine, 2, 4-diaminopyridine, 2, 5-diaminopyridine, 3, 4-diaminophenol, 2, 5-diaminophenol, 3, 6-diaminocarbazole, 2, 6-diaminopyrazine, 1, 5-naphthalenediamine, 1, 8-naphthalenediamine, 2, 3-naphthalenediamine, and 2-methyl-1, 4-phenylenediamine, 2, 5-diaminobenzotrifluoride, 3, 5-diaminobenzotrifluoride, 2, 3-diaminopyridine, 2, 4-diaminopyridine, 2, 5-diaminopyridine 3, 4-diaminophenol, 2, 5-diaminophenol, 3, 6-diaminocarbazole, 2, 6-diaminopyrazine, 1, 5-naphthalenediamine, 1, 8-naphthalenediamine, 2, 3-naphthalenediamine, monomers such as 2,2 '-diaminobenzidine, 3',5 '-tetramethyl-4, 4' -diaminodiphenylmethane and 1, 4-bis (4-aminophenoxy) benzene may be used alone or in combination of two or more kinds.

Preferably, Z represents a terminal blocking agent for the polyamide acid terminal, and is represented by formula III, preferably any one of dimethyl dicarbonate, diisopropyl dicarbonate, di-tert-butyl dicarbonate, diethyl peroxydicarbonate, fluorenylmethoxycarbonyl chloride, acetyl chloride, benzoyl chloride, maleic anhydride, 3-phenylethynyl phthalic anhydride, itaconic anhydride, benzyl chloroformate, and 1,2,3, 6-tetrahydrophthalic anhydride.

Preferably, the ionic liquid is an imidazole ionic liquid.

Further preferred, the ionic liquid is one or more of 1-ethyl-3-methylimidazole tetrafluoroborate, 1-ethyl-3-methylimidazole acetate, 1-n-butyl-3-methylimidazole bromide, 1-ethyl-3-methylimidazole ethyl sulfate, 1-ethyl-3-methylimidazole dicyanoammonium salt, 1-ethyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole trifluoroacetate, 1-propyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole tetrafluoroborate, chlorinated 1-hydroxyethyl-3-methylimidazole, 1-butyl-3-methylimidazole iron tetrachloride, 1-butyl-3-methylimidazole hexafluorophosphate, 1-ethyl-3-methylimidazole, 1-butyl-3-methylimidazole trifluoromethane sulfonate, chlorinated 1, 3-bis (2-methoxy-2-oxyethyl) imidazole, 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate.

Still more preferably, the ionic liquid is 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride or 1-n-butyl-3-methylimidazole chloride.

Preferably, the ionic liquid has a concentration of < 5000ppm.

Preferably, the ionic liquid has a concentration of < 3000ppm.

Further preferably, the concentration of the ionic liquid is 500-1000ppm.

Preferably, the polyamic acid solution has a weight-average molecular weight of 30000 to 100000g/mol and a molecular weight distribution width of 1.1 to 3.0.

Preferably, the polyamic acid solution has a viscosity of 500 to 10000cp at 25 ℃.

Further preferably, the polyamic acid solution has a viscosity of 1000 to 8000cp at 25 ℃. When the viscosity is more than 1000cp, polyamide acid with higher molecular weight can be obtained, so that the mechanical strength of polyimide is ensured, and when the viscosity is more than 8000cp, the fluidity is poor when the polyimide is coated into a film, and a uniform and flat film is difficult to obtain.

Preferably, the polyamic acid solution has a solid content of 5 to 70wt%.

More preferably, the polyamic acid solution has a solid content of 5 to 50% by weight.

Further preferably, the polyamic acid solution has a solid content of 10 to 30% by weight.

If the solid content of the polyamic acid solution is 10% by weight or less, the variation in film thickness at the time of imidization to form a polyimide film is not easily controlled, and if the solid content is 30% by weight or more, the thickness of the polyimide film obtained during the preparation of the polyimide film is difficult to control.

The invention also provides a preparation method of the polyamic acid solution, which specifically comprises the following steps:

(1) Adding diamine and dianhydride into an aprotic polar solvent under inert gas for polymerization reaction to obtain a first-stage mixed solution;

(2) Adding diamine, dianhydride, a blocking agent and ionic liquid into an aprotic polar solvent under inert gas for polymerization reaction, separating out the obtained reaction liquid in a poor solvent, filtering and drying to obtain primary mixed powder;

(3) And adding the primary mixed powder into the primary mixed solution, and mixing and dissolving to obtain the polyamic acid solution.

The beneficial effects of the above preferable technical scheme are as follows: in the invention, a small amount of ionic liquid remains after the primary mixed powder is prepared, and in the subsequent imidization process of polyamide acid, because hydrogen bonds are formed between imidazole ionic liquid containing nitrogen heterocycle and polyimide molecular chains to replace Van der Waals force between polyimide molecular chains, polyimide networks crosslinked by the ionic liquid are more prone to be formed inside, so that the distribution of the molecular chains is disturbed, the probability of ordered arrangement of the molecular chains is reduced, and isotropic molecular chain structures are more prone to be formed inside, thereby reducing the double refractive index. At the same time, the cross-linked structure can increase the light passing path, so that the double refractive index of the polyimide film can be reduced without damaging the thermal performance and mechanical performance of the polyimide.

Preferably, the molar ratio of said diamine to said dianhydride in step (1) is (0.9-1.1): 1, a step of; the temperature of the polymerization reaction is 20-120 ℃ and the time is 1-12 h;

the molar ratio of the diamine to the dianhydride in step (2) is (0.9-1.1): 1, a step of; the mass ratio of the ionic liquid to the dianhydride is (0.05-0.5): 1, a step of; the end capping agent is the diamine with the mass ratio of 0.01% -5%; the temperature of the polymerization reaction is 20-120 ℃ and the time is 1-12 h; the mass ratio of the poor solvent to the reaction liquid is 1: (5-50).

Preferably, the aprotic polar solvent includes N-methylpyrrolidone, N-ethylpyrrolidone, N-dimethylacetamide, N-dimethylformamide, N-diethylacetamide, N-diethylformamide, 3-methoxy-N, N-dimethylpropionamide, 3-N-butoxy-N, N-dimethylpropionamide, N-dimethylisobutylamide, 1, 3-dimethyl-2-imidazolidinone, N, N-dimethylpropenyl urea, dimethyl sulfoxide, N-methyl-2-oxazolidinone, delta-valerolactone, gamma-butyrolactone, cyclohexanone, diethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, propylene glycol diacetate, propylene glycol methyl ether, propylene glycol propyl ether, propylene glycol butyl ether, propylene glycol phenyl ether, dipropylene glycol methyl ether, dipropylene glycol propyl ether, 1, 4-butanediol diacetate, 1, 3-butanediol diacetate, 1, 6-hexanediol diacetate, 3-methoxybutanol, 1, 3-butanediol, 3-methoxy-3-methyl-1-butanol, methanol, ethanol, N-propanol, isopropanol, ethyl lactate, butyl benzoate, diacetone alcohol.

Preferably, the poor solvent in step (2) comprises one or more of water, methanol, and ethanol.

Preferably, the inert gas in step (1) and step (2) comprises nitrogen or argon.

Preferably, the molar ratio of the diamine to the dianhydride in step (1) and step (2) is (0.95-1.05): 1.

preferably, in the step (2), the mass ratio of the ionic liquid to the dianhydride is (0.1-0.3): 1.

preferably, in the step (2), the mass ratio of the poor solvent to the reaction solution is 1: (10-25).

Preferably, in the step (2), the mass ratio of the poor solvent to the reaction solution is 1: (5-15).

The beneficial effects of the above preferable technical scheme are as follows: when the ionic liquid added in the polymerization process is too little or the proportion of poor solvent is too high when the polyamic acid powder is separated out, the content of the final residual ionic liquid is too low; when the ionic liquid is added too much or the proportion of poor solvent is too low when the polyamic acid powder is precipitated in the polymerization process, the content of the finally remained ionic liquid is too high, and the heat resistance of the formed polyimide is not ideal.

Preferably, the polymerization temperature in step (1) and step (2) is from 30℃to 100 ℃.

It is further preferred that the polymerization temperature in step (1) and step (2) is 40℃to 80 ℃.

Preferably, the polymerization time in step (1) and step (2) is 2h to 8h.

It is further preferred that the polymerization time in step (1) and step (2) is 3h to 6h.

The invention also provides a polyimide film prepared from the polyamic acid solution.

Preferably, the polyimide film has a light transmittance of > 70% at a wavelength of 500 nm. Further preferably, the polyimide film has a light transmittance of > 75% at a wavelength of 500 nm.

In addition, the polyimide film preferably has a birefringence of < 0.1. Further preferably, the polyimide film has a birefringence of < 0.05. Still more preferably, the polyimide film has a birefringence of < 0.01. Wherein the birefringence is the difference in refractive index between the direction perpendicular to the film surface and the direction horizontal to the film surface.

Preferably, the polyimide film has a linear expansion coefficient of < 30 ppm/DEG C at 50℃ to 200 deg. Further preferably, the polyimide film has a linear expansion coefficient of < 10 ppm/DEG C at 50℃ to 200 deg.

Preferably, the polyimide film has a birefringence of 0.05 or less and a linear expansion coefficient of < 10 ppm/DEG C of 50℃ to 200 ℃.

The invention further provides a preparation method of the polyimide film, which specifically comprises the following steps: coating the polyamic acid solution on a substrate, drying, and then controlling the temperature to rise for curing to obtain the polyimide film; the drying temperature is 80-180 ℃ and the drying time is 10-100min; the highest temperature of the solidification is 350-480 ℃, the holding time of 150-250 ℃ in the heating process is more than 10min, and the solidification time is 2-5h.

Preferably, the drying temperature is 110 ℃ to 180 ℃.

Preferably, the drying temperature is 80-150 ℃.

Preferably, the curing treatment is to raise the temperature from room temperature to 80-100 ℃ at a heating rate of 1-5 ℃/min, and maintain the temperature at 80-100 ℃ for 60-120min; then the temperature is raised to 120-170 ℃ at the heating rate of 1-5 ℃/min, and the temperature is maintained at 120-170 ℃ for 30-120min; then the temperature is raised to 220-280 ℃ at a heating rate of 1-5 ℃/min, and the temperature is maintained at 220-280 ℃ for 60-120min; finally, the temperature is raised to 350-480 ℃ at a heating rate of 1-5 ℃/min, and maintained at 350-480 ℃ for 10-120min.

In addition, the invention provides application of the polyimide film in a display, a touch panel or a solar cell substrate.

Compared with the prior art, the invention discloses a polyamic acid solution and a preparation method thereof, a polyimide film and a preparation method and application thereof, and has the following beneficial effects:

according to the invention, 1-butyl-3-methylimidazole trifluoroacetate is added in the reaction process of dianhydride and diamine, and the plasma solution of 1-hydroxyethyl-3-methylimidazole chloride and 1-butyl-3-methylimidazole chloride plays a role in catalysis, so that the reaction is more complete, meanwhile, the ionic liquid remained in the reaction is found unexpectedly, and the birefringence performance of the film can be improved under the condition of not affecting the mechanical performance and the thermal performance;

the polyamic acid solution obtained by the synthesis method can be imidized to obtain a polyimide film with excellent heat resistance, low birefringence and low coefficient of linear expansion (CTE);

further, a polyimide film produced from the polyamic acid solution according to the present invention can be used as a substrate to obtain a flexible and highly reliable image display device, solar cell panel, or the like.

Detailed Description

The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The compounds used in the examples are described below for short.

PDA: para-phenylenediamine

BPDA:3,3', 4' -biphenyltetracarboxylic dianhydride

DAE:4,4' -diaminodiphenyl ether

BTDA:3,3', 4' -BenzotSicarboxylic acid

NMP: n-methyl-2-pyrrolidone

PDA-Boc: n- (tert-butoxy) -1, 4-phenylenediamine

Boc: di-tert-butyl dicarbonate

Example 1

The embodiment 1 of the invention discloses a polyamic acid solution, which comprises a compound I, a compound II and an ionic liquid; the chemical structural formula of the compound I is shown as formula I:

the chemical structural formula of the compound II is shown as a formula II:

in the formulas I and II, X is an alicyclic or aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4; y is an alicyclic or aromatic 2-valent diamine residue with the carbon number more than or equal to 4; n is an integer of 50 to 300; m is an integer of 50 to 300;

z has the chemical structural formula III:

wherein R is an olefin having 2 to 18 carbon atoms, an alkylsilyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a cycloalkoxy group having 3 to 8 carbon atoms, an alkali metal ion, an ammonium ion, an imidazolium ion or a pyridinium ion;

In order to optimize the technical scheme, in the polyimide solution, the total content of the compound I with X being an aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4 and Y being an aromatic 2-valent diamine residue with the carbon number more than or equal to 4 and the compound II with X being an aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4 and Y being an aromatic 2-valent diamine residue with the carbon number more than or equal to 4 is more than 50mol percent relative to the total content of the compound I and the compound II.

In order to optimize the technical scheme, in the polyimide solution, the total content of the compound I with X being an aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4 and Y being an aromatic 2-valent diamine residue with the carbon number more than or equal to 4 and the compound II with X being an aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4 and Y being an aromatic 2-valent diamine residue with the carbon number more than or equal to 4 is more than 80mol percent relative to the total content of the compound I and the compound II.

In order to optimize the technical scheme, in the polyimide solution, the total content of the compound I with X being an aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4 and Y being an aromatic 2-valent diamine residue with the carbon number more than or equal to 4 and the compound II with X being an aromatic 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4 and Y being an aromatic 2-valent diamine residue with the carbon number more than or equal to 4 is more than 90mol percent relative to the total content of the compound I and the compound II.

In order to optimize the technical scheme, X is an aromatic ring 4-valent tetracarboxylic dianhydride residue with the carbon number more than or equal to 4; y is an aromatic ring 2-valent diamine residue with the carbon number more than or equal to 4.

In order to optimize the technical scheme, the chemical structural formula of X is shown as formula IV:

wherein A is any one of direct bond, ether bond, methylene, ester bond, ketone bond, amide bond, dimethylsilylene, alkylene with 1-6 carbon atoms, and aromatic group with less than 12 carbon atoms, R ₁ Is any one of hydrogen atom, aromatic group with carbon number less than 12, alkyl with carbon number of 1-3, halogen and hydroxy, R ₂ Is any one of a hydrogen atom, an aromatic group having a carbon number of less than 12, an alkyl group having a carbon number of 1 to 3, a halogen, and a hydroxyl group, and p is an integer of 0 to 3.

In order to optimize the technical scheme, A is direct bonding, R ₁ Is a hydrogen atom, R ₂ Is a hydrogen atom, and p is 1. The polyimide film thus produced can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

In order to optimize the technical scheme, X is a residue of 4-valent tetracarboxylic dianhydride, and the 4-valent tetracarboxylic dianhydride can be phenyltetracarboxylic acid, 2,3,5, 6-pyridine tetracarboxylic acid, 3',4' -biphenyl tetracarboxylic acid, 2, 3',4' -biphenyl tetracarboxylic acid and 2,2', 3' -biphenyl tetracarboxylic acid; 3,3',4' -benzophenone tetracarboxylic acid, 2',3,3' -benzophenone tetracarboxylic acid, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane, 2-bis (2, 3-dicarboxyphenyl) hexafluoropropane, 2-bis (3, 4-dicarboxyphenyl) propane 2, 2-bis (2, 3-dicarboxyphenyl) propane, 1-bis (3, 4-dicarboxyphenyl) ethane, 1-bis (2, 3-dicarboxyphenyl) ethane, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] hexafluoropropane one or more combinations of 2, 2-bis [4- (2, 3-dicarboxyphenoxy) phenyl ] hexafluoropropane, 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane, 2-bis [4- (2, 3-dicarboxyphenoxy) phenyl ] propane, 1,2,5, 6-naphthalene tetracarboxylic acid, 1,4,5, 8-naphthalene tetracarboxylic acid, 2,3,6, 7-naphthalene tetracarboxylic acid, 3,4,9, 10-perylene tetracarboxylic acid.

In order to optimize the technical scheme, the chemical structural formula of Y is as formula V:

in formula V, B is a direct bond, an ether bond, a methylene, an ester bond, or a ketoneA bond, an amide bond, a dimethylsilylene group, an alkylene group having 1 to 6 carbon atoms, or an aromatic group having 12 or less carbon atoms, R ₃ Is any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; r is R ₄ Is any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; q is an integer of 0 to 3.

In order to optimize the technical scheme, B is direct bonding, R ₃ Is a hydrogen atom, R ₄ Is a hydrogen atom, p is 1; the polyimide film thus produced can be made to have high heat resistance, high mechanical strength and low linear expansion coefficient.

In order to optimize the technical scheme, Y is a 2-valent diamine residue, the 2-valent diamine may be m-phenylenediamine, p-phenylenediamine, 3, 5-diaminobenzoic acid, 1, 5-naphthalenediamine, 2, 6-naphthalenediamine, 9, 10-anthracenediamine, 2, 7-diaminofluorene, 4 '-diaminobenzanilide, 3,4' -diaminodiphenyl ether, 4 '-diaminodiphenyl ether, 3-carboxy-4, 4' -diaminodiphenyl ether, 3-sulfonic acid-4, 4 '-diaminodiphenyl ether, 3,4' -diaminodiphenyl methane, 4 '-diaminodiphenyl methane, 3,4' -diaminodiphenyl sulfone, 4 '-diaminodiphenyl sulfone, 3,4' -diaminodiphenyl sulfide, 4 '-diaminodiphenyl sulfide, and 4-aminophenyl 4-aminobenzoate, 9-bis (4-aminophenyl) fluorene, 1, 3-bis (4-anilino) tetramethyldisiloxane, e.g. 4,4' -diaminobiphenyl, 2 '-dimethyl-4, 4' -diaminobiphenyl, 2 '-diethyl-4, 4' -diaminobiphenyl, 3 '-dimethyl-4, 4' -diaminobiphenyl 3,3 '-diethyl-4, 4' -diaminobiphenyl, bis (4-aminophenoxyphenyl) sulfone, bis (3-aminophenoxyphenyl) sulfone, bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl ] ether, 2-bis [4- (4-aminophenoxy) phenyl ] propane, one or more combinations of 2, 2-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane.

In order to optimize the technical scheme, Z is any one of dimethyl dicarbonate, diisopropyl dicarbonate, di-tert-butyl dicarbonate, diethyl dicarbonate peroxide, fluorenylmethoxycarbonyl chloride, acetyl chloride, benzoyl chloride, maleic anhydride, 3-phenylethynyl phthalic anhydride, itaconic anhydride, benzyl chloroformate and 1,2,3, 6-tetrahydrophthalic anhydride.

In order to optimize the technical scheme, the ionic liquid is imidazole ionic liquid.

Further in order to optimize the technical scheme, the ionic liquid is one or more of 1-ethyl-3-methylimidazole tetrafluoroborate, 1-ethyl-3-methylimidazole acetate, 1-n-butyl-3-methylimidazole bromide, 1-ethyl-3-methylimidazole ethyl sulfate, 1-ethyl-3-methylimidazole dicyanoammonium salt, 1-ethyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole trifluoroacetate, 1-propyl-3-methylimidazole chloride, 1-butyl-3-methylimidazole tetrafluoroborate, chlorinated 1-hydroxyethyl-3-methylimidazole, 1-butyl-3-methylimidazole iron tetrachloride, 1-butyl-3-methylimidazole hexafluorophosphate, 1-ethyl-3-methylimidazole, 1-butyl-3-methylimidazole trifluoromethane sulfonate, chlorinated 1, 3-bis (2-methoxy-2-oxyethyl) imidazole and 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate.

Furthermore, in order to optimize the technical scheme, the ionic liquid is 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride or 1-n-butyl-3-methylimidazole chloride.

In order to optimize the technical scheme, the concentration of the ionic liquid is less than 5000ppm.

In order to optimize the technical scheme, the concentration of the ionic liquid is less than 3000ppm.

Further in order to optimize the technical scheme, the concentration of the ionic liquid is 500-1000ppm.

In order to optimize the technical scheme, the weight average molecular weight of the polyamic acid solution is 30000-100000 g/mol, and the molecular weight distribution width is 1.1-3.0.

In order to optimize the technical scheme, the viscosity of the polyamic acid solution is 500cp-10000cp at 25 ℃.

Further in order to optimize the technical scheme, the viscosity of the polyamic acid solution is 1000cp-8000cp at 25 ℃.

In order to optimize the technical scheme, the solid content of the polyamic acid solution is 5 to 70 weight percent.

In order to optimize the technical scheme, the solid content of the polyamic acid solution is 5 to 50 weight percent.

Further in order to optimize the technical scheme, the solid content of the polyamic acid solution is 10 to 30 weight percent.

Example 2

The embodiment 2 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) Under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a first-stage mixed solution is obtained for standby;

(2) 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-necked flask with a stirring paddle and a thermometer under the protection of nitrogen, the stirring speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and the mixture is reacted for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) The polyamic acid powder obtained by drying was dissolved in the primary mixed solution to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 3

The embodiment 3 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) Under the protection of nitrogen, 350g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a first-stage mixed solution is obtained for standby;

(2) 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-necked flask with a stirring paddle and a thermometer under the protection of nitrogen, the stirring speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and the mixture is reacted for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate; filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) The polyamic acid powder obtained by drying was dissolved in the primary mixed solution to obtain a polyamic acid solution having a solid content of 10% by weight.

Example 4

The embodiment 4 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) Under the protection of nitrogen, 83.3g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a first-stage mixed solution is obtained for standby;

(2) Under the protection of nitrogen, 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added for reaction for 3 hours, a reaction product is obtained, the reaction product is slowly added into 3000g of purified water under the stirring condition with the rotation speed of 500rpm to separate out yellow precipitate, the yellow precipitate is filtered out and then is dried for 12 hours in a vacuum oven at 80 ℃ to obtain polyamic acid powder;

Example 5

The embodiment 5 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) Under the protection of nitrogen, 83.3g of NMP and 4.6g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 15.22g of BTDA and 10g of NMP are added, and after 3 hours of reaction, a first-stage mixed solution is obtained for standby;

(2) Under the protection of nitrogen, 81.1g of NMP, 1.84g of 1-butyl-3-methylimidazole trifluoroacetate and 4.6g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 15.22g of BTDA, 10g of NMP and 0.41g of PDA-Boc are added, and after 3 hours of reaction, the reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

Example 6

The embodiment 6 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(1) Under the protection of nitrogen, 83.3g of NMP and 8.03g of DAE are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until PDA is dissolved, 11.8g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a first-stage mixed solution is obtained for standby;

(2) Under the protection of nitrogen, 81.1g of NMP, 3.212g of 1-butyl-3-methylimidazole trifluoroacetate and 8.03g of DAE are added into a four-neck flask with a stirring paddle and a thermometer, the stirring speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 11.8g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after 3 hours of reaction, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

Example 7

The embodiment 7 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(2) 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer under the protection of nitrogen, the stirring speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.43g of Boc are added, and after 3 hours of reaction, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

Example 8

The embodiment 8 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a first-stage mixed solution is obtained for standby;

81.1g of NMP, 1.064g of 1-butyl-3-methylimidazole trifluoroacetate, 1.064g of 1-hydroxyethyl-3-methylimidazole chloride and 5.32g of PDA are added into a four-necked flask with a stirring paddle and a thermometer under the protection of nitrogen, the stirring speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after 3 hours of reaction, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder; the polyamic acid powder obtained by drying was dissolved in the primary mixed solution to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 9

The embodiment 9 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(2) 81.1g of NMP, 0.71g of 1-butyl-3-methylimidazole trifluoroacetate, 0.71g of 1-hydroxyethyl-3-methylimidazole chloride, 0.71g of 1-butyl-3-methylimidazole chloride and 5.32g of PDA are added into a four-necked flask with a stirring paddle and a thermometer under the protection of nitrogen, the mixture is stirred at 300rpm under the condition of 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and the mixture is reacted for 3 hours to obtain a reaction product; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

Example 10

The embodiment 10 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(2) Under the protection of nitrogen, 81.1g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after 3 hours of reaction, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) The polyamic acid powder obtained by drying was dissolved in the primary mixed solution, and 0.1111g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 11

The embodiment 11 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(3) The polyamic acid powder obtained by drying was dissolved in the primary mixed solution, and 0.1333g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 12

The embodiment 12 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(3) The polyamic acid powder obtained by drying was dissolved in the primary mixed solution, and 0.1667g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 13

The embodiment 13 of the invention discloses a preparation method of a polyamic acid solution, which specifically comprises the following steps:

(3) The polyamic acid powder obtained by drying was dissolved in the primary mixed solution, and 0.222g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Example 14

The embodiment 14 of the invention discloses a preparation method of a polyimide film, which specifically comprises the following steps:

the polyamic acid solutions prepared in example 2 were each placed on a silicon wafer plate, coated to a film using a spin coater, and then the silicon wafer coated with the film was moved to a heating plate of 120 ℃ and dried for 15min. And (5) after the drying is finished, placing the mixture into a high-temperature clean oven for imidization film formation. The curing process is as follows: raising the temperature from room temperature to 100 ℃ at a heating rate of 5 ℃/min, and maintaining the temperature at 100 ℃ for 60min; then the temperature is raised to 170 ℃ at a heating rate of 5 ℃/min, and the temperature is maintained at 170 ℃ for 30min; then the temperature is raised to 280 ℃ at a heating rate of 5 ℃/min, and maintained at 280 ℃ for 100min; finally, the temperature is raised to 450 ℃ at a heating rate of 5 ℃/min, and the temperature is maintained at 450 ℃ for 20min. And naturally cooling to room temperature, soaking the silicon crystal plate with the film in water, peeling and drying to obtain the polyimide film.

Example 15

Example 15 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 3".

Example 16

Example 16 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 4".

Example 17

Example 15 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 5".

Example 18

Example 18 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 6".

Example 19

Example 19 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 7".

Example 20

Example 20 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 8".

Example 21

Example 21 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 9".

Example 22

Example 15 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 10".

Example 23

Example 15 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 11".

Example 24

Example 24 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 12".

Example 25

Example 15 of the present invention discloses a method for producing a polyimide film, which differs from example 14 only in that "the polyamic acid solution produced in example 2" is replaced with "the polyamic acid solution produced in example 13".

Comparative example 1

The invention discloses a preparation method of a polyimide film, which specifically comprises the following steps:

(1) Under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a mixed solution is obtained for standby;

(2) 81.1g of NMP and 5.32g of PDA were charged into a four-necked flask equipped with a stirring paddle and a thermometer under nitrogen protection at a rotation speed of 300rpm, stirred at 55℃until the PDA was dissolved, and 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc were added to react for 3 hours to obtain a reaction product. Slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) Dissolving the dried polyamic acid powder in the mixed solution, and adding 0.0556g of 1-butyl-3-methylimidazole trifluoroacetate to obtain a polyamic acid solution with a solid content of 18 wt%;

(4) The same as in example 13 is that "the polyamic acid solution prepared in example 2" is replaced with "the polyamic acid solution prepared in step (3)".

Comparative example 2

(2) Under the protection of nitrogen, 81.1g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc are added, and after 3 hours of reaction, a reaction product is obtained;

slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) The polyamic acid powder obtained by drying was dissolved in the mixed solution, and 0.555g of 1-butyl-3-methylimidazole trifluoroacetate was added to obtain a polyamic acid solution having a solid content of 18% by weight.

Comparative example 3

(1) Introducing nitrogen into a three-neck flask with a mechanical stirring device, firstly adding 10.64g of PDA, then adding 399.9g of ionic liquid 1, 3-bis (2-methoxy-2-oxyethyl) imidazole tetrafluoroborate, opening mechanical stirring, heating to dissolve, and at the moment, the temperature of a mixed solution in the three-neck flask is not higher than 50 ℃; after diamine is completely dissolved, adding 28.95g of BPDA into the three-neck flask, stirring for 10min, extruding a nitrogen bag, and removing air in the three-neck flask as much as possible; slowly heating the mixed solution in the three-neck flask to 180 ℃, stirring at the constant temperature of 180 ℃ for 9 hours, and naturally cooling to room temperature to obtain a pale yellow polyimide prepolymer;

(2) Pouring 65mL of methanol into a three-neck flask filled with a pale yellow polyimide prepolymer solution, stirring for 10min, standing, precipitating a pale yellow precipitate, washing with 65mL of methanol at least three times each time, carrying out suction filtration (the filtration mode can be suction filtration), and drying in a vacuum oven at 80 ℃ for 12h to obtain brown polyimide prepolymer powder; 1.50g of dried polyimide prepolymer powder is dissolved in 6.83g of polar solution N, N-dimethylacetamide solution to prepare clear polyimide prepolymer glue solution with the solid content of 10 percent;

(3) Uniformly coating the obtained polyimide prepolymer glue solution on a clean flat plate, which can be a glass plate, at 50 ℃, and placing the flat plate into a vacuum oven for curing, wherein the curing process is as follows: curing at 50 ℃ for 1h, then curing at 80 ℃ for 1h, then curing at 100 ℃ for 1h, then curing at 130 ℃ for 1h, then curing at 160 ℃ for 1h, then curing at 180 ℃ for 3h, and finally closing an oven, cooling to room temperature, and stripping to obtain film-shaped polyimide; after the polyimide film was naturally cooled to room temperature, the polyimide film was peeled off from the glass plate with warm water to obtain a colorless transparent polyimide film having a thickness of 20. Mu.m.

Comparative example 4

(1) 172.2g of NMP followed by 10.64g of PDA were placed in a 500ml three-necked flask equipped with nitrogen protection and mechanical stirring, and dissolved by stirring at 10 ℃; then adding 0.0945mol of 4,4' - (trifluoromethyl phenyl isopropyl) diphthalic anhydride to react with diamine, and stirring for 8 hours at 10 ℃ to obtain a copolyamide acid solution; 14.17g of 1-butyl-3-methylimidazole trifluoroacetate is added into the transparent copolyamide acid solution, and the solution is mechanically stirred for 3 hours to be uniformly dispersed in the transparent copolyamide acid solution, so that a colorless and transparent homogeneous mixed solution is finally formed;

(2) Defoaming the colorless transparent homogeneous mixed solution for one hour, casting the mixture onto a clean dust-free glass plate, then coating the glass plate with a thin film (raw material) to a preset thickness by using a scraper, and placing the glass plate with the thin film (raw material) into an oven to complete thermal imidization according to the following process, wherein the temperature is 150 ℃, the temperature is 40 minutes, the temperature is 240 ℃, the temperature is 40 minutes, the temperature is 310 ℃, the temperature is 40 minutes, and the temperature is 350 ℃ and the time is 40 minutes; and after a period of time, cooling the temperature of the oven to room temperature, and taking out the glass substrate to obtain the transparent polyimide composite film.

Comparative example 5

(2) 81.1g of NMP and 5.32g of PDA were charged into a four-necked flask equipped with a stirrer and a thermometer under nitrogen protection at a rotation speed of 300rpm, stirred at 55℃until PDA was dissolved, and 14.475g of BPDA, 10g of NMP and 0.41g of PDA-Boc were added to react for 3 hours to obtain a reaction product. Slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) Dissolving the polyamic acid powder obtained by drying in the mixed solution to obtain a polyamic acid solution with the solid content of 18 weight percent;

Comparative example 6

(1) Under the protection of nitrogen, 172.2g of NMP and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a polyamic acid solution is obtained for standby;

(2) Under the protection of nitrogen, 81.1g of NMP, 2.128g of sodium n-hexane sulfonate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and after 3 hours of reaction, a reaction product is obtained; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) The polyamic acid powder obtained by drying was dissolved in a polyamic acid solution to obtain a polyamic acid solution having a solid content of 18% by weight.

Comparative example 7

(2) Under the protection of nitrogen, 81.1g of NMP, 2.128g of 1-butyl-3-methylimidazole trifluoroacetate and 5.32g of PDA are added into a four-neck flask with a stirring paddle and a thermometer, the rotation speed is 300rpm, the mixture is stirred at 55 ℃ until the PDA is dissolved, 14.475g of BPDA and 10g of NMP are added, and the reaction product is obtained after 3 hours of reaction; slowly adding the reaction product into 3000g of purified water under the stirring condition with the rotating speed of 500rpm to separate out yellow precipitate, filtering out the yellow precipitate, and then placing the yellow precipitate in a vacuum oven at 80 ℃ for drying for 12 hours to obtain polyamic acid powder;

(3) Dissolving the polyamic acid powder obtained by drying in the mixed solution to obtain a polyamic acid solution with a solid content of 18 wt%;

Effect verification

1. Polyamide acid solution viscosity test

The viscosity of the polyamic acid solution used in examples 14 to 25, the polyamic acid solution obtained in step (3) of comparative examples 1 to 2 and comparative examples 5 to 7, the polyimide prepolymer dope obtained in step (2) of comparative example 3, and the colorless transparent homogeneous mixed solution obtained in step (1) of comparative example 4 were measured by a Brookfiled rotational viscometer at 25℃to obtain the test results shown in tables 1 to 3 below.

2. Molecular weight and polydispersity index test of molecular weight of Polyamic acid solution

The polyamide acid solutions used in examples 14 to 25, the polyamide acid solutions prepared in steps (3) of comparative examples 1 to 2 and comparative examples 5 to 7, the polyimide prepolymer dope prepared in step (2) of comparative example 3, and the colorless transparent homogeneous mixture obtained in step (1) of comparative example 4 were used to test the weight average molecular weight and the polydispersity index of the molecular weight of the polyamic acid by gel permeation chromatography (Waters-2695, waters), the standard was polystyrene, the chromatographic column was water Styrage, the mobile phase was N-methyl-2-pyrrolidone, and the test temperature was 40℃to obtain the results shown in tables 1 to 3 below.

3. Polyimide film 500nm transmittance

The polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were measured for light transmittance at a wavelength of 550nm using an ultraviolet-visible spectrophotometer (model TU-1810 PC), and the obtained results are shown in tables 1 to 3 below.

4. Polyimide film linear Coefficient of Thermal Expansion (CTE):

the polyamide acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were each cut into a rectangle of 13mm by 4mm in thickness, and used as test sample pieces. The test piece was heated from 30℃to 400℃under conditions of a temperature rising rate of 10℃per minute, a temperature rising rate of 30℃per minute, a temperature holding period of 30 minutes, a temperature lowering rate of 5℃per minute, and a temperature rising rate of 5℃per minute, and a temperature measuring period of the test piece. The linear thermal expansion coefficient thereof was measured at 50℃to 300℃and the final results are shown in tables 1 to 3 below.

5. Polyimide film glass transition temperature (Tg):

the polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were each prepared by preparing a polyimide film having a thickness of about 10 μm as a test sample piece, cutting into 15mm x 5mm rectangular samples with a knife washed with acetone, and heating the test piece from room temperature to 500℃at a heating rate of 5℃per minute in a nitrogen stream using a dynamic thermo-mechanical analyzer (DMA, model Q800) produced by the United states. The temperature corresponding to the peak value of the damping coefficient (Tan delta) in the energy curve, that is, the glass transition temperature of the film was measured, and the final results are shown in tables 1 to 3 below.

6. Thermal decomposition temperature Td (Td 1% and Td 5%)

The polyamic acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were each prepared by preparing a polyimide film having a thickness of about 10 μm as a test sample piece, taking about 10mg of the sample piece, and heating the sample piece to 150℃at a heating rate of 10℃per minute for 30 minutes in the first stage, cooling to 50℃in the second stage, and heating from 50℃to 800℃in the third stage at a heating rate of 10℃per minute under a nitrogen flow using a thermogravimetric analyzer of Germany type TG209F 1. From the resulting weight-temperature curves, the 1% and 5% weight loss temperatures were determined, with the final results shown in tables 1-3 below.

7. Polyimide film tensile Strength (Strength), tensile Modulus (module), elongation at break (elingation):

the polyamide acid films prepared in examples 14 to 25 and comparative examples 1 to 7 were prepared, respectively, as test samples, and were cut into dumbbell-shaped pieces with 50mm by 4mm in size using a punching die, and the film samples were stretched by using a universal tester (model: AG-I, shimadzu, kyoto, japan) at a clamp pitch of 3mm and a stretching rate of 2mm/min, converted into stress-strain curves based on stretching data, and tensile strength, tensile modulus and elongation at break were determined from the curves, and the final results are shown in tables 1 to 3 below.

8. Determination of the Birefringence index

The polyamic acid films prepared in examples 14 to 26 and comparative examples 1 to 7 were measured for TE refractive index (n (TE)) and TM refractive index (n (TM)) at a wavelength of 632.8nm using prism couplers (PC 2010, manufactured by METRICON Co., ltd.). n (TE) and n (TM) are refractive indices in the parallel direction and the perpendicular direction with respect to the polyimide film surface, respectively. The average refractive index n (AV) is calculated from ((2×n (TE) 2+n (TM) 2)/3)/(0.5), and the birefringence is calculated as the difference between n (TE) and n (TM), i.e., (n (TE) -n (TM)), and the final results are shown in tables 1 to 3 below.

9. Determination of the content of Ionic liquids

The polyamic acid solutions used in examples 14 to 25, the polyamic acid solutions prepared in step (3) of comparative examples 1 to 2 and comparative examples 5 to 7, the polyimide prepolymer dope prepared in step (2) of comparative example 3, and the colorless transparent homogeneous mixed solution prepared in step (1) of comparative example 4 were each measured by using a liquid chromatograph mass spectrometer (liquid chromatograph: LC-20A manufactured by Shimadzu corporation, mass spectrometer: AB Sciexpte.Ltd. API 4000), and standard curves were prepared from the products obtained in comparative example 5, and the ionic liquid contents in the polyamic acid solutions were measured, with the results shown in tables 1 to 3 below.

TABLE 1

TABLE 2

TABLE 3 Table 3

	Comparative example 3	Comparative example 4	Comparative example 5	Comparative example 6	Comparative example 7
						Viscosity (CP)	5364	4061	4632	5023	8130
Mw	62423	65721	66872	69482	88690
						Mw/Mn	2.94	1.96	1.83	1.89	2.6
Light transmittance (400 nm)	70	84	81	80	69
						Content of ionic liquid	215	9462	0	731	687
Birefringence index	0.06	0.1	0.05	0.04	0.02
						CTE(ppm/℃)	26	4	22.5	8.8	21.1
Tg(℃)	370.3	353.4	314.5	432.9	306.0
						Td1％	467.4	456.8	415.3	501.6	385.4
Td5％	508.3	501.3	463.9	431.2	455.8
						Fracture stress (Mpa)	361	329	239	254	303
Young's modulus (Gpa)	3.1	2.6	3.5	3.2	1.4
						Elongation at break (%)	23.5	26.5	25.3	26.7	11％

As can be seen from the test data in tables 1 to 3, the polyimide films prepared by the method have smaller linear expansion coefficients at high temperature and simultaneously have smaller birefringence. Examples 22-25 demonstrate that ionic liquid content is inversely related to birefringence properties over a range by adding ionic liquids in the range claimed. Comparative examples 1-2 the birefringence of the polyimide film showed a significant trend toward an increase when the ionic liquid content was varied outside the scope of the present invention. Comparative examples 3-4, in which polyimide films were synthesized by known methods, had residual amounts of ionic liquid that were not within the scope of the patent claims, and thus exhibited poor birefringence. Examples 5 and 6 respectively adopted the formulations without imidazole ionic liquid and without ionic liquid, and the birefringence performance of the final polyimide film was also poor. Example 7 without the addition of an end-capping agent, the resulting polyimide film had poor thermal properties and birefringence.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended 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 polyamic acid solution comprising a first polymer, a second polymer, and an ionic liquid; the chemical structural formula of the polymer I is shown in the formula I:

the chemical structural formula of the polymer II is shown as a formula II:

In the formula I and the formula II, n is an integer of 50-300; m is an integer of 50 to 300;

wherein the chemical structural formula of X is shown as formula IV:

wherein A in the formula IV is any one of direct bond, ether bond, ester bond, ketone bond, amide bond, dimethylsilylene, alkylene with 1-6 carbon atoms and aromatic group with less than 12 carbon atoms, R ₁ Is any one of hydrogen atom, aromatic group with carbon number less than 12, alkyl with carbon number of 1-3, halogen and hydroxy, R ₂ Is any one of hydrogen atom, aromatic group with carbon number less than 12, alkyl with carbon number of 1-3, halogen and hydroxyl, p is an integer of 0-3;

the chemical structural formula of Y is shown as formula V:

wherein B in formula V is any one of direct bond, ether bond, ester bond, ketone bond, amide bond, dimethylsilylene, alkylene having 1 to 6 carbon atoms, and aromatic group having 12 or less carbon atoms, R ₃ Is any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; r is R ₄ Is any one of a hydrogen atom, an aromatic group having 12 or less carbon atoms, an alkyl group having 1 to 3 carbon atoms, a halogen, and a hydroxyl group; q is an integer of 0 to 3;

Z has the chemical structural formula III:

the ionic liquid is one or more of 1-butyl-3-methylimidazole trifluoroacetate, 1-hydroxyethyl-3-methylimidazole chloride and 1-butyl-3-methylimidazole chloride, and the mass concentration of the ionic liquid relative to the polyamic acid solution is 500-1000ppm.

2. The polyamic acid solution according to claim 1, which has a viscosity of 500 to 10000cp at 25 ℃ and a solid content of 5 to 70wt%; the weight average molecular weight of the polyamic acid solution is 30000-100000 g/mol, and the molecular weight distribution width is 1.1-3.0.

3. A process for the preparation of a polyamic acid solution according to any one of claims 1 to 2, comprising in particular the steps of:

(3) Adding the primary mixed powder into the primary mixed solution, and mixing and dissolving to obtain the polyamic acid solution;

wherein the molar ratio of the diamine to the dianhydride in step (1) is (0.9-1.1): 1, a step of; the temperature of the polymerization reaction is 20-120 ℃ and the time is 1-12 h;

the molar ratio of the diamine to the dianhydride in step (2) is (0.9-1.1): 1, a step of; the mass ratio of the ionic liquid to the dianhydride is (0.05-0.5): 1, a step of; the mass ratio of the end capping agent to the diamine is 0.01% -5%; the temperature of the polymerization reaction is 20-120 ℃ and the time is 1-12 h; the mass ratio of the poor solvent to the reaction liquid is 1: (5-15).

4. A polyimide film prepared from the polyamic acid solution according to any one of claims 1 to 2.

5. The method for preparing the polyimide film according to claim 4, which comprises the following steps: coating the polyamic acid solution on a substrate, drying, and then controlling the temperature to rise for curing to obtain the polyimide film; the drying temperature is 80-180 ℃ and the drying time is 10-100min; the highest temperature of the solidification is 350-480 ℃, the holding time of 150-250 ℃ in the heating process is more than 10min, and the solidification time is 2-5h.

6. Use of the polyimide film of claim 4 in a display, touch panel or solar cell substrate.