CN111205457B - Manufacturing method of polyimide film - Google Patents

Abstract

The invention is a method for preparing polyimide film, it includes providing a polyamic acid copolymer, it must include semi-aromatic polyamic acid at least, the semi-aromatic polyamic acid is obtained through 1,2,3, 4-cyclobutyltetracarboxyl dianhydride (CBDA) and aromatic ring diamine reaction; adding a dehydrating agent, a pyridine catalyst without an ortho-position substituent and an acid into the polyamic acid copolymer; and performing imidization reaction on the polyamic acid copolymer by a chemical cyclization method to prepare a polyimide film.

Description

Manufacturing method of polyimide film

【Technical field】

The present invention relates to a manufacturing method of a polyimide film, in particular to a manufacturing method of a polyimide film which has better mechanical properties and is relatively simple to manufacture.

【Background technique】

The manufacture of polyimide film is obtained by imidization reaction of polyimide precursor polyamic acid, and the method of imidization reaction is divided into chemical cyclization and thermal cyclization; thermal cyclization The cyclization is to imidize the polyamic acid precursor under high temperature conditions, while the chemical cyclization is to use a dehydrating agent and a catalyst to allow the polyamic acid precursor to achieve partial imidization at a lower temperature, and then release it. Bake at high temperature to make the imidization more complete. Thermal cyclization requires more baking time in production, and the mechanical properties of the polyimide film will also decrease and the color will turn yellow under long-term baking. The chemical cyclization method has a fast production time and can maintain good mechanical properties, so it is a better choice to use the chemical cyclization method in mass production.

The polyimide film containing 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) has good optical properties and thermal stability, so it is often used in liquid crystal alignment treatment agents for liquid crystal elements, semiconductor elements , or used in protective films, insulating films, and optical waveguide materials for optical communications. Patent No. US5053480A mentions that CBDA is reacted with diamine to form polyamic acid, and cyclization is carried out in a thermally closed loop method, and a polyimide film with good optical penetration and heat resistance can be produced. Patent No. US6489431B1 uses CBDA and a constituent diamine with hexafluoropropylene, and performs cyclization through thermal ring closure to produce a polyimide film with better optical properties. The above articles all use the thermal closed loop method for film formation, but because the thermal closed loop method will take a lot of baking time, and the mechanical properties of the resulting polyimide film are worse than those produced by the chemical cyclization method, so There are many researchers trying to make membranes by chemical cyclization, but Hasegawa mentioned in the journal High Perform.Polym.2001, 13, S93–S106 that the use of polyamic acid with CBDA component will produce chemical cyclization. Solubility problems cause precipitation. Up to now, in the technical field of chemical cyclization method, no product based on this dianhydride has been found.

Therefore, the present invention provides a method to make a polyimide film with 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) component into a film by chemical cyclization, and the method produced by this method Polyimide films can have better mechanical properties.

[Content of the invention]

The present invention provides a method for manufacturing a polyimide film, which is characterized in that the method comprises: providing a polyamic acid copolymer, which includes a semi-aromatic polyamic acid, the semi-aromatic polyamic acid is composed of 1, 2, It is obtained by reacting 3,4-cyclobutanetetracarboxylic dianhydride (CBDA) with aromatic ring diamine; adding a dehydrating agent, an ortho-position unsubstituted pyridine catalyst and an acid to the polyamic acid copolymer, and using a chemical cyclization method The imidization reaction was performed to prepare a polyimide film.

Specifically, the aromatic ring diamine is selected from p-phenylenediamine (PDA), 4,4'-diaminodiphenyl ether (ODA), 2,2'-bis[4-(4-aminophenoxybenzene) base)] propane (BAPP), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 3,5-diaminobenzoic acid (35DABA), 4,4'-diaminobenzoic acid Aniline (44DABA), 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane (TMDA), 4,4'-bis(4-aminophenoxy) ) Diphenylsulfone (BAPS), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 1,4-bis(4-aminophenoxy)benzene (TPEQ), 2,2' -Bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3 , 3,3-hexafluoropropane (HFBAPP), 9,9-bis(4-aminophenyl)fluorene (BAFL), 2-(4-aminophenyl)-5-aminobenzoxazole (5BPOA), m-phenylenediamine (mPDA), 4,4'-diaminodiphenylsulfone (44DDS), 2,2-bis(4-aminophenyl)hexafluoropropane (Bis-A-AF), 2,2-bis (3-Amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline](FAPB) .

Further, the polyamic acid copolymer also includes an aromatic polyamic acid, which is obtained by reacting an aromatic diamine with an aromatic dianhydride.

Specifically, the aromatic dianhydride is selected from 1,2,4,5-mellitic anhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4, 4'-Oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3,4,4-diphenylsulfone tetracarboxylate Acid dianhydride (DSDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 4,4-hexafluoroisopropylphthalic anhydride (6FDA), 4,4 '-(4,4'-isopropyldiphenoxy)diphthalic anhydride (BPADA); the aromatic diamine is selected from 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) , 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1, 1,3,3,3-Hexafluoropropane (HFBAPP), 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane (TMDA), terephthalic acid Amine (PDA), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA ), 4,4'-bis(4-aminophenoxy)diphenylsulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4'-diaminodiphenylsulfone (44DDS), 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminobenzoic anilide (44DABA), 2,2-bis(4-aminophenyl)hexafluoropropane (Bis -A-AF), m-phenylenediamine (mPDA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 3,5-diaminobenzoic acid (35DABA), 2 -(4-Aminophenyl)-5-aminobenzoxazole (5BPOA), 1,4-bis(4-aminophenoxy)benzene (TPEQ), 4,4'-[1,4-phenyl Bis(oxy)]bis[3-(trifluoromethyl)aniline](FAPB).

Further, the ortho-position unsubstituted pyridine-based catalyst is selected from pyridine, 3-picoline, 4-picoline, isobenzopyridine, and benzopyridine.

Specifically, the acid is selected from organic acids; preferably acetic acid, propionic acid, butyric acid, oxalic acid, benzoic acid, terephthalic acid, terephthalic acid or phthalic acid.

Preferably, the number of moles added of the organic acid is greater than or equal to the number of moles added of the ortho-position unsubstituted pyridine catalyst; the organic acid is preferably acetic acid, and the ortho-position unsubstituted pyridine catalyst It is preferably 3-picoline, and the dehydrating agent is preferably acetic anhydride; the number of moles of the semi-aromatic polyamic acid dianhydride can be more than 60 percent of the total number of moles of the acid anhydride of the copolymerized polyamic acid.

One of the specific embodiments provided by the present invention is to add 412.5 grams of N,N-dimethylacetamide to 0.1675 moles of 2,2'-bis(trifluoromethyl)diaminobiphenyl, and wait until all the After dissolving, add 0.134 moles of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, stir the reaction, then add 0.0558 moles of 2,2'-bis(trifluoromethyl)diaminobiphenyl and stir until completely dissolved Then add 0.1074 moles of 4,4-hexafluoroisopropylphthalic anhydride, stir, dissolve and react to obtain a polyamic acid copolymer with a solid content of 25%; take 54.4 grams of the polyamic acid copolymer, use N,N-Dimethylacetamide (DMAc) diluted the solid content to 17%, then added 8 ml of acetic acid, 4.3 ml of 3-methylpyridine and 12.5 ml of acetic anhydride, stirred evenly, and coated and dried. have to.

The present invention also provides the polyimide film prepared by any of the aforementioned methods, characterized in that, when the thickness of the polyimide film is 22-50um, the chromaticity b* is less than 1.5.

The present invention also provides a polyimide film prepared from copolyamic acid, characterized in that the copolyamic acid includes semi-aromatic polyamic acid, and the semi-aromatic polyamic acid is composed of 1 ,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) is obtained by reacting with aromatic ring diamine; the thickness of the polyimide film is 22-50um, and the chromaticity is b*0.9-1.5.

【Description of drawings】

FIG. 1 is a flow chart of the manufacturing method of the polyimide film of the present invention.

Among them, the description of each symbol is as follows:

Provide a polyamic acid copolymer (S1)

Add dehydrating agent, ortho-unsubstituted pyridine catalyst and acid (S2)

The imidization reaction (S3) is carried out by chemical cyclization.

【Detailed ways】

Please refer to FIG. 1, the present invention is a method of manufacturing a polyimide film, which includes: providing a polyamic acid copolymer (S1), which must contain at least a semi-aromatic polyamic acid, the semi-aromatic polyamic acid The polyamic acid is obtained through the reaction of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) with aromatic ring diamine; the polyamic acid copolymer is added with a dehydrating agent, ortho-position unsubstituted pyridines The catalyst and the acid (S2) are used to carry out the imidization reaction (S3) of the polyamic acid copolymer by the chemical cyclization method, thereby producing a polyimide film.

Wherein, the semi-aromatic polyamic acid is obtained by reacting 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) with an aromatic ring diamine, wherein the aromatic ring diamine can be p-phenylenediamine (PDA). ), 4,4'-diaminodiphenyl ether (ODA), 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2'-bis(trifluoro) Methyl)diaminobiphenyl (TFMB), 3,5-diaminobenzoic acid (35DABA), 4,4'-diaminobenzoic anilide (44DABA), 5(6)-amino-1-(4- Aminophenyl)-1,3,3-trimethylindane (TMDA), 4,4'-bis(4-aminophenoxy)diphenylsulfone (BAPS), 4,4'-bis(4- Aminophenoxy)biphenyl (BAPB), 1,4-bis(4-aminophenoxy)benzene (TPEQ), 2,2'-bis(trifluoromethyl)-4,4'-diaminobenzene Base ether (6FODA), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), 9,9-bis (4-Aminophenyl)fluorene (BAFL), 2-(4-aminophenyl)-5-aminobenzoxazole (5BPOA), m-phenylenediamine (mPDA), 4,4'-diaminodiphenyl Sulfone (44DDS), 2,2-bis(4-aminophenyl)hexafluoropropane (Bis-A-AF), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) , one or more of 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline](FAPB).

The polyamic acid copolymer may further include an aromatic polyamic acid, which is obtained by reacting an aromatic diamine with an aromatic dianhydride.

The aromatic diamine contains 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP) ), 2,2-bis[4-(4-aminophenoxy)benzene

base]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindan (TMDA), p-phenylenediamine (PDA), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 2,2'-bis(trifluoromethyl)-4,4'- Diaminophenyl ether (6FODA), 4,4'-bis(4-aminophenoxy)diphenylsulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (BAFL), 4,4 '-Diaminodiphenylsulfone (44DDS), 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminobenzyl anilide (44DABA), 2,2-bis(4-aminobenzene) base) hexafluoropropane (Bis-A-AF), m-phenylenediamine (mPDA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 3,5-diamino Benzoic acid (35DABA), 2-(4-aminophenyl)-5-aminobenzoxazole (5BPOA), 1,4-bis(4-aminophenoxy)benzene (TPEQ), 4,4'- One or more of [1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline](FAPB). Among them, aromatic dianhydrides include 1,2,4,5-mellitic anhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxygen Diphthalic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride ( DSDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 4,4-hexafluoroisopropylphthalic anhydride (6FDA), 4,4'-(4 One or more of ,4'-isopropyldiphenoxy)diphthalic anhydride (BPADA).

The polyamic acid copolymer uses a chemical cyclization method to carry out imidization reaction, and adds a dehydrating agent, an unsubstituted pyridine catalyst at the ortho position and an acid, wherein the pyridine catalyst without a substituent at the ortho position can be pyridine, 3- Methyl pyridine, 4-picoline, benzopyridine, benzopyridine. The acid is an organic acid, and can be acetic acid, propionic acid, butyric acid, oxalic acid, benzoic acid, terephthalic acid, terephthalic acid, or phthalic acid. The number of moles of the acid added is preferably greater than or equal to the number of moles of the ortho-position unsubstituted pyridine-based catalyst added.

Example

<Detection method>

Chromaticity b*: Measured according to ASTM E313 using a model NE-4000 instrument produced by Nippon Denshoku.

<Example 1>

Manufacture of polyamic acid copolymers

53.645 grams of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.1675

moles, the ratio of moles to the total diamine is 0.75), add 412.5 grams of N,N-dimethylacetamide (DMAc), and add 26.282 grams of 1,2,3,4-cyclobutanetetracarboxylate after all dissolved Anhydride (CBDA, 0.134 moles, accounting for 60% of the total acid anhydride moles), stirred and reacted for six hours and the temperature was maintained at 25° C. to form a semi-aromatic polyamic acid solution. After six hours, add 17.882 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.0558 mol) to the above-mentioned semi-aromatic polyamic acid solution, stir until completely dissolved, and then add 38.698 g of 4 ,4-hexafluoroisopropylphthalic anhydride (6FDA, 0.1074 mol), stir for a certain period of time to dissolve and react, and the temperature of the solution is maintained at 25 ° C, and finally a polyamic acid copolymer with a solid content of 25% is obtained. thing.

Polyimide film production

54.4 g was taken out of the above polyamic acid copolymer, and the solid content was diluted to 17% with N,N-dimethylacetamide (DMAc), after which 8 ml of acetic acid (0.14 mol), 4.3 ml of acetic acid were added sequentially of 3-picoline (0.044 mol) and 12.5 mL of acetic anhydride, after uniform stirring, the solution was applied to a glass plate and then applied using a doctor blade with a 900 μm gap. The coated samples were placed in a 50°C oven for 20 minutes, then slowly heated to 170°C for 20 minutes, and then the oven was heated to 260°C for 20 minutes as the final treatment.

The polyimide film prepared above is a polyimide film with a lower chromaticity b* of 1.5.

<Example 2>

Manufacture of polyamic acid copolymers

18.606 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB, 0.0581

mol), add 90 g of N,N-dimethylacetamide (DMAc), add 11.394 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA, 0.0581 mol) after all dissolved, add The temperature is controlled to be 25° C., the reaction is stirred for 24 hours and the temperature is continuously maintained at 25° C. to finally obtain a polyamic acid solution with a solid content of 25%.

Production of polyimide film

20.2 g of the above polyamic acid copolymer was taken out, and the solid content was diluted to 15.8% with N,N-dimethylacetamide (DMAc), after which 1.2 g (0.02 mol) of acetic acid and 0.9 g of acetic acid were added respectively. 3-methylpyridine (0.0097 mol), 2.0 g of acetic anhydride was added after uniform stirring, and the solution was applied to a glass plate using a doctor blade with a gap of 400 μm. The coated samples were placed in a 50°C oven for 20 minutes, then slowly heated to 170°C for 20 minutes, and then the oven was heated to 260°C for 20 minutes as the final treatment.

The polyimide prepared above can be formed into a film and has a lower chromaticity b* of 0.9.

<Example 3>

Production of polyamic acid copolymer

18.948 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA,

0.0564 mol), add 90 g of N,N-dimethylacetamide (DMAc), and after all dissolved, add 11.052 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA, 0.0564 mol), When adding, the temperature is controlled to be 25° C., the reaction is stirred for 24 hours and the temperature is continuously maintained at 25° C. to finally obtain a polyamic acid copolymer with a solid content of 25%.

Production of polyimide film

20.2 g of the above polyamic acid copolymer was taken out, and the solid content was diluted to 15.8% with N,N-dimethylacetamide (DMAc), after which 1.1 g of acetic acid (0.018 mol) and 0.9 g of acetic acid were added, respectively. 3-methylpyridine (0.0097 mol), 1.9 g of acetic anhydride was added after uniform stirring, and the solution was applied to a glass plate using a doctor blade with a gap of 600 μm. The coated samples were placed in a 50°C oven for 20 minutes, then slowly heated to 170°C for 20 minutes, and then the oven was heated to 260°C for 20 minutes as the final treatment.

The transparent polyimide prepared above can be formed into a film and has a lower chromaticity b* of 1.0.

<Comparative Example 1>

Production of polyamic acid copolymer

The preparation method is the same as that of Example 1.

Production of polyimide film

54.4 g of the above copolyamic acid solution was taken out, and the solid content was diluted to 17% with N,N-dimethylacetamide (DMAc), and the solution was applied to a glass plate using a doctor blade with a gap of 900 μm. cloth. The coated samples were placed in a 50°C oven for 20 minutes, then slowly heated to 170°C for 20 minutes, and then the oven was heated to 260°C for 20 minutes as the final treatment.

The transparent polyimide prepared above can be formed into a film and has a higher chromaticity b* of 3.6.

<Comparative Example 2>

Production of polyamic acid copolymer

The preparation method is the same as that of Example 2.

Production of polyimide film

20.2 g of the above polyamic acid copolymer was taken out, and the solid content was diluted to 15.8% with N,N-dimethylacetamide (DMAc), and the solution was applied to a glass plate using a doctor blade with a gap of 400 μm. cloth. The coated samples were placed in a 50°C oven for 20 minutes, then slowly heated to 170°C for 20 minutes, and then the oven was heated to 260°C for 20 minutes as the final treatment.

The above-mentioned production method cannot form a film.

<Comparative Example 3>

Production of polyamic acid copolymer

The preparation method is the same as that of Example 3.

Production of polyimide film

In the above polyamic acid copolymer, 54.4 g was taken out, and the solid content was diluted to 17% with N,N-dimethylacetamide (DMAc), and then 4.3 ml of 3-picoline and 12.5 ml of 3-picoline were added sequentially. acetic anhydride rapidly gels after stirring, so it cannot form a film.

<Comparative Example 4>

Production of polyamic acid copolymer

The preparation method is the same as that of Example 3.

Production of polyimide film

20.2 g of the above polyamic acid copolymer was taken out, and the solid content was diluted to 15.8% with N,N-dimethylacetamide (DMAc), and the solution was applied to a glass plate using a doctor blade with a gap of 600 μm. cloth. The coated samples were placed in a 50°C oven for 20 minutes, then slowly heated to 170°C for 20 minutes, and then the oven was heated to 260°C for 20 minutes as the final treatment.

It can be made into a polyimide film with a chromaticity b* of 3.8.

Experimental comparison table

X: Can not form film; O: Can form film

The contents of the above-mentioned specific embodiments are intended to illustrate the present invention in detail, however, these embodiments are only for illustration and are not intended to limit the present invention. It will be understood by those skilled in the art that the present invention is directed to the present invention without departing from the scope defined by the appended claims. Various changes or modifications made are part of the present invention.

Claims (11)

1. a manufacture method of polyimide film, is characterized in that, this method comprises: A polyamic acid copolymer is provided, which includes a semi-aromatic polyamic acid, the semi-aromatic polyamic acid is obtained by reacting 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) with an aromatic ring diamine; A dehydrating agent, an ortho-unsubstituted pyridine-based catalyst, and an acid are added to the polyamic acid copolymer, and imidization reaction is carried out by a chemical cyclization method to prepare a polyimide film. 2. The method according to claim 1, wherein the aromatic ring diamine is selected from p-phenylenediamine (PDA), 4,4'-diaminodiphenyl ether (ODA), 2,2'- Bis[4-(4-Aminophenoxyphenyl)]propane (BAPP), 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 3,5-diaminobenzoic acid (35DABA) ), 4,4'-diaminobenzoic anilide (44DABA), 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane (TMDA), 4 ,4'-bis(4-aminophenoxy)diphenylsulfone (BAPS), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 1,4-bis(4-aminobenzene) Oxy)benzene (TPEQ), 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 2,2-bis[4-(4-aminophenoxy) )phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), 9,9-bis(4-aminophenyl)fluorene (BAFL), 2-(4-aminophenyl) -5-Aminobenzoxazole (5BPOA), m-phenylenediamine (mPDA), 4,4'-diaminodiphenylsulfone (44DDS), 2,2-bis(4-aminophenyl)hexafluoropropane ( Bis-A-AF), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 4,4'-[1,4-phenylbis(oxy)]bis[3 -(trifluoromethyl)aniline](FAPB). 3. The method according to claim 1, wherein the polyamic acid copolymer further comprises an aromatic polyamic acid, which is obtained by reacting an aromatic diamine with an aromatic dianhydride. have to. 4. The method according to claim 3, wherein the aromatic dianhydride is selected from 1,2,4,5-mellitic anhydride (PMDA), 3,3',4,4'-linked Benzenetetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3, 3,4,4-Diphenylsulfone tetracarboxylic dianhydride (DSDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 4,4-hexafluoroisopropyl Phthalic anhydride (6FDA), 4,4'-(4,4'-isopropyldiphenoxy)diphthalic anhydride (BPADA); the aromatic diamine is selected from 2,2'-bis( Trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP), 2,2-bis[4-(4-amino) Phenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), 5(6)-amino-1-(4-aminophenyl)-1,3,3- Trimethylindane (TMDA), p-phenylenediamine (PDA), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 2,2'-bis(trifluoromethyl)- 4,4'-Diaminophenyl ether (6FODA), 4,4'-bis(4-aminophenoxy)diphenylsulfone (BAPS), 9,9-bis(4-aminophenyl)fluorene (BAFL) ), 4,4'-diaminodiphenyl sulfone (44DDS), 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminobenzoic anilide (44DABA), 2,2-bis (4-Aminophenyl)hexafluoropropane (Bis-A-AF), m-phenylenediamine (mPDA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 3 , 5-Diaminobenzoic acid (35DABA), 2-(4-aminophenyl)-5-aminobenzoxazole (5BPOA), 1,4-bis(4-aminophenoxy)benzene (TPEQ), 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] (FAPB). 5. according to the arbitrary described method of claim 1-4, it is characterized in that, the pyridine catalyst of described ortho position unsubstituted group is selected from pyridine, 3-picoline, 4-picoline, isobenzopyridine , Benzopyridine. 6. The method according to any one of claims 1-4, wherein the acid is selected from organic acids. 7. The method according to claim 6, wherein the organic acid is acetic acid, propionic acid, butyric acid, oxalic acid, benzoic acid, terephthalic acid, terephthalic acid or phthalic acid. 8. The method according to claim 6, wherein the added mole of the organic acid is greater than or equal to the added mole of the ortho-unsubstituted pyridine catalyst; the organic acid is acetic acid, so The pyridine catalyst without substituent in the ortho position is 3-methylpyridine, and the dehydrating agent is acetic anhydride; percentage above 60. 9. The method of claim 8, wherein Add 412.5 grams of N,N-dimethylacetamide to 0.1675 moles of 2,2'-bis(trifluoromethyl)diaminobiphenyl, and after all dissolved, add 0.134 moles of 1,2,3,4 -Cyclotetracarboxylic dianhydride, stir the reaction, then add 0.0558 moles of 2,2'-bis(trifluoromethyl)diaminobiphenyl, stir until completely dissolved, and then add 0.1074 moles of 4,4-hexafluoroisopropyl base phthalic anhydride, stirring and dissolving and reacting, obtaining the polyamic acid copolymer that solid content is 25%; Take 54.4 g of the polyamic acid copolymer, dilute the solid content to 17% with N,N-dimethylacetamide (DMAc), then add 8 ml of acetic acid, 4.3 ml of 3-picoline and 12.5 ml of acetic acid. Milliliter of acetic anhydride, uniformly stirred, coated and dried. 10. The polyimide film prepared by the method of any one of claims 1-9. 11. The polyimide film according to claim 10, wherein when the thickness of the polyimide film is 22-50um, the chromaticity b* is less than 1.5.

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