Tetracarboxylic dianhydrides, methods for their preparation and use, polyimide copolymers, methods for their preparation and polyimide films

Abstract

The application provides a tetracarboxylic dianhydride, a preparation method and application thereof, a polyimide copolymer, a preparation method thereof and a polyimide film. The tetracarboxylic dianhydride is a novel dianhydride monomer with a semi-alicyclic structure of a double norbornene skeleton containing a 'Spiro' spiro ring structure. The 'Spiro' spiro ring structure makes the polyimide film have better heat resistance. Meanwhile, the dianhydride monomer can effectively weaken the CTC conjugation effect together with the norbornene skeleton structure. The prepared colorless polyimide film has excellent optical performance, good thermal stability and mechanical properties. The tetracarboxylic dianhydride has the structure shown in the following formula.

Description

Technical Field

[0001] This invention relates to the fields of chemical synthesis technology and organic polymer materials technology, and in particular to a tetracarboxylic acid dianhydride and its preparation method and application, a polyimide copolymer and its preparation method, and a polyimide film. Background Technology

[0002] Polyimide (PI) is a special type of polymer material containing an imide ring structure in its main chain. Polyimides are generally prepared by the polymerization reaction of diamine monomers and dianhydride monomers. Based on different types of molecular structural units, polyimides can generally be divided into aromatic and aliphatic types. Aromatic polyimides obtained using existing aromatic tetracarboxylic dianhydrides exhibit excellent heat resistance. However, due to the strong interaction between alternating electron donors and acceptors in their molecular chains, intramolecular and intermolecular charge-transfer complexes (CTCs) are formed, resulting in a brownish-yellow color in fully aromatic PI films and low transmittance in the ultraviolet-visible region (wavelength 400-800 nm), especially at 400 nm where it is almost 100% absorbed. This makes the optical properties of fully aromatic PI materials unsuitable for some optoelectronic applications requiring high transmittance, such as optical communication, optoelectronic materials, and liquid crystal displays. Furthermore, aromatic polyimides reduce the structural rigidity of the molecular chain and intermolecular forces, leading to a decrease in their thermal and mechanical properties. However, with the rapid development of the modern consumer electronics industry, especially the continuous upgrading of display technologies represented by smartphones, polyimide materials are expanding from the traditional aerospace and military industries to industries such as flexible displays. Compared with other materials, aromatic PI has good plasticity and thermal stability. Therefore, how to improve the optical properties of polyimide while maintaining its excellent heat resistance and mechanical properties is of great significance for its expansion in new consumer electronics technologies.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the purpose of the present invention is to provide a tetracarboxylic dianhydride and its preparation method and application, a polyimide copolymer and its preparation method, and a polyimide film. The polyimide film made of tetracarboxylic dianhydride provided by the present invention has excellent optical properties and can meet some applications in the optoelectronic field that require high transmittance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a tetracarboxylic dianhydride having the structure of Formula I:

[0007]

[0008] In Formula I, R1 and R2 are each independently selected from hydrogen, fluorine, alkyl groups having 1 to 15 carbon atoms, and heteroalkyl groups having 1 to 15 carbon atoms; X1 and X2 are each independently selected from oxygen, alkylene groups having 1 to 5 carbon atoms, and fluoroalkylene groups having 1 to 5 carbon atoms; Ar is a divalent aromatic group or heteroaromatic group having 4 to 50 carbon atoms.

[0009] Furthermore, in Formula I, the number of R1 on the bridged ring hydrocarbon can be one or more, and the number of R2 can be one or more;

[0010] And / or, the substituents on the aromatic or heteroaromatic rings in Ar are trifluoromethyl or fluorine;

[0011] And / or, Ar is selected from one of the following structures:

[0012]

[0013] In addition, the present invention also provides a method for preparing the above-mentioned tetracarboxylic dianhydride, characterized by comprising the following steps:

[0014] In a protective atmosphere, a mixed reaction system comprising an anhydride with an imidized or esterified spirocyclic norbornene skeleton structure, a dihalogenated aromatic or heteroaromatic compound, a transition metal-based catalyst, a ligand, a basic substance, a reducing agent, and a solvent is reacted to prepare a diimide compound or a tetracarboxylic acid ester compound. These compounds are then subjected to hydrolysis, acidification, and dehydration to obtain a tetracarboxylic acid dianhydride having the structure of Formula I. The structural formulas of the imidized anhydride with a spirocyclic norbornene skeleton structure are shown in Formulas II-1 and II-2.

[0015]

[0016] In formulas II-1 and II-2, the definitions of R1, R2, X1, and X2 are the same as those in formula I; R11 and R21 independently represent any one of aryl and alkyl groups having 1 to 5 carbon atoms.

[0017] The structural formulas of the esterified anhydrides with a spirocyclic norbornene skeleton are shown in Formulas III-1 and III-2:

[0018]

[0019] In formulas III-1 and III-2, the definitions of R1, R2, X1, and X2 are the same as those in formula I; R12, R13, R22, and R23 each independently represent any one of the alkyl groups having 1 to 5 carbon atoms.

[0020] The structural formula of the dihalogenated aromatic or heteroaromatic compound is shown in Formula IV:

[0021]

[0022] In Formula IV, Ar is defined in the same way as Ar in Formula I; R3 and R4 are each independently selected from any one of Cl, Br, I, OTf, ONf, p-toluenesulfonyl, and methanesulfonyl.

[0023] The structural formula of the diimide compound is shown in Formula V:

[0024]

[0025] In Formula V, the definitions of Ar, R1, R2, X1, and X2 are the same as those in Formula I; R11 and R21 each independently represent any one of aryl and alkyl groups having 1 to 5 carbon atoms.

[0026] The structural formula of the tetracarboxylic acid ester compound is shown in Formula VI:

[0027]

[0028] In Formula VI, the definitions of Ar, R1, R2, X1, and X2 are the same as those in Formula I; R12, R13, R22, and R23 each independently represent any one of the alkyl groups having 1 to 5 carbon atoms.

[0029] Further, the molar ratio of the anhydride with the spirocyclic norbornene skeleton structure, the dihalogenated aromatic or heteroaromatic compound, the transition metal-based catalyst, the ligand, the basic substance, and the reducing agent is (2-4):(1-1.1):(0.02-0.2):(0.04-0.4):(2-4):(2-4);

[0030] And / or, the mass percentage of the solvent in the mixed reaction system is 35-95 wt%;

[0031] And / or, the reaction temperature is 60–120°C, and the reaction time is 1–48 h;

[0032] And / or, the transition metal-based catalyst includes, but is not limited to, at least one of rhodium chloride, nickel chloride, palladium chloride, and palladium acetate;

[0033] And / or, the ligand comprises at least one of triphenylphosphine, triphenylarsine, and tricyclohexylphosphine;

[0034] And / or, the alkaline substance includes at least one of triethylamine, piperidine, pyrrolidine, cesium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, potassium acetate, calcium acetate, magnesium acetate, potassium phosphate, sodium phosphate, and potassium hydrogen phosphate;

[0035] And / or, the reducing agent includes at least one of formic acid and water;

[0036] And / or, the solvent includes any one of tetrahydrofuran, 1,4-dioxane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0037] And / or, the protective atmosphere includes either nitrogen or argon;

[0038] And / or, the hydrolysis and acidification treatment includes: mixing the bisimide compound or tetracarboxylic acid ester compound with an aqueous sodium hydroxide solution and refluxing for 6 to 48 hours, cooling to room temperature, filtering out insoluble impurities, adjusting the pH of the filtrate to 4-5 with acid, precipitating a white solid, filtering, washing the filter cake, and drying.

[0039] And / or, the preparation method of an imide compound with the structural formula shown in Formula II-1 includes the following steps:

[0040] The amine represented by R11-NH2 reacts with an anhydride with the structure shown in Formula VII to obtain an imide compound with the structure shown in Formula II-1, wherein R11 represents any one of aryl or alkyl with 1 to 5 carbon atoms;

[0041]

[0042] In Equation VII, the definitions of R1 and X1 are the same as those in Equation I;

[0043] Alternatively, an imide with the structural formula shown in Formula VIII reacts with a compound with the structural formula shown in Formula IX to obtain an imide compound with the structural formula shown in Formula II-1.

[0044]

[0045] In equation VIII, R 11 The definition of R in Equation II-1 11 The definitions are the same;

[0046]

[0047] In Equation IX, the definitions of R1 and X1 are the same as those in Equation I;

[0048] And / or, the preparation method of a dicarboxylic acid ester compound with the structural formula shown in Formula III-1 includes the following steps:

[0049] The alcohols represented by R12-OH and R13-OH react with the anhydrides with the structure shown in Formula VII to obtain dicarboxylic acid ester compounds with the structure shown in Formula III-1, wherein R12 and R13 represent any one of the alkyl groups having 1 to 5 carbon atoms;

[0050] Alternatively, the diester with the structural formula shown in Formula X reacts with a compound with the structural formula shown in Formula IX to obtain a dicarboxylic acid ester compound with the structural formula shown in Formula III-1.

[0051]

[0052] In Equation X, the definitions of R12 and R13 are the same as those in Equation III.

[0053] Further, itaconic anhydride is reacted with a compound with the structural formula shown in Formula IX to obtain an anhydride with the structural formula shown in Formula VII, comprising: adding the compound with the structural formula shown in Formula IX dropwise to the itaconic anhydride at 25-60°C, reacting at 25-60°C for 6-10 hours, and then concentrating and drying to obtain the anhydride with the structural formula shown in Formula VII;

[0054] And / or, the amine represented by R11-NH2 includes at least one of methylamine, ethylamine, propylamine, butylamine, and aniline;

[0055] And / or, the alcohols represented by R12-OH and R13-OH react with anhydrides of the structural formula shown in Formula VII to obtain a dicarboxylic acid ester compound of the structural formula shown in Formula III-1, comprising: dissolving anhydrides of the structural formula shown in Formula VII in alcohols represented by general formulas R12-OH and R13-OH, adding concentrated sulfuric acid dropwise after dissolution and refluxing for 6-18 hours, then cooling to room temperature and adding sodium bicarbonate to quench the reaction, and then evaporating, extracting, drying, filtering and concentrating to obtain the esterified dicarboxylic acid ester compound of the structural formula shown in Formula III-1;

[0056] And / or, the alcohols represented by R12-OH and R13-OH are independently selected from any one of methanol, ethanol, isopropanol, and tert-butanol.

[0057] In addition, the present invention also provides the application of the above-mentioned tetracarboxylic dianhydride or the tetracarboxylic dianhydride prepared by the above preparation method in the preparation of polyimide copolymers.

[0058] Furthermore, the polyimide copolymer has repeating units as shown in Formula XI:

[0059]

[0060] In formula XI, R1 and R2 are each independently selected from hydrogen, fluorine, alkyl groups having 1 to 15 carbon atoms, and heteroalkyl groups having 1 to 15 carbon atoms; X1 and X2 are each independently selected from oxygen, alkylene groups having 1 to 5 carbon atoms, and fluoroalkylene groups having 1 to 5 carbon atoms; Ar is a divalent aromatic group or heteroaromatic group having 4 to 50 carbon atoms; R is selected from substituted or unsubstituted aryl or heteroaryl groups having 6 to 50 carbon atoms; preferably, when R is a substituted aryl or heteroaryl group having 6 to 50 carbon atoms, the substituent is at least one of trifluoromethyl, fluorine, methyl, and ethyl; preferably, R is selected from one of the following structures:

[0061]

[0062] Preferably, the polyimide copolymer is obtained by reacting a tetracarboxylic acid dianhydride as described above with an aromatic diamine of formula XII.

[0063] H2N-R-NH2Ⅻ

[0064] In Formula XII, R is defined in the same way as R in Formula XI, and is selected from arylene or heteroarylene with 6 to 50 carbon atoms, whether substituted or unsubstituted.

[0065] More preferably, the aromatic diamine with the structural formula shown in Formula XII includes at least one of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether.

[0066] Furthermore, it includes the following steps:

[0067] S1. Mix the tetracarboxylic acid dianhydride as described in claim 1 or 2, the aromatic diamine with the structural formula shown in formula XII, and the reaction solvent to carry out a polymerization reaction to obtain a polyamic acid solution.

[0068] S2. The polyamic acid is imidized to obtain a polyimide copolymer having repeating units as shown in Formula XI;

[0069] Preferably, the reaction solvent includes a polar aprotic solvent, including but not limited to at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone;

[0070] Preferably, the polyamic acid has at least one repeating unit as shown in general formulas XIII-1 to XIII-3:

[0071]

[0072] In formulas XIII-1 to XIII-3, R1 and R2 are defined the same as in formula I, and are each independently selected from hydrogen, fluorine, alkyl groups with 1 to 15 carbon atoms, and heteroalkyl groups with 1 to 15 carbon atoms; X1 and X2 are defined the same as in formula I, and are each independently selected from oxygen, alkylene groups with 1 to 5 carbon atoms, and fluoroalkylene groups with 1 to 5 carbon atoms; Ar is defined the same as in formula I, and is a divalent aromatic group or heteroaromatic group with 4 to 50 carbon atoms; R is defined the same as in formula XI, and is selected from substituted or unsubstituted aryl or heteroaryl groups with 6 to 50 carbon atoms.

[0073] Preferably, the reaction atmosphere is an inert gas atmosphere, the inert gas including nitrogen, the reaction temperature is 30-100°C, and the reaction time is 2-24 hours;

[0074] Preferably, in step S1, the molar ratio of the tetracarboxylic acid dianhydride to the aromatic diamine with the structural formula shown in Formula XII is 1:1;

[0075] Preferably, in step S1, the solid content of the polyamic acid solution is 10wt% to 20wt%.

[0076] In addition, the present invention also provides a polyamic acid, which is prepared by using the tetracarboxylic dianhydride prepared by the above-mentioned tetracarboxylic dianhydride or the tetracarboxylic dianhydride prepared by the above-mentioned tetracarboxylic dianhydride preparation method.

[0077] In addition, the present invention also provides a colorless and transparent polyimide film, which is made from the polyimide copolymer prepared by the above-mentioned method of preparing the polyimide copolymer or the polyamic acid.

[0078] Compared with the prior art, the present invention has at least the following beneficial effects:

[0079] 1. The polyimide film made of tetracarboxylic acid dianhydride provided by the present invention has excellent optical properties and can meet the needs of some optoelectronic applications that require high transmittance.

[0080] 2. The tetracarboxylic acid dianhydride provided by this invention is a novel dianhydride monomer with a semi-alicyclic structure containing a "Spiro" spiro ring and a bisnorbornene skeleton. The "Spiro" spiro ring structure gives the polyimide film better heat resistance. At the same time, its structure with the norbornene skeleton can effectively reduce the CTC conjugation effect, and the prepared colorless polyimide film has excellent optical properties.

[0081] 3. The tetracarboxylic acid dianhydride provided by the present invention contains a spirocyclic ring but does not contain a four-membered ring structure, which makes the polyimide PI prepared therefrom have excellent solubility and the resulting film is more transparent.

[0082] 4. The tetracarboxylic acid dianhydride monomer and the prepared polyimide polymer provided by this invention are more stable and can remain stable for a longer period of time under ultraviolet irradiation above 300 nm.

[0083] 5. This invention develops a dianhydride monomer with a semi-alicyclic structure containing a "Spiro" spirocyclic bisnorbornene skeleton, which is polymerized with various aromatic and heteroaromatic diamine monomers to prepare semi-aromatic polyimides and their films, which have excellent optical properties as well as good thermal stability and mechanical properties. Attached Figure Description

[0084] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0085] Figure 1 The image shows the 1H NMR spectrum of the tetracarboxylic acid dianhydride monomer prepared in Example 1 of this invention, using deuterated chloroform as a solvent. Detailed Implementation

[0086] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0087] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0088] Unless otherwise stated, the terms used in the specification and claims have the following meanings.

[0089] The term "alkyl" refers to a saturated aliphatic hydrocarbon group, which is a straight-chain or branched group containing 1 to 15 carbon atoms. Non-limiting examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl, 2,2-dimethylpropyl, 1-ethylpropyl, 2-methylbutyl, and their various branched isomers. An alkyl group can also be a saturated aliphatic hydrocarbon group in which some or all of its branches are replaced by substituents selected independently from one or more of halogens, haloalkyl groups, alkoxy groups, haloalkoxy groups, alkylamino groups, hydroxyl groups, cyano groups, and amino groups.

[0090] The term "heteroalkyl" refers to an alkyl group having one or more skeletal chain atoms selected from atoms other than carbon, such as oxygen, nitrogen, sulfur, phosphorus or combinations thereof on the carbon backbone. Specifically, the skeletal chain or backbone contains acyl groups, ester groups, etc.

[0091] The term "heteroaromatic group" refers to a hydrocarbon group (containing heteroatoms such as oxygen, nitrogen, sulfur, phosphorus, etc.) that contains at least one heteroaromatic ring, and the number of rings can be one or more.

[0092] The number of carbon atoms in the aromatic ring forming the aromatic group (the term "number of carbon atoms forming the aromatic ring" here includes the number of carbon atoms of the substituents on the aromatic ring. For example, in the case of 2-ethyl-1,4-phenylene, the number of carbon atoms forming the aromatic ring is 8) is 4 to 50.

[0093] In a first aspect, the present invention provides a tetracarboxylic acid dianhydride having a structure of Formula I:

[0094]

[0095] In Formula I, R1 and R2 are each independently selected from hydrogen, fluorine, alkyl groups with 1 to 15 carbon atoms (e.g., 1, 3, 5, 7, 11, 13 or 15), and heteroalkyl groups with 1 to 15 carbon atoms (e.g., 1, 3, 5, 7, 11, 13 or 15); X1 and X2 are each independently selected from oxygen, alkylene groups with 1 to 5 carbon atoms (e.g., 1, 3 or 5), and fluoroalkylene groups with 1 to 5 carbon atoms (e.g., 1, 3 or 5); Ar is a divalent aromatic group or heteroaromatic group with 4 to 50 carbon atoms (e.g., 4, 6, 10, 12, 18, 24, 36 or 48).

[0096] The tetracarboxylic acid dianhydride provided by this invention is a novel dianhydride monomer with a semi-alicyclic structure containing a "Spiro" spiro ring and a bisnorbornene backbone. The "Spiro" spiro ring structure gives the polyimide film better heat resistance. At the same time, its structure with the norbornene backbone can effectively reduce the CTC conjugation effect. The colorless polyimide film prepared has excellent optical properties and has good application prospects in flexible displays, thin-film solar cells, optoelectronic engineering and other fields.

[0097] In the above-mentioned tetracarboxylic acid dianhydride, as an optional embodiment, the number of R1 on the bridged ring hydrocarbon in Formula I can be one or more, and the number of R2 can be one or more.

[0098] In the above-mentioned tetracarboxylic acid dianhydride, as an optional embodiment, the substituent on the aromatic ring or heteroaromatic ring of Ar is trifluoromethyl or fluorine.

[0099] In the above-mentioned tetracarboxylic dianhydride, as an optional embodiment, Ar is selected from one of the following structures:

[0100]

[0101] In one optional embodiment of the above-mentioned tetracarboxylic dianhydride, the tetracarboxylic dianhydride is selected from, but is not limited to, the following compounds:

[0102]

[0103] Preferably, the tetracarboxylic dianhydride is selected from, but not limited to, the following compounds:

[0104]

[0105] In a second aspect, the present invention provides a method for preparing tetracarboxylic acid dianhydride as described in the first aspect, the method comprising the following steps:

[0106] In a protective atmosphere, a mixed reaction system comprising an anhydride with an imidized or esterified spirocyclic norbornene skeleton structure, a dihalogenated aromatic or heteroaromatic compound, a transition metal-based catalyst, a ligand, a basic substance, a reducing agent, and a solvent is reacted to prepare a diimide compound or a tetracarboxylic acid ester compound. These compounds are then subjected to hydrolysis, acidification, and dehydration to obtain a tetracarboxylic acid dianhydride with the structure of formula (I). The structural formulas of the imidized anhydride with a spirocyclic norbornene skeleton structure are shown in formulas II-1 and II-2.

[0107]

[0108] In formulas II-1 and II-2, the definitions of R1, R2, X1, and X2 are the same as those in formula I; R11 and R21 independently represent any one of aryl (e.g., phenyl) and alkyl groups having 1 to 5 carbon atoms (e.g., 1, 3, or 5).

[0109] The structural formulas of the esterified anhydrides with a spirocyclic norbornene skeleton are shown in Formulas III-1 and III-2:

[0110]

[0111] In Formulas III-1 and III-2, the definitions of R1, R2, X1, and X2 are the same as those in Formula I; R12, R13, R22, and R23 each independently represent any one of alkyl groups having 1 to 5 carbon atoms (for example, 1, 3, or 5).

[0112] The structural formula of the dihalogenated aromatic or heteroaromatic compound is shown in Formula IV:

[0113]

[0114] In Formula IV, Ar is defined in the same way as Ar in Formula I; R3 and R4 are each independently selected from any one of Cl, Br, I, OTf, ONf, p-toluenesulfonyl, and methanesulfonyl, preferably Br or I;

[0115] The structural formula of the diimide compound is shown in Formula V:

[0116]

[0117] In Formula V, Ar, R1, R2, X1, and X2 are defined in the same way as Ar, R1, R2, X1, and X2 in Formula I; R11 and R21 each independently represent any one of aryl (e.g., phenyl) and alkyl groups having 1 to 5 carbon atoms (e.g., 1, 3, or 5).

[0118] The structural formula of the tetracarboxylic acid ester compound is shown in Formula VI:

[0119]

[0120] In Formula VI, the definitions of Ar, R1, R2, X1, and X2 are the same as those in Formula I; R12, R13, R22, and R23 each independently represent any one of alkyl groups with 1 to 5 carbon atoms (for example, 1, 3, or 5).

[0121] Here, the imidized or esterified anhydride having a spirocyclic norbornene skeleton structure is an imide compound having a spirocyclic norbornene skeleton structure (structural formulas such as II-1 and II-2) or a dicarboxylic acid ester compound having a spirocyclic norbornene skeleton structure (structural formulas such as III-1 and III-2).

[0122] In the preparation process, the reducing agent and the base can be added separately, or a salt consisting of the reducing agent and the base can be added to the mixture. The salt consisting of the reducing agent (e.g., formic acid) and the base can be, for example, triethylamine formate, sodium formate, potassium formate, etc.

[0123] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the reaction temperature is 60-120℃ (e.g., 60℃, 80℃, 100℃ or 120℃), and the reaction time is 1-48h (e.g., 1h, 5h, 10h, 15h, 20h, 25h, 30h, 40h or 48h).

[0124] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the transition metal-based catalyst includes, but is not limited to, at least one of rhodium chloride, nickel chloride, palladium chloride, and palladium acetate.

[0125] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the ligand includes, but is not limited to, at least one of triphenylphosphine, triphenylarsine, and tricyclohexylphosphine.

[0126] In the above-mentioned method for preparing tetracarboxylic acid dianhydride, as an optional embodiment, the alkaline substance includes, but is not limited to, at least one of triethylamine, piperidine, pyrrolidine, cesium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, potassium acetate, calcium acetate, magnesium acetate, potassium phosphate, sodium phosphate, and potassium hydrogen phosphate.

[0127] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the reducing agent includes at least one of formic acid and water, preferably formic acid, as formic acid as a reducing agent results in a higher yield.

[0128] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the solvent includes, but is not limited to, one of tetrahydrofuran, 1,4-dioxane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0129] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the protective atmosphere includes, but is not limited to, at least one of nitrogen and argon.

[0130] In the above-mentioned method for preparing tetracarboxylic dianhydrides, as an optional embodiment, the method for preparing an imide compound with the structural formula shown in Formula II-1 includes the following steps:

[0131] The amine represented by R11-NH2 reacts with an anhydride with the structure shown in Formula VII to obtain an imide compound with the structure shown in Formula II-1, wherein R11 represents any one of an aryl group (e.g., phenyl) or an alkyl group having 1 to 5 carbon atoms (e.g., 1, 2 or 5).

[0132]

[0133] In Equation VII, the definitions of R1 and X1 are the same as those in Equation I;

[0134] Alternatively, an imide with the structural formula shown in Formula VIII reacts with a compound with the structural formula shown in Formula IX to obtain an imide compound with the structural formula shown in Formula II-1.

[0135]

[0136] In Equation VIII, the definition of R11 is the same as that in Equation II-1;

[0137]

[0138] In Equation IX, the definitions of R1 and X1 are the same as those in Equation I.

[0139] The preparation method of imide compounds with structural formula II-2 is basically the same as that of imide compounds with structural formula II-1, except that the raw materials are replaced accordingly. For example, R11-NH2 can be replaced with R21-NH2, and R11 in structural formula VIII can be replaced with R21.

[0140] In the above-mentioned method for preparing tetracarboxylic dianhydrides, as an optional embodiment, the method for preparing dicarboxylic acid ester compounds with the structural formula shown in Formula III-1 includes the following steps:

[0141] The alcohols represented by R12-OH and R13-OH react with the anhydrides with the structure shown in Formula VII to obtain dicarboxylic acid ester compounds with the structure shown in Formula III-1, wherein R12 and R13 represent any one of the alkyl groups having 1 to 5 carbon atoms;

[0142] Alternatively, the diester with the structural formula shown in Formula X reacts with a compound with the structural formula shown in Formula IX to obtain a dicarboxylic acid ester compound with the structural formula shown in Formula III-1.

[0143]

[0144] In Equation X, the definitions of R12 and R13 are the same as those in Equation III.

[0145] The preparation method of dicarboxylic acid ester compounds with structural formula III-2 is basically the same as that of dicarboxylic acid ester compounds with structural formula III-1, except that the raw materials are replaced accordingly. For example, R12-OH and R13-OH can be replaced with R22-OH and R23-OH, respectively, and R12 in structural formula X can be replaced with R22 and R13 can be replaced with R23.

[0146] In the above-mentioned method for preparing tetracarboxylic dianhydrides, as an optional embodiment, the method for preparing an anhydride with the structural formula shown in Formula VII includes the following steps:

[0147] Itaconic anhydride is reacted with a compound with the structural formula shown in Formula IX to obtain an anhydride with the structural formula shown in Formula VII.

[0148] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the molar ratio of the anhydride containing a norbornene skeleton structure with a spirocyclic structure, a dihalogenated aromatic or heteroaromatic compound, a transition metal-based catalyst, a ligand, an alkaline substance and the reducing agent is (2-4):(1-1.1):(0.02-0.2):(0.04-0.4):(2-4):(2-4).

[0149] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the mass percentage of the solvent in the mixed reaction system is 35-95 wt%, for example, it can be 35 wt%, 45 wt%, 55 wt%, 65 wt%, 85 wt%, or 95 wt%.

[0150] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the amine represented by R11-NH2 reacts with an anhydride with the structural formula shown in Formula VII to obtain an imide compound with the structural formula shown in Formula II-1, comprising:

[0151] The amine represented by R11-NH2 is dissolved in toluene with an acid anhydride of formula VII, a catalyst (including triethylamine, pyridine, etc.) and a water-binding agent (e.g., acetic anhydride) are added, and the reaction is carried out at 100–140 °C (e.g., 100 °C, 120 °C, or 140 °C). The mixture is then extracted, dried, filtered, concentrated, or separated by column chromatography to obtain an imide compound of formula II-1. Excessive reaction temperature can easily lead to side reactions, while insufficient temperature prevents toluene from carrying away water, resulting in a low yield.

[0152] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the amine represented by R11-NH2 includes, but is not limited to, any one or a combination of two or more of methylamine, ethylamine, propylamine, butylamine, and aniline.

[0153] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the imide with the structural formula VIII reacts with a compound with the structural formula IX to obtain an imide compound with the structural formula II-1, comprising:

[0154] An imide with the structural formula VIII was dissolved in THF (tetrahydrofuran) solution, and a compound with the structural formula IX was added dropwise at room temperature. The reaction was carried out at room temperature for 6–10 h. The mixture was then separated by column chromatography, concentrated, and dried to obtain an imide compound with the structural formula II-1.

[0155] In the above-mentioned method for preparing tetracarboxylic acid dianhydride, as an optional embodiment, the alcohol represented by R12-OH and R13-OH reacts with an anhydride with the structural formula shown in Formula VII to obtain a dicarboxylic acid ester compound with the structural formula shown in Formula III-1. This includes: dissolving the anhydride with the structural formula shown in Formula VII in alcohols represented by general formulas R12-OH and R13-OH; adding concentrated sulfuric acid dropwise after dissolution and refluxing for 6-18 hours; then cooling to room temperature and adding sodium bicarbonate to quench the reaction; and then evaporating, extracting, drying, filtering, and concentrating to obtain the esterified dicarboxylic acid ester compound with the structural formula shown in Formula III-1.

[0156] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the alcohols represented by R12-OH and R13-OH are independently selected from any one of methanol, ethanol, isopropanol, and tert-butanol.

[0157] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the diester with the structural formula X reacts with a compound with the structural formula IX to obtain a dicarboxylic acid ester compound with the structural formula III-1, comprising:

[0158] The diester with the structural formula X was dissolved in THF solution, and the compound with the structural formula IX was added dropwise at room temperature. The reaction was carried out at room temperature for 6 to 10 hours. The product was then separated by column chromatography, concentrated, and dried to obtain the dicarboxylic acid ester compound with the structural formula III-1.

[0159] In the above-mentioned method for preparing tetracarboxylic dianhydrides, as an optional embodiment, the step of reacting itaconic anhydride with a compound having the structural formula shown in Formula IX to obtain an anhydride having the structural formula shown in Formula VII includes:

[0160] A compound with the structural formula shown in Formula IX was added dropwise to the itaconic anhydride at 25-60℃, and the reaction was carried out at 25-60℃ for 6-10 hours. The anhydride with the structural formula shown in Formula VII was obtained by concentration and drying.

[0161] In the above-mentioned method for preparing tetracarboxylic acid dianhydride, as an optional embodiment, the hydrolysis and acidification treatment includes: mixing the bisimide compound or tetracarboxylic acid ester compound with an aqueous sodium hydroxide solution and refluxing for 6-48 hours (for example, 6 hours, 12 hours, 18 hours, 24 hours, 36 hours, or 48 hours), cooling to room temperature, filtering out insoluble impurities, adjusting the pH of the filtrate to 4-5 with acid, precipitating a white solid, filtering, washing the filter cake, drying, and obtaining a tetracarboxylic acid monomer with a hemi-alicyclic structure containing a spirocyclic ("Spiro") bisnorbornene skeleton.

[0162] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the acid in the hydrolysis and acidification steps includes, but is not limited to, at least one of hydrochloric acid and sulfuric acid.

[0163] In the above-mentioned method for preparing tetracarboxylic dianhydride, as an optional embodiment, the dehydration treatment includes: dissolving the tetracarboxylic acid monomer with a hemicyclic structure of a spirocyclic ("Spiro") bisnorbornene skeleton in acetic anhydride under stirring conditions, refluxing for 2-8 hours, cooling, filtering, and drying the filter cake to obtain the tetracarboxylic dianhydride with a hemicyclic structure of a spirocyclic ("Spiro") bisnorbornene skeleton.

[0164] Thirdly, the present invention provides the application of tetracarboxylic dianhydride prepared by the method described in the first aspect or the second aspect in the preparation of polyimide copolymers.

[0165] Fourthly, the present invention provides a polyimide copolymer having repeating units as shown in Formula XI:

[0166]

[0167] In formula XI, R1 and R2 are each independently selected from hydrogen, fluorine, alkyl with 1 to 15 carbon atoms (e.g., 1, 3, 5, 7, 11, 13 or 15), and heteroalkyl with 1 to 15 carbon atoms (e.g., 1, 3, 5, 7, 11, 13 or 15); X1 and X2 are each independently selected from oxygen, alkylene with 1 to 5 carbon atoms (e.g., 1, 3 or 5), and fluoroalkylene with 1 to 5 carbon atoms (e.g., 1, 3 or 5); Ar is a divalent aromatic group or heteroaromatic group with 4 to 50 carbon atoms (e.g., 4, 6, 10, 12, 18, 24, 36 or 48); R is selected from substituted or unsubstituted aryl or heteroaryl groups with 6 to 50 carbon atoms (e.g., 6, 12, 18, 24, 36 or 48).

[0168] In the above-mentioned polyimide copolymer, as an optional embodiment, when R is a substituted arylene or heteroarylene with 6 to 50 carbon atoms, the substituent is at least one of trifluoromethyl, fluorine, methyl, and ethyl.

[0169] In the above-mentioned polyimide copolymer, as an optional embodiment, R is selected from one of the following structures:

[0170]

[0171] In one optional embodiment of the above-mentioned polyimide copolymer, the polyimide copolymer is obtained by reacting a tetracarboxylic dianhydride as described in the first aspect with an aromatic diamine having the structural formula shown in Formula XII.

[0172] H2N-R-NH2Ⅻ

[0173] In Formula XII, R is defined in the same way as R in Formula XI, and is selected from arylene or heteroarylene with 6 to 50 carbon atoms (e.g., 6, 12, 18, 24, 36 or 48).

[0174] In the above-mentioned polyimide copolymer, as an optional embodiment, the aromatic diamine with the structural formula shown in Formula XII includes at least one of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether.

[0175] Fifthly, the present invention provides a method for preparing a polyimide copolymer as described in the fourth aspect, the method comprising the following steps:

[0176] S1. Mix the tetracarboxylic acid dianhydride as described in the first aspect, the aromatic diamine with the structural formula shown in Formula XII, and the reaction solvent to carry out a polymerization reaction to obtain a polyamic acid solution.

[0177] S2. The polyamic acid is imidized to obtain a polyimide copolymer having repeating units as shown in Formula XI.

[0178] In the above-mentioned method for preparing polyimide copolymers, as an optional embodiment, the reaction solvent includes polar aprotic solvents, including but not limited to at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0179] In the above-described method for preparing polyimide copolymers, as an optional embodiment, the polyamic acid has at least one of the repeating units shown in general formulas XIII-1 to XIII-3:

[0180]

[0181]

[0182] In formulas XIII-1 to XIII-3, R1 and R2 are defined the same as in formula I, and are each independently selected from hydrogen, fluorine, alkyl groups with 1 to 15 carbon atoms (e.g., 1, 3, 5, 7, 11, 13, or 15), and heteroalkyl groups with 1 to 15 carbon atoms (e.g., 1, 3, 5, 7, 11, 13, or 15); X1 and X2 are defined the same as in formula I, and are each independently selected from oxygen, alkylene groups with 1 to 5 carbon atoms (e.g., 1, 3, or 5), and heteroalkyl groups with 1 to 5 carbon atoms (e.g., 1, 3, 5, 7, 11, 13, or 15). The alkylene group is any one of 1, 3, or 5 fluoroalkylene groups; Ar is defined as in Formula I, and is a divalent aromatic group or heteroaromatic group (selected from divalent aromatic or heteroaromatic groups with 2 to 50 carbon atoms that may have substituents and form an aromatic ring) having 4 to 50 carbon atoms; R is defined as in Formula XI, and is selected from arylene or heteroarylene groups with 6 to 50 carbon atoms that have 6 to 50 carbon atoms (e.g., 6, 12, 18, 24, 36, or 48 carbon atoms) that have substituted or unsubstituted carbon atoms.

[0183] In the above-mentioned method for preparing polyimide copolymers, as an optional embodiment, in step S1, the reaction atmosphere is an inert gas atmosphere, including nitrogen, the reaction temperature is 30–100°C (e.g., 30°C, 50°C, 70°C, or 100°C), and the reaction time is 2–24 h (e.g., 2 h, 6 h, 12 h, 18 h, or 24 h). More preferably, the reaction temperature is 90°C; at 90°C, a high molecular weight polymer can be obtained rapidly through the reaction, and insoluble substances such as gels are less likely to be generated.

[0184] In the above-mentioned method for preparing polyimide copolymers, as an optional embodiment, in step S1, the molar ratio of the tetracarboxylic dianhydride to the aromatic diamine with the structural formula shown in Formula XII is 1:1.

[0185] In the above-mentioned method for preparing polyimide copolymers, as an optional embodiment, in step S1, the solid content of the polyamic acid solution is 10wt% to 20wt%.

[0186] In the above-mentioned method for preparing polyimide copolymers, as an optional embodiment, in step S2, the polyamic acid imidization includes:

[0187] A polyamic acid solution is applied to a carrier to form a coating film. The glass plate with the coating film is then placed in an oven at 40–120°C for 1–24 hours, and then at 150–350°C for another 1–12 hours to cure the coating film, i.e., imidize it, thus forming a thin film on the carrier. Subsequently, the carrier with the film formed is removed from the oven and immersed in water at 25–100°C for 1–12 hours. The film is then recovered from the carrier to obtain a colorless and transparent film composed of polyimide, i.e., a film-like polyimide copolymer.

[0188] Further, the polyamic acid solution is deposited on a hot plate at 40–90°C to obtain a polyamic acid wet film. After being kept at the hot plate for 3–6 hours, it is placed in an oven for thermal cyclization (e.g., 100°C–2 hours, 150°C–2 hours, 200°C–2 hours, 250°C–2 hours, 300°C–2 hours, 350°C–2 hours) to perform thermal imidization treatment on the polyamic acid wet film, thereby obtaining a polyimide copolymer with repeating units shown in Formula XI in the form of a film.

[0189] In the above-mentioned method for preparing polyimide copolymer, as an optional embodiment, in step S2, the heating process includes: holding at 150°C for 1 hour, then heating to 200°C and holding for 1 hour; then heating to 250°C and holding for 1 hour; then heating to 300°C and holding for 1 hour; and after cooling, peeling off from the substrate to obtain a polyimide copolymer with the structure shown in Formula XI in the form of a film.

[0190] In a sixth aspect, the present invention provides a polyamic acid, which is prepared by using tetracarboxylic dianhydride prepared by the method described in the first aspect or the method described in the second aspect.

[0191] In a seventh aspect, the present invention provides a colorless and transparent polyimide film, wherein the colorless and transparent polyimide film is a polyimide copolymer as described in the fourth aspect, or a polyimide copolymer prepared by the preparation method of the polyimide copolymer as described in the fifth aspect, or a polyamic acid as described in the sixth aspect. Specifically, the preparation method is as described in the preparation method of the polyimide copolymer.

[0192] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0193] Example 1

[0194] The structural formula of the tetracarboxylic acid dianhydride provided in this embodiment is shown below:

[0195]

[0196] The preparation method of tetracarboxylic dianhydride provided in this embodiment includes the following steps:

[0197] 1) Add itaconic anhydride (100g, 0.8mol) and THF (tetrahydrofuran, 300ml) to a 500ml three-necked flask; add cyclopentadiene (1.4mol, 102.6ml) dropwise to the solution at 50℃; after the addition is complete, stir at 50℃ for 6h; dry the solid after rotary evaporation at 50℃ for 4h to obtain a white solid (in the two configurations, the ratio of internal to external is 7:3), 122.2g, yield 85.7%, purity 99.5%. The structural formula of the white solid (anhydride) is:

[0198] 2) Add the white solid (acid anhydride, 17.8 g, 0.1 mol) and toluene (100 mL) prepared in step 1) to a 250 mL flask equipped with a water separator. After dissolving by stirring at room temperature, add ethylamine aqueous solution (7.0 g, 0.1 mol ethylamine) dropwise at room temperature and continue stirring for 15 min. React at 120 °C until no more water is produced in the water separator. After cooling to room temperature, extract three times with sodium hydroxide aqueous solution. Add anhydrous sodium sulfate to the organic phase, stir, and filter. Rotary evaporate the filtrate under reduced pressure and dry under vacuum at 60 °C for 12 h to obtain 15.4 g of oily substance, with a yield of 75.1% and a purity of 99.2%. This oily substance is an imidized acid anhydride, and its structural formula is [structural formula missing].

[0199] 3) Under a nitrogen atmosphere, palladium acetate (449.0 mg, 2.0 mmol), triphenylarsine (1224.9 mg, 4.0 mmol), and N,N-dimethylformamide (60 mL) were added to a 100 mL three-necked flask and stirred at 40 °C for 15 min. Then, p-diiodobenzene (3.3 g, 10.0 mmol), the imidized acid anhydride obtained in step 2) (5.1 g, 25 mmol), triethylamine (5.6 mL, 40.0 mmol), and formic acid (1.5 mL, 40.0 mmol) were added, and the mixture was reacted at 65 °C for 10 h. After cooling to room temperature, the mixture was filtered through diatomaceous earth, extracted with water and dichloromethane, and the organic phase was concentrated to obtain a crude product. The crude product was recrystallized in dichloromethane to give 2.2 g of a white diimide compound, with a yield of 45.6% and a purity of 99.1%. The structural formula of the diimide compound is [insert structural formula here].

[0200] 4) Add sodium hydroxide solution (20 mL, 50 mmol) and the bisimide compound intermediate (2.0 g, 4 mmol) prepared in step 3) to a 50 mL three-necked flask. Reflux at 110 °C for 8 h. After the reaction is complete, cool to room temperature, filter out insoluble impurities, adjust the pH to 5 with 35 wt% hydrochloric acid, and a white solid precipitates. Filter, rinse the filter cake with pure water, and dry at 100 °C for 6 h to obtain 1.6 g of tetracarboxylic acid, with a yield of 85.6% and a purity of 99.2%. The structural formula of tetracarboxylic acid is [insert structural formula here].

[0201] 5) Add acetic anhydride (20 mL) and tetracarboxylic acid (1.5 g, 3.4 mmol) prepared in step 4) to a 50 mL three-necked flask under stirring. Reflux at 120 °C for 6 h, cool to room temperature, filter, and vacuum dry the filter cake at 120 °C for 2 h to obtain 1.3 g of white solid (tetracarboxylic acid dianhydride), with a yield of 87.6% and a purity of 99.8%.

[0202] The proton NMR spectrum of the product from step 5) is shown below. Figure 1 The fact that the integral area of ​​the peak matches the synthesis of tetracarboxylic dianhydride proves the successful synthesis of tetracarboxylic dianhydride.

[0203] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0204]

[0205] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this embodiment includes the following steps:

[0206] 1) Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)diaminobiphenyl (320.2 mg, 1 mmol) and 5 mL of dimethylformamide were added to a 50 mL three-necked flask. After the diamine was completely dissolved, tetracarboxylic acid dianhydride (434.49 mg, 1 mmol) prepared in this example was added. The mixture was stirred at 60 °C for 6 h, cooled, and filtered to obtain a polyamic acid solution.

[0207] 2) The polyamic acid solution (solid content of about 12wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 60℃. After keeping it at this temperature for 4 hours, it is placed in a vacuum oven and left to stand at 90℃ for 5 hours. Then, it is left to stand at 150℃, 200℃, 250℃, 300℃ and 350℃ for 1.5 hours respectively to allow the polymer to cyclize, thereby performing thermal imidization treatment on the wet film.

[0208] 3) After cooling the glass plate from which the film is formed to 100°C, immerse it in water at 100°C for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film (a polyimide copolymer in film form) made of polyimide.

[0209] Example 2

[0210] The structural formula of the tetracarboxylic acid dianhydride provided in this embodiment is shown below:

[0211]

[0212] The preparation method of tetracarboxylic dianhydride provided in this embodiment includes the following steps:

[0213] 1) Add itaconic anhydride (50 g, 0.4 mol) and furan (600 ml) to a 100 ml three-necked flask; stir at 35 °C for 10 h; dry the solid after rotary evaporation at 25 °C for 4 h to obtain a white solid (internal form:external form ratio 1:1), 18.1 g, yield 25.2%, purity 99.2%. The structural formula of the white solid (anhydride) is:

[0214] 2) Add the white solid (acid anhydride, 18.0 g, 0.1 mol) and acetic anhydride (100 mL) prepared in step 1) to a 250 mL three-necked flask. After dissolving by stirring at room temperature, add methylamine alcohol solution (10.4 g, 0.1 mol methylamine) dropwise at room temperature. Continue stirring for 15 min and react at 100 °C for 6 h. After cooling to room temperature, a large amount of white solid precipitates. After filtration, wash with deionized water and dry under vacuum at 60 °C for 12 h to obtain 16.0 g of white solid, with a yield of 83.1% and a purity of 99.6%. This white solid is an imidized acid anhydride with the following structural formula:

[0215] 3) Under a nitrogen atmosphere, palladium acetate (449.0 mg, 2.0 mmol), triphenylphosphine (1049.2 mg, 4.0 mmol), and N,N-dimethylformamide (60 mL) were added to a 100 mL three-necked flask and stirred at 40 °C for 15 min. Then, m-diiodobenzene (3.3 g, 10.0 mmol), the imidized acid anhydride obtained in step 2) (4.8 g, 25 mmol), triethylamine (5.6 mL, 40.0 mmol), and formic acid (1.5 mL, 40.0 mmol) were added, and the mixture was reacted at 65 °C for 10 h. After cooling to room temperature, the mixture was filtered through diatomaceous earth, extracted with water and dichloromethane, and concentrated to obtain a crude product. The crude product was recrystallized in dichloromethane to give 2.0 g of a white diimide compound, with a yield of 43.6% and a purity of 99.8%. The structural formula of the diimide compound is [insert structural formula here].

[0216] 4) Add sodium hydroxide solution (20 mL, 50 mmol) and the bisimide compound intermediate (1.9 g, 4 mmol) prepared in step 3) to a 50 mL three-necked flask. Reflux at 110 °C for 8 h. After the reaction is complete, cool to room temperature, filter out insoluble impurities, adjust the pH to 5 with 35 wt% hydrochloric acid, and a white solid precipitates. Filter, wash the filter cake with pure water, and dry at 100 °C for 6 h to obtain 1.7 g of tetracarboxylic acid, with a yield of 89.57% and a purity of 99.7%. The structural formula of tetracarboxylic acid is [insert structural formula here].

[0217] 5) Add acetic anhydride (20 mL) and tetracarboxylic acid (1.6 g, 3.4 mmol) prepared in step 4) to a 50 mL three-necked flask under stirring. Reflux at 120 °C for 6 h, cool to room temperature, filter, and vacuum dry the filter cake at 120 °C for 2 h to obtain 1.4 g of white solid (tetracarboxylic acid dianhydride), with a yield of 93.9% and a purity of 99.6%.

[0218] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0219]

[0220] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this embodiment includes the following steps:

[0221] 1) Under a nitrogen atmosphere, 2,2-bis(4-aminophenyl)hexafluoropropane (334.3 mg, 1 mmol) and 5 mL of dimethylformamide were added to a 50 mL three-necked flask. After the diamine was completely dissolved, tetracarboxylic acid dianhydride (438.1 mg, 1 mmol) prepared in this example was added. The mixture was stirred at 60 °C for 6 h, cooled, and filtered to obtain a polyamic acid solution.

[0222] 2) The polyamic acid solution (solid content approximately 12 wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 60°C. After being kept at this temperature for 4 hours, it is placed in a vacuum oven and allowed to stand at 90°C for 5 hours. Then, it is allowed to stand at 150°C, 200°C, 250°C, 300°C, and 350°C for 1.5 hours each to allow the polymer to cyclize, thereby performing thermal imidization treatment on the wet film.

[0223] 3) After cooling the glass plate from which the film is formed to 100°C, immerse it in water at 100°C for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film (a polyimide copolymer in film form) made of polyimide.

[0224] Example 3

[0225] The structural formula of the tetracarboxylic acid dianhydride provided in this embodiment is shown below:

[0226] The preparation method of tetracarboxylic dianhydride provided in this embodiment includes the following steps:

[0227] 1) Add itaconic anhydride (100 g, 0.8 mol) and toluene (300 ml) to a 500 ml three-necked flask; add cyclopentadiene (1.4 mol, 102.6 ml) dropwise to the solution at 0 °C; after the addition is complete, continue stirring for 6 h; dry the solid after rotary evaporation at 80 °C for 4 h to obtain 116.5 g of white solid anhydride (endotype), yield 81.8%, purity 99.8%. The structure of the white solid anhydride is...

[0228] 2) Under nitrogen protection, add 53.4 g (0.3 mol) of the white solid acid anhydride prepared in step 1) to a 100 mL three-necked flask. Phthalic dimethyl ether (60 ml) was stirred at 200 °C for 1.5 h. After cooling to room temperature, a solid precipitated out. The solid was filtered to obtain 48.7 g of white solid acid anhydride (appearance ~80%), with a yield of 91.2% and a purity of 99.5%.

[0229] 3) Add the white solid acid anhydride (appearance) prepared in step 2) to a 250ml flask equipped with a water separator. (Acid anhydride (26.7g, 0.15mol) Dissolve the anhydride in toluene (100 mL) at room temperature by stirring. Then, add aniline solution (14.0 g, 0.15 mol aniline) dropwise at room temperature and continue stirring for 15 min. React at 120 °C until no more water is produced in the separator. Separate by column chromatography to obtain 24.8 g of exoimide-modified acid anhydride, with a yield of 65.2% and a purity of 99.7%. The structural formula of the exoimide-modified acid anhydride is [insert structural formula here].

[0230] 4) Under a nitrogen atmosphere, palladium acetate (449.0 mg, 2.0 mmol), tricyclohexylphosphine (1121.7 mg, 4.0 mmol), and N,N-dimethylformamide (60 mL) were added to a 100 mL three-necked flask and stirred at 40 °C for 15 min. Then, 4,4'-diiodobiphenyl (4.1 g, 10.0 mmol), the imidized acid anhydride prepared in step 3) (6.3 g, 25 mmol), and potassium formate (3.4 g, 40.0 mmol) were added, and the mixture was reacted at 80 °C for 6 h. After cooling to room temperature, the mixture was filtered through diatomaceous earth, extracted with water and dichloromethane, and concentrated to obtain a crude product. Recrystallization of the crude product in dichloromethane yielded 2.8 g of a white diimide compound, with a yield of 42.3% and a purity of 99.5%. The structural formula of the diimide compound is [insert structural formula here].

[0231] 5) Add sodium hydroxide solution (20 mL, 50 mmol) and the bisimide compound intermediate (2.6 g, 4 mmol) prepared in step 4) to a 50 mL three-necked flask. Reflux at 110 °C for 8 h. After the reaction is complete, cool to room temperature, filter out insoluble impurities, adjust the pH to 5 with 35 wt% hydrochloric acid, and a white solid precipitates. Filter, rinse the filter cake with pure water, and dry at 100 °C for 6 h to obtain 2.1 g of tetracarboxylic acid, with a yield of 96.1% and a purity of 99.5%. The structural formula of tetracarboxylic acid is [insert structural formula here].

[0232] 6) Add acetic anhydride (20 mL) and the tetracarboxylic acid (1.9 g, 3.4 mmol) prepared in step 5) to a 50 mL three-necked flask under stirring. Reflux at 120 °C for 6 h, cool to room temperature, filter, and vacuum dry the filter cake at 120 °C for 2 h to obtain 1.7 g of white solid (tetracarboxylic acid dianhydride), with a yield of 97.9% and a purity of 99.8%.

[0233] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0234] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this embodiment includes the following steps:

[0235] 1) Under a nitrogen atmosphere, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (336.2 mg, 1 mmol) and 5 mL of dimethylformamide were added to a 50 mL three-necked flask. After the diamine was completely dissolved, tetracarboxylic acid dianhydride (512.6 mg, 1 mmol) prepared in this example was added. The mixture was stirred at 60 °C for 6 h, cooled, and filtered to obtain a polyamic acid solution.

[0236] 2) The polyamic acid solution (solid content of about 14 wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 60°C to form a coating film. After keeping it at this temperature for 4 hours, it is placed in a vacuum oven and left to stand at 80°C for 10 hours. Then, it is left to stand at 150°C, 200°C, 250°C, 300°C and 350°C for 1.5 hours each to allow the polymer to cyclize, thereby performing thermal imidization treatment on the wet film.

[0237] 3) After cooling the glass plate forming the film to 100°C, immerse it in water at 100°C for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film made of polyimide (a polyimide copolymer in film form).

[0238] Example 4

[0239] The structural formula of the tetracarboxylic acid dianhydride provided in this embodiment is shown below:

[0240]

[0241] The preparation method of tetracarboxylic dianhydride provided in this embodiment includes the following steps:

[0242] 1) Add itaconic anhydride (50 g, 0.4 mol) and toluene (100 ml) to a 250 ml three-necked flask; add 1,3-cyclohexadiene (0.8 mol, 70 ml) dropwise to the solution at 0 °C; after the addition is complete, continue stirring for 24 h; dry the solid after rotary evaporation at 50 °C for 8 h to obtain 46.8 g of white solid, with a yield of 60.9% and a purity of 99.5%. The structural formula of this white solid (endo-type anhydride) is:

[0243] 2) Add the white solid (acid anhydride, 19.2 g, 0.1 mol) and acetic anhydride (100 mL) prepared in step 1) to a 250 mL three-necked flask. After dissolving by stirring at room temperature, add methylamine alcohol solution (10.4 g, 0.1 mol) dropwise at room temperature, continue stirring for 15 min, and react at 100 °C for 6 h. After cooling to 0 °C, a large amount of white solid precipitates. After filtration and washing with ethanol, dry under vacuum at 60 °C for 12 h to obtain 13.2 g of white solid, yield 64.3%, purity 99.6%. This white solid is an imidized acid anhydride with the structural formula [structural formula missing].

[0244] 3) Under a nitrogen atmosphere, palladium acetate (449.0 mg, 2.0 mmol), triphenylarsine (1224.9 mg, 4.0 mmol), and dioxane (60 mL) were added to a 100 mL three-necked flask and stirred at 40 °C for 15 min. Then, 1,2-bis(4-bromophenyl)ethane (3.4 g, 10.0 mmol), the imidized anhydride obtained in step 2) (5.1 g, 25 mmol), triethylamine (5.6 mL, 40.0 mmol), and formic acid (1.5 mL, 40.0 mmol) were added, and the mixture was reacted at 65 °C for 10 h. After cooling to room temperature, the mixture was filtered through diatomaceous earth, extracted with water and chloroform, and concentrated to obtain a crude product. Recrystallization of the crude product in toluene yielded 1.8 g of a white diimide compound, with a yield of 12.7% and a purity of 99.5%. The structural formula of the diimide compound is [insert structural formula here].

[0245] 4) Add sodium hydroxide solution (20 mL, 50 mmol) and the bisimide compound intermediate (1.8 g, 3 mmol) prepared in step 3) to a 50 mL three-necked flask. Reflux at 110 °C for 8 h. After the reaction is complete, cool to room temperature, filter out insoluble impurities, adjust the pH to 5 with 35 wt% hydrochloric acid, and a white solid precipitates. Filter, rinse the filter cake with pure water, and dry at 100 °C for 6 h to obtain 1.2 g of tetracarboxylic acid, with a yield of 69.6% and a purity of 99.6%. The structural formula of tetracarboxylic acid is [insert structural formula here].

[0246]

[0247] 5) Add acetic anhydride (20 mL) and tetracarboxylic acid (1.1 g, 1.9 mmol) prepared in step 4) to a 50 mL three-necked flask under stirring. Reflux at 120 °C for 6 h, cool to room temperature, filter, and vacuum dry the filter cake at 120 °C for 2 h to obtain 1.0 g of white solid (tetracarboxylic acid dianhydride), with a yield of 94.5% and a purity of 99.8%.

[0248] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0249]

[0250] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this embodiment includes the following steps:

[0251] 1) Under a nitrogen atmosphere, add 4,4'-diaminodiphenylmethane (198.3 mg, 1 mmol) and 5 mL of dimethylformamide to a 50 mL three-necked flask; after the diamine is completely dissolved, add tetracarboxylic acid dianhydride (566.7 mg, 1 mmol) prepared in this example, stir at 90 °C for 8 h, cool and filter to obtain a polyamic acid solution.

[0252] 2) The polyamic acid solution (solid content 13wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 60°C to form a coating film. After keeping it at this temperature for 5 hours, it is placed in a vacuum oven and left to stand at 90°C for 5 hours. Then, it is left to stand at 150°C, 200°C, 250°C, 300°C and 350°C for 1.5 hours each to allow the polymer to cyclize, i.e., to perform thermal imidization treatment on the wet film.

[0253] 3) After cooling the glass plate to 100°C, immerse it in 100°C water for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film (a polyimide copolymer in film form) made of polyimide.

[0254] Example 5

[0255] The structural formula of the tetracarboxylic acid dianhydride provided in this embodiment is shown below:

[0256]

[0257] The preparation method of tetracarboxylic dianhydride provided in this embodiment includes the following steps:

[0258] 1) Same as step 1) in Example 1.

[0259] 2) Same as step 2) in Example 1.

[0260] 3) Under a nitrogen atmosphere, palladium acetate (449.0 mg, 2.0 mmol), triphenylphosphine (1049.2 mg, 4.0 mmol), and dioxane (60 mL) were added to a 100 mL three-necked flask, and stirred at 40 °C for 15 min; then 1,3-bis(4-bromophenyl)adamantane (2.2 g, 10.0 mmol) was added, with the structural formula shown in the figure: The imidized acid anhydride (5.1 g, 25 mmol) and sodium formate (0.7 g, 10 mmol) were reacted at 35 °C for 72 h. The mixture was filtered through diatomaceous earth, extracted with water and chloroform, concentrated to obtain a crude product, and recrystallized from toluene to give 3.5 g of a white diimide compound, yield 50.1%, purity 99.8%. The structural formula is shown in the figure.

[0261] 4) Add sodium hydroxide solution (20 mL, 50 mmol) and the bisimide compound intermediate (2.1 g, 3 mmol) prepared in step 3) to a 50 mL three-necked flask. Reflux at 110 °C for 8 h. After the reaction is complete, cool to room temperature, filter out insoluble impurities, adjust the pH to 5 with 35 wt% hydrochloric acid, and a white solid precipitates. Filter, rinse the filter cake with pure water, and dry at 100 °C for 6 h to obtain 1.7 g of tetracarboxylic acid, with a yield of 83.2% and a purity of 99.6%. The structural formula of tetracarboxylic acid is [insert structural formula here].

[0262]

[0263] 5) Add acetic anhydride (20 mL) and tetracarboxylic acid (1.4 g, 2 mmol) prepared in step 4) to a 50 mL three-necked flask under stirring. Reflux at 120 °C for 6 h, cool to room temperature, filter, and vacuum dry the filter cake at 120 °C for 2 h to obtain 1.1 g of white solid (tetracarboxylic acid dianhydride), with a yield of 85.3% and a purity of 99.5%.

[0264] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0265]

[0266] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this embodiment includes the following steps:

[0267] 1) Under a nitrogen atmosphere, add 4,4'-diaminodiphenyl ether (200.2 mg, 1 mmol) and 5 mL of dimethylacetamide to a 50 mL three-necked flask; after the diamine is completely dissolved, add tetracarboxylic acid dianhydride (644.8 mg, 1 mmol) prepared in this example, stir at 60 °C for 10 h, cool and filter to obtain a polyamic acid solution.

[0268] 2) The polyamic acid solution (solid content 13wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 60°C to form a coating film. After keeping it at this temperature for 5 hours, it is placed in a vacuum oven and left to stand at 90°C for 5 hours. Then, it is left to stand at 150°C, 200°C, 250°C, 300°C and 350°C for 1.5 hours each to allow the polymer to cyclize, i.e., to perform thermal imidization treatment on the wet film.

[0269] 3) After cooling the glass plate to 100°C, immerse it in 100°C water for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film (a polyimide copolymer in film form) made of polyimide.

[0270] Example 6

[0271] The structural formula of the tetracarboxylic acid dianhydride provided in this embodiment is shown below:

[0272]

[0273] 1) Same as step 1) in Example 1.

[0274] 2) Same as step 2) in Example 1.

[0275] 3) Under an argon atmosphere, palladium chloride (354.7 mg, 2.0 mmol), triphenylphosphine (1049.2 mg, 4.0 mmol), and N,N-dimethylacetamide (60 mL) were added to a 100 mL three-necked flask, and the mixture was stirred at 35 °C for 15 min. Then, 4-(4-(4-iodophenoxy)phenyl)-2-(4-iodophenyl)-o-phthalazin-1(2-hydro)-one (6.4 g, 10.0 mmol) was added. The structural formula is as follows: The imidized acid anhydride (5.1 g, 25 mmol) and potassium formate (0.8 g, 10 mmol) were reacted at 120 °C for 6 h. Separation by column chromatography yielded 4.8 g of a white diimide compound, with a yield of 59.9% and a purity of 99.9%. The structural formula is:

[0276] 4) Add sodium hydroxide solution (20 mL, 50 mmol) and the bisimide compound intermediate (2.4 g, 3 mmol) prepared in step 3) to a 50 mL three-necked flask. Reflux at 110 °C for 8 h. After the reaction is complete, cool to room temperature, filter out insoluble impurities, adjust the pH to 5 with 35 wt% hydrochloric acid, and a white solid precipitates. Filter, wash the filter cake with pure water, and dry at 100 °C for 6 h to obtain 1.8 g of tetracarboxylic acid, with a yield of 76.6% and a purity of 99.8%. The structural formula of tetracarboxylic acid is [insert structural formula here].

[0277] 5) Add acetic anhydride (20 mL) and tetracarboxylic acid (1.6 g, 2 mmol) prepared in step 4) to a 50 mL three-necked flask under stirring. Reflux at 120 °C for 6 h, cool to room temperature, filter, and vacuum dry the filter cake at 120 °C for 2 h to obtain 1.3 g of white solid (tetracarboxylic acid dianhydride), with a yield of 87.0% and a purity of 99.9%.

[0278] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0279]

[0280] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this embodiment includes the following steps:

[0281] 1) Under a nitrogen atmosphere, add 20 mL of N-methylpyrrolidone (mg, 1 mmol) to a 50 mL three-necked flask; after the diamine is completely dissolved, add the tetracarboxylic acid dianhydride (746.8 mg, 1 mmol) prepared in this example, stir at 90 °C for 12 h, and filter after cooling to obtain a polyamic acid solution.

[0282] 2) The polyamic acid solution (solid content 10wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 80°C to form a coating film. After keeping it at this temperature for 5 hours, it is placed in a vacuum oven and left to stand at 100°C for 5 hours. Then, it is left to stand at 150°C, 200°C, 250°C, 300°C and 350°C for 1.5 hours each to allow the polymer to cyclize, i.e., to perform thermal imidization treatment on the wet film.

[0283] 3) After cooling the glass plate to 100°C, immerse it in 100°C water for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film (a polyimide copolymer in film form) made of polyimide.

[0284] Comparative Example 1

[0285] The polyimide copolymer provided in this embodiment has repeating units as shown in the following formula:

[0286]

[0287] The method for preparing the polyimide copolymer (polyimide film) in thin film form provided in this comparative example includes the following steps:

[0288] 1) Under a nitrogen atmosphere, add 4,4'-diaminodiphenyl ether (400.4 mg, 2 mmol) and 6 mL of N-methylpyrrolidone to a 50 mL three-necked flask; after the diamine is completely dissolved, add biphenyltetracarboxylic acid dianhydride (588.4 mg, 2 mmol), stir at 60 °C for 24 h, cool and filter to obtain a polyamic acid solution.

[0289] 2) The polyamic acid solution (solid content of about 12wt%) prepared in step 1) is uniformly coated onto a glass plate on a hot plate at 80°C to form a coating film. After keeping it at this temperature for 5 hours, it is placed in a vacuum oven and left to stand at 100°C for 5 hours. Then, it is left to stand at 150°C, 200°C, 250°C, 300°C and 350°C for 1.5 hours each to allow the polymer to cyclize, i.e., to perform thermal imidization treatment on the wet film.

[0290] 3) After cooling the glass plate to 100°C, immerse it in 100°C water for 0.5 hours. Peel the film off the glass plate to obtain a colorless and transparent film (a polyimide copolymer in film form) made of polyimide.

[0291] Performance testing and results data

[0292] Test method:

[0293] (1) Film thickness test:

[0294] A Mitutoyo MDC-25MX / 25PX micrometer was used to measure three times and the average value was taken.

[0295] (2) Optical performance testing:

[0296] The transmittance of the polymer film was measured using a Lambda 750S UV / Vis / NIR spectrophotometer. The test mode was transmission mode, and the test wavelength was 200 to 800 nm.

[0297] (3) Determination of glass transition temperature (Tg):

[0298] The glass transition temperature (Tg) or phase transition temperature of polymers was tested using a TA Q20 differential scanning calorimeter (DSC) under a nitrogen atmosphere, with a heating rate of 10℃ / min and a test range of 50 to 450℃.

[0299] (4) 5% thermogravimetric test (T) d5％ ):

[0300] A TAQ500 thermogravimetric analyzer was used with a nitrogen flow rate of 50 ml / min and a heating rate of 20℃ / min. The test range was 30-800℃. Before testing, the film was dried in a vacuum oven at 100℃ for more than 10 hours to eliminate interference from solvents such as water.

[0301] (5) Linear thermal expansion coefficient (CTE) test:

[0302] The coefficient of thermal expansion (CTE) of the thin film was tested using a Netzsch TMA402 F3 thermomechanical analyzer (TMA) from Germany. The temperature range was 50–250 °C, the heating rate was 5 °C / min, and the applied static force was 0.05 N. The CTE value was taken as the average length change per 1 °C between 100 and 200 °C.

[0303] (6) Molecular weight and its distribution test:

[0304] Using the G7820B,1260 Infinity II High Temperature GPC SYSTEM, with polystyrene as the external standard and NMP as the eluent, the number-average molecular weight (Mn), weight-average molecular weight (Mw), and molecular weight distribution index (PD) were tested.

[0305] (7) Thin film mechanical property testing:

[0306] The film was tested on an Instron-5869 electronic tensile testing machine. The sample length was 4.5-5.0 cm, the width was 0.6 cm, the thickness was 70-80 μm, the load was 100 N, the tensile speed was 5 mm / min, and the test temperature was room temperature. Five samples were used for each sample, and the average value of the test results was taken.

[0307] (8) Solubility test:

[0308] Weigh 10 mg of polyimide film sample at room temperature and place it in 1 mL of the organic solvent to be tested for 24 h. Observe and record the dissolution of the polymer. Place the polymer sample that cannot be completely dissolved in an oven and keep it at a temperature 20 °C below the boiling point of the organic solvent for 12 h. Observe and record the dissolution of the polymer again.

[0309] (9) UV stability test:

[0310] The samples were subjected to a 12-hour ultraviolet aging test according to GB / T16422.3—2014 standard. Mechanical properties were tested according to (7), the retention rate was calculated, and the average value of five tests was taken as the final value.

[0311]

[0312] The data above shows that the polyimide films prepared in Examples 1-6 achieved a maximum transmittance of 92% at 500 nm and a glass transition temperature T0. g Temperature ranges from 390 to 456℃; 5% thermogravimetric temperature T 5％ The temperature range is 492–531°C. Comparative Example 1, prepared using conventional techniques, showed significantly lower transmittance at 500 nm compared to Examples 1-6. Meanwhile, the polyimide films prepared in Examples 1-6 exhibited excellent solubility, good thermal stability, and mechanical properties.

[0313] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tetracarboxylic acid dianhydride, characterized in that, The tetracarboxylic dianhydride has the structure of Formula I: Equation I In Formula I, R1 and R2 are each hydrogen atoms; X1 and X2 are each independently selected from oxygen and alkylene groups having 1 to 3 carbon atoms; Ar is selected from one of the following structures: 。 2. A method for preparing tetracarboxylic acid dianhydride as described in claim 1, characterized in that, Includes the following steps: In a protective atmosphere, a mixed reaction system comprising an acid anhydride with an imidized or esterified spirocyclic norbornene skeleton, a dihalogenated aromatic or heteroaromatic compound, a transition metal-based catalyst, a ligand, a basic substance, a reducing agent, and a solvent is reacted to prepare a diimide compound or a tetracarboxylic acid ester compound. These compounds are then subjected to hydrolysis, acidification, and dehydration to obtain a tetracarboxylic acid dianhydride with the structure of formula I. The transition metal-based catalyst includes at least one of rhodium chloride, nickel chloride, palladium chloride, and palladium acetate; The ligand includes at least one of triphenylphosphine, triphenylarsine, and tricyclohexylphosphine; The reducing agent includes at least one of formic acid and water; The structural formulas of the imidized anhydride with a spirocyclic norbornene skeleton are shown in Formula II-1 and Formula II-2: Ⅱ-1， Ⅱ-2； In formulas II-1 and II-2, the definitions of R1, R2, X1, and X2 are the same as those in formula I; R11 and R21 independently represent phenyl and any one of alkyl groups having 1 to 5 carbon atoms, respectively. The structural formulas of the esterified anhydrides with a spirocyclic norbornene skeleton are shown in Formulas III-1 and III-2: III-1, III-2; In formulas III-1 and III-2, the definitions of R1, R2, X1, and X2 are the same as those in formula I; R12, R13, R22, and R23 each independently represent any one of the alkyl groups having 1 to 5 carbon atoms. The structural formula of the dihalogenated aromatic or heteroaromatic compound is shown in Formula IV: Ⅳ In Formula IV, Ar is defined in the same way as Ar in Formula I; R3 and R4 are each independently selected from any one of Cl, Br, I, OTf, ONf, p-toluenesulfonyl, and methanesulfonyl. The structural formula of the diimide compound is shown in Formula V: Ⅴ In Formula V, the definitions of Ar, R1, R2, X1, and X2 are the same as those in Formula I; R11 and R21 each independently represent any one of phenyl or alkyl groups having 1 to 5 carbon atoms. The structural formula of the tetracarboxylic acid ester compound is shown in Formula VI: Ⅵ In Formula VI, the definitions of Ar, R1, R2, X1, and X2 are the same as those in Formula I; R12, R13, R22, and R23 each independently represent any one of the alkyl groups having 1 to 5 carbon atoms.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the anhydride with a spirocyclic norbornene skeleton structure, the dihalogenated aromatic or heteroaromatic compound, the transition metal-based catalyst, the ligand, the basic substance and the reducing agent is (2~4):(1~1.1):(0.02~0.2):(0.04~0.4):(2~4):(2~4).

4. The preparation method according to claim 2 or 3, characterized in that, The solvent in the mixed reaction system has a mass percentage of 35-95 wt%.

5. The preparation method according to claim 2 or 3, characterized in that, The reaction temperature is 60~120℃, and the reaction time is 1~48h.

6. The preparation method according to claim 2 or 3, characterized in that, The alkaline substance includes at least one of triethylamine, piperidine, pyrrolidine, cesium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, potassium acetate, calcium acetate, magnesium acetate, potassium phosphate, sodium phosphate, and potassium hydrogen phosphate.

7. The preparation method according to claim 2 or 3, characterized in that, The solvent includes any one of tetrahydrofuran, 1,4-dioxane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

8. The preparation method according to claim 2 or 3, characterized in that, The protective atmosphere includes either nitrogen or argon.

9. The preparation method according to claim 2 or 3, characterized in that, The hydrolysis and acidification treatment includes: mixing the bisimide compound or tetracarboxylic acid ester compound with an aqueous sodium hydroxide solution and refluxing for 6-48 hours, cooling to room temperature, filtering out insoluble impurities, adjusting the pH of the filtrate to 4-5 with acid, precipitating a white solid, filtering, washing the filter cake, and drying.

10. The preparation method according to claim 2, characterized in that, The preparation method of an imide compound with the structural formula shown in Formula II-1 includes the following steps: The amine represented by R11-NH2 reacts with an anhydride with the structure shown in Formula VII to obtain an imide compound with the structure shown in Formula II-1, wherein R11 represents any one of phenyl or alkyl groups having 1 to 5 carbon atoms. Ⅶ In Equation VII, the definitions of R1 and X1 are the same as those in Equation I; Alternatively, an imide with the structural formula shown in Formula VIII reacts with a compound with the structural formula shown in Formula IX to obtain an imide compound with the structural formula shown in Formula II-1. Ⅷ In equation VIII, R 11 The definition of R in Equation II-1 11 The definitions are the same; Ⅸ In Equation IX, the definitions of R1 and X1 are the same as those in Equation I.

11. The preparation method according to claim 2, characterized in that, The preparation method of a dicarboxylic acid ester compound with the structural formula shown in Formula III-1 includes the following steps: The alcohols represented by R12-OH and R13-OH react with anhydrides with the structure shown in Formula VII to obtain dicarboxylic acid ester compounds with the structure shown in Formula III-1, wherein R12 and R13 represent any one of alkyl groups having 1 to 5 carbon atoms; Ⅶ In Equation VII, the definitions of R1 and X1 are the same as those in Equation I; Alternatively, the diester with the structural formula shown in Formula X reacts with a compound with the structural formula shown in Formula IX to obtain a dicarboxylic acid ester compound with the structural formula shown in Formula III-1. Ⅹ In Equation X, the definitions of R12 and R13 are the same as those in Equation III. Ⅸ In Equation IX, the definitions of R1 and X1 are the same as those in Equation I.

12. The preparation method according to claim 10 or 11, characterized in that, The process of reacting itaconic anhydride with a compound of formula IX to obtain an anhydride of formula VII includes: adding a compound of formula IX dropwise to the itaconic anhydride at 25-60°C, reacting at 25-60°C for 6-10 hours, and then concentrating and drying the mixture to obtain the anhydride of formula VII.

13. The preparation method according to claim 10, characterized in that, The amine represented by R11-NH2 includes at least one of methylamine, ethylamine, propylamine, butylamine, and aniline.

14. The preparation method according to claim 11, characterized in that, The alcohols represented by R12-OH and R13-OH react with anhydrides of the structural formula shown in Formula VII to obtain dicarboxylic acid ester compounds of the structural formula shown in Formula III-1. The reaction process includes: dissolving anhydrides of the structural formula shown in Formula VII in alcohols represented by general formulas R12-OH and R13-OH; adding concentrated sulfuric acid dropwise after dissolution and refluxing for 6-18 hours; cooling to room temperature and adding sodium bicarbonate to quench the reaction; and then evaporating, extracting, drying, filtering, and concentrating the solution to obtain the esterified dicarboxylic acid ester compound of the structural formula shown in Formula III-1.

15. The preparation method according to claim 11 or 14, characterized in that, The alcohols represented by R12-OH and R13-OH are independently selected from any one of methanol, ethanol, isopropanol, and tert-butanol.

16. The use of a tetracarboxylic dianhydride as described in claim 1 or prepared by any one of claims 2 to 15 in the preparation of polyimide copolymers.

17. The polyimide copolymer as described in claim 16, characterized in that, The polyimide copolymer has repeating units as shown in Formula XI: Ⅺ In formula XI, R1 and R2 are each hydrogen atoms; X1 and X2 are each independently selected from oxygen and alkylene groups having 1 to 3 carbon atoms; Ar is selected from one of the following structures: R is selected from one of the following structures: 。 18. The polyimide copolymer according to claim 17, characterized in that, The polyimide copolymer is obtained by reacting the tetracarboxylic dianhydride as described in claim 1 with an aromatic diamine of formula XII. H2N-R-NH2Ⅻ In equation XII, the definition of R is the same as the definition of R in equation XI.

19. The polyimide copolymer according to claim 18, characterized in that, The aromatic diamine with the structural formula shown in Formula XII includes at least one of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, and 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether.

20. The method for preparing the polyimide copolymer according to any one of claims 17 to 19, characterized in that, Includes the following steps: S1. Mix the tetracarboxylic acid dianhydride as described in claim 1, the aromatic diamine with the structural formula shown in formula XII, and the reaction solvent to carry out a polymerization reaction to obtain a polyamic acid solution. S2. The polyamic acid is imidized to obtain a polyimide copolymer having repeating units as shown in Formula XI.

21. The preparation method according to claim 20, characterized in that, The reaction solvent includes polar aprotic solvents.

22. The preparation method according to claim 20, characterized in that, The reaction solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

23. The preparation method according to claim 20, characterized in that, The polyamic acid has at least one of the repeating units shown in general formulas XIII-1 to XIII-3: ⅩⅢ-1， ⅩⅢ-2， ⅩⅢ-3； In equations XIII-1 to XIII-3, the definitions of R1 and R2 are the same as those in equation I; the definitions of X1 and X2 are the same as those in equation I; the definition of Ar is the same as that in equation I; and the definition of R is the same as that in equation XI.

24. The preparation method according to claim 20, characterized in that, The reaction atmosphere is an inert gas atmosphere, including nitrogen, the reaction temperature is 30~100℃, and the reaction time is 2~24h.

25. The preparation method according to claim 20, characterized in that, In step S1, the molar ratio of the tetracarboxylic acid dianhydride to the aromatic diamine with the structural formula shown in Formula XII is 1:

1.

26. The preparation method according to claim 20, characterized in that, In step S1, the solid content of the polyamic acid solution is 10wt%~20wt%.

27. A polyamic acid, characterized in that, The polyamic acid is prepared using the tetracarboxylic dianhydride described in claim 1 or the tetracarboxylic dianhydride prepared by any one of claims 2 to 15.

28. A colorless and transparent polyimide film, characterized in that, The colorless and transparent polyimide film is prepared from the polyimide copolymer of any one of claims 17 to 19, or the polyimide copolymer prepared by any one of claims 20 to 24, or the polyamic acid of claim 27.

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