Lewis acid-base pair catalytic system, polyamide acid composition, preparation method and application thereof

Abstract

This invention provides a Lewis acid-base pair catalytic system, a polyamic acid composition, a preparation method, and applications. The Lewis acid-base pair catalytic system comprises a Lewis acid, a Lewis base, and a silane activator. The polyamic acid composition comprises an aromatic tetracarboxylic acid dianhydride, the Lewis acid-base pair catalytic system, a monohydric alcohol, an aromatic diamine, a crosslinking agent, and an aprotic polar solvent. By incorporating the Lewis acid-base pair catalytic system, the polyamic acid composition of this invention effectively disrupts hydrogen bonds between or within polyamic acid molecules, inhibits the formation of charge-transfer complexes in polyimide, and restricts the stacking of polyimide molecules, thereby reducing the yellowness value of the film, increasing the transmittance of the polyimide film, and simultaneously reducing the viscosity of the polyamic acid solution and increasing its solid content.

Description

Technical Field

[0001] This invention relates to polymer materials technology, and more particularly to a Lewis acid-base pair catalytic system, a polyamic acid composition, its preparation method, and its application. Background Technology

[0002] As the "cornerstone" of the OLED display industry chain, the substrate material supports the entire device structure, and its performance directly determines the rigidity / flexibility, transparency, lifespan, and production cost of the display screen. Currently, commercially available flexible OLED substrates are predominantly plastic substrates. Among them, polyimide (PI) film, due to its comprehensive advantages of high temperature resistance, high mechanical strength, and chemical corrosion resistance, has become the mainstream substrate material for foldable screen phones and flexible wearable devices, occupying more than 90% of the flexible OLED substrate market share. Yellow polyimide (YPI), as an important branch of polyimide, has been widely used in flexible display technology, flexible printed circuit boards, flexible touch sensors, automotive electronics, flexible wearable devices, and related fields due to its cost advantages, excellent thermal stability, and balance of optical performance.

[0003] Yellow polyimide refers to a polymer material with an imide ring structure in its main chain, exhibiting a yellow appearance and possessing high heat resistance, high strength, high insulation, strong weather resistance, and strong process adaptability. Its molecular design is based on the combination of aromatic diamines and aromatic dianhydrides to obtain aromatic polyimides. Aromatic polyimides possess strong electron donors and acceptors in their molecular structure, forming strong charge-transfer complexes (CTCs) within or between molecular chains, which significantly affects the light transmittance of polyimides.

[0004] To improve the light transmittance of yellow polyimide, researchers such as Li et al. have studied the introduction of flexible bonds (such as -O-, -S-, -CH2-), bulky substituents, fluorinated monomers, aliphatic monomers, or reduction of chain symmetry to regulate intermolecular or intramolecular charge transfer complexation effects, thereby increasing the light transmittance of polyimide (Yi C, Li W, Shi S, et al. High-temperature-resistant and colorless polyimide: Preparations, properties, and applications[J]. Solar Energy, 2020, 195: 340-354.). However, these methods reduce the mechanical and thermal properties of polyimide films to some extent. Furthermore, structural modifications complicate processing and increase production costs, limiting the industrialization of highly transparent polyimide.

[0005] Patents CN108587163B and CN114716825B focus on adding specific substances to improve the transmittance of polyimide, such as adding fluorinated ionic liquids, whose anions and cations interact with the polyimide molecular chains, interfering with the formation of CTC, or doping with SiO2, TiO2, fluorescent dyes, and UV absorbers. While physical doping can improve the transmittance of polyimide, it suffers from problems such as easy agglomeration and poor heat resistance. Improving the transmittance of polyimide without altering the monomer structure and product composition is a key research direction. Patents CN118109160A and CN115141359A both disclose low-temperature catalytic imidization, which can lower the imidization temperature to below 250°C, a reduction of 150°C compared to traditional processes. This significantly reduces molecular chain oxidation and depolymerization, and can increase the 450nm transmittance to 85%, but it carries the risk of catalyst residue. Patents CN116284972A and CN109762335A report that vacuum curing, by reducing system pressure (below 50 Torr), lowers the boiling point of NMP from 202℃ to 135℃, increases the solvent evaporation rate by 3 times, and reduces the residual amount to <100ppm (only 1 / 5 of that of atmospheric pressure processes), completely eliminating light scattering caused by the "popcorn effect," achieving a transmittance of up to 88% at 450nm. This method requires expensive equipment. The above methods improve the transmittance of polyimide by adjusting the film process (reducing molecular chain oxidation and depolymerization, and reducing light scattering), while interfering with or reducing the CTC effect is also an effective way to improve transmittance.

[0006] Polyimides can be synthesized via one-step and two-step methods. The two-step method involves curing the polyimide precursor by heating or by chemically curing it with a catalyst. Polyamic acid compositions are precursors to polyimides, obtained by the polycondensation of diamines and tetracarboxylic dianhydrides in a solvent, or by adding a catalyst to improve the production efficiency of polyamic acid. For example, in the polymerization reactions studied by Ma Yukun et al. and Liu Hanyu et al., Lewis acid-base pairs can act as catalysts, with the catalytic synergistic effect mainly manifested in the activation of monomers. Lewis acids can coordinate with π bonds or polar groups (such as carbonyl oxygen) in monomers, thereby altering the electron cloud distribution of monomer molecules and enhancing their electrophilicity; while Lewis bases (such as amines and alcohols) provide nucleophilic sites to attack carbonyl carbons, resulting in intermediates with higher activity and easier attack by nucleophiles with weaker nucleophilicity (Ma Yukun, Shen Yong, Li Zhibo. Study on bulk ring-opening polymerization of L-lactide homopolymerization and copolymerization with glycolide catalyzed by high thermal stability Lewis acid-base pair [J]. Acta Polymerica Sinica, 2022, 53(08): 923-932).

[0007] In the field of polyimide synthesis, Lewis acid-base pairs can catalyze the condensation-cyclization reaction of dianhydrides and diamines. For example, in existing patent CN119978339A, pyridine and triethylamine are used as Lewis bases, and halogen metal salts such as lithium chloride and lithium bromide are used as Lewis acids to synthesize polyimides. However, in the semiconductor processing field, the introduction of halide ions may corrode substrate materials or electronic circuits, and metal ions can affect the dielectric properties of polyimides. Therefore, the use of halogen metal salts (or other metal complexes) as Lewis acids in polyimide synthesis has certain limitations.

[0008] In summary, there is an urgent need to develop a yellow polyimide with high light transmittance that does not introduce halogens and metal ions. Summary of the Invention

[0009] The purpose of this invention is to address the problems of low light transmittance and easy introduction of halogens and metal ions in existing polyimides by proposing a Lewis acid-base pair catalytic system. This catalytic system uses a silane activator in conjunction with Lewis acid and Lewis base to effectively disrupt the hydrogen bonds between or within polyamic acid molecules in the polyamic acid composition, inhibit the formation of charge-transfer complexes (CTC) in the polyimide, and limit the stacking between polyimide molecules. This reduces the yellowness value (YI) of the film, increases the light transmittance of the polyimide film, and simultaneously reduces the viscosity of the polyamic acid solution (800~6000 mPa·s) and increases its solid content (40~50 wt%).

[0010] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," "consisting of," etc., and similar meanings.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is: a Lewis acid-base pair catalytic system, comprising Lewis acid, Lewis base and silane activator, wherein the molar ratio of Lewis acid to Lewis base is 0.75~1:1, and the amount of silane activator accounts for 0.1~5 mol of the total molar amount of Lewis acid and Lewis base.

[0012] Furthermore, the preferred molar ratio of the Lewis acid to the Lewis base is 0.8 to 0.95:1.

[0013] Furthermore, the silane activator is preferably used in an amount of 0.5 to 3 mol of the total molar amount of Lewis acid and Lewis base.

[0014] Furthermore, the Lewis acid is an organoboron compound containing trivalent boron.

[0015] Furthermore, the Lewis acid is one or more of trialkylboron, dialkylalkoxyboron, trialkoxyboron, and trisubstituted arylboron.

[0016] Furthermore, the Lewis acid is preferably a trisubstituted arylboron.

[0017] Furthermore, the trialkylborane is one or more of triethylborane, tripropylborane, and tributylborane.

[0018] Furthermore, the dialkylalkoxyborane is diethylmethoxyborane.

[0019] Furthermore, the trialkoxyboron is trimethyl borate and / or triisopropyl borate.

[0020] Furthermore, the trisubstituted arylborane is triphenylborane.

[0021] Further, the silane activator is one or more selected from trimethylsilane, triethylsilane, triisopropylsilane, triphenylsilane, trimethoxysilane, triethoxysilane, triisopropoxysilane, methyltriethoxysilane, methyltrimethoxysilane, methyltripropoxysilane, ethyltriethoxysilane, and propyltriethoxysilane.

[0022] Furthermore, the silane activator is preferably triphenylsilane.

[0023] Furthermore, the Lewis base is one or more of the following: tertiary amines, amidines, guanidines, imidazoles, pyridines, and triaminophosphines.

[0024] Further, the tertiary amine is NR3, wherein R is one or more of a substituted or unsubstituted C1-5 alkyl group, a substituted or unsubstituted C1-5 alcohol hydroxyl group, and a C6-10 aromatic group. In this invention, the substituents on the alkyl group and the alcohol hydroxyl group are not particularly limited and can be any substituent feasible in the art. Specifically, the substituents on the alkyl group and the alcohol hydroxyl group can be hydroxyl, nitro, sulfonic acid, cyano, mercapto, etc.; preferably, R is one or more of C2H5, C3H7, C2H5OH, and phenyl.

[0025] Furthermore, the structural formula of the amidines is shown in general formula (Ⅰ);

[0026]

[0027] (I)

[0028] In general formula (Ⅰ), R1 is C n H 2n n is any integer from 1 to 5, preferably R1 is CH2 or C3H6.

[0029] Furthermore, the structural formula of the guanidine is shown in general formula (II) or (III);

[0030]

[0031] (II) (III)

[0032] In general formula (II), R2 is a substituted or unsubstituted C1-5 alkyl group. The present invention does not particularly limit the substituents on the alkyl group; they can be any substituent feasible in the art. Specifically, the substituents on the alkyl group can be hydroxyl, nitro, sulfonic acid, cyano, mercapto, etc.

[0033] In general formula (Ⅲ), R5 is H, a substituted or unsubstituted C1-5 alkyl group. The present invention does not particularly limit the substituents on the alkyl group, and they can be any substituents feasible in the art. Specifically, the substituents on the alkyl group can be hydroxyl, nitro, sulfonic acid, cyano, mercapto, etc.; preferably, R5 is H or CH3.

[0034] Furthermore, the structural formula of the imidazole class is shown in general formula (Ⅳ);

[0035]

[0036] (IV)

[0037] In general formula (Ⅳ), R3 is H, a substituted or unsubstituted C1-5 alkyl group. In this invention, the substituents on the alkyl group are not particularly limited and can be any substituent feasible in the art. Specifically, the substituents on the alkyl group can be hydroxyl, nitro, sulfonic acid, cyano, mercapto, etc.; preferably, R3 is H or CH3.

[0038] Furthermore, the structural formula of the pyridine class is shown in general formula (V);

[0039]

[0040] (V)

[0041] In general formula (V), R4 is H, a substituted or unsubstituted C1-5 alkyl group, or a substituted or unsubstituted amino group. In this invention, the substituents on the alkyl and amino groups are not particularly limited and can be any substituent feasible in the art. Specifically, the substituents on the alkyl and amino groups can be hydroxyl, nitro, sulfonic acid, cyano, mercapto, etc.; preferably, R4 is H, CH3, NH2, or N(C m H 2m+1 )3, where m is 1 or 2.

[0042] Furthermore, the structural formula of the triaminophosphine class is shown in general formula (VI);

[0043]

[0044] (VI)

[0045] In general formula (VI), R6 is a substituted or unsubstituted C1-5 alkyl group. The present invention does not particularly limit the substituents on the alkyl group; they can be any substituent feasible in the art. Specifically, the substituents on the alkyl group can be alkyl, hydroxyl, nitro, sulfonic acid, cyano, mercapto, etc.; preferably, R6 is a C1-5 alkyl group. z H 2z+1 , where z is 1 or 2.

[0046] Further, the Lewis base includes, but is not limited to, one or more of the following: imidazole, 4-aminopyridine, 4-dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, pyridine, piperidine, triethylamine, tri-n-propylamine, 1,5-diazabicyclo[4.3.0]non-5-ene, triphenylamine, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, tetramethylguanidine, 1,1,2,3,3-pentamethylguanidine, and N,N-dimethylethanolamine.

[0047] Furthermore, the Lewis base is most preferably 1,8-diazabicyclo[5.4.0]undec-7-ene.

[0048] In the Lewis acid-base pair catalytic system of this invention, the added silane activator significantly improves the catalytic performance of Lewis acids and Lewis bases:

[0049] (1) Silane activators coordinate with Lewis acids through electronic effects (σ(Si-H)-p and dp hyperconjugation effects) to generate a stronger and more active coordination adduct in situ. This coordination adduct (with B as the electron-deficient center) has extremely high electron deficiency and can efficiently activate carbonyl compounds.

[0050] (2) Silane activators form a “spatial barrier” around Lewis acids through steric effects, protecting their empty orbitals (electron-deficient centers) and preventing excessive coordination between Lewis acids and Lewis bases, which would deactivate them.

[0051] (3) For some Lewis acid-base pair catalytic systems, Lewis acid and Lewis base will form adducts, which will quench the catalytic activity. However, the addition of silane activator consumes part of the Lewis acid and converts it into a more active coordination adduct, which changes the reaction pattern and avoids this deactivation pathway.

[0052] Another object of the present invention is to disclose a polyamic acid composition comprising the above-described Lewis acid-base pair catalytic system.

[0053] Furthermore, the Lewis acid-base catalytic system accounts for 0.1 to 0.5 mol of the total molar amount of the polyamic acid composition.

[0054] Furthermore, the Lewis acid-base pair catalytic system is particularly suitable for the preparation of polyamic acid compositions.

[0055] Furthermore, when using the Lewis acid-base pair catalytic system to prepare polyamic acid compositions, the Lewis acid and silane activator are added to the reaction system first, followed by the Lewis base. The purpose of adding the Lewis acid and silane activator first is to generate a stronger and more active coordination adduct in situ, and the resulting "steric barrier" can effectively prevent the Lewis acid and Lewis base from directly forming a coordination adduct, thus avoiding the loss of catalytic activity.

[0056] Another object of the present invention discloses a polyamic acid composition comprising an aromatic tetracarboxylic dianhydride, the Lewis acid-base pair catalytic system, a monohydric alcohol, an aromatic diamine, a crosslinking agent, and an aprotic polar solvent; wherein, in molar quantities, the ratio of aromatic tetracarboxylic dianhydride to aromatic diamine is 0.85~1:1, the ratio of monohydric alcohol to aromatic tetracarboxylic dianhydride is 0.005~0.15:1, the ratio of crosslinking agent to monohydric alcohol is 0.01~0.5:1, the aprotic polar solvent accounts for 50~60 wt% of the total mass of the aromatic tetracarboxylic dianhydride and aromatic diamine, and the Lewis acid-base pair catalytic system accounts for 0.1~0.5 mol% of the total molar mass of the polyamic acid composition.

[0057] Furthermore, the ratio of aromatic tetracarboxylic acid dianhydride to aromatic diamine is 0.85~0.96:1, expressed in molar quantities.

[0058] Furthermore, on a molar basis, the ratio of the monohydric alcohol to the aromatic tetracarboxylic acid dianhydride is 0.05 to 0.115:1.

[0059] Further, in molar terms, the crosslinking agent: monohydric alcohol ratio is 0.11~0.25:1.

[0060] Further, the aromatic tetracarboxylic dianhydride is one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride.

[0061] Further, the monohydric alcohol is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, 2-pentanol, 3-pentanol, isopentanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol.

[0062] Further, the aromatic diamine is p-phenylenediamine, m-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diaminodiphenyl sulfone, 3,4-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminobenzoylaniline ...4,4'-diaminobenzoylaniline, 4,4'-diaminobenzoylaniline, 4 One or more of (4-aminophenyl)hexafluoropropane, 1,4-bis(2-trifluoromethyl4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenylmethane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene and 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane.

[0063] Furthermore, the crosslinking agent is a cyclic anhydride monomer containing unsaturated bonds.

[0064] Further, the crosslinking agent is one or more of 4-phenylacetylene phthalic anhydride, phenylacetylene tricarboxylic anhydride, maleic anhydride, norbornene anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride and benzonorbornene anhydride.

[0065] In this invention, the crosslinking agent, acting as a capping agent, reduces the molecular weight of polyamic acid, contributing to high solids content and low viscosity.

[0066] Further, the aprotic polar solvent is one or more of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), γ-butyrolactone (GBL), and tetrahydrofuran (THF).

[0067] Another object of the present invention is to disclose a method for preparing a polyamic acid composition, comprising the following steps:

[0068] (1) In an inert atmosphere, aromatic tetracarboxylic acid dianhydride, Lewis acid and silane activator are mixed and reacted in an aprotic polar solvent, followed by the addition of Lewis base and monohydric alcohol, and the reaction is carried out at low temperature to obtain mixed solution A.

[0069] (2) Under the inert atmosphere, the mixed solution A is cooled to a first temperature, an aromatic diamine is added to react, and then the temperature is raised to a second temperature to continue the reaction to obtain a polyamic acid slurry;

[0070] (3) Add a crosslinking agent to the polyamic acid slurry and carry out a crosslinking reaction at a second temperature to obtain the polyamic acid composition.

[0071] Furthermore, the method for preparing the polyamic acid composition specifically includes the following steps:

[0072] (1) In a N2 and dry atmosphere, aromatic tetracarboxylic acid dianhydride is dispersed in an aprotic polar solvent, and Lewis acid and silane activator are added respectively. After stirring evenly, Lewis base is added and stirring is continued. Then, a monohydric alcohol is added and reacted at low temperature (0~5℃) for 0.5~8h to obtain a mixed solution A containing tetracarboxylic acid dianhydride and monoanhydride monoester monocarboxylic acid (or monoanhydride dicarboxylic acid) compounds;

[0073] (2) In a N2 and dry atmosphere, the mixture A is cooled to the first temperature (below 10°C), and an aromatic diamine is added. During the addition process, the temperature of the reaction system is controlled below 10°C. After the addition is completed, the reaction is carried out at 10°C for 0.5~2h, and then the temperature is raised to the second temperature (30~80°C) and the reaction is carried out for 24~48h to obtain a slurry.

[0074] (3) Add a crosslinking agent to the slurry and react at a second temperature (30~80℃) for 3~6 hours to obtain a polyamic acid composition.

[0075] Further, in step (2), the mixture A is cooled to 0~10℃ and an aromatic diamine is added. During the addition process, the temperature of the reaction system is controlled at 0~10℃. After the addition is completed, the reaction is carried out at 0~10℃ for 0.5~2h.

[0076] Furthermore, the heating in step (2) is a gradient heating, specifically: first, equilibrate at 20~50℃ for 5~30min, and then heat to the reaction temperature of 30~80℃ at a heating rate of 5℃ / min.

[0077] Further, the polyamic acid composition in step (3) has a solid content of 40-50 wt% and a viscosity of 800-6000 mPa·s.

[0078] In the polyamic acid composition of the present invention, the addition of Lewis acid-base pair catalytic system significantly improves the slurry performance:

[0079] (1) Lewis acid-base reacts with the catalytic system and aromatic tetracarboxylic acid dianhydride to generate active intermediates, which improves the reaction efficiency of monohydric alcohols. At the same time, Lewis acid-base reacts with the catalytic system and dianhydride to generate active intermediates, which synergistically catalyze the polycondensation reaction, making the synthesis of highly sterically hindered polyamic acid more efficient.

[0080] (2) The polyamic acid composition contains groups such as -NH2, -COOH and -CONH-, and the intermolecular and intramolecular interaction forces (hydrogen bonds) are strong, which makes the system viscosity high. The addition of Lewis base can destroy these interaction forces, making the viscosity easier to control. At the same time, these interaction forces enhance the orientation of polyamic acid molecules and the intermolecular forces, promote the stacking between polyimide molecules, make it easier to form charge transfer complexes, deepen the color of slurry and film. Lewis base destroys the interaction forces between polyamic acid molecules, thereby improving the color of slurry and increasing the light transmittance of film.

[0081] (3) The Lewis acid-base pair catalytic system can be removed during the thermal imidization process without destroying the molecular structure of polyimide, thus ensuring the original mechanical and thermal properties of the polyimide film.

[0082] Another object of the present invention is to disclose a method for preparing polyimide, comprising the following steps: subjecting the polyamic acid composition to thermal imidization treatment to obtain polyimide.

[0083] Further, the polyamic acid composition is first subjected to vacuum degassing at room temperature for 6-24 hours, then vacuum dried at 50-200°C for 0.5-2 hours, and subsequently thermal imidized at 200-500°C for 1-6 hours to obtain polyimide (film).

[0084] Furthermore, the polyimide has a yellowness value (YI) <20, a transmittance (380~780nm) >90%, and a transmittance (450nm) >90%.

[0085] Another object of the present invention is to disclose a polyimide prepared by the above method.

[0086] Another object of the present invention is to disclose the application of polyimide in the field of flexible OLED substrates.

[0087] The Lewis acid-base pair catalytic system, polyamic acid composition, preparation method, and application of the present invention have the following advantages compared with the prior art:

[0088] 1) The Lewis acid-base pair catalytic system of the present invention includes a silane activator, a Lewis acid, and a Lewis base. During the preparation of polyamic acid, the silane activator in the Lewis acid-base pair catalytic system coordinates with the Lewis acid to generate a stronger and more reactive coordination adduct in situ. This coordination adduct and the Lewis base form a new Lewis acid-base pair catalytic system, avoiding the deactivation of the Lewis acid-base pair catalyst. At the same time, without changing the molecular structure of polyamic acid, this catalytic system weakens the intermolecular or intramolecular interaction forces (hydrogen bonds) of polyamic acid, significantly reduces the viscosity of the polyamic acid solution (800~6000 mPa·s), and increases its solid content (40~50 wt%), resulting in higher light transmittance of the polyimide film.

[0089] 2) This invention introduces a monohydric alcohol as a capping agent to participate in the reaction, generating a monohydric anhydride monocarboxylic acid compound, which makes the polyamic acid molecules more uniformly distributed and has a lower molecular weight, achieving the purpose of high solid content and low viscosity. This can effectively avoid ripples during the coating process and improve the stability of the film.

[0090] The polyimide of this invention has good application prospects and large-scale promotion potential in the field of flexible OLED substrates. Attached Figure Description

[0091] Figure 1 Optical image of the thin film prepared from polyamic acid in Example 17;

[0092] Figure 2 Optical image of the thin film prepared from polyamic acid, Comparative Example 7;

[0093] Figure 3 The transmittance diagram is for the film prepared from polyamic acid in Example 17. Detailed Implementation

[0094] The present invention will be further described below with reference to embodiments. The description of the technical features described below is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0095] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0096] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0097] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0098] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0099] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0100] In this instruction manual, when "room temperature" or "room temperature" is used, the temperature can be 15-25℃.

[0101] Unless otherwise specified, all reagents or instruments used in this instruction manual are commercially available products.

[0102] Examples 1-9

[0103] Examples 1-9 disclose various Lewis acid-base pair catalytic systems, the components of which are shown in Table 1.

[0104] Table 1 Lewis acid-base pair catalytic systems of Examples 1-9

[0105]

[0106] In Table 1, the percentage of silane activator is the percentage of the molar amount of the silane activator relative to the total molar amount of Lewis acid and Lewis base.

[0107] Examples 10-18

[0108] Examples 10-18 disclose various polyamic acid compositions, the preparation methods of which are as follows:

[0109] (1) In a dry atmosphere of N2, aromatic tetracarboxylic acid dianhydride is dispersed in an aprotic polar solvent, and Lewis acid and silane activator are added respectively. After stirring evenly, Lewis base is added and stirred, followed by the addition of a monohydric alcohol. The mixture is reacted at 0°C for 6 hours to obtain mixed solution A.

[0110] (2) In a N2 and dry atmosphere, the mixture A is cooled to 0°C and an aromatic diamine is added. During the addition process, the temperature of the reaction system is controlled at 0°C. After the addition is completed, the reaction is carried out at 0°C for 1 hour, and then the temperature is raised to 60°C for 32 hours to obtain a slurry.

[0111] (3) Add crosslinking agent to slurry and react at 60°C for 3 hours to obtain polyamic acid composition.

[0112] The raw materials and dosages used in this method are shown in Table 2.

[0113] Table 2. Raw materials and dosage of polyamic acid compositions

[0114]

[0115] In Table 2, the Lewis acid-base pair catalytic system percentage represents the total molar amount of the Lewis acid-base pair catalytic system relative to the total molar amount of the polyamic acid composition. The aprotic polar solvent percentage represents the mass percentage of the aprotic polar solvent relative to the total mass of the aromatic tetracarboxylic dianhydride and aromatic diamine.

[0116] Comparative Examples 1-8

[0117] Comparative Examples 1-8 disclose various Lewis acid-base pair catalytic systems, the components of which are shown in Table 3.

[0118] Table 3 Comparative Examples 1-8 Lewis Acid-Base Relation Catalytic Systems

[0119]

[0120] In Table 3, the percentage of silane activator is the percentage of the molar amount of the silane activator relative to the total molar amount of Lewis acid and Lewis base.

[0121] Comparative Examples 9-18

[0122] Comparative Examples 9-18 disclose various polyamic acid compositions, which are prepared in the same way as those in Examples 10-18. The raw materials and amounts used in this method are shown in Table 4.

[0123] Table 4. Raw materials and dosage of polyamic acid compositions

[0124]

[0125] The polyamic acid compositions of Examples 10-18 and the polyamic acid compositions of Comparative Examples 9-18 were tested respectively, and the test results are shown in Table 5.

[0126] The solid content, viscosity, and color (YI) of the polyamic acid solution, as well as the optical properties (Tr%@380~780nm) of the polyimide film, were determined.

[0127] Solid content test:

[0128] Accurately weigh a certain amount of polyamic acid solution, spread it evenly on a glass substrate, dry it at 300℃ for 3 hours, and weigh the dried polyimide after cooling to obtain the solid content of the polyamic acid solution. Perform the test in parallel three times and take the average value.

[0129] Viscosity test:

[0130] The viscosity of the sample was tested using an NDJ-8S digital rotational viscometer at a temperature of 25°C. The unit is mPa·s. The test was performed in triplicate, and the average value was taken.

[0131] Colorimetric test:

[0132] The colorimetry YI of the polyamic acid solution was measured using a colorimeter.

[0133] Tr%@380~780nm test:

[0134] The transmittance at 380~780nm was measured using a D65 light source, and the average value was taken. The thin film sample size was 50mm*50mm, and the test frequency was 1nm.

[0135] Table 5 Performance Tests

[0136]

[0137] Note: The YI value in the table is the YI value of the polyimide film, and Tr% is the average transmittance of the polyimide film in the range of 380~780nm.

[0138] As shown in Table 5, the addition of the Lewis acid-base pair catalytic system significantly improves the transmittance and yellowness (YI) of polyimide. The preferred solid content of the polyamic acid solution is 40-50 wt%, and the preferred viscosity is 800-6000 mPa·s. The resulting polyimide film exhibits a yellowness (YI) <20, transmittance (380-780 nm) >90%, and transmittance (450 nm) >90%. In contrast, the catalytic system of Comparative Example 9, which did not contain silane compounds, showed a significant decrease in the transmittance of the polyimide film. This is because the Lewis acid consumes the lone pair electrons in the Lewis base, preventing the Lewis base from providing additional lone pairs to accept protons. In other words, the Lewis acid-base pair exists independently as a whole, without disrupting the interactions (hydrogen bonds) between polyamic acid molecules. This results in stronger orientation of the polyimide and facilitates the formation of intermolecular charge-transfer complexes.

[0139] In Comparative Example 10, no Lewis acid was added to the catalytic system. After the reaction was complete, the viscosity of the slurry increased to 7558 mPa·s. On the one hand, without the synergistic catalysis of Lewis acid, the reaction efficiency decreased and the time for the polycondensation reaction to be complete increased. On the other hand, the ability to destroy intermolecular or intramolecular interaction forces was weakened, resulting in an increase in viscosity.

[0140] In Comparative Example 11, no Lewis base was added to the catalytic system, and it was clearly observed that the transmittance reached the lowest value, only 55.35%. This is because the Lewis base can destroy the interaction forces between polyamic acid molecules, thereby destroying the charge transfer complex effect, which explains why Comparative Example 11 has the lowest transmittance.

[0141] In the catalytic system of Comparative Example 12, FeCl3 was used as the Lewis acid because Fe 3+The introduction of chloride ions increases the amount of metallic impurities in the system, reducing the insulating properties of the film. Furthermore, the introduction of chloride ions increases the cost of subsequent processing, such as requiring additional purification steps to remove chloride ions. Meanwhile, Fe... 3+ It forms chelates with -NH2 and -CONH- in polyamic acid, which increases intermolecular interaction forces and thus increases viscosity;

[0142] Comparative Example 13, without crosslinking agent, achieved a viscosity of 6872 mPa·s. This is because the free amino and carboxyl groups in the polyamic acid molecule formed more weak interactions (weak ionic bonds: -NH). 3+ COO - This further increases intermolecular and intramolecular interaction forces;

[0143] In Comparative Example 14, due to the excessive crosslinking agent, more -COOH groups were released from the ends of the polyamic acid, and a crosslinking network was formed between the carboxyl groups by hydrogen bonds, resulting in a relatively high viscosity.

[0144] In Comparative Example 15, the molar ratio of Lewis acid to Lewis base was 0.3:1. Too little Lewis acid reduced the catalytic activity of the system. In the same reaction time, the viscosity of the polyamic acid obtained was lower than that of the same solid content. To prepare a film of the same thickness, more polyamic acid solution was required.

[0145] In Comparative Example 16, the molar ratio of Lewis acid to Lewis base was 2:1, which led to a deterioration in the optical properties of the polyimide film (increased YI value and decreased Tr%). This is because excessive Lewis acid is more likely to form adducts with Lewis base through weak interaction forces, resulting in less Lewis base being completely released, and stronger intermolecular and intramolecular charge transfer complexation effects in polyimide.

[0146] In Comparative Example 17, the amount of silane activator accounted for 0.05 mol% of the total molar amount of Lewis acid and Lewis base. The transmittance of the polyimide film was approximately 68.06%, and the viscosity was lower compared to polyamic acid with the same solid content. The small amount of silane activator was due to two factors. Firstly, the Lewis acid that did not form an adduct with the silane activator was consumed by the Lewis base, and the two directly formed a hindered acid-base pair, resulting in weaker or deactivated catalytic activity. Consequently, the viscosity of the polyamic acid obtained within the same reaction time was lower. Secondly, because the Lewis acid and Lewis base directly formed an adduct, there was less free Lewis base in the system, which could not effectively break the hydrogen bonds in the polyamic acid. This made it easier for charge-transfer complexes to form between or within polyimide molecules.

[0147] In Comparative Example 18, the amount of silane activator accounted for 10 mol% of the total molar amount of Lewis acid and Lewis base. Although it did not have a significant impact on the various properties in Table 5, most silane activators have high reactivity. If free silane activators are present in the system, they can react with water, which increases the difficulty of storing the polyamic acid solution. In addition, there is a possibility that excessive silane activators may be wasted.

[0148] Figure 1 Optical image of the thin film prepared from polyamic acid in Example 17; Figure 2 Optical images of the thin film prepared by comparative example 7 (polyamic acid); it can be seen that the addition of Lewis base significantly reduces the yellowness value of the polyimide film and also greatly improves its transparency;

[0149] Figure 3 The transmittance diagram is for the polyamic acid film prepared in Example 17. The transmittance of the polyimide film at 450 nm exceeds 85%.

[0150] 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 polyamic acid composition, characterized in that, The raw materials for preparation include Lewis acid-base pair catalytic system, aromatic tetracarboxylic acid dianhydride, monohydric alcohol, aromatic diamine, crosslinking agent and aprotic polar solvent; The Lewis acid-base catalytic system comprises a Lewis acid, a Lewis base, and a silane activator. The molar ratio of the Lewis acid to the Lewis base is 0.75 to 1:1, and the amount of the silane activator accounts for 0.1 to 5 mol% of the total molar amount of the Lewis acid and Lewis base. The Lewis acid is one or more selected from trialkylboron, dialkylalkoxyboron, trialkoxyboron, and trisubstituted arylboron; The silane activator is one or more selected from trimethylsilane, triethylsilane, triisopropylsilane, triphenylsilane, trimethoxysilane, triethoxysilane, triisopropoxysilane, methyltriethoxysilane, methyltrimethoxysilane, methyltripropoxysilane, ethyltriethoxysilane, and propyltriethoxysilane. The Lewis base is one or more of the following: tertiary amines, amidines, guanidines, imidazoles, pyridines, and triaminophosphines; The crosslinking agent is a cyclic acid anhydride monomer containing unsaturated bonds; In preparing the polyamic acid composition, Lewis acid and silane activator are first added to the reaction system, followed by the addition of Lewis base.

2. The polyamic acid composition according to claim 1, characterized in that, The tertiary amine is NR3, wherein R is one or more of substituted or unsubstituted C1-5 alkyl, substituted or unsubstituted C1-5 alcohol hydroxyl and C6-10 aromatic group; And / or, the structural formula of the amidines is shown in general formula (I); ； （Ⅰ）； In general formula (Ⅰ), R1 is C n H 2n n is any integer from 1 to 5; And / or, the structural formula of the guanidine is shown in general formula (II) or (III); ； （Ⅱ） （Ⅲ）； In general formula (II), R2 is a substituted or unsubstituted C1-5 alkyl group; In general formula (Ⅲ), R5 is H, substituted or unsubstituted C1-5 alkyl; And / or, the structural formula of the imidazole class is shown in general formula (Ⅳ); ； （Ⅳ）； In general formula (Ⅳ), R3 is H, substituted or unsubstituted C1-5 alkyl; And / or, the structural formula of the pyridine class is shown in general formula (V); ； （Ⅴ）； In general formula (V), R4 is H, a substituted or unsubstituted C1-5 alkyl group, or a substituted or unsubstituted amino group; And / or, the structural formula of the triaminophosphine class is shown in general formula (VI); ； （Ⅵ）； In general formula (VI), R6 is H, or a substituted or unsubstituted C1-5 alkyl group.

3. The polyamic acid composition according to claim 1, characterized in that, In molar terms, the ratio of aromatic tetracarboxylic dianhydride to aromatic diamine is 0.85~1:1, the ratio of monohydric alcohol to aromatic tetracarboxylic dianhydride is 0.005~0.15:1, the ratio of crosslinking agent to monohydric alcohol is 0.01~0.5:1, the aprotic polar solvent accounts for 50~60wt% of the total mass of aromatic tetracarboxylic dianhydride and aromatic diamine; and / or, the Lewis acid-base pair catalytic system accounts for 0.1~0.5mol% of the total molar amount of the polyamic acid composition.

4. The polyamic acid composition according to claim 1, characterized in that, The aromatic tetracarboxylic dianhydride is one or more of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride. And / or, the monohydric alcohol is one or more selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, 2-pentanol, 3-pentanol, isopentanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol; And / or, the aromatic diamine is p-phenylenediamine, m-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diaminodiphenyl sulfone, 3,4-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminobenzoylaniline ...4,4'-diaminobenzoylaniline, 4,4'-diaminobenzoylaniline, 4,4'-diaminobenzoylaniline, 4,4'-diaminobenzoylaniline, 4,4'-diaminobenzoyl One or more of the following: (4-aminophenyl)hexafluoropropane, 1,4-bis(2-trifluoromethyl4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenylmethane, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)benzene, and 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane; And / or, the crosslinking agent is one or more of 4-phenylacetylene phthalic anhydride, phenylacetylene tricarboxylic anhydride, maleic anhydride, norbornene anhydride, methyl-5-norbornene-2,3-dicarboxylic anhydride and benzonorbornene anhydride.

5. A method for preparing the polyamic acid composition according to any one of claims 1-4, characterized in that, Includes the following steps: (1) In an inert atmosphere, aromatic tetracarboxylic acid dianhydride, Lewis acid and silane activator are mixed and reacted in an aprotic polar solvent, followed by the addition of Lewis base and monohydric alcohol, and the reaction is carried out at low temperature to obtain mixed solution A. (2) Under the inert atmosphere, the mixed solution A is cooled to a first temperature, an aromatic diamine is added to react, and then the temperature is raised to a second temperature to continue the reaction to obtain a polyamic acid slurry; (3) Add a crosslinking agent to the polyamic acid slurry and carry out a crosslinking reaction at a second temperature to obtain the polyamic acid composition.

6. A method for preparing polyimide, characterized in that, The method includes the following steps: subjecting the polyamic acid composition according to any one of claims 1-4 or the polyamic acid composition prepared by the method of claim 5 to thermal imidization treatment to obtain polyimide.

7. A polyimide, characterized in that, It is prepared by the method described in claim 6.

8. The application of the polyimide of claim 7 in the field of flexible OLED substrates.

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