Polyamic acid solution, preparation method thereof and polyimide film

Abstract

The invention discloses a polyamide acid solution, a preparation method thereof and a polyimide film. The preparation method of the polyamide acid solution comprises the following steps: mixing diamine, dianhydride, an auxiliary agent and a solvent to obtain a reaction system; and reacting the reaction system to obtain the polyamide acid solution, wherein the auxiliary agent comprises a composition of fatty acid and polypeptide, and the mass ratio of the fatty acid to the polypeptide is 1: (0.01-0.6). According to the preparation method, the auxiliary agent is introduced in the preparation process of the polyamide acid solution, so that the polyamide acid solution has relatively high solid content, relatively low dynamic viscosity, proper molecular weight, relatively good storage stability and relatively good film-forming property.

Description

Technical Field

[0001] This invention relates to the field of polyamic acid synthesis technology, and particularly to a polyamic acid solution, its preparation method, and a polyimide film. Background Technology

[0002] Polyimide is a heterocyclic polymer (R-CO-NH-CO-R') containing imide groups in its molecular structure. It possesses superior heat resistance, strong corrosion resistance, excellent aging resistance, good wear resistance, excellent insulation properties, high insulation resistance, high heat distortion temperature, and good thermal stability. It can be used in the range of room temperature to 300℃ and is suitable for applications in ultra-high temperature, ultra-high vacuum, and corrosive environments. Polyimide is mainly used in aerospace, automotive manufacturing, medical devices, pressure vessels, gas separation, and flexible displays. Polyimide can be prepared using one-step, two-step, and three-step methods. Currently, industrial production mostly uses the simple "two-step method," which involves polymerizing aromatic dianhydrides and diamines in an aprotic polar solvent to obtain a polyamic acid solution, followed by heat treatment or chemical imidization to obtain polyimide. Therefore, the characteristics of the polyamic acid precursor determine the quality of the final product.

[0003] The solid content and viscosity of polyamic acid solutions are crucial factors affecting processability. In industrial production, after synthesis, polyamic acid is used to prepare coatings and films through methods such as spraying, casting, and spinning. Appropriate viscosity and solid content can enhance the performance of these products. In practice, polyamic acid molecules readily form numerous hydrogen bonds within and between chains, and the ionization of carboxylic acid groups enhances the polyelectrolyte effect. This results in high-solid-content polyamic acid solutions typically exhibiting very high kinetic viscosity, sometimes even gelling, which is detrimental to subsequent processing applications. Reducing the solid content of polyamic acid solutions can lower their kinetic viscosity to some extent, but this increases solvent consumption, affecting product quality and reducing production efficiency. Therefore, preparing polyamic acid solutions with low viscosity and high solid content is fundamental for subsequent processing. Furthermore, molecular weight is another important factor influencing the properties of polyamic acid. Polyamic acid with a molecular weight generally between 30,000 and 90,000 exhibits good processability; however, the monomers, additives, and polymerization methods all affect the relationship between molecular weight, solid content, and viscosity.

[0004] Furthermore, polyamic acid solutions spontaneously degrade during storage. The root cause of this degradation is the nucleophilic addition of nucleophilic hydroxyl groups in the polyamic acid to the amide carbonyl groups within the molecule, resulting in depolymerization. The presence of moisture in the system causes the anhydride end groups formed during molecular chain depolymerization to hydrolyze, forming two carboxylic acid groups. This irreversible reaction alters the properties of the polyamic acid, leading to a short shelf life and poor batch stability. Currently, methods to extend the shelf life of polyamic acid mainly include dry preparation, ultra-low temperature storage, adding molecular sieves to absorb water, and molecular chain end-capping. However, these methods suffer from cumbersome processes, high reagent toxicity, and high processing costs.

[0005] CN101558102A describes a method for preparing a polyamic acid solution and the polyamic acid solution itself. The method involves reacting a diamine with a tetracarboxylic dianhydride in excess of the diamine in an aqueous solvent, wherein the amount of water exceeds one-third of the molar amount of the tetracarboxylic dianhydride, thereby preparing a polyamic acid solution. Subsequently, the diamine and / or the tetracarboxylic dianhydride are added to the polyamic acid solution such that the molar amount of the diamine component is substantially equal to the molar amount of the tetracarboxylic acid component, and the resulting mixture is further reacted to prepare the polyamic acid solution. This method allows for the adjustment of the polyamic acid to a given low molecular weight by controlling the water content of the reaction system, thus enabling the reproducible and reliable preparation of polyamic acid solutions with high concentrations and low viscosity.

[0006] CN106589371A discloses a viscosity-controllable polyamic acid composition, its preparation method, and its application. It proposes a method to control the viscosity of polyamic acid by adding tetracarboxylic acid to the reaction system of dianhydride and diamine. However, this method requires operation under N2 atmosphere, which increases the complexity of the reaction.

[0007] CN104292459A discloses a method for adjusting adhesion by adding polysiloxane-based adhesives, but this method has problems such as requiring multiple additions of material, replenishing solvent, and long waiting times for material addition.

[0008] CN103788651A discloses a method for preparing a polyamic acid solution with low apparent viscosity. This method involves adding 5% to 40% (by weight of the polyamic acid) of trimethylchlorosilane to a polyamic acid solution and stirring at room temperature for 1 to 5 hours to obtain a polyamic acid solution with an apparent viscosity of 0.2 to 1.5 kPa. However, this method uses a large proportion of the additive trimethylchlorosilane, increasing the difficulty of subsequent material processing and additive removal.

[0009] CN106589368A discloses a polyamic acid composition, its preparation method, and its applications. The preparation method involves adding tetracarboxylic acid in controlled proportions and adding tetracarboxylic dianhydride in batches to control the viscosity of the polyamic acid solution. However, this method requires operation under a nitrogen atmosphere, increasing the difficulty of experimental operation, and it does not optimize the stability of polyamic acid during storage.

[0010] CN115678010A discloses a polyamic acid, a polyimide resin, and a method for preparing the same. The method involves adding a diamine containing a nitrogen-containing heteroaromatic ring to a solvent, followed by the addition of a dianhydride containing a flexible chain structure in three separate additions to obtain the polyamic acid. This polyamic acid is then used to prepare a low-temperature imidized polyimide material with good thermal stability and mechanical properties. However, this preparation method requires batch feeding, increasing the number of steps, and it does not investigate the molecular weight, viscosity, and storage stability of the polyamic acid solution.

[0011] CN113185693A discloses a polyamic acid solution, its preparation method, polyimide, and polyimide film. The preparation method of the polyamic acid solution includes: mixing a diamine monomer and an aprotic polar solvent under a protective atmosphere, then adding a dianhydride monomer for a condensation reaction to obtain a reaction solution; adding an amino acid and / or its derivatives to the reaction solution for a reaction, then adding the diamine monomer and dianhydride monomer for a condensation reaction to obtain the polyamic acid solution. This method, by introducing an amino acid and / or its derivatives carrying one amino and one carboxyl group, achieves molecular chain growth, which can improve the mechanical properties, heat resistance, and dimensional stability of the polyimide prepared from the polyamic acid solution; it also reduces the viscosity of the polyamic acid solution while maintaining a certain solid content. However, this preparation method requires batch feeding, increasing the number of operation steps, and the storage stability of the polyamic acid solution is not investigated.

[0012] Furthermore, current methods for preparing polyimide fiber membranes typically employ electrospinning, but this method suffers from problems such as polyamic acid solution agglomeration leading to spinneret clogging, uneven spinneret direction, and unsuitable viscosity, resulting in poor membrane uniformity. Therefore, improving the polyamic acid solution to enhance its subsequent film-forming properties remains a technical challenge in this field.

[0013] Therefore, preparing polyamic acid solutions with high solid content, low viscosity, suitable molecular weight, high storage stability, and good film-forming properties through simple preparation methods is a problem that urgently needs to be solved in this field. Summary of the Invention

[0014] To address the aforementioned technical problems, the present invention aims to provide a polyamic acid solution, its preparation method, and a polyimide film. By introducing additives during the preparation of the polyamic acid solution, the present invention enables the polyamic acid solution to possess high solid content, low kinetic viscosity, suitable molecular weight, good storage stability, and good film-forming properties.

[0015] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a polyamic acid solution, comprising the following steps:

[0016] (I) Mix diamine, dianhydride, auxiliaries and solvent to obtain a reaction system;

[0017] (II) After reacting the reaction system obtained in step (I), the polyamic acid solution is obtained;

[0018] The adjuvant comprises a composition of fatty acids and polypeptides, wherein the mass ratio of the fatty acids to the polypeptides is 1:(0.01-0.6).

[0019] According to a specific embodiment of the present invention, preferably, the mass ratio of the total amount of the auxiliary agent to the total amount of the diamine and dianhydride is (0.01-0.5):1.

[0020] According to a specific embodiment of the present invention, preferably, the fatty acid includes fatty acids with 4 or more carbon atoms.

[0021] According to a specific embodiment of the present invention, preferably, the fatty acid includes one or more of the following: sebacic acid, tridecanoic acid, adipic acid, octadecanoic acid, hexadecanoic acid, butyric acid, hexanoic acid, decanoic acid, and octanoic acid.

[0022] According to a specific embodiment of the present invention, preferably, the polypeptide comprises a polypeptide containing 3-30 amino acid molecules. More preferably, the polypeptide comprises one or more of the following: lysine polypeptide, palmitoyl tripeptide, palmitoyl tetrapeptide, palmitoyl pentapeptide, acetyl tripeptide, acetyl tetrapeptide, acetyl pentapeptide, acetyl hexapeptide, acetyl heptapeptide, and acetyl octapeptide.

[0023] According to a specific embodiment of the present invention, preferably, the solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and hexamethylphosphoric triamine.

[0024] According to a specific embodiment of the present invention, preferably, the diamine includes one or more of the following: m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, hydroquinone diether diamine, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, ethylenediamine, 1,6-hexanediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, and bisphenol A diether diamine.

[0025] According to a specific embodiment of the present invention, preferably, the dianhydride includes one or more of the following: pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, triphenyl diether dianhydride, diphenyl ether dianhydride, diphenyl sulfide dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, hydroquinone diether dianhydride, hexafluoro dianhydride, resorcinol diether dianhydride, bisphenol A diether dianhydride, and 4,4'-oxobisphthalic dianhydride.

[0026] According to a specific embodiment of the present invention, preferably, the molar ratio of the diamine to the dianhydride is (0.99-1.01):(0.99-1.01), and the total mass of the diamine and the dianhydride accounts for 10-30% of the total mass of the reaction system.

[0027] According to a specific embodiment of the present invention, preferably, the system temperature in steps (I) and (II) is -15 to 50°C.

[0028] According to a specific embodiment of the present invention, preferably, the reaction time in step (II) is 1-10 hours.

[0029] A second aspect of the present invention provides a polyamic acid solution, which is prepared by the above-described method for preparing polyamic acid solution.

[0030] According to a specific embodiment of the present invention, preferably, the kinetic viscosity of the polyamic acid solution is below 10000 cP.

[0031] According to a specific embodiment of the present invention, preferably, the solid content of the polyamic acid solution is 10 wt% or more.

[0032] According to a specific embodiment of the present invention, preferably, the weight-average molecular weight of the polyamic acid solution is between 30,000 and 90,000.

[0033] According to a specific embodiment of the present invention, preferably, the polyamic acid solution, when stored in an environment at a temperature of 25°C and a pressure of normal for 960 hours, exhibits a change rate of less than 1% in its weight-average molecular weight.

[0034] A third aspect of the present invention provides a polyimide film obtained by at least imidizing the above-mentioned polyamic acid solution.

[0035] The present invention has at least the following beneficial effects:

[0036] This invention introduces an auxiliary agent into the preparation process of a polyamic acid solution. This auxiliary agent comprises a composition of fatty acids and peptides. The fatty acids and peptides exhibit a synergistic effect, resulting in a polyamic acid solution with high solids content, low kinetic viscosity, suitable molecular weight, and excellent storage stability. The fatty acids in the auxiliary agent increase free hydrogen ions in the reaction system, weakening intermolecular and intramolecular hydrogen bonding in polyamic acid, while simultaneously shielding the polyelectrolyte effect of polyamic acid. Therefore, the polyamic acid solution exhibits both high solids content and low kinetic viscosity. Furthermore, the synergistic effect between the fatty acids and peptides in this invention prevents the aggregation of polyamic acid molecular chains, thereby increasing the molecular weight of polyamic acid and resulting in a polyamic acid solution with a suitable molecular weight. Furthermore, the terminal amino and carboxyl groups of the polypeptides in the additives of this invention can promote the forward reaction, ensuring a full reaction between the diamine and dianhydride, and inhibiting the degradation of the polyamic acid solution during storage, while also increasing the molecular weight of the polyamic acid. Simultaneously, the synergistic effect of the fatty acids and polypeptides in this invention reduces the rate of depolymerization in the polyamic acid solution. Therefore, the polyamic acid solution exhibits better storage stability, improving upon the problems of its susceptibility to environmental temperature fluctuations and difficulty in storage. In addition, the polyamic acid solution of this invention, through the synergistic effect between the additives and the diamine and dianhydride, results in excellent film-forming properties after subsequent processing, especially after forming polyimide fiber films using electrospinning. Attached Figure Description

[0037] Figure 1 The infrared spectrum of the polyimide fiber membrane prepared from the polyamic acid solution of Example 1.

[0038] Figure 2 The polyamic acid solution prepared in Example 2 was stored at 25°C and atmospheric pressure for 2160 hours, and the change curve of its weight-average molecular weight was obtained. Detailed Implementation

[0039] To provide a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the present invention will now be described in detail below, but this should not be construed as limiting the scope of the invention.

[0040] According to a specific embodiment of the first aspect of the present invention, the present invention provides a method for preparing a polyamic acid solution, which includes the following steps:

[0041] (I) Mix diamine, dianhydride, auxiliaries and solvent to obtain a reaction system;

[0042] (II) After reacting the reaction system obtained in step (I), the polyamic acid solution is obtained;

[0043] The adjuvant comprises a composition of fatty acids and polypeptides, wherein the mass ratio of the fatty acids to the polypeptides is 1:(0.01-0.6), such as, but not limited to, 1:0.01, 1:0.05, 1:0.1, 1:0.2, 1:0.4 or 1:0.6; preferably, the mass ratio of the fatty acids to the polypeptides is 1:(0.1-0.6).

[0044] In some embodiments, the mass ratio of the auxiliary agent to the total amount of the diamine and dianhydride (i.e., auxiliary agent:(diamine + dianhydride)) is (0.01-0.5):1, for example, but not limited to, 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, or 0.5:1. Preferably, the mass ratio of the auxiliary agent to the total amount of the diamine and dianhydride is (0.1-0.5):1.

[0045] In some embodiments, the fatty acid includes fatty acids with 4 or more carbon atoms, preferably fatty acids with 4-18 carbon atoms. Specifically, the fatty acid includes one or more of the following: sebacic acid (i.e., 1,10-sebacic acid), tridecanoic acid (i.e., brassic acid), adipic acid, octadecanoic acid, hexadecanoic acid, butyric acid, hexanoic acid, decanoic acid, and octanoic acid.

[0046] In some embodiments, the polypeptide comprises a polypeptide containing 3-30 amino acid molecules, preferably a polypeptide containing 3-11 amino acid molecules. More preferably, the polypeptide comprises one or more of the following: lysine polypeptide, palmitoyl tripeptide, palmitoyl tetrapeptide, palmitoyl pentapeptide, acetyl tripeptide, acetyl tetrapeptide, acetyl pentapeptide, acetyl hexapeptide, acetyl heptapeptide, and acetyl octapeptide. Specifically, the lysine polypeptide has the sequence Ac-RFAAKAA-COOH and the molecular formula C0. 35 H 57 N 11O9. The palmitoyl tripeptide may, for example, include one or more of palmitoyl tripeptide-1, palmitoyl tripeptide-5, and palmitoyl tripeptide-8. The palmitoyl tetrapeptide may, for example, include one or more of palmitoyl tetrapeptide-5, palmitoyl tetrapeptide-7, and palmitoyl tetrapeptide-10. The palmitoyl pentapeptide may, for example, include palmitoyl pentapeptide-4. The acetyl tripeptide may, for example, include acetyl tripeptide-1. The acetyl tetrapeptide may, for example, include one or more of acetyl tetrapeptide-3, acetyl tetrapeptide-5, and acetyl tetrapeptide-11. The acetyl pentapeptide may, for example, include acetyl pentapeptide-1. The acetyl hexapeptide may, for example, include one or more of acetyl hexapeptide-1, acetyl hexapeptide-8, and acetyl hexapeptide-37. The acetyl heptapeptide may, for example, include acetyl heptapeptide-4. The acetyl octapeptide may, for example, include one or two of acetyl octapeptide-1 and acetyl octapeptide-3.

[0047] In some embodiments, the solvent comprises an aprotic polar solvent. Preferably, the solvent comprises one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and hexamethylphosphoric triamine.

[0048] In some embodiments, the diamine includes one or more of aromatic diamines and aliphatic diamines. Preferably, the diamine includes one or more of m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, hydroquinone diether diamine, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, ethylenediamine, 1,6-hexanediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, and bisphenol A diether diamine.

[0049] In some embodiments, the dianhydride comprises one or more aromatic dicarboxylic anhydrides. Preferably, the dianhydride comprises one or more of the following: pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, triphenyl diether dianhydride, diphenyl ether dianhydride, diphenyl sulfide dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, hydroquinone diether dianhydride, hexafluoro dianhydride, resorcinol diether dianhydride, bisphenol A diether dianhydride, and 4,4'-oxophthalic dianhydride.

[0050] In some embodiments, the molar ratio of the diamine to the dianhydride is (0.99-1.01):(0.99-1.01), such as, but not limited to, 0.99:1.01, 1.01:0.99, or 1:1; the total mass of the diamine and the dianhydride accounts for 10-30% of the total mass of the reaction system, such as, but not limited to, 10%, 15%, 20%, 25%, or 30%. The reaction system is a combination of the solvent, auxiliaries, diamine, and dianhydride of the present invention.

[0051] In some embodiments, the solvent and one of the diamine and dianhydride can be added to the reaction vessel first for dissolution, and then the other of the diamine and dianhydride can be added. After reaction, the polyamic acid solution is obtained. The additive can be added at any time before the reaction. There is no particular limitation on the order of addition of the diamine and dianhydride. Those skilled in the art are familiar with methods such as the forward addition method (adding the diamine first, then the dianhydride), the reverse addition method (adding the dianhydride first, then the diamine), and simultaneous addition methods. The forward addition method is preferred, i.e., adding the diamine first, then the dianhydride. Furthermore, the dianhydride can be added all at once or in batches; when added in batches, it can be added in three or more batches. In addition, it is preferable to first mix the diamine, additive, and solvent, and then add the dianhydride to obtain the reaction system. This allows the additive to fully exert its effect, resulting in better reduction of the kinetic viscosity of the polyamic acid solution, ensuring its high solid content, giving it a suitable molecular weight, and better storage stability.

[0052] In some embodiments, the system temperature in steps (I) and (II) is -15 to 50°C, preferably -5 to 30°C.

[0053] In some embodiments, the reaction time in step (II) is 1-10 hours, preferably 2-5 hours.

[0054] According to a specific embodiment of the second aspect of the present invention, the present invention provides a polyamic acid solution, which is prepared by the above-described method for preparing polyamic acid solution.

[0055] In some embodiments, the kinetic viscosity of the polyamic acid solution is below 10,000 cP (i.e., centipoise), preferably below 8,000 cP, and more preferably 3,000-8,000 cP.

[0056] In some embodiments, the solid content of the polyamic acid solution is 10 wt% or more, preferably 10-30 wt%.

[0057] In some embodiments, the weight-average molecular weight (g / mol) of the polyamic acid solution is between 30,000 and 90,000, preferably between 30,000 and 80,000.

[0058] In some embodiments, the polyamic acid solution, after being stored in an environment at 25°C and atmospheric pressure for 960 hours, exhibits a change in weight-average molecular weight of less than 1%, preferably less than 0.1%.

[0059] According to a specific embodiment of a third aspect of the present invention, the present invention provides a polyimide film obtained by at least imidizing the above-described polyamic acid solution.

[0060] In some embodiments, the polyimide film is obtained by electrospinning the polyamic acid solution to obtain a polyamic acid fiber membrane, followed by imidization treatment of the polyamic acid fiber membrane. In this case, the polyimide film is a polyimide fiber membrane. The equipment and conditions used for electrospinning can be those found in the prior art. Specifically, the conditions for electrospinning may include, for example: a voltage of 15-25 kV; a flow rate of 0.0008-0.0015 mm / s; a spinneret model and specification of 21G-26G (inner diameter of 0.50-0.24 mm); the use of a roller receiver with a receiver rotation speed of 50-200 r / min; and a distance of 10-20 cm between the spinneret and the surface of the roller receiver. The imidization treatment can be performed using thermal imidization, and its conditions may include, for example: a temperature of 60℃-370℃ and a time of 1-7 h.

[0061] In some embodiments, the imidization rate of the polyimide film (preferably a polyimide fiber film) is 100%.

[0062] In some embodiments, the polyimide film (preferably a polyimide fiber film) has a tensile strength of 320-390 MPa, preferably 330-380 MPa, and a tensile modulus of 4.5-5 GPa.

[0063] In some embodiments, the glass transition temperature of the polyimide film (preferably a polyimide fiber film) is 420-490°C.

[0064] In some embodiments, the thickness of the polyimide film (preferably a polyimide fiber film) is 20-30 μm.

[0065] The present invention is illustrated below by way of examples and comparative examples, but the present invention is not limited to these examples. Of course, various modifications can be made within the scope of the present invention.

[0066] The test methods used in the examples and comparative examples are as follows:

[0067] (1) Solid content

[0068] The solid content is calculated using the following formula:

[0069] Solid content (%) = Solid mass (g) / Total mass (g) × 100%

[0070] Spread the polyamic acid solution evenly in a container and place it in an oven to dry at 100°C for 2 hours. Weigh the polyamic acid solution before and after drying, taking the mass after drying as the solid mass and the mass before drying as the total mass.

[0071] (2) Weight-average molecular weight

[0072] The tests were performed using an Agilent gel permeation chromatography system. Test conditions included: a Waters Styragel HR4 column, N,N-dimethylformamide (DMF) as the mobile phase, a test temperature of 35°C, and a polyamic acid solution with a concentration of 0.5–10 mg / mL. The test sample was prepared by dilution with the mobile phase.

[0073] (3) Kinetic viscosity

[0074] The test was conducted using an Anton Paar Visco QC 300 kinematic viscometer. Test conditions included: 40 seconds runtime, 150 rpm rotation speed, rotor #4, and room temperature (23℃±2℃). An appropriate amount of polyamic acid solution was poured into the test container; the solution level should reach the indicator line on the rotor. The kinetic viscosity of the polyamic acid solution was obtained after the test.

[0075] (4) Preservation stability

[0076] The polyamic acid solution was stored at 25°C and atmospheric pressure (0.1013 MPa) for 960 hours. The weight-average molecular weight (MAM) of the polyamic acid solution before storage and after 960 hours of storage was measured. The rate of change of MAM was calculated using the following formula: Rate of change of MAM (%) = (Weight-average molecular weight before storage - Weight-average molecular weight after 960 hours of storage) / Weight-average molecular weight before storage × 100. Furthermore, for the polyamic acid solution of Example 2, the MAM was measured at 0, 24, 120, 350, 960, 1200, 1440, and 2160 hours after the start of storage, and curves were plotted.

[0077] (5) Film-forming properties

[0078] A polyamic acid solution is electrospun to obtain a polyamic acid fiber membrane, which is then subjected to imidization treatment to obtain a polyimide fiber membrane.

[0079] Imidification rate: The polyimide fiber film was pressed onto a diamond stage and infrared spectra were obtained using a Thermo Nicoleti S20 Fourier transform infrared spectrometer. Test conditions included 16 scans and a resolution of 4 cm⁻¹. -1 Background acquisition mode. Based on this infrared spectrum, the imidization rate was calculated using the following method: In the formula, S 1380 For 1380cm -1 The peak area of ​​the nearby absorption peak (as a characteristic absorption peak of polyamide), S 1500 For 1500cm-1 The peak area of ​​the nearby absorption peak (vibrational peak of the benzene ring skeleton), (S 1380 / S 1500 ) 测试样品 The ratio of the peak areas of the two absorption peaks of the polyimide fiber membranes prepared in the following examples and comparative examples is given by (S). 1380 / S 1500 ) 比较样品 This is the ratio of the peak areas of the two absorption peaks of the polyimide film (comparative sample) prepared by the following method, and the imidization rate of the polyimide film is considered to be 100%. It should be noted that if the calculated imidization rate exceeds 100%, it is still expressed as 100%.

[0080] The comparative sample preparation method includes the following steps: 4,4'-diaminodiphenyl ether (ODA) is dissolved in N-methylpyrrolidone (NMP) in a three-necked flask equipped with a mechanical stirrer and a nitrogen inlet tube. Then, pyromellitic dianhydride (PMDA) is gradually added over 2 hours, with a molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride of 1:0.997, to obtain a reaction mixture. The mass of 4,4'-diaminodiphenyl ether in the reaction mixture is 3.9225 g (0.01959 mol), and the mass of pyromellitic dianhydride is... 4.2596 g (0.01953 mol) of N-methylpyrrolidone (60 g) was added to the reaction mixture and stirred in an ice bath for 12 hours to obtain a polyamic acid (PAA) solution. Then, 0.9999 g of acetic anhydride was added to the polyamic acid solution to obtain a mixed solution. The mixed solution was then spin-coated onto a glass plate and placed in a muffle furnace. The plate was then held at 100 °C for 1 h, 200 °C for 1 h, and 300 °C for 1 h to obtain a polyimide film. The imidization rate of the polyimide film was considered to be 100%, and it was used as a comparative sample.

[0081] Tensile strength and tensile modulus: The polyimide fiber membrane was tested using an i-STRENTEK 1510 electronic universal testing machine. The test conditions included: room temperature, tensile speed of 50 mm / min, sample width of 15 mm, length of 100 mm, and thickness of the membrane prepared in the following examples and comparative examples. The stress-strain curve was obtained from the tensile data, and the tensile strength and tensile modulus of the sample were determined from the curve.

[0082] Glass transition temperature: The polyimide fiber membrane was tested using a TMA Q400 thermomechanical analyzer. The sample was heated from about 40°C to 450°C in a helium flow at a rate of 10°C / min. The temperature corresponding to the peak value of the damping coefficient (Tanδ) in the obtained energy curve is the glass transition temperature of the sample.

[0083] Example 1

[0084] 73.09 g of N,N-dimethylformamide and 0.0877 g of an auxiliary agent (composed of 0.0731 g of sebacic acid and 0.0146 g of lysine polypeptide, wherein the sequence of the lysine polypeptide is Ac-RFAAKAA-COOH and the molecular formula is C 35 H 57 N 11 O9) was added to a three-necked flask and stirred to dissolve at -5°C. Then, 2.7122 g (25.08 mmol) of p-phenylenediamine was added and stirred to dissolve. Next, 5.5250 g (25.33 mmol) of pyromellitic dianhydride was added, and the mixture was heated to 10°C and stirred for 4 hours to obtain a polyamic acid solution with a solid content of 10 wt%, a weight-average molecular weight of 37560, and a kinetic viscosity of 3600 cP. The polyamic acid solution, after being stored at 25°C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of only 0.05%.

[0085] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 15 kV; a flow rate of 0.0008 mm / s; a 22G spinneret; a roller receiver with a receiver rotation speed of 50 r / min; and a distance of 17 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 120°C and a time of 5 hours.

[0086] The polyimide fiber membrane has a thickness of 22 μm. The infrared spectrum of the polyimide fiber membrane is shown below. Figure 1 As shown, the imidization rate of this polyimide fiber membrane is 100%.

[0087] The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0088] Example 2

[0089] 49.57 g of N-methylpyrrolidone and 1.22 g (20.31 mmol) of ethylenediamine were added to a three-necked flask, followed by 0.779 g of an auxiliary agent (composed of 0.76 g of tridecanoic acid and 0.019 g of acetyl tetrapeptide-11). After dissolving by stirring at 0°C, 4.43 g (20.31 mmol) of pyromellitic dianhydride was added, and the mixture was stirred at 0°C for 5 hours to obtain a polyamic acid solution with a solid content of 11 wt%, a weight-average molecular weight of 67560, and a kinetic viscosity of 3152 cP. The polyamic acid solution, after being stored at 25°C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of only 0.02%. Figure 2 The polyamic acid solution prepared for this embodiment was stored at 25°C and atmospheric pressure for 2160 hours, and the change curve of its weight-average molecular weight was obtained.

[0090] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 18 kV; a flow rate of 0.0015 mm / s; a 26G spinneret; a roller receiver with a rotation speed of 90 r / min; and a distance of 10 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 70°C and a time of 3 hours.

[0091] The polyimide fiber membrane has a thickness of 25 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0092] Example 3

[0093] 52.27 g of N,N-dimethylacetamide and 1.59 g of an auxiliary agent (composed of 1.06 g of adipic acid and 0.53 g of acetyl hexapeptide-8) were added to a three-necked flask, followed by the addition of 2.8895 g (26.72 mmol) of p-phenylenediamine. After dissolving by stirring at 5 °C, 7.8998 g (26.85 mmol) of biphenyltetracarboxylic dianhydride was added, and the mixture was stirred at 5 °C for 2 hours to obtain a polyamic acid solution with a solid content of 17 wt%, a weight-average molecular weight of 58430, and a kinetic viscosity of 3503 cP. The polyamic acid solution, after being stored at 25 °C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of 0.07%.

[0094] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 25 kV; a flow rate of 0.001 mm / s; a 21G spinneret model; a roller receiver with a receiver rotation speed of 100 r / min; and a distance of 17 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 140°C and a time of 2 hours.

[0095] The polyimide fiber membrane has a thickness of 30 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0096] Example 4

[0097] 62.47 g of dimethyl sulfoxide and 0.1584 g of an auxiliary agent (composed of 0.099 g of octadecanoic acid and 0.0594 g of lysine peptide, the same as in Example 1) were added to a three-necked flask. Then, 5.9396 g (27.46 mmol) of 4,4'-diaminodiphenyl sulfide was added, and the mixture was stirred and dissolved at -15°C. Next, 8.4284 g (27.17 mmol) of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride was added, and the mixture was stirred and reacted at -15°C for 3 hours to obtain a polyamic acid solution with a solid content of 19 wt%, a weight-average molecular weight of 64,400, and a kinetic viscosity of 5450 cP. The polyamic acid solution, after being stored at 25°C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of only 0.03%.

[0098] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 20 kV; a flow rate of 0.0013 mm / s; a 24G spinneret; a roller receiver with a receiver rotation speed of 80 r / min; and a distance of 19 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 240°C and a time of 5 hours.

[0099] The polyimide fiber membrane has a thickness of 27 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0100] Example 5

[0101] 69.41 g of hexamethylphosphoric triamine and 0.3888 g of an auxiliary agent (composed of 0.3471 g of hexadecanoic acid and 0.0417 g of acetyl hexapeptide-8) were added to a three-necked flask, followed by the addition of 7.1871 g (36.25 mmol) of 4,4'-diaminodiphenylmethane. After dissolving by stirring at 25 °C, 10.6861 g (36.32 mmol) of biphenyltetracarboxylic dianhydride was added, and the mixture was stirred at 25 °C for 8 hours to obtain a polyamic acid solution with a solid content of 21 wt%, a weight-average molecular weight of 65510, and a kinetic viscosity of 6040 cP. The polyamic acid solution, after being stored at 25 °C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of 0.09%.

[0102] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 23 kV; a flow rate of 0.0009 mm / s; a 26G spinneret model; a roller receiver with a receiver rotation speed of 180 r / min; and a distance of 19 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 200°C and a time of 1 hour.

[0103] The polyimide fiber membrane has a thickness of 22 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0104] Example 6

[0105] 57.36 g of N,N-dimethylacetamide and 0.5885 g of an auxiliary agent (composed of 0.5162 g of butyric acid and 0.0723 g of acetyl tetrapeptide-11) were added to a three-necked flask, followed by 8.0529 g (37.23 mmol) of 4,4'-diaminodiphenyl sulfide. After dissolving by stirring at 35 °C, 16.5479 g (37.27 mmol) of hexafluorodianhydride was added, and the mixture was stirred at 35 °C for 10 hours to obtain a polyamic acid solution with a solid content of 22 wt%, a weight-average molecular weight of 67,800, and a kinetic viscosity of 6580 cP. The polyamic acid solution, stored at 25 °C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of 0.01%.

[0106] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 21 kV; a flow rate of 0.0012 mm / s; a 24G spinneret; a roller receiver with a receiver rotation speed of 110 r / min; and a distance of 14 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 300°C and a time of 2 hours.

[0107] The polyimide fiber membrane has a thickness of 29 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0108] Example 7

[0109] 62.14 g of hexamethylphosphoric triamine and 1.7409 g of an auxiliary agent (composed of 1.658 g of hexanoic acid and 0.0829 g of acetyl hexapeptide-8) were added to a three-necked flask, followed by the addition of 6.9122 g (59.48 mmol) of 1,6-hexanediamine. The mixture was stirred and dissolved at 30 °C, and then 13.013 g (59.66 mmol) of pyromellitic dianhydride was added. The mixture was stirred at 30 °C for 5 hours to obtain a polyamic acid solution with a solid content of 26 wt%, a weight-average molecular weight of 72,000, and a kinetic viscosity of 7135 cP. After storage at 25 °C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 0.06%.

[0110] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 15 kV; a flow rate of 0.0011 mm / s; a 26G spinneret model; a roller receiver with a receiver rotation speed of 180 r / min; and a distance of 18 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 280°C and a time of 2.5 h.

[0111] The polyimide fiber membrane has a thickness of 30 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0112] Example 8

[0113] 90.47 g of N-methylpyrrolidone, 1.1868 g of an auxiliary agent (composed of 1.032 g of decanoic acid and 0.1548 g of lysine peptide, the same as in Example 1) and 9.3004 g (50.21 mmol) of 4,4'-diaminodiphenyl ether were added to a three-necked flask and stirred at 20 °C to dissolve. Then, 25.9514 g (49.86 mmol) of bisphenol A diether dianhydride was added, and the mixture was stirred at 20 °C for 7 hours to obtain a polyamic acid solution with a solid content of 29 wt%, a weight-average molecular weight of 78,600, and a kinetic viscosity of 7950 cP. The polyamic acid solution, after being stored at 25 °C and atmospheric pressure for 960 hours, showed a weight-average molecular weight change of 0.07%.

[0114] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 22 kV; a flow rate of 0.0012 mm / s; a spinneret model of 21G; a roller receiver with a receiver rotation speed of 55 r / min; and a distance of 16 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 100°C and a time of 3.5 h.

[0115] The polyimide fiber membrane has a thickness of 20 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0116] Example 9

[0117] 85.14 g of dimethyl sulfoxide and 0.3893 g of an auxiliary agent (composed of 0.3507 g of octanoic acid and 0.0386 g of acetyl hexapeptide-370) were added to a three-necked flask, followed by the addition of 7.6077 g (70.35 mmol) of p-phenylenediamine. The mixture was stirred and dissolved at 50 °C, and then 20.6778 g (70.28 mmol) of biphenyltetracarboxylic dianhydride was added. The mixture was stirred at 50 °C for 1 hour to obtain a polyamic acid solution with a solid content of 25 wt%, a weight-average molecular weight of 67560, and a kinetic viscosity of 6570 cP. After storage at 25 °C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 0.04%.

[0118] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 22 kV; a flow rate of 0.0014 mm / s; a 25G spinneret; a roller receiver with a receiver rotation speed of 170 r / min; and a distance of 15 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 310°C and a time of 6.5 h.

[0119] The polyimide fiber membrane has a thickness of 28 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0120] Example 10

[0121] 60 g of N,N-dimethylformamide, 4 g of an auxiliary agent (composed of 2.8571 g of hexanoic acid and 101.1429 g of palmitoyl tetrapeptide-10) and 4.1569 g (18.83 mmol) of 4,4'-diaminodiphenyl ether were added to a three-necked flask and stirred at 45 °C to dissolve. Then, 4.1287 g (18.83 mmol) of pyromellitic dianhydride was added, and the mixture was stirred at 45 °C for 5 hours to obtain a polyamic acid solution with a solid content of 17 wt%, a weight-average molecular weight of 85347, and a kinetic viscosity of 3450 cP. After storage at 25 °C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 0.04%.

[0122] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 18 kV; a flow rate of 0.0009 mm / s; a spinneret model of 23G; a roller receiver with a receiver rotation speed of 60 r / min; and a distance of 14 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 290°C and a time of 1.5 h.

[0123] The polyimide fiber membrane has a thickness of 24 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0124] Example 11

[0125] 60 g of N,N-dimethylacetamide, 2.486 g of an auxiliary agent (composed of 1.9123 g of octanoic acid and 0.5737 g of acetyl tetrapeptide-11) and 4.2324 g (18.5 mmol) of 2-(4-aminophenyl)-5-aminobenzimidazole were added to a three-necked flask and stirred at 45 °C to dissolve. Then, 4.0543 g (18.5 mmol) of pyromellitic dianhydride was added, and the mixture was stirred at 45 °C for 3 hours to obtain a polyamic acid solution with a solid content of 15 wt%, a weight-average molecular weight of 65214, and a kinetic viscosity of 3180 cP. After storage at 25 °C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 0.05%.

[0126] The polyamic acid solution of this embodiment was electrospun to obtain a polyamic acid fiber membrane, which was then subjected to imidization treatment to obtain a polyimide fiber membrane. The electrospinning conditions included: a voltage of 20 kV; a flow rate of 0.0008 mm / s; a 21G spinneret model; a roller receiver with a receiver rotation speed of 160 r / min; and a distance of 19 cm between the spinneret and the roller receiver surface. The imidization treatment was thermal imidization, with conditions including: a temperature of 270°C and a time of 5.5 h.

[0127] The polyimide fiber membrane has a thickness of 25 μm. The imidization rate of the polyimide fiber membrane is 100%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0128] Comparative Example 1

[0129] This comparative example is compared with Example 3, and is basically the same as Example 3, except that no additives were added, while the amounts of other raw materials and reaction conditions were the same as in Example 3. The prepared polyamic acid solution had a weight-average molecular weight of 113050 and a kinetic viscosity of 115390 cP. After being stored at 25°C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 12%.

[0130] A polyimide fiber membrane was prepared using the same method as in Example 3. The thickness of the polyimide fiber membrane was 40 μm. The imidization rate of the polyimide fiber membrane was 80%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0131] Comparative Example 2

[0132] This comparative example is compared with Example 3, and is basically the same as Example 3, except that: only 1.59g of acetyl hexapeptide-8 was used as the auxiliary agent, and adipic acid was not added. The amounts of other raw materials and reaction conditions are the same as in Example 3. The prepared polyamic acid solution has a weight-average molecular weight of 218625 and a kinetic viscosity of 321451 cP. After being stored at 25°C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 25%.

[0133] A polyimide fiber membrane was prepared using the same method as in Example 3. The thickness of the polyimide fiber membrane was 42 μm. The imidization rate of the polyimide fiber membrane was 77%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0134] Comparative Example 3

[0135] This comparative example is compared with Example 3, and is basically the same as Example 3, except that only 1.59g of adipic acid was used as the additive, and acetyl hexapeptide-8 was not added. The amounts of other raw materials and reaction conditions are the same as in Example 3. The prepared polyamic acid solution has a weight-average molecular weight of 184,781 and a kinetic viscosity of 298,452 cP. After being stored at 25°C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 34%.

[0136] A polyimide fiber membrane was prepared using the same method as in Example 3. The thickness of the polyimide fiber membrane was 45 μm. The imidization rate of the polyimide fiber membrane was 85%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0137] Comparative Example 4

[0138] This comparative example is compared with Example 3, and is basically the same as Example 3, except that acetyl hexapeptide-8 in the auxiliary agent is replaced with phenylalanine, while the amount remains the same (0.53 g). The amounts of other raw materials and reaction conditions are the same as in Example 3. The prepared polyamic acid solution has a weight-average molecular weight of 254,500 and a kinetic viscosity of 350050 cP. After being stored at 25°C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 20%.

[0139] A polyimide fiber membrane was prepared using the same method as in Example 3. The thickness of the polyimide fiber membrane was 50 μm. The imidization rate of the polyimide fiber membrane was 70%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0140] Comparative Example 5

[0141] This comparative example is compared with Example 3, and is basically the same as Example 3, except that the additives consist of 0.53g of adipic acid and 1.06g of acetyl hexapeptide-8, while the amounts of other raw materials and reaction conditions are the same as in Example 3. The prepared polyamic acid solution has a weight-average molecular weight of 164230 and a kinetic viscosity of 207562 cP. After being stored at 25°C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 41%.

[0142] A polyimide fiber membrane was prepared using the same method as in Example 3. The thickness of the polyimide fiber membrane was 48 μm. The imidization rate of the polyimide fiber membrane was 85%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0143] Comparative Example 6

[0144] This comparative example is compared with Example 3, and is basically the same as Example 3, except that the amount of the auxiliary agent is 0.054 g, which consists of 0.036 g of adipic acid and 0.018 g of acetyl hexapeptide-8. The amounts of the remaining raw materials and the reaction conditions are the same as in Example 3. The prepared polyamic acid solution has a weight-average molecular weight of 103658 and a kinetic viscosity of 121201 cP. After being stored at 25°C and atmospheric pressure for 960 hours, the weight-average molecular weight of this polyamic acid solution changed by 37%.

[0145] Polyimide fiber membranes were prepared using the same method as in Example 3. The thickness of the polyimide fiber membrane was 52 μm. The imidization rate of the polyimide fiber membrane was 70%. The tensile strength, tensile modulus, and glass transition temperature of the polyimide fiber membrane are shown in Table 1 below.

[0146] Table 1

[0147]

[0148] As can be seen from the above, the polyamic acid solutions of the various embodiments of the present invention possess high solid content, low kinetic viscosity, suitable molecular weight, good storage stability, and good film-forming properties. The polyimide fiber membranes prepared using the polyamic acid solutions of these embodiments exhibit high tensile strength and tensile modulus, high glass transition temperature, and 100% imidization rate. Generally, by controlling the imidization temperature at a high temperature and / or the imidization time at a long time, a 100% imidization rate can be achieved in polyimide films; however, this causes surface scorching of the membrane, leading to a decrease in its performance. The present invention, through the synergistic effect between the additives and diamines and dianhydrides, enables the polyamic acid solution of the present invention to achieve a 100% imidization rate at a lower temperature and in a shorter time, while ensuring good membrane integrity. Therefore, the present invention achieves a 100% imidization rate as well as high mechanical and thermal properties. Furthermore, during the preparation of the polyimide fiber membrane, observations revealed that no spinneret clogging or other adverse phenomena occurred during the electrospinning process of the various embodiments of the present invention. Meanwhile, since the polyimide fiber membranes of the various embodiments of the present invention have high mechanical and thermal properties, it can be proven that the membrane has high uniformity.

Claims

1. A method for preparing a polyamic acid solution, comprising the following steps: (I) Mix diamine, dianhydride, auxiliaries and solvent to obtain a reaction system; (II) After reacting the reaction system obtained in step (I), the polyamic acid solution is obtained; The adjuvant comprises a composition of fatty acids and polypeptides, wherein the mass ratio of the fatty acids to the polypeptides is 1:(0.01-0.6).

2. The method for preparing the polyamic acid solution according to claim 1, wherein, The mass ratio of the auxiliary agent to the total amount of the diamine and dianhydride is (0.01-0.5):

1.

3. The method for preparing the polyamic acid solution according to claim 1, wherein, The fatty acids include fatty acids with 4 or more carbon atoms.

4. The method for preparing the polyamic acid solution according to claim 3, wherein, The fatty acids include one or more of sebacic acid, tridecanoic acid, adipic acid, octadecanoic acid, hexadecanoic acid, butyric acid, hexanoic acid, decanoic acid, and octanoic acid.

5. The method for preparing the polyamic acid solution according to claim 1, wherein, The polypeptides include polypeptides containing 3-30 amino acid molecules.

6. The method for preparing the polyamic acid solution according to claim 5, wherein, The polypeptide includes one or more of the following: lysine polypeptide, palmitoyl tripeptide, palmitoyl tetrapeptide, palmitoyl pentapeptide, acetyl tripeptide, acetyl tetrapeptide, acetyl pentapeptide, acetyl hexapeptide, acetyl heptapeptide, and acetyl octapeptide.

7. The method for preparing the polyamic acid solution according to claim 1, wherein, The solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and hexamethylphosphoric triamine.

8. The method for preparing the polyamic acid solution according to claim 1, wherein, The diamine includes one or more of the following: m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, hydroquinone diether diamine, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylmethane, ethylenediamine, 1,6-hexanediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, and bisphenol A diether diamine.

9. The method for preparing the polyamic acid solution according to claim 1, wherein, The dianhydride includes one or more of the following: pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, triphenyl diether dianhydride, diphenyl ether dianhydride, diphenyl sulfide dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, hydroquinone diether dianhydride, hexafluoro dianhydride, resorcinol diether dianhydride, bisphenol A diether dianhydride, and 4,4'-oxobisphthalic dianhydride.

10. The method for preparing the polyamic acid solution according to claim 1, wherein, The molar ratio of the diamine to the dianhydride is (0.99-1.01):(0.99-1.01), and the total mass of the diamine and the dianhydride accounts for 10-30% of the total mass of the reaction system.

11. The method for preparing the polyamic acid solution according to claim 1, wherein, The system temperature in steps (I) and (II) is -15 to 50°C.

12. The method for preparing the polyamic acid solution according to claim 1, wherein, The reaction time in step (II) is 1-10 hours.

13. A polyamic acid solution, which is prepared by the method for preparing polyamic acid solution according to any one of claims 1-12.

14. The polyamic acid solution according to claim 13, wherein, The kinetic viscosity of the polyamic acid solution is below 10000 cP; and / or The solid content of the polyamic acid solution is 10 wt% or more; and / or The polyamic acid solution has a weight-average molecular weight of 30,000-90,000; and / or The polyamic acid solution, when stored at 25°C and normal pressure for 960 hours, exhibits a weight-average molecular weight change of less than 1%.

15. A polyimide film obtained by at least imidizing a polyamic acid solution according to claim 13 or 14.

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