A kind of polyimide fiber and preparation method thereof

Abstract

The present invention relates to a polyimide fiber and a preparation method thereof, the method comprising the following steps: a certain pre-imidization degree, slightly gelled polyamic acid, according to a dry spinning process, the slightly gelled polyamic acid is extruded through a spinneret and enters a spinning tunnel, and a first step of drafting is performed; the fiber subjected to the first step of drafting is entered into a hot drafting furnace through a guide roller for a second step of hot drafting, and a fully imidized polyimide fiber is obtained. The two-step drafting process enables the draft ratio of the fiber to reach more than 15, greatly improving the production efficiency and orientation degree of the polyimide fiber, and the inventive method can also improve the fiber surface and internal defects caused by the double diffusion effect during wet or dry-wet spinning, and the prepared polyimide fiber has more excellent mechanical properties.

Description

Technical Field

[0001] The invention belongs to the field of material science and technology, and specifically relates to a polyimide fiber and a preparation method thereof. Technical Background

[0002] Polyimide fiber has good mechanical properties, heat resistance, acid and alkali corrosion resistance and flame retardancy, and is widely used in aerospace, military defense, rail transportation, atomic energy industry, fire protection and other fields.

[0003] Common preparation methods of polyimide fibers mainly include one-step solution spinning and two-step solution spinning. Among them, the one-step method requires the use of highly toxic phenolic solvents during the preparation process, and the monomer types are limited, which limits its application in large-scale industrial production. The two-step wet spinning process is simple and has low requirements on the properties of the solution. It is currently the most commonly used two-step spinning method. However, the fiber is prone to form a skin-core structure during the coagulation bath stage, which limits its initial spray-to-pulling ratio, resulting in slow spinning speed and low production efficiency. In order to solve the above problems, dry-wet spinning and dry spinning processes have been developed on the basis of wet spinning.

[0004] Patent CN 101338452 B discloses a method for preparing polyimide fibers by dry-wet method. The gradient heating method adopted in the imidization process overcomes the shortcomings of inaccurate temperature control and complicated operation of the two-stage hot furnace technology, but its heat treatment temperature range is 50-500℃, the heating rate is 1-10℃ / min, and the thermal imidization time takes 1-10 hours, and the production efficiency is not high. Patent CN 102242415 B adopts a dry spinning preparation method to improve the spinnability and post-processing characteristics of polyimide fibers, but the mechanical properties of the prepared polyimide fibers have not been reported. Patent CN 104294391 B discloses a method for preparing polyimide fibers by dry spinning technology. The fiber winding speed can reach 150m / min, which greatly improves the production efficiency of the fiber, but it needs to be heat treated at 200℃ for 1 hour in a mixed gas with an oxygen content of 30%-50%, and then heated to 350℃ for heat treatment for 3-5 hours, which is not conducive to the continuous production of fibers. Patent CN 104357944 B solves the problem that toluene diisocyanate is highly toxic and difficult to preserve as a raw material. Polyimide fibers with dense structure and fewer defects are prepared by dry spinning using polyimide spinning stock solution, but the mechanical properties of the prepared fibers are not high.

[0005] Although there are studies and improvements on the preparation method of polyimide fibers in the prior art, there are still a series of problems. For example, the fiber is prone to form a skin-core structure in the coagulation bath stage of the current fiber preparation technology, which limits the spray-to-pull ratio in the initial stage of spinning, resulting in a slow spinning speed and low production efficiency overall. Therefore, it is urgent to develop a preparation method for polyimide fibers that can effectively improve the initial spray-to-pull ratio of the fiber, improve production efficiency and fiber orientation. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the conventional wet and dry-wet spinning processes, such as the easy formation of fiber crusts and defective structures in the coagulation bath stage, which in turn affects the mechanical properties of the fibers, and the complex heat treatment process of the existing dry spinning process, which is not conducive to continuous production and has low mechanical properties. Provided is a polyimide fiber and a preparation method thereof, which adopts a two-step drafting process, can greatly improve the drafting ratio of the fiber, thereby improving the production efficiency and fiber orientation, and the prepared polyimide fiber has more excellent mechanical properties.

[0007] At the same time, the present invention utilizes the imidization treatment process before spinning to obtain a polyamic acid solution with a certain degree of pre-imidization and slight gelation. The slightly gelled polyamic acid solution in such a specific state has the conditions for spinning and stretching, and the coagulation bath stage of the wet method can be directly omitted, thereby avoiding the organization and structure of the fiber being destroyed when the fiber passes through the bath, and avoiding the fiber from forming a skin-core structure after passing through the coagulation bath. Therefore, the fiber surface obtained by the present invention is smooth, the intrinsic structure remains intact, and it is also conducive to the improvement of the fiber strength in the later stage.

[0008] To achieve the above object, the present invention discloses a polyimide fiber and a preparation method thereof, comprising the following steps:

[0009] (1) adding a diamine monomer and a dianhydride monomer into a reaction solvent and stirring them sufficiently to cause a condensation polymerization reaction to obtain a homogeneous polyamic acid solution, wherein the solid content ratio of the polyamic acid solution is controlled to be 10%-30%;

[0010] (2) adding a certain amount of a dehydrating agent and a catalyst in a certain ratio to the above polyamic acid solution and stirring thoroughly to obtain a polyamic acid with a certain degree of pre-imidization and slight gelation, wherein the degree of pre-imidization is 20%-40%;

[0011] (3) spinning the slightly gelled polyamic acid obtained according to the dry spinning process, and the spinning solution is extruded through the spinneret and enters the spinning tunnel, during which the primary fibers are subjected to the first high-multiple drawing; the spinning tank is filled with nitrogen at a pressure of 0.2-0.5 MPa;

[0012] (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 350-500°C at a uniform speed for further thermal cyclization treatment, and at the same time, a second step of hot drawing is performed for 1-6 minutes to obtain a fully imidized polyimide fiber.

[0013] Preferably, the solid content of the polyamic acid solution in step (1) is 10%-20%. The molar ratio of the dianhydride monomer to the diamine monomer is 0.98:1-1.02:1.

[0014] Preferably, the dianhydride monomer in step (1) is one of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), 2,3',3,4'-biphenyltetracarboxylic dianhydride (α-BPDA), bisphenol A dianhydride (BPADA), 4,4'-oxydiphthalic anhydride (ODPA), hexafluoroisopropylenephthalic acid (6FDA), diphenyl sulfide tetracarboxylic dianhydride (TDPA) and 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride. The invention relates to a method for preparing an alkyl amine, wherein the alkyl amine is a mixture of one or more of p-phenylenediamine (PDA), m-phenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), 4,4'-diaminodiphenyl sulfone, and 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl in any proportion; and the reaction solvent is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-vinylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

[0015] Preferably, the volume ratio of the dehydrating agent to the catalyst in step (2) is 2:1-1:5.

[0016] Preferably, the dehydrating agent in step (2) is a mixture of one or more of acetic anhydride, propionic anhydride, and butyric anhydride; and the catalyst is a mixture of one or more of pyridine, triethylamine, imidazole, isoquinoline, 2-methylpyridine, and 3-methylpyridine.

[0017] Another object of the present invention is to provide a polyimide fiber with excellent mechanical properties prepared by the above method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The method of the present invention obtains a polyamic acid having a certain degree of pre-imidization and microgelation by adding a certain amount of a dehydrating agent and a catalyst to a polyamic acid solution (such as Figure 2 The primary fiber has high strength and can withstand a larger spray-pull ratio, thus improving the fiber production efficiency.

[0020] (2) The method of the present invention adopts a two-step drafting process, which can greatly improve the fiber draft ratio and orientation degree, thereby improving the fiber mechanical properties;

[0021] (3) The method for preparing the polyimide fiber of the present invention overcomes the surface and internal structural defects caused by the double diffusion of solvent in the coagulation bath stage of the conventional wet spinning process and the dry-wet spinning process, and the prepared fiber structure is more compact and the surface is smoother (such as Figure 3 shown).

[0022] (4) The polyimide fiber preparation method of the present invention has simple fiber synthesis process and subsequent spinning process, which are convenient for continuous and industrialized production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the dry spinning process of polyimide fiber;

[0024] Figure 2 The load-bearing state of the primary polyamic acid fiber with a certain degree of pre-imidization and microgelation in Example 1;

[0025] Figure 3 Surface morphology of the conventional wet-spun polyimide fiber of comparative example 1 and dry-spun polyimide fiber of embodiment 1 of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. If no specific conditions are specified in the examples, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar modules or modules with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0028] In the description of this specification, the description with reference to the terms "one embodiment", "another embodiment", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0029] The present invention provides a process flow for preparing a polyimide fiber, as follows: Figure 1 As shown, the general process includes: preparing raw materials → polymerization reaction → obtaining polyamic acid solution → adding chemical imidization agent → obtaining microgel polyamic acid spinning solution → spinning → first high-multiple stretching of the filaments → entering the hot furnace for drying and second stretching → collecting the filaments to obtain finished fibers.

[0030] During the entire fiber preparation process, the spinning solution goes through the following related equipment in sequence: spinneret → spinning tunnel → spinning roller → hot furnace → collecting roller.

[0031] In the preparation process of the polyimide fiber of the present invention, the state and tissue morphology of the gelled polyamic acid spinning solution obtained in the intermediate step have a crucial influence on the subsequent spinning process, and play an important role in preparing fibers with higher strength and capable of withstanding a larger spinning ratio, thereby improving fiber production efficiency.

[0032] Example 1

[0033] (1) adding equimolar amounts of PMDA and ODA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0034] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 40%, wherein the molar ratio of acetic anhydride to PMDA is 0.8:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0035] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and enters a spinning shaft at a temperature of 100-250° C. for the first step of drawing, the drawing ratio is 18, and the spinning speed is 220 m / min;

[0036] (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 460° C. at a uniform speed for thermal cyclization and second step drawing, with a drawing ratio of 4.0 and a time of 2 min, to obtain a fully imidized polyimide fiber.

[0037] Figure 2 The load-bearing condition of the spun fiber obtained in Example 1 is shown in Figure 2. The single spun fiber can support a load of 20 g without deformation. It can be seen that the spun fiber prepared by the method of the present invention has a higher strength and can therefore withstand a larger draft ratio. At the same time, Figure 3 As shown, compared with the fibers obtained by conventional wet spinning in the prior art (left picture), it can be seen that the fibers prepared by the dry spinning method of the present invention (right picture) have fewer defective structures and a smoother surface than those prepared by conventional wet spinning.

[0038] Comparative Example 1

[0039] (1) adding equimolar amounts of PMDA and ODA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0040] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 3, and the spinning speed is 20 m / min;

[0041] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 460° C. for thermal cyclization and stretching with a stretching ratio of 4.0 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0042] Table 1 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0043]

[0044] Example 2

[0045] (1) adding equimolar amounts of BPDA and PDA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 12%;

[0046] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 30%, wherein the molar ratio of acetic anhydride to BPDA is 0.6:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0047] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and enters a spinning shaft at a temperature of 100-250° C. for the first step of drawing, the drawing ratio is 17, and the spinning speed is 205 m / min;

[0048] (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 470° C. at a uniform speed for thermal cyclization and second step drawing, with a drawing ratio of 3.0 and a time of 2 min, to obtain a fully imidized polyimide fiber.

[0049] Comparative Example 2

[0050] (1) adding equimolar amounts of BPDA and PDA into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 12%;

[0051] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 3, and the spinning speed is 20 m / min;

[0052] (3) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. at a uniform speed for drying for 3 min; then passed through a tubular furnace at a temperature of 470° C. at a uniform speed for thermal cyclization and stretching with a stretching ratio of 2.0 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0053] Table 2 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0054]

[0055] Example 3

[0056] (1) adding BPDA / PMDA / PDA with a molar ratio of 5 / 5 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0057] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 20%, wherein the molar ratio of acetic anhydride to PDA is 0.4:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0058] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and enters a spinning shaft at a temperature of 100-250° C. for the first step of drawing, the drawing ratio is 16, and the spinning speed is 230 m / min;

[0059] (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 450° C. at a uniform speed for thermal cyclization and second step drawing, with a drawing ratio of 2.5 and a time of 2 min, to obtain a fully imidized polyimide fiber.

[0060] Comparative Example 3

[0061] (1) adding BPDA / PMDA / PDA with a molar ratio of 5 / 5 / 10 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0062] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 3, and the spinning speed is 25 m / min;

[0063] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and stretching with a stretching ratio of 1.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0064] Table 3 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0065]

[0066] Example 4

[0067] (1) adding BPDA / PDA / ODA in a molar ratio of 10 / 6 / 4 into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0068] (2) adding acetic anhydride and pyridine to the above polyamic acid solution and stirring thoroughly to obtain a microgel polyamic acid with a pre-imidization degree of 40%, wherein the molar ratio of acetic anhydride to BPDA is 0.8:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0069] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and enters a spinning shaft at a temperature of 100-250° C. for the first step of drawing, the drawing ratio is 15, and the spinning speed is 225 m / min;

[0070] (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 450° C. at a uniform speed for thermal cyclization and second step drawing, with a drawing ratio of 6 and a time of 2 min, to obtain a fully imidized polyimide fiber.

[0071] Comparative Example 4

[0072] (1) adding BPDA / PDA / ODA in a molar ratio of 10 / 6 / 4 into a DMAc solvent and stirring to cause a condensation polymerization reaction to obtain a polyamic acid solution with a solid content of 15%;

[0073] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.35 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 2, and the spinning speed is 22 m / min;

[0074] (3) The polyamic acid precursor fibers are uniformly passed through a tubular furnace at a temperature of 130° C. for drying for 3 min; and then uniformly passed through a tubular furnace at a temperature of 450° C. for thermal cyclization and drawing with a drawing ratio of 5.5 for 2 min, thereby obtaining fully imidized polyimide fibers.

[0075] Table 4 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0076]

[0077] Example 5

[0078] (1) adding PMDA / PDA / BIA with a molar ratio of 10 / 5 / 5 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0079] (2) adding acetic anhydride and pyridine to the above polyamic acid solution, stirring thoroughly, to obtain a microgel polyamic acid spinning solution with a pre-imidization degree of 30%, wherein the molar ratio of acetic anhydride to PMDA is 0.6:1, and the volume ratio of acetic anhydride to pyridine is 2:1;

[0080] (3) spinning the obtained polyamic acid with a certain degree of pre-imidization and microgelation according to a dry spinning process, the spinning solution is extruded from a spinneret into a spinning tunnel at a temperature of 100-250° C. under a nitrogen pressure of 0.40 MPa, and the first step of drawing is performed, the spray-draw ratio is 18, and the spinning speed is 255 m / min;

[0081] (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 490° C. at a uniform speed for thermal cyclization and second step drawing, with a drawing ratio of 3 and a time of 2 min, to obtain a fully imidized polyimide fiber.

[0082] Comparative Example 5

[0083] (1) adding PMDA / PDA / BIA with a molar ratio of 10 / 5 / 5 into DMAc solvent and stirring to cause condensation polymerization to obtain a polyamic acid solution with a solid content of 15%;

[0084] (2) spinning the polyamic acid solution according to the wet spinning process, the spinning solution is extruded from a spinneret under a nitrogen pressure of 0.40 MPa and then enters a coagulation bath (aqueous solution with a volume fraction of DMAc of 7%), the spin ratio is 4, and the spinning speed is 30 m / min;

[0085] (3) The polyamic acid precursor is passed through a tubular furnace at a temperature of 130° C. for drying at a uniform speed for 3 min; and then passed through a tubular furnace at a temperature of 490° C. for thermal cyclization and drawing at a drawing ratio of 1.5 for 2 min, thereby obtaining a fully imidized polyimide fiber.

[0086] Table 5 Comparison of mechanical properties of polyimide fibers obtained by different methods

[0087]

[0088] It can be seen from Tables 1-5 that the dry spinning process described in the present invention can greatly increase the spinning speed and draft ratio of the fiber, thereby improving the fiber production efficiency and orientation degree, and the prepared polyimide fiber has more excellent mechanical properties.

[0089] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing polyimide fiber, The following steps are involved: (1) adding a diamine monomer and a dianhydride monomer into a reaction solvent and stirring them sufficiently to cause a condensation polymerization reaction to obtain a homogeneous polyamic acid solution, wherein the solid content ratio of the polyamic acid solution is controlled to be 10%-30%; (2) adding a certain amount of dehydrating agent and catalyst in a certain ratio to the above polyamic acid solution and stirring thoroughly to obtain a polyamic acid with a certain degree of pre-imidization and slight gelation, wherein the degree of pre-imidization is 20%-40%; the volume ratio of the dehydrating agent to the catalyst in step (2) is 2:1-1:5; the dehydrating agent in step (2) is a mixture of one or more of acetic anhydride, propionic anhydride, and butyric anhydride; the catalyst is a mixture of one or more of pyridine, triethylamine, imidazole, isoquinoline, 2-methylpyridine and 3-methylpyridine; (3) spinning the slightly gelled polyamic acid obtained according to the dry spinning process, and the spinning solution is extruded through the spinneret and enters the spinning tunnel, during which the primary fibers are subjected to the first high-multiple drawing; the spinning tank is filled with nitrogen at a pressure of 0.2-0.5 MPa; (4) The fiber after the first step of drawing is passed through a tubular furnace at a temperature of 350-500° C. at a uniform speed for further thermal cyclization treatment, and at the same time, a second step of hot drawing is performed for 1-6 minutes to obtain a fully imidized polyimide fiber.

2. The method according to claim 1, It is characterized in that In step (1), the solid content of the polyamic acid solution is 10%-30%, and the molar ratio of the dianhydride monomer to the diamine monomer is 0.98:1-1.02:

1.

3. The method according to claim 1 or 2, It is characterized in that The dianhydride monomer in step (1) is a mixture of one or more of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, bisphenol A dianhydride, 4,4'-oxydiphthalic anhydride, diphenyl sulfide tetracarboxylic dianhydride and 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride in any proportion; the diamine monomer is a mixture of one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, 4,4'-diaminodiphenyl sulfone and 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl in any proportion; and the reaction solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-vinyl pyrrolidone and dimethyl sulfoxide.

4. A polyimide fiber prepared according to the method according to any one of claims 1 to 3.

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