Polyimide fiber prepolymer, preparation method thereof and polyimide fiber

Abstract

The invention provides a polyimide fiber prepolymer, a preparation method thereof and a polyimide fiber.The preparation method comprises the steps that monobasic saturated alcohol and an aromatic dianhydride monomer with the molar ratio being 0.02: 1-0.2: 1 are added into a polar organic solvent system and stirred in the N2 atmosphere for an esterification reaction, and a mixed solution containing diacid diester and the aromatic dianhydride monomer is formed; adding an aromatic diamine monomer into the mixed solution, and continuously stirring, so that one part of the aromatic diamine monomer reacts with diacid diester in the mixed solution to generate polyamide acid ester, and the other part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer which is not subjected to esterification reaction in the mixed solution to generate polyamide acid; and finally obtaining a mixed prepolymer comprising polyamic acid ester and polyamic acid, wherein the mixed prepolymer is the polyimide fiber prepolymer. The purpose of preparing the high-solid-content low-viscosity polyimide fiber prepolymer from the high-reaction-activity monomer can be achieved, the use amount of the solvent is reduced, the production efficiency is improved, and the production cost of polyimide is reduced.

Description

Technical Field

[0001] This application belongs to the technical field of polyimide production. More specifically, it relates to a polyimide fiber prepolymer, a preparation method thereof, and polyimide fibers. Background Art

[0002] Polyimide fiber materials are high-molecular fiber materials with an imide ring structure in which a large proportion of aromatic rigid molecules such as benzene rings are present in the molecular chain. Their special molecular structure endows them with excellent properties such as high strength, high modulus, resistance to low and high temperatures, flame retardancy, chemical corrosion resistance, and radiation resistance, and they are widely used in high-tech fields such as aerospace, weaponry, transportation, and the atomic energy industry. At present, the preparation process of polyimide fibers is mainly the wet two-step spinning process. In this process, the slurry of the polyamic acid prepolymer is first ejected from the spinneret and forms nascent fibers in the coagulation bath, and then the nascent fibers are washed, dried and enter a high-temperature drying tunnel, and are subjected to thermal imidization dehydration ring closure under a certain stretching effect to form polyimide fibers. In the actual production process, the polyamic acid prepolymer used to prepare polyimide fibers, that is, the polyamic acid solution, is usually generated by the polycondensation reaction of dianhydride and diamine monomers in a polar solution. However, due to the large reactivity of the monomers, it is easy to cause a high solid content and too high viscosity when preparing the prepolymer, resulting in a large spinning pressure at the spinneret and poor process stability in the subsequent wet spinning process; and if the prepolymer is adjusted to a low solid content, the solvent usage will increase, thereby reducing the production efficiency and increasing the production cost. Therefore, according to the current wet two-step spinning process method, there is an urgent need for a preparation method of a polyimide fiber prepolymer with a relatively high solid content and low viscosity, which has a simple synthesis process and obvious cost advantages. Summary of the Invention

[0003] The purpose of the embodiments of this application is to provide a preparation method of a polyimide fiber prepolymer to solve the above technical problems existing in the prior art.

[0004] To achieve the above purpose, the technical solution adopted in this application is: to provide a preparation method of a polyimide fiber prepolymer, and the preparation method of the polyimide fiber prepolymer includes the following steps:

[0005] Add a monohydric saturated alcohol and an aromatic dianhydride monomer to a polar organic solvent system, and stir under a N2 atmosphere for an esterification reaction to form a mixed solution including a diacid diester and an aromatic dianhydride monomer, and the molar ratio of the monohydric saturated alcohol to the aromatic dianhydride monomer is 0.02:1 - 0.2:1;

[0006] An aromatic diamine monomer is added to the mixed solution and stirring is continued. Part of the aromatic diamine monomer reacts with the diacid diester in the mixed solution to form a polyamide acid ester, and the other part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer that has not undergone an esterification reaction in the mixed solution to form a polyamic acid. Finally, a mixed prepolymer including the polyamide acid ester and the polyamic acid is obtained as the polyimide fiber prepolymer.

[0007] Optionally, the reaction solid content of the monohydric saturated alcohol and the aromatic dianhydride monomer in the polar organic solvent is 10%-30%.

[0008] Optionally, in the step of adding the monohydric saturated alcohol and the aromatic dianhydride monomer to the polar organic solvent system and stirring under a N2 atmosphere for an esterification reaction, the stirring rate is 50 rpm - 150 rpm, the reaction temperature is 20°C - 35°C, and the reaction time is 1 h - 3 h.

[0009] Optionally, the molar ratio of the aromatic dianhydride monomer to the aromatic diamine monomer is 0.99:1 - 1:1.

[0010] Optionally, in the step of adding the aromatic diamine monomer to the mixed solution and continuing stirring, part of the aromatic diamine monomer reacts with the diacid diester in the mixed solution to form a polyamide acid ester, and the other part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer that has not undergone an esterification reaction in the mixed solution to form a polyamic acid. Finally, a mixed prepolymer including the polyamide acid ester and the polyamic acid is obtained as the polyimide fiber prepolymer, the stirring rate is 30 rpm - 100 rpm, the reaction temperature is 30°C - 80°C, and the reaction time is 2 h - 20 h.

[0011] Optionally, the structural formula of the diacid diester is as shown in A, and the structural formula of the polyamide acid ester is as shown in B:

[0012]

[0013] Among them, Ar1 is any one of the following structural formulas:

[0014]

[0015] Ar2 is any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl;

[0016] Ar3 is any one of the following structural formulas:

[0017]

[0018] Optionally, the monohydric saturated alcohol is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol;

[0019] The aromatic dianhydride monomer is one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, bisphenol A type diether dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 4,4'-biphenylether dianhydride;

[0020] The polar organic solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone;

[0021] The aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, m-xylylenediamine, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, p,p'-diaminobiphenyl, and 2-(4-aminophenyl)-5-aminobenzoxazole.

[0022] This application also provides a polyimide fiber prepolymer, which is prepared by the aforementioned method for preparing a polyimide fiber prepolymer.

[0023] Optionally, the solid content of the polyimide fiber prepolymer is 15%-35%, and the viscosity is 20,000 cps - 200,000 cps.

[0024] This application also provides a polyimide fiber, which is prepared by subjecting the slurry prepared from the aforementioned polyimide fiber prepolymer to spinning, coagulation, washing, drying, and high-temperature imidization;

[0025] Among them, the polyamic acid in the polyimide fiber prepolymer forms a polyimide fiber through thermal imidization dehydration and ring closure, and the polyamic acid ester in the polyimide fiber prepolymer forms an imide ring through high-temperature alcohol elimination reaction to also form a polyimide fiber.

[0026] The beneficial effects of the preparation method of the polyimide fiber prepolymer provided by this application are as follows: By adding a small amount of saturated monohydric alcohol in the first-step reaction, the diacid diester formed by the esterification reaction of the monosaturated alcohol and part of the aromatic dianhydride monomer will react with part of the aromatic diamine monomer added subsequently to form polyamic acid ester. Since the formation of polyamic acid ester consumes part of the dianhydride and water molecules are generated, it has the effect of inhibiting the reaction process and the actual molecular weight of the prepolymer, thereby achieving the purpose of preparing a polyimide fiber prepolymer with high reaction activity monomers, high solid content and low viscosity. In addition, the technical solution of this application can also avoid low-temperature reaction by cooling, and can quickly react to the equilibrium end point under natural uncontrolled temperature or heating at high temperature, which is beneficial to improving the synthesis efficiency of the polyimide fiber prepolymer. Moreover, since the reaction temperature can be relatively high, compared with the existing low-temperature reaction, this reaction is easier to reach the reaction equilibrium end point, and its forward and reverse reactions are relatively slow. Therefore, the polyimide fiber prepolymer prepared by this application can maintain a relatively stable viscosity at room temperature of 20°C to 30°C for a long time, and its viscosity will not increase or decrease significantly with time. In addition, by adjusting the molar ratio of the added monohydric alcohol, the molecular weight of this polyimide fiber prepolymer can be controlled, thereby increasing the reaction solid content of this polyimide fiber prepolymer, which is beneficial to reducing the solvent usage, saving costs, and keeping the polyimide fiber prepolymer at a relatively low viscosity. Of course, in the subsequent process of polyimide fiber, in addition to the polyamic acid can undergo thermal imidization dehydration and ring closure to form polyimide fiber, the polyamic acid ester in this polyimide fiber prepolymer will undergo a dealcoholization reaction at high temperature to form an imide ring, which will not affect the various properties of the polyimide fiber. To sum up, the synthesis reaction of this application can not only control the molecular weight of the polyimide fiber prepolymer, control the polyimide fiber prepolymer to maintain a relatively low viscosity stably for a long time, but also further reduce the solvent usage, thereby achieving the purpose of reducing the solvent recovery pressure and cost, improving the production efficiency, and reducing the production cost of polyimide fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a flowchart of the preparation method of the polyimide fiber prepolymer provided by the embodiment of this application;

[0029] Figure 2 It is a flowchart of the preparation of the polyimide fiber provided by the embodiment of this application;

[0030] Figure 3 It is a graph showing the change of the viscosity of the prepolymer with time in Examples 1-4 and Comparative Examples 1 and 2 of the present application. Detailed implementation manners

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear and understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] The embodiment of the present application provides a method for preparing a polyimide fiber prepolymer.

[0033] Please refer to Figure 1 , in one embodiment, the method for preparing the polyimide fiber prepolymer specifically includes the following steps:

[0034] S1. Add a monohydric saturated alcohol and an aromatic dianhydride monomer into a polar organic solvent system, and stir under a N2 atmosphere for an esterification reaction to form a mixed solution including a diacid diester and an aromatic dianhydride monomer, and the molar ratio of the monohydric saturated alcohol to the aromatic dianhydride monomer is 0.02:1 - 0.2:1;

[0035] S2. Add an aromatic diamine monomer to the mixed solution and continue stirring. A part of the aromatic diamine monomer reacts with the diacid diester in the mixed solution to form a polyamic acid ester, and another part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer that has not undergone an esterification reaction in the mixed solution to form a polyamic acid. Finally, the obtained mixed prepolymer including the polyamic acid ester and the polyamic acid is the polyimide fiber prepolymer.

[0036] Based on this design, in the technical solution of this application, by adding a small amount of saturated monohydric alcohol in the first-step reaction, the diester acid formed by the esterification reaction of the monosaturated alcohol and part of the aromatic dianhydride monomers will react with part of the aromatic diamine monomers added subsequently to form polyamic acid ester. Since the formation of polyamic acid ester consumes part of the dianhydride and water molecules are generated, it has the effect of inhibiting the reaction process and the actual molecular weight of the prepolymer, thereby achieving the purpose of preparing a polyimide fiber prepolymer with high reaction activity monomers, high solid content and low viscosity. In addition, the technical solution of this application can also carry out the low-temperature reaction without cooling, and can quickly react to the equilibrium end point under natural uncontrolled temperature or heating at high temperature, which is beneficial to improving the synthesis efficiency of the polyimide fiber prepolymer. Moreover, since the reaction temperature can be relatively high, compared with the existing low-temperature reaction, this reaction is easier to reach the reaction equilibrium end point, and its forward and reverse reactions are relatively slow. Therefore, the polyimide fiber prepolymer prepared in this application can maintain a relatively stable viscosity at room temperature of 20°C to 30°C for a long time, and its viscosity will not increase or decrease significantly over time. In addition, by adjusting the molar ratio of the added monohydric alcohol, the molecular weight of this polyimide fiber prepolymer can be controlled, thereby increasing the reaction solid content of this polyimide fiber prepolymer, which is beneficial to reducing the solvent usage, saving costs, and enabling this polyimide fiber prepolymer to maintain a relatively low viscosity. Of course, in the subsequent process of polyimide fiber, in addition to the polyamic acid can undergo thermal imidization dehydration and ring closure to form polyimide fiber, the polyamic acid ester in this polyimide fiber prepolymer will undergo a de-alcoholization reaction at high temperature to form an imide ring, which will not affect the various properties of the polyimide fiber. To sum up, the synthesis reaction of this application can not only control the molecular weight of this polyimide fiber prepolymer and keep the viscosity of this polyimide fiber prepolymer relatively low and stable for a long time, but also further reduce the solvent usage, thereby achieving the purpose of reducing the solvent recovery pressure and cost, improving the production efficiency, and reducing the production cost of polyimide fiber.

[0037] It should be noted here that in the preparation method of this polyimide fiber prepolymer, the monosaturated alcohol is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol. The aromatic dianhydride monomer is one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, bisphenol A type diether dianhydride, 3,3'4,4'-benzophenone tetracarboxylic dianhydride, 4,4′-biphenylether dianhydride. The polar organic solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone. The aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, m-xylylenediamine, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, p,p'-diaminobiphenyl, 2-(4-aminophenyl)-5-aminobenzoxazole.

[0038] Further, in one embodiment, the reaction solid content of the monohydric saturated alcohol and the aromatic dianhydride monomer in the polar organic solvent is 10%-30%. Here, this preferred reaction solid content range is conducive to a more sufficient and efficient subsequent reaction for generating polyamide acid ester and polyamide acid, and can better control the molecular weight of the polyimide fiber prepolymer, thereby achieving the purpose of controlling the viscosity of the prepolymer.

[0039] Further, in one embodiment, in the step of adding the monohydric saturated alcohol and the aromatic dianhydride monomer to the polar organic solvent system and stirring under a N2 atmosphere for the esterification reaction, the stirring rate is 50 rpm - 150 rpm, the reaction temperature is 20°C - 35°C, and the reaction time is 1 h - 3 h. Specifically, first, the polar organic solvent is added to the reaction kettle. It can be understood that in this esterification reaction step, a stirring rate of 50 rpm - 150 rpm is preferably used to make the mixing of each reactant more sufficient, which is conducive to increasing the reaction rate and making the esterification reaction more complete. Since the boiling point of the monohydric saturated alcohol is relatively low, this reaction is a low-temperature reaction with a reaction temperature of 20°C - 35°C. The reaction time is preferably 1 h - 3 h, which can result in a relatively high synthesis efficiency, and the higher the reaction temperature, the shorter the reaction time.

[0040] After the reaction in this step is completed, the diacid diester formed by the reaction of the monohydric saturated alcohol and the aromatic dianhydride monomer has the following structural formula:

[0041]

[0042] Among them, Ar1 is any one of the following structural formulas.

[0043]

[0044] Ar2 is any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl.

[0045] Further, in one embodiment, preferably, the molar ratio of the aromatic dianhydride monomer to the aromatic diamine monomer is 0.99:1 - 1:1. Of course, if the aromatic dianhydride monomer includes multiple different dianhydrides, the molar ratio between different types of dianhydrides can be any proportional combination as long as the overall dianhydride molar ratio meets the requirements. Similarly, if the aromatic diamine monomer includes multiple different diamines, the molar ratio between different types of diamines can also be any proportional combination as long as the overall diamine molar ratio meets the requirements.

[0046] Further, in one embodiment, an aromatic diamine monomer is added to the mixed solution and stirred continuously. A part of the aromatic diamine monomer reacts with the diacid diester in the mixed solution to form a polyamide acid ester, and another part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer that has not undergone an esterification reaction in the mixed solution to form a polyamic acid. In the step of finally obtaining a mixed prepolymer including the polyamide acid ester and the polyamic acid as the polyimide fiber prepolymer, the stirring rate is 30 rpm - 100 rpm, the reaction temperature is 30°C - 80°C, and the reaction time is 2 h - 20 h. Here, the reaction temperature for the formation of the polyimide fiber prepolymer can be relatively high. Since the higher the reaction temperature, the shorter the reaction time can be, which is beneficial to improving the synthesis efficiency of the polyimide fiber prepolymer.

[0047] Specifically, in the present application, the structural formula of the polyamide acid ester is as shown in B:

[0048]

[0049] Among them, Ar1 is any one of the following structural formulas:

[0050]

[0051] Ar2 is any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl;

[0052] Ar3 is any one of the following structural formulas:

[0053]

[0054] The present application also provides a polyimide fiber prepolymer, which is prepared by the preparation method of the polyimide fiber prepolymer described above.

[0055] Preferably, in one embodiment, the solid content of the polyimide fiber prepolymer is 15% - 35%, and the viscosity is 20000 cps - 200000 cps. It can be understood that the polyimide fiber prepolymer prepared by the above-mentioned preparation method of the polyimide fiber prepolymer has the advantages of a relatively high solid content and a relatively low viscosity, which is beneficial to reducing the spinning pressure in the subsequent wet spinning process and reducing the solvent usage amount, thereby improving the quality of the polyimide fiber and reducing the production cost at the same time.

[0056] The present application also provides a polyimide fiber, which is prepared by subjecting a slurry made from the aforementioned polyimide fiber prepolymer to spinning, coagulation, washing, drying, and high-temperature imidization. Among them, the polyamic acid in the polyimide fiber prepolymer forms a polyimide fiber through thermal imidization and dehydration to form a closed loop, and the polyamic acid ester in the polyimide fiber prepolymer forms an imide ring through a high-temperature alcohol elimination reaction to also form a polyimide fiber. Specifically, the aforementioned polyimide fiber prepolymer can be used to obtain polyimide fibers with excellent mechanical properties through a wet two-step spinning process. In this spinning process, the spinning coagulation bath used is a mixed solution of deionized water and a solvent, and its concentration is specifically 20%-40%. The detergent used for washing is pure deionized water, the drying temperature is 90°C-120°C, and the highest temperature for imidization is 450°C-500°C.

[0057] Specifically, as Figure 2 shown, the manufacturing process of the polyimide fiber includes the following steps:

[0058] S31. Transfer the aforementioned polyimide fiber prepolymer to a spinning device, and the slurry made from the aforementioned polyimide fiber prepolymer is ejected from a spinneret and forms polyimide nascent fibers in a coagulation bath;

[0059] S32. Wash the polyimide nascent fibers clean with pure deionized water;

[0060] S33. Dry the washed polyimide nascent fibers at a drying temperature of 90°C-120°C;

[0061] S34. Gradually heat the dried polyimide nascent fibers to 450°C-500°C in an inert atmosphere, and generate polyimide fibers through thermal imidization of the dehydration ring-closure reaction.

[0062] The technical solutions of the present application will be further described in detail below with multiple specific examples. However, the present application is not limited to the following listed examples, and only a part of the examples are listed. All reagents and test instruments used in the examples listed in the present application are conventional products that can be obtained through normal commercial channels without indicating the manufacturer.

[0063] Example 1

[0064] First, add 595 g of DMAc (N,N-Dimethylacetamide) to a 1000 ml three-necked flask, then add 54.74 g of PMDA (Pyromellitic Dianhydride) to the three-necked flask. Introduce N2 and stir evenly in the N2 atmosphere. Control the reaction temperature at 28 °C, then add 0.32 g of methanol, stir at a predetermined stirring rate, and react for 1.5 h;

[0065] Then, add 50.26 g of ODA (4,4'-Oxydianiline) to the above solution at one time, continue stirring and reacting, control the reaction temperature at 60 °C, after stirring for 2 h, cool down to 25 °C, test the viscosity, end the reaction, and obtain a polyimide fiber prepolymer;

[0066] Finally, transfer the above polyimide fiber prepolymer to a spinning device, and obtain polyimide fibers after spinning, coagulation, washing, drying, and high-temperature imidization according to the wet spinning process.

[0067] Example 2

[0068] First, add 469 g of DMAc to a 1000 ml three-necked flask, then add 120.44 g of PMDA (Pyromellitic Dianhydride) to the three-necked flask. Introduce N2 and stir evenly in the N2 atmosphere. Control the reaction temperature at 28 °C, then add 2.30 g of methanol, stir at a predetermined stirring rate, and react for 1.5 h;

[0069] Then, add 110.56 g of ODA to the above solution at one time, continue stirring and reacting, control the reaction temperature at 60 °C, after stirring for 2 h, cool down to 25 °C, test the viscosity, end the reaction, and obtain a polyimide fiber prepolymer;

[0070] Finally, transfer the above polyimide fiber prepolymer to a spinning device, and obtain polyimide fibers after spinning, coagulation, washing, drying, and high-temperature imidization according to the wet spinning process.

[0071] Comparative Example 1

[0072] First, add 630 g of DMAc to a 1000 ml three-necked flask, then add 33.50 g of ODA to the three-necked flask. Introduce N2 and stir until completely dissolved in the N2 atmosphere, then add 36.31 g of PMDA (Pyromellitic Dianhydride), stop stirring and reacting after 2 h, test the viscosity, and obtain a polyamic acid prepolymer;

[0073] Finally, transfer the above polyamic acid prepolymer to a spinning device, and obtain polyimide fibers through wet spinning process, including spinning, coagulation, washing, drying, and high-temperature imidization.

[0074] The relevant processes and test data of Example 1, Example 2 and Comparative Example 1 are shown in Table 1 below.

[0075] Table 1

[0076]

[0077] From the data in Table 1 above, it can be seen that when the technical solution of the present application is adopted, the viscosity of the obtained prepolymer is much lower than that of the prior art solution without adding monohydric saturated alcohol, but the fiber tensile strength of the polyimide fibers obtained by the two methods is not much different. Moreover, through the data comparison between Example 1 and Example 2, it can be seen that when the methanol content is higher, the reaction solid content of the obtained polyimide fiber prepolymer is higher, and its viscosity will also increase accordingly, but the fiber tensile strength of the polyimide fibers obtained by the two examples is not much different.

[0078] Example 3

[0079] First, add 595 g of DMAc to a 1000 ml three-necked flask, then add 63.12 g of BPDA (Biphenyltetracarboxylic Dianhydride, 3,3',4,4'-Biphenyltetracarboxylic Dianhydride) to the three-necked flask, introduce N2 and stir evenly in an N2 atmosphere, control the reaction temperature at 28 °C, then add 0.34 g of methanol, stir at a predetermined stirring rate, and stir and react for 1.5 h;

[0080] Then, add 36.08 g of APBIA (2-(4-Aminophenyl)-5-aminobenzimidazole, 2-(4-Aminophenyl)-5-aminobenzimidazole) and 5.80 g of p-PDA (p-Phenylenediamine, p-Phenylenediamine) to the above solution at one time, continue stirring and reacting, control the reaction temperature at 60 °C, stir for 2 h, then cool down to 25 °C, test the viscosity, and end the reaction to obtain a polyimide fiber prepolymer;

[0081] Transfer the above polyimide fiber prepolymer to a spinning device, and obtain polyimide fibers through wet spinning process, including spinning, coagulation, washing, drying, and high-temperature imidization.

[0082] Example 4

[0083] First, add 483 g of DMAc into a 1000 ml three-necked flask, then add 130.44 g of BPDA into this three-necked flask, introduce N2 and stir evenly in the N2 atmosphere, control the reaction temperature at 28 °C, then add 2.41 g of methanol, stir at a predetermined stirring rate, and stir and react for 1.5 h;

[0084] Then, add 74.57 g of APBIA and 11.99 g of p-PDA into the above solution at one time, continue to stir and react, control the reaction temperature at 60 °C, after stirring for 2 h, cool down to 25 °C, test the viscosity, end the reaction, and obtain the polyimide fiber prepolymer;

[0085] Finally, transfer the above polyimide fiber prepolymer to the spinning equipment, and obtain polyimide fibers after wet spinning, coagulation, washing, drying, and high-temperature imidization according to the wet spinning process.

[0086] Comparative Example 2

[0087] First, add 630 g of DMAc into a 1000 ml three-necked flask, then add 24.06 g of APBIA and 3.87 g of p-PDA into this three-necked flask, introduce N2 and stir until completely dispersed and uniform in the N2 atmosphere, then add 42.08 g of BPDA, stop stirring after stirring and reacting for 2 h, test the viscosity, and obtain the polyamic acid prepolymer;

[0088] Transfer the above polyamic acid prepolymer to the spinning equipment, and obtain polyimide fibers after wet spinning, coagulation, washing, drying, and high-temperature imidization according to the wet spinning process.

[0089] The relevant processes and test data of Example 3, Example 4, and Comparative Example 2 are shown in Table 2 below.

[0090] Table 2

[0091]

[0092] As can be seen from the data in Table 2 above, when the technical solution of the present application is adopted, the viscosity of the prepolymer obtained is much lower than that of the prior art solution without adding monohydric saturated alcohol, but the fiber tensile strength of the polyimide fibers obtained by the two methods is not much different. Moreover, through the data comparison between Example 3 and Example 4, it can be seen that the higher the methanol content, the higher the reaction solid content of the polyimide fiber prepolymer obtained, and its viscosity will also increase accordingly, but the fiber tensile strength of the polyimide fibers obtained in the two examples is not much different. In addition, in Example 3 and Example 4, since part of the aromatic diamine monomer used is p-PDA, and p-PDA, as a rigid diamine monomer, reacts with dianhydride to form polyamic acid, the para-position structure of its benzene ring can enhance the linear arrangement of the polymer chain, and the introduction of the aromatic diamine monomer APBIA also enhances the intramolecular and intermolecular strong hydrogen bond interactions in the molecular chain segment, thereby improving the thermal stability and mechanical strength of the material. Therefore, the fiber tensile strength of the polyimide fibers obtained in Example 3 and Example 4 is higher than that in Example 1 and Example 2.

[0093] Example 5

[0094] First, add 595 g of DMAc to a 1000 ml three-necked flask, then add 52.11 g of BPDA and 9.66 g of PMDA to this three-necked flask, introduce N2 and stir evenly in the N2 atmosphere, control the reaction temperature at 28 °C, then add 0.25 g of methanol, stir at a predetermined stirring rate, and stir and react for 1.5 h;

[0095] Then, add 37.24 g of APBIA and 5.99 g of p-PDA to the above solution at one time, continue to stir and react, control the reaction temperature at 60 °C, after stirring for 2 h, cool down to 25 °C, test the viscosity, end the reaction, and obtain the polyimide fiber prepolymer;

[0096] Finally, transfer the above polyimide fiber prepolymer to a spinning device, and obtain polyimide fibers after spinning, coagulation, washing, drying, and high-temperature imidization according to the wet spinning process.

[0097] Example 6

[0098] First, add 455 g of DMAc to a 1000 ml three-necked flask, then add 121.60 g of BPDA and 22.54 g of PMDA to this three-necked flask, introduce N2 and stir evenly in the N2 atmosphere, control the reaction temperature at 28 °C, then add 3.31 g of methanol, stir at a predetermined stirring rate, and stir and react for 1.5 h;

[0099] Then, 86.90 g of APBIA and 13.97 g of p-PDA were added to the above solution at one time, and the reaction was continued with stirring. The reaction temperature was controlled at 60 °C. After stirring for 2 h, the temperature was lowered to 25 °C, the viscosity was measured, and the reaction was terminated to obtain a polyimide fiber prepolymer;

[0100] Finally, the above polyimide fiber prepolymer was transferred to a spinning device, and according to the wet spinning process, polyimide fibers were obtained after spinning, coagulation, washing, drying, and high-temperature imidization.

[0101] Comparative Example 3

[0102] First, 630 g of DMAc was added to a 1000 ml three-necked flask, and then 24.83 g of APBIA and 3.99 g of p-PDA were added to the three-necked flask. N2 was introduced and stirred in an N2 atmosphere until completely dispersed and uniform. Then, 34.53 g of BPDA and 6.44 g of PMDA were added, and the stirring reaction was stopped after 2 h of stirring. The viscosity was measured to obtain a polyamic acid prepolymer;

[0103] The above polyamic acid prepolymer was transferred to a spinning device, and according to the wet spinning process, polyimide fibers were obtained after spinning, coagulation, washing, drying, and high-temperature imidization.

[0104] The relevant processes and test data of Example 5, Example 6, and Comparative Example 3 are shown in Table 3 below.

[0105] Table 3

[0106]

[0107] As can be seen from the data in Table 3 above, when the technical solution of the present application is adopted, the viscosity of the prepolymer obtained is much lower than that of the prior art solution without adding monohydric saturated alcohol, but the fiber tensile strengths of the polyimide fibers obtained by the two methods are not much different. Moreover, through the data comparison of Example 5 and Example 6, it can be seen that when the methanol content is higher, the reaction solid content of the polyimide fiber prepolymer obtained is higher, and its viscosity will also increase accordingly, but the fiber tensile strengths of the polyimide fibers obtained in the two examples are not much different. Here, the fiber tensile strengths of the polyimide fibers obtained in Example 5 and Example 6 are different from those in Examples 1-4 because the reaction raw materials used are different.

[0108] Example 7

[0109] First, after adding 595 g of DMAc to a 1000 ml three-necked flask, 69.73 g of BPDA was added to the three-necked flask. N2 was introduced and stirred evenly in an N2 atmosphere. The reaction temperature was controlled at 28 °C, and then 0.30 g of methanol was added, and the reaction was stirred for 1.5 h;

[0110] Then, 18.60 g of APBIA and 16.66 g of p-PDA were added to the above solution at one time, and the stirring reaction was continued. The reaction temperature was controlled at 60 °C. After stirring for 2 h, the temperature was lowered to 25 °C, the viscosity was measured, and the reaction was terminated to obtain a polyimide fiber prepolymer;

[0111] Finally, the above polyimide fiber prepolymer was transferred to a spinning device, and according to the wet spinning process, polyimide fibers were obtained after spinning, coagulation, washing, drying, and high-temperature imidization.

[0112] Example 8

[0113] First, 490 g of DMAc was added to a 1000 ml three-necked flask, and then 139.47 g of BPDA was added to the three-necked flask. N2 was introduced and stirred evenly in the N2 atmosphere. The reaction temperature was controlled at 28 °C, and then 2.73 g of methanol was added, and the stirring reaction was carried out for 1.5 h;

[0114] Then, 37.21 g of APBIA and 33.32 g of p-PDA were added to the above solution at one time, and the stirring reaction was continued. The reaction temperature was controlled at 60 °C. After stirring for 2 h, the temperature was lowered to 25 °C, the viscosity was measured, and the reaction was terminated to obtain a polyimide fiber prepolymer;

[0115] Finally, the above polyimide fiber prepolymer was transferred to a spinning device, and according to the wet spinning process, polyimide fibers were obtained after spinning, coagulation, washing, drying, and high-temperature imidization.

[0116] Comparative Example 4

[0117] First, 630 g of DMAc was added to a 1000 ml three-necked flask, and then 12.40 g of APBIA and 11.11 g of p-PDA were added to the three-necked flask. N2 was introduced and stirred until completely dispersed and uniform in the N2 atmosphere, and then 46.26 g of BPDA was added. After stirring the reaction for 2 h, the stirring was stopped, the viscosity was measured, and a polyamic acid prepolymer was obtained;

[0118] The above polyamic acid prepolymer was transferred to a spinning device, and according to the wet spinning process, polyimide fibers were obtained after spinning, coagulation, washing, drying, and high-temperature imidization.

[0119] The relevant processes and test data of Example 7, Example 8, and Comparative Example 4 are shown in Table 4 below.

[0120] Table 4

[0121]

[0122] As can be seen from the data in Table 4 above, when the technical solution of the present application is adopted, the viscosity of the prepolymer obtained is much lower than that of the prior art solution without adding monohydric saturated alcohol, but the fiber tensile strength of the polyimide fibers obtained by the two methods is not much different. Moreover, through the data comparison of Example 7 and Example 8, it can be seen that when the methanol content is higher, the reaction solid content of the polyimide fiber prepolymer obtained is higher, and its viscosity will also increase accordingly, but the fiber tensile strength of the polyimide fibers obtained in the two examples is not much different.

[0123] In addition, for the polyimide fiber prepolymers prepared in Examples 1 to 4 using the solution of the present application and the polyimide fiber prepolymers prepared in Comparative Examples 1 and 2 using the prior art, the viscosity change data curves of the prepolymer slurries after long-term storage are shown in Table 5 below, and the corresponding curve graph of Table 5 is as Figure 3 shown. The 5 thicker curves from top to bottom represent the viscosity data changes of Comparative Example 1, Comparative Example 2, Example 2, Example 1, Example 4, and Example 3 in sequence:

[0124] Table 5

[0125] 0day / cp 7day / cp 14day / cp Example 1 120560 119850 114560 Example 2 183210 174520 176530 Example 3 86950 80210 78950 Example 4 112300 111200 108630 Comparative Example 1 501900 321020 182560 Comparative Example 2 421300 342100 284600

[0126] From Figure 3 and the content in Table 5, it can be seen that the polyimide fiber prepolymer obtained by adopting the technical solution of the present application can maintain a relatively stable viscosity for a long time under the room temperature conditions of 20°C - 30°C, that is, the viscosity will not increase or decrease significantly with time, which is beneficial to the storage of the polyimide fiber prepolymer and the subsequent wet spinning process. While for the polyamic acid prepolymers of Comparative Examples 1 and 2 using the prior art, their viscosities cannot be maintained relatively stable for a long time under the same temperature and time conditions, specifically, the viscosity decreases significantly with the increase of the storage time.

[0127] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A preparation method of a polyimide fiber prepolymer, characterized in that, The preparation method of the polyimide fiber prepolymer comprises the following steps: Adding a monohydric saturated alcohol and an aromatic dianhydride monomer into a polar organic solvent system, and stirring under a N2 atmosphere for an esterification reaction to form a mixed solution comprising a diacid diester and the aromatic dianhydride monomer, wherein the molar ratio of the monohydric saturated alcohol to the aromatic dianhydride monomer is 0.02:1 - 0.2:1; Adding an aromatic diamine monomer into the mixed solution and continuing to stir. A part of the aromatic diamine monomer reacts with the diacid diester in the mixed solution to form a polyamic acid ester, and another part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer that has not undergone an esterification reaction in the mixed solution to form a polyamic acid. Finally, a mixed prepolymer comprising the polyamic acid ester and the polyamic acid is obtained as the polyimide fiber prepolymer.

2. The preparation method of the polyimide fiber prepolymer according to claim 1, characterized in that, The reaction solid content of the monohydric saturated alcohol and the aromatic dianhydride monomer in the polar organic solvent is 10% - 30%.

3. The preparation method of the polyimide fiber prepolymer according to claim 2, characterized in that, In the step of adding the monohydric saturated alcohol and the aromatic dianhydride monomer into the polar organic solvent system and stirring under a N2 atmosphere for an esterification reaction, the stirring rate is 50 rpm - 150 rpm, the reaction temperature is 20°C - 35°C, and the reaction time is 1 h - 3 h.

4. The preparation method of the polyimide fiber prepolymer according to claim 1, characterized in that, The molar ratio of the aromatic dianhydride monomer to the aromatic diamine monomer is 0.99:1 - 1:

1.

5. The preparation method of the polyimide fiber prepolymer according to claim 4, characterized in that, In the step of adding the aromatic diamine monomer into the mixed solution and continuing to stir, a part of the aromatic diamine monomer reacts with the diacid diester in the mixed solution to form a polyamic acid ester, and another part of the aromatic diamine monomer reacts with the aromatic dianhydride monomer that has not undergone an esterification reaction in the mixed solution to form a polyamic acid. Finally, a mixed prepolymer comprising the polyamic acid ester and the polyamic acid is obtained as the polyimide fiber prepolymer. In this step, the stirring rate is 30 rpm - 100 rpm, the reaction temperature is 30°C - 80°C, and the reaction time is 2 h - 20 h.

6. The preparation method of the polyimide fiber prepolymer according to claim 1, wherein, The structural formula of the diacid diester is as shown in A, and the structural formula of the polyamic acid ester is as shown in B: Wherein, Ar1 is any one of the following structural formulas: Ar2 is any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl; Ar3 is any one of the following structural formulas:

7. The preparation method of the polyimide fiber prepolymer according to any one of claims 1 to 6, characterized in that, The monohydric saturated alcohol is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; The aromatic dianhydride monomer is one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, bisphenol A type diether dianhydride, 3,3'4,4'-benzophenone tetracarboxylic dianhydride, and 4,4′-biphenyl ether dianhydride; The polar organic solvent is one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; The aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, m-xylylenediamine, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, p,p'-diaminobiphenyl, and 2-(4-aminophenyl)-5-aminobenzoxazole.

8. A polyimide fiber prepolymer, characterized in that, The polyimide fiber prepolymer is made by the preparation method of the polyimide fiber prepolymer according to any one of claims 1 to 7.

9. The polyimide fiber prepolymer according to claim 8, wherein, The solid content of the polyimide fiber prepolymer is 15%-35%, and the viscosity is 20,000 cps-200,000 cps.

10. A polyimide fiber, characterized in that, The polyimide fiber is made from a slurry containing the polyimide fiber prepolymer according to claim 8 or 9 through spinning, coagulation, washing, drying, and high-temperature imidization. Among them, the polyamic acid in the polyimide fiber prepolymer forms the polyimide fiber through thermal imidization and dehydration to form a closed loop, and the polyamic acid ester in the polyimide fiber prepolymer forms an imide ring through a high-temperature alcohol elimination reaction to also form the polyimide fiber.

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