CN114181392B - High solid content and low viscosity polyamic acid solution and its preparation method and application - Google Patents

Abstract

The invention relates to a high-solid content and low-viscosity polyamic acid solution, a preparation method and application thereof, and solves the problem that in the prior art, when the solid content of the polyamic acid solution is relatively high in the synthesis process of the polyamic acid solution, the gel is likely to lose fluidity, and the next step cannot be carried out. Coating or spinning problems. The method comprises the following steps: performing a condensation polymerization reaction on a dianhydride monomer and a diamine monomer in a reaction solvent to obtain a high-concentration polyamic acid gel with a solid content of more than 30% and difficult to process, with a viscosity in the range of 1,000,000-2,000,000 cP Add a dehydrating agent and a catalyst to the above-mentioned high-concentration polyamic acid gel and mix fully, and the polyamic acid gel is gradually disentangled to obtain a polyamic acid solution with good fluidity and low viscosity, and the viscosity range is 1000-10000cP . Using the high solid content and low viscosity polyamic acid solution obtained by this method for coating and spinning, the prepared polyimide film has more excellent mechanical properties and lower thermal expansion coefficient, and the polyimide fiber has higher Draft ratio and better mechanical properties.

Description

High solid content low viscosity polyamic acid solution and its preparation method and application

technical field

The invention belongs to the field of material science and technology, and in particular relates to a polyamic acid solution with high solid content and low viscosity, a preparation method and application thereof.

technical background

Polyimide is a class of high-performance polymers containing imide rings in the main molecular chain. Because of its excellent thermomechanical properties, radiation resistance, low thermal expansion coefficient and electrical insulation, it is widely used in aviation, Aerospace, microelectronics, rail transit and nuclear industry and other fields. The common product forms of polyimide are films and fibers, etc. The preparation methods of these products mostly adopt the "two-step method", that is, polyamic acid solution is first synthesized, and then the final polyimide is obtained by chemical imidization or thermal imidization. imine products. Therefore, a high-quality polyamic acid solution is the key to preparing high-performance polyimide products.

The study found that the solid content of the polyamic acid solution increased appropriately, for example, from 10% to 19%, and the tensile strength and modulus of the corresponding polyimide fibers increased to varying degrees, increasing from 0.72GPa and 42.2GPa, respectively. To 1.21GPa and 99.9GPa (RSC Adv., 2015, 5, 69555), it can be seen that the polyimide prepared from the polyamic acid solution with high solid content has better mechanical properties. However, when the solid content of the solution is too high, the viscosity of the solution rises rapidly due to the strong hydrogen bond interaction, and even gels and loses further processing performance.

Patent CN 103788651 B discloses a polyamic acid solution with low apparent viscosity and its preparation method. The addition of trimethylchlorosilane can reduce the apparent viscosity of polyamic acid solution by more than 90%, but trimethylchlorosilane The addition of silane will affect the mechanical properties and thermal decomposition temperature of the final polyimide product.

Patent CN 104292459 B discloses a method for preparing a high-solid content low-viscosity polyimide material. By adding an adhesion promoter and an end-capping agent, a polyamic acid solution with a viscosity range of 500-10000 cp is obtained, but this research does not compare the auxiliary The effect of the addition of adhesive and end-capping agent on the properties of the final polyimide product.

Patent CN 112409612 A discloses a method for preparing a polyamic acid solution with high solid content and low viscosity. The polyamic acid solution prepared by adding carboxylate ammonium salt gemini surfactant has excellent tape casting performance.

Although there are some researches and developments on high-solid-content and low-viscosity polyimide materials in the prior art, there are some problems in the above inventive method. In the preparation process of high-solid-content and low-viscosity polyimide materials in the prior art, other ( Chlorosilanes, surfactants, etc.) reagents can improve its solid content, reduce its viscosity and improve its subsequent processing and molding performance, but in the prior art, it will affect the final polyimide product while reducing the viscosity of high solid content polyamic acid solution. Mechanical and thermal properties. Therefore, it is urgent to develop a preparation process that can obtain a polyamic acid solution with high solid content and low viscosity, improve its processing performance and ensure that the mechanical and thermal properties of the polyimide products are not affected.

Contents of the invention

The purpose of the present invention is to overcome the high viscosity of high solid content polyamic acid solution in the prior art, easy to gel and lose fluidity, difficult to process, to provide a kind of preparation method of high solid content low viscosity polyamic acid solution, by the method The prepared polyimide film obtained by solution processing has more excellent mechanical properties and lower coefficient of thermal expansion, and the polyimide fiber has higher draft ratio and better mechanical properties.

In order to achieve the above object, a kind of high solid content low viscosity polyamic acid solution disclosed by the present invention and its preparation method comprise the following steps:

(1) Add the diamine monomer and the dianhydride monomer into the reaction solvent and stir fully to make it undergo condensation polymerization to obtain a polyamic acid gel with a solid content of more than 30%, loss of fluidity, and difficulty in processing. The viscosity range is 1000000-2000000cP, the solid content of the polyamic acid gel is 30-35wt%;

(2) A certain amount of dehydrating agent and catalyst are added to the above-mentioned polyamic acid gel according to a certain ratio and fully stirred, and the polyamic acid gel is gradually disentangled to obtain a polyamic acid solution with good fluidity and low viscosity. The viscosity range is 1000-10000cP.

Preferably, the polyamic acid gel in step (1) has a solid content of 10%-50%, a viscosity of 1,000,000-2,000,000 cP, and loses fluidity and is difficult to coat or spin. The molar ratio of the dianhydride monomer to the diamine monomer is 0.98:1-1.02:1. The low-viscosity polyamic acid solution in step (2) has good fluidity for film coating and spinning, and the viscosity range is 1000-10000cP.

Preferably, the dianhydride monomer in step (1) is 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyl tetra Formic dianhydride (BPDA), pyromellitic dianhydride (PMDA), 2,3', 3,4'-biphenyltetracarboxylic dianhydride (α-BPDA), bisphenol A dianhydride (BPADA), 4 ,4'-oxydiphthalic anhydride (ODPA), hexafluoroisopropylene phthalic acid (6FDA), diphenylsulfide tetraacid dianhydride (TDPA) and 3,3',4,4'-di One or more of phenyl sulfone tetracarboxylic dianhydrides are mixed in any proportion;

Preferably, the diamine monomer described in step (1) is p-phenylenediamine (PDA), m-phenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 2-(4-aminophenyl One of )-5-aminobenzimidazole (BIA), 4,4'-diaminodiphenylsulfone, 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl (TFMB) or multiple mixed in any proportion; the reaction solvent is N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-vinylpyrrolidone (NMP) and dimethyl One of the base sulfoxide (DMSO).

Preferably, the volume ratio of the dehydrating agent to the catalyst described in step (2) is 5:1-1:5, and the molar ratio of the dehydrating agent to the dianhydride monomer is 0.2:1-0.8:1.

Preferably, the dehydrating agent described in step (2) is a mixture of one or more of acetic anhydride, propionic anhydride, butyric anhydride; the catalyst is pyridine, triethylamine, imidazole, isoquinoline, 2-methyl A mixture of one or more of base pyridine and 3-picoline.

Another object of the present invention is to provide a polyamic acid solution with high solid content and low viscosity prepared by the above method and a method for processing the polyimide film or fiber obtained from the solution.

Preferably, further, the prepared polyamic acid solution is coated on a glass plate with a thickness of about 30 μm, and heated at 60°C, 135°C, and 300°C for 1 hour respectively to obtain the corresponding polyimide film; Or further, the prepared polyamic acid solution is filtered and defoamed, spun by a wet spinning process, and the obtained as-spun fibers are successively cyclized by heating furnaces at 270°C, 350°C and 430°C to obtain the corresponding Polyimide fiber.

Preferably, the obtained film has a tensile strength of 150-350MPa, a tensile modulus of 2-10GPa; a fiber tensile strength of 1.2-4.4GP, and a tensile modulus of 18-150GPa.

Compared with prior art, the beneficial effect of the present invention is:

(1) The present invention destroys the strong hydrogen bond interaction in the polyamic acid gel by adding a dehydrating agent and a catalyst in the polyamic acid gel with high solid content, so that the viscosity of the polyamic acid gel can be greatly reduced, and at the same time It has improved its processing performance, so that it can be directly used as raw material for preparing polyimide film or fiber;

(2) The polyamic acid solution with high solid content and low viscosity prepared by the method, the polyimide film obtained by further processing the polyimide solution after imidization has higher in-plane orientation and better performance It tends to be stable and optimized, with more excellent mechanical properties and lower thermal expansion coefficient, and polyimide fibers have higher draft ratio and better mechanical properties.

(3) The process of the method of the invention is simple to operate, does not need to change existing synthesis and processing equipment, and is easy for industrialized production.

Description of drawings

Figures 1-5 are respectively (a) the polyamic acid gel state before adding the imidizing agent and (b) the polyamic acid solution state after adding the imidizing agent in Examples 1-5 of the present invention.

6-10 respectively show the change of the loss tangent (Tan) of the polyamic acid solution with the solid content at different angular frequencies during the dynamic rheological test in Comparative Examples 1-5 of the present invention.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar modules or modules having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

In the description of this specification, description with reference to the terms "one embodiment", "another embodiment", etc. means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention . In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

Compared with the high solid content and low viscosity polyimide material preparation process in the prior art, adding other reagents (chlorosilane, surfactant and other reagents) can reduce its viscosity in order to improve its processing performance, but in the prior art Reducing the viscosity of polyamic acid solution with high solid content will affect the mechanical and thermal properties of the final polyimide product. The high-solid-content and low-viscosity polyamic acid solution of the present invention can obtain low-viscosity polyamic acid with suitable imidization degree, solid content and precise viscosity range by controlling the selection of suitable imidization reagents and the ratio of components. solution, while ensuring post-processing performance, the mechanical properties such as mechanical properties and chemical properties such as thermal properties of the final polyimide product are avoided from being adversely affected.

The present invention provides the following specific examples and comparative examples to further illustrate the solution of the present invention.

Example 1

(1) Dissolve 10.594g (0.05297mol) ODA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 11.547g (0.05297mol) PMDA to the above system in batches, and continue to After 24 hours of reaction, a polyamic acid gel with a solid content of 32wt% and a viscosity of 1,918,000 cP was obtained, which made it difficult to coat or spin due to loss of fluidity;

(2) Add 2.0mL (0.0212mol) of acetic anhydride and 1.0mL of pyridine to the above gel, stir at room temperature (30°C) for 12 hours to mix evenly, and obtain a gel with a degree of imidization of 20% and good fluidity. A high solid content low viscosity polyamic acid solution with a viscosity of 8130cP.

Figure 1(a) and (b) respectively show the state of the polyamic acid gel in Example 1 (a) before adding the imidizing agent and (b) the state of the polyamic acid solution after adding the imidizing agent. It can be clearly seen from the comparison that after adding the specific imidization reagent of the application, although its solid content increases, its viscosity decreases, and the previous gel is transformed into a clear, uniform, and fluid low-viscosity polyamide acid solution.

Comparative example 1

Dissolve 4.942g (0.02471mol) of ODA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 5.386g (0.02471mol) of PMDA to the above system in batches, and continue the reaction for 24h under the condition of ice-water bath (0°C). A polyamic acid solution with a solid content of 18 wt % and a viscosity of 8500 cP was obtained.

Figure 6 is the change of loss tangent value (Tan) of polyamic acid solution with solid content under different angular frequencies during dynamic rheological test in Comparative Example 1. According to Winter and Chambon theory, loss tangent value during solution-gel transition (Tan) has nothing to do with the angular frequency. It can be seen that in the conventional synthesis process of the polyamic acid solution in Comparative Example 1, when the solid content exceeds 18%, the solution-gel transition will occur and the fluidity will be lost, making it difficult to carry out the next step of coating or spinning. Therefore, in order to ensure its processing fluidity, the solid content of the polyamic acid solution described in Comparative Example 1 in the conventional synthesis process is up to 18%.

In order to investigate the performance of the polyimide film or fiber obtained by processing the polyamic acid solution prepared by the method of the present invention. (1) Coating the prepared polyamic acid solution on a glass plate with a thickness of about 30 μm, and heating at 60°C, 135°C, and 300°C for 1 hour respectively to obtain the corresponding polyimide film; (2) The prepared polyamic acid solution is filtered and defoamed, and spun by wet spinning process, and the obtained as-spun fibers are cyclized in sequence at 270°C, 350°C and 430°C to obtain the corresponding polyimide fiber. The performance comparison of polyimide film and fiber is as follows:

Table 1 Polyimide film and fiber performance comparison

Tensile Strength Tensile modulus elongation at break Thermal expansion coefficient Maximum draft ratio Embodiment 1 (thin film) 165.6 MPa 2.81GPa 49% 28.3ppm/℃ / Comparative example 1 (thin film) 130.1 MPa 1.89GPa 46% 32.8ppm/℃ / Embodiment 1 (fiber) 1.21GPa 18.9GPa 13% / 5.5 Comparative example 1 (fiber) 0.82GPa 11.9GPa 15% / 4.0

Example 2

(1) Dissolve 5.417g (0.05016mol) of PDA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 14.747g (0.05016mol) of BPDA to the above system in batches, and continue to After 24 hours of reaction, a polyamic acid gel with a solid content of 30wt% was obtained, with a viscosity of 1,826,000 cP, which was difficult to coat or spin due to loss of fluidity;

(2) Add 1.0mL (0.01mol) of acetic anhydride and 0.5mL of pyridine to the above gel, stir at room temperature (30°C) for 12 hours to mix evenly, and obtain a gel with a degree of imidization of 10% and good fluidity. A high solid content low viscosity polyamic acid solution with a viscosity of 7850cP.

Figure 2(a) and (b) respectively show the state of the polyamic acid gel in Example 2 (a) before adding the imidizing agent and (b) the state of the polyamic acid solution after adding the imidizing agent. It can be clearly seen from the comparison that after adding the specific imidization reagent of the application, although its solid content increases, its viscosity decreases, and the previous gel is transformed into a clear, uniform, and fluid low-viscosity polyamide acid solution.

Comparative example 2

Dissolve 2.775g (0.02569mol) of PDA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 7.553g (0.02569mol) of BPDA to the above system in batches, and continue the reaction for 24h under the condition of ice-water bath (0°C). A polyamic acid solution with a solid content of 18 wt % and a viscosity of 8380 cP was obtained.

Figure 7 is the change of loss tangent value (Tan) of polyamic acid solution with solid content under different angular frequencies during the dynamic rheological test in Comparative Example 2. According to Winter and Chambon theory, the loss tangent value during solution-gel transition (Tan) has nothing to do with the angular frequency. It can be seen that in the conventional synthesis process of the polyamic acid solution in Comparative Example 2, when the solid content exceeds 20%, the solution-gel transition will occur and the fluidity will be lost, making it difficult to carry out the next step of coating or spinning. Therefore, in order to ensure its processing fluidity, the solid content of the polyamic acid solution described in Comparative Example 2 in the conventional synthesis process is at most 20%.

In order to investigate the performance of the polyimide film or fiber obtained by processing the polyamic acid solution prepared by the method of the present invention. (1) Coating the prepared polyamic acid solution on a glass plate with a thickness of about 30 μm, and heating at 60°C, 135°C, and 300°C for 1 hour respectively to obtain the corresponding polyimide film; (2) The prepared polyamic acid solution is filtered and defoamed, and spun by wet spinning process, and the obtained as-spun fibers are cyclized in sequence at 270°C, 350°C and 430°C to obtain the corresponding polyimide fiber. The performance comparison of polyimide film and fiber is as follows:

Table 2 Polyimide film and fiber performance comparison

Example 3

(1) Dissolve 8.964g (0.04482mol) ODA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 7.898 (0.04482mol) BPDA to the above system in batches, and continue the reaction under the condition of ice-water bath (0°C) In 24 hours, a polyamic acid gel with a solid content of 32wt% was obtained, with a viscosity of 1,768,000 cP, which lost fluidity and was difficult to coat or spin;

(2) Add 2.5mL (0.02689mol) of acetic anhydride and 1.25mL of pyridine to the above gel, stir at room temperature (30°C) for 5h to mix evenly, and obtain a gel with a degree of imidization of 30% and good fluidity. A high solid content low viscosity polyamic acid solution with a viscosity of 5650cP.

Figure 3(a) and (b) respectively show the state of polyamic acid gel in Example 3 (a) before adding imidization reagent and (b) the state of polyamic acid solution after adding imidization reagent. It can be clearly seen from the comparison that after adding the specific imidization reagent of the application, although its solid content increases, its viscosity decreases, and the previous gel is transformed into a clear, uniform, and fluid low-viscosity polyamide acid solution.

Comparative example 3

Dissolve 4.181g (0.02091mol) of ODA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 6.147g (0.02091mol) of BPDA to the above system in batches, and continue the reaction for 24h under the condition of ice-water bath (0°C). A polyamic acid solution with a solid content of 18 wt % and a viscosity of 8570 cP was obtained.

Figure 8 is the variation of the loss tangent value (Tan) of polyamic acid solution with solid content at different angular frequencies during the dynamic rheological test in Comparative Example 3. According to Winter and Chambon theory, the loss tangent value during solution-gel transition (Tan) has nothing to do with the angular frequency. It can be seen that in the conventional synthesis process of the polyamic acid solution in Comparative Example 3, when the solid content exceeds 18%, the solution-gel transition will occur and the fluidity will be lost, making it difficult to carry out the next step of coating or spinning. Therefore, in order to ensure its processing fluidity, the solid content of the polyamic acid solution described in Comparative Example 3 in the conventional synthesis process is up to 18%.

In order to investigate the performance of the polyimide film or fiber obtained by processing the polyamic acid solution prepared by the method of the present invention. (1) Coating the prepared polyamic acid solution on a glass plate with a thickness of about 30 μm, heating at 60°C, 135°C, and 300°C for 1 hour to obtain the corresponding polyimide film; (2) The prepared polyamic acid solution is filtered and defoamed, and the wet spinning process is used for spinning, and the obtained as-spun fibers are successively cyclized by heating furnaces at 270°C, 350°C and 430°C to obtain the corresponding polyimide fibers . The performance comparison of polyimide film and fiber is as follows:

Table 3 Polyimide film and fiber performance comparison

Tensile Strength Tensile modulus elongation at break Thermal expansion coefficient Maximum draft ratio Embodiment 3 (thin film) 181.9MPa 3.05GPa 71% 41.2ppm/℃ / Comparative example 3 (thin film) 143.6MPa 2.46GPa 66% 46.9ppm/℃ / Embodiment 3 (fiber) 1.81GPa 46.3GPa 6.5% / 6.9 Comparative example 3 (fiber) 1.2GPa 30.6GPa 9.8% / 5.0

Example 4

(1) Dissolve 3.792g (0.03511mol) of PDA and 3.010g (0.01505mol) of ODA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 14.747 (0.05016mol) of BPDA to the above system in batches. (0°C) under the condition of continuous reaction for 24 hours to obtain a polyamic acid gel with a solid content of 30wt%, a viscosity of 1958000cP, and losing fluidity, it is difficult to carry out coating or spinning;

(2) Add 2.4mL (0.02508mol) of acetic anhydride and 1.7mL of pyridine to the above gel, stir at room temperature (30°C) for 12 hours to mix evenly, and obtain a gel with a degree of imidization of 25% and good fluidity. A high solid content low viscosity polyamic acid solution with a viscosity of 6250cP.

Figure 4(a) and (b) respectively show the state of the polyamic acid gel in Example 4 (a) before adding the imidizing agent and (b) the state of the polyamic acid solution after adding the imidizing agent. It can be clearly seen from the comparison that after adding the specific imidization reagent of the application, although its solid content increases, its viscosity decreases, and the previous gel is transformed into a clear, uniform, and fluid low-viscosity polyamide acid solution.

Comparative example 4

1.942g (0.01798mol) of PDA and 1.541g (0.00771mol) of ODA were dissolved in 50mL of DMAc solvent. After the diamine was completely dissolved, 7.553g (0.02569mol) of BPDA was added to the above system in batches. The reaction was continued for 24 hours under the condition of °C) to obtain a polyamic acid solution with a solid content of 18 wt%, and a viscosity of 8730 cP.

Figure 9 is the change of loss tangent value (Tan) of polyamic acid solution with solid content at different angular frequencies during the dynamic rheological test in Comparative Example 4. According to Winter and Chambon theory, the loss tangent value during solution-gel transition (Tan) has nothing to do with the angular frequency. It can be seen that in the conventional synthesis process of the polyamic acid solution in Comparative Example 4, when the solid content exceeds 20%, the solution-gel transition will occur and the fluidity will be lost, making it difficult to carry out the next step of coating or spinning. Therefore, in order to ensure its processing fluidity, the solid content of the polyamic acid solution described in Comparative Example 4 in the conventional synthesis process is at most 20%.

In order to investigate the performance of the polyimide film or fiber obtained by processing the polyamic acid solution prepared by the method of the present invention. (1) Coating the prepared polyamic acid solution on a glass plate with a thickness of about 30 μm, heating at 60°C, 135°C, and 300°C for 1 hour to obtain the corresponding polyimide film; (2) The prepared polyamic acid solution is filtered and defoamed, and the wet spinning process is used for spinning, and the obtained as-spun fibers are successively cyclized by heating furnaces at 270°C, 350°C and 430°C to obtain the corresponding polyimide fibers . The performance comparison of polyimide film and fiber is as follows:

Table 4 Polyimide film and fiber performance comparison

Example 5

(1) Dissolve 4.334g (0.04012mol) of PDA and 2.247g (0.01003mol) of BIA in 50mL of DMAc solvent. After the diamine is completely dissolved, add 14.747g (0.05016mol) of BPDA to the above system in batches, and place in an ice-water bath (0°C) continuous reaction for 24 hours to obtain a polyamic acid gel with a solid content of 30wt%, a viscosity of 1,806,000 cP, and losing fluidity, it is difficult to carry out coating or spinning;

(2) Add 0.9 (0.01003mol) acetic anhydride and 0.45mL pyridine to the above gel, stir at room temperature (30°C) for 24 hours to make it evenly mixed, that is to say, the degree of imidization is 10%, and it has good fluidity. High solid content low viscosity polyamic acid solution with a viscosity of 5080cP.

Figure 5(a) and (b) respectively show the state of the polyamic acid gel in Example 5 (a) before adding the imidizing agent and (b) the state of the polyamic acid solution after adding the imidizing agent. It can be clearly seen from the comparison that after adding the specific imidization reagent of the present application, although its solid content increases, its viscosity decreases, and the previous gel is transformed into a clear, uniform, and fluid low-viscosity polyamide acid solution.

Comparative example 5

2.220g (0.02055mol) of PDA and 1.151g (0.00514mol) of BIA were dissolved in 50mL of DMAc solvent. After the diamine was completely dissolved, 7.553g (0.02569mol) of BPDA was added to the above system in batches, and ice-water bath (0 The reaction was continued for 24 hours under the condition of °C) to obtain a polyamic acid solution with a solid content of 18 wt%, and a viscosity of 9210 cP.

Figure 10 is the change of loss tangent (Tan) of polyamic acid solution with solid content at different angular frequencies during the dynamic rheological test in Comparative Example 5. According to Winter and Chambon theory, the loss tangent of solution-gel transition (Tan) has nothing to do with the angular frequency. It can be seen that in the conventional synthesis process of the polyamic acid solution in Comparative Example 5, when the solid content exceeds 18%, the solution-gel transition will occur and the fluidity will be lost, making it difficult to carry out the next step of coating or spinning. Therefore, in order to ensure its processing fluidity, the solid content of the polyamic acid solution described in Comparative Example 5 in the conventional synthesis process is up to 18%.

In order to investigate the performance of the polyimide film or fiber obtained by processing the polyamic acid solution prepared by the method of the present invention. (1) Coating the prepared polyamic acid solution on a glass plate with a thickness of about 30 μm, heating at 60°C, 135°C, and 300°C for 1 hour to obtain the corresponding polyimide film; (2) The prepared polyamic acid solution is filtered and defoamed, and the wet spinning process is used for spinning, and the obtained as-spun fibers are sequentially cyclized by heating furnaces at 270°C, 350°C and 430°C to obtain the corresponding polyimide fibers . The performance comparison of polyimide film and fiber is as follows:

Table 5 Polyimide film and fiber performance comparison

Tensile Strength Tensile modulus elongation at break Thermal expansion coefficient Maximum draft ratio Embodiment 5 (thin film) 350.3 MPa 7.73GPa 25% 8.8ppm/℃ / Comparative example 5 (thin film) 246.9MPa 5.87GPa twenty two% 9.6ppm/℃ / Embodiment 5 (fiber) 3.98GPa 141.2GPa 2.9% / 4.3 Comparative example 5 (fiber) 3.21GPa 124.4GPa 3.4% / 3.0

As can be seen from Table 1-5, the preparation method of the present invention can solve the problem that the high solid content polyamic acid solution has a high viscosity and is difficult to process, and the polyimide film obtained by the solution processing prepared by the method has More excellent mechanical properties and lower thermal expansion coefficient, polyimide fiber has higher draft ratio and better mechanical properties.

The preferred embodiments of the present invention have been described in detail above, however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the disclosed content of the present invention. All belong to the protection scope of the present invention.

Claims (7)

1. A preparation method of a high-solid-content low-viscosity polyamic acid solution comprises the following steps:

(1) Adding a diamine monomer and a dianhydride monomer into a reaction solvent, and fully stirring to perform condensation polymerization reaction to obtain polyamic acid gel which has the solid content of more than 30%, loses fluidity and is difficult to process, wherein the viscosity range is 1000000-2000000cP, and the solid content of the polyamic acid gel is 30-35wt%;

(2) Adding a certain amount of dehydrating agent and catalyst into the polyamic acid gel according to a certain proportion, fully stirring, and gradually disentangling the polyamic acid gel to obtain a polyamic acid solution with good fluidity and low viscosity, wherein the viscosity range is 1000-10000cP.

2. The method of claim 1, wherein the molar ratio of dianhydride monomer to diamine monomer in step (1) is 0.98 to 1.02.

3. The method according to claim 1 or 2, wherein the dianhydride monomer in step (1) is one or more of 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3,3',4,4' -biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride, 2,3',3,4' -biphenyl tetracarboxylic dianhydride, bisphenol a type dianhydride, 4,4' -oxydiphthalic anhydride, hexafluoroisopropylphthalic acid, diphenyl sulfide tetracarboxylic dianhydride, and 3,3',4,4' -diphenylsulfone tetracarboxylic dianhydride mixed in any proportion; the diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, 4,4 '-diaminodiphenyl ether, 2- (4-aminophenyl) -5-aminobenzimidazole, 4,4' -diaminodiphenyl sulfone, 4,4 '-diamino-2,2' -bis-trifluoromethyl biphenyl mixed in any proportion; the reaction solvent is one of N, N-dimethylformamide, N-dimethylacetamide, N-vinyl pyrrolidone and dimethyl sulfoxide.

4. The process of claim 1, wherein the volume ratio of dehydrating agent to catalyst in step (2) is 5:1-1:5, and the molar ratio of dehydrating agent to dianhydride monomer is 0.2 to 1-0.8.

5. The method according to claim 1, wherein the dehydrating agent in step (2) is a mixture of one or more of acetic anhydride, propionic anhydride, butyric anhydride; the catalyst is one or a mixture of pyridine, triethylamine, imidazole, isoquinoline, 2-methylpyridine and 3-methylpyridine.

6. A method for processing a high-solid-content low-viscosity polyamic acid solution prepared according to any one of claims 1 to 5 to obtain a polyimide film or fiber, characterized in that:

further, coating the prepared polyamic acid solution on a glass plate with the thickness of 30 microns, and sequentially heating the polyamic acid solution for 1 hour at 60 ℃,135 ℃ and 300 ℃ respectively to obtain a corresponding polyimide film; or further filtering and defoaming the prepared polyamic acid solution, spinning by adopting a wet spinning process, and cyclizing the obtained nascent fiber by sequentially passing through hot furnaces at 270 ℃,350 ℃ and 430 ℃ to obtain the corresponding polyimide fiber.

7. The method of processing polyimide film or fiber according to claim 6, wherein the resulting film has a tensile strength of 150 to 350MPa, a tensile modulus of 2 to 10GPa; or the obtained fiber has the tensile strength of 1.2-4.4GPa and the tensile modulus of 18-150GPa.

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