Process for the continuous preparation of a polyamic acid solution

Abstract

The application belongs to the field of polymer synthesis, and provides a method for continuously preparing a polyamide acid solution, comprising the following steps: (1) providing a reaction solution, wherein the reaction solution comprises solution A and solution B, the solution A comprises a dianhydride and a first solvent, and the solution B comprises a diamine and a second solvent; (2) introducing the solution A, the solution B and an inert gas into the pipeline of a microreactor respectively, carrying out gas-liquid two-phase mixing, and controlling the gas flow to be greater than the sum of the flow of the solution A and the solution B, so that the gas-liquid mixture in the pipeline forms Taylor flow, and the dianhydride and the diamine are reacted to form polyamide acid within a predetermined residence time, and the polyamide acid solution is obtained. The method of the application introduces a gas-liquid two-phase into the pipeline of a microreactor and forms Taylor flow, reduces the viscosity in the reactor through the heterogeneous system, and further reduces the risk of microreactor blockage caused by excessively high viscosity of the system.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis, and specifically, to a method for the continuous preparation of polyamic acid solutions. Background Technology

[0002] Polyimide is a special engineering plastic with excellent comprehensive performance. It can be applied in many fields such as aerospace, electrical insulation, liquid crystal display, automotive and medical, microelectronics, precision machinery and packaging in the form of films, composite materials, foam plastics, engineering plastics and fibers.

[0003] The most common method for synthesizing polyimide is to dissolve monomers (usually dianhydrides and diamines) in a strongly polar solution and undergo condensation polymerization to obtain polyamic acid, followed by dehydration and cyclization to obtain a polymer with a five-membered heterocyclic imide ring. Polyamic acid solutions, as precursors to polyimide, are currently mostly prepared using batch reactors. To avoid overly vigorous reactions, processes involving temperature control or monomer feeding sequence are often employed. However, this can lead to problems such as excessively long residence times of some materials within the reactor, increased byproducts, or unstable reactions, ultimately resulting in an excessively wide molecular weight distribution of the polyimide product. Furthermore, batch reactors are mostly intermittent operations, making continuous production difficult, resulting in low equipment utilization and a higher risk of safety accidents such as material overflow during operation.

[0004] With the continuous advancement of reaction engineering technology, chemical synthesis is developing towards greater efficiency, safety, and automation. Continuous flow synthesis technology, represented by microreactors, is being applied to various types of polymerization reactions. Microreactors allow for convenient setting of reaction operating conditions through temperature control systems and flow rate regulation, and the relatively closed system is less susceptible to intrusion by impurities such as water and air. However, in the production of polyamic acid using microreactors, as the polycondensation reaction proceeds and the polymer molecular weight increases, the polyamic acid solution may develop a high viscosity, leading to blockage of the microreactor tubing and hindering the reaction's progress. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] This invention proposes a method for the continuous preparation of polyamic acid solutions, comprising the following steps:

[0007] (1) Provide reaction solution

[0008] The reaction solution includes solution A and solution B, wherein solution A contains dianhydride and a first solvent, and solution B contains diamine and a second solvent;

[0009] (2) The solution A, the solution B and the inert gas are introduced into the pipeline of the microreactor to mix the gas and liquid phases, and the gas flow rate is controlled to be greater than the sum of the flow rates of the solution A and the solution B, so that the gas-liquid mixture in the pipeline forms a Taylor flow, and the dianhydride and the diamine react to form polyamic acid within a predetermined residence time to obtain the polyamic acid solution.

[0010] The method of this invention introduces a gas phase (inert gas) and a liquid phase (solution A and solution B) into the microreactor channel, and controls the gas phase flow rate (gas flow rate) to be greater than the liquid phase flow rate (the sum of the flow rates of solution A and solution B) to form Taylor flow in the channel of the microreactor, thereby enhancing the diffusion mixing and reaction of the two reaction solutions. Furthermore, the viscosity within the reactor is reduced through the heterogeneous system, thereby reducing the risk of microreactor blockage caused by excessive system viscosity and improving the operational stability of continuous preparation of polyamic acid solutions using a microreactor.

[0011] According to an embodiment of the present invention, the gas flow rate is 0.01 mL / min to 10 mL / min.

[0012] According to an embodiment of the present invention, the flow rates of solution A and solution B are independently 0.005 mL / min to 4.9 mL / min.

[0013] According to an embodiment of the present invention, the ratio of the gas flow rate to the sum of the flow rates of solution A and solution B is (1.05 to 10):1.

[0014] Furthermore, the ratio of the gas flow rate to the sum of the flow rates of solution A and solution B is (1.05 to 5):1, which is beneficial for forming a more stable flow pattern.

[0015] According to an embodiment of the present invention, the inner diameter of the pipe is 0.5 mm to 2 mm. Therefore, the microreactor can exhibit good mass and heat transfer characteristics within the pipe, and the pressure drop within the pipe is moderate, requiring less driving force from the feed pump.

[0016] According to embodiments of the present invention, the first solvent and the second solvent may be the same or different, and each independently includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

[0017] According to embodiments of the present invention, the dianhydride comprises at least one of 1,2,4,5-pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-biphenyl ether dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride. This is advantageous for reducing system viscosity and production costs.

[0018] According to embodiments of the present invention, the diamine comprises at least one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, p-phenylenediamine, and m-phenylenediamine. This is advantageous for reducing system viscosity and production costs.

[0019] According to an embodiment of the present invention, the molar ratio of the diamine to the dianhydride is 1:(1 to 1.1). This is beneficial for improving the reaction conversion rate and the product yield.

[0020] According to an embodiment of the present invention, the mass concentration of the dianhydride in solution A is 5% to 20%.

[0021] According to an embodiment of the present invention, the reaction temperature is -10°C to 40°C.

[0022] Furthermore, the reaction temperature is between 20°C and 40°C. This reduces both the viscosity of the system and energy consumption.

[0023] According to an embodiment of the present invention, the predetermined stay time is 10 min to 3 h.

[0024] According to an embodiment of the present invention, the polyamic acid has a number-average molecular weight of 8 × 10⁻⁶. 3 g / mol ~ 50 × 10 3 The molecular weight distribution coefficient is 2–5 g / mol. Therefore, the obtained polyamic acid solution has a moderate viscosity, is less prone to clogging pipelines, and is beneficial for maintaining the long-term stability of the synthesis reaction. Attached Figure Description

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0026] Figure 1 These are schematic diagrams of the polyamic acid solution preparation process in some embodiments;

[0027] Figure 2 This is the 1H NMR spectrum of the polyamic acid from Example 1;

[0028] Figure 3 This is the GPC spectrum of the polyamic acid from Example 1.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1: Solution A feed pump; 2: Solution B feed pump; 3: Inert gas storage tank; 4: High-speed camera; 5: Microreactor. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0032] This invention proposes a method for the continuous preparation of polyamic acid solutions, comprising the following steps:

[0033] (1) Provide reaction solution

[0034] The reaction solution includes solution A and solution B, wherein solution A contains dianhydride and a first solvent, and solution B contains diamine and a second solvent;

[0035] (2) The solution A, the solution B and the inert gas are introduced into the pipeline of the microreactor to mix the gas and liquid phases, and the gas flow rate is controlled to be greater than the sum of the flow rates of the solution A and the solution B, so that the gas-liquid mixture in the pipeline forms a Taylor flow, and the dianhydride and the diamine react to form polyamic acid within a predetermined residence time to obtain the polyamic acid solution.

[0036] The method of this invention introduces a gas phase (inert gas) and a liquid phase (solution A and solution B) into the microreactor channel, and controls the gas phase flow rate (gas flow rate) to be greater than the liquid phase flow rate (the sum of the flow rates of solution A and solution B) to form Taylor flow in the channel of the microreactor, thereby enhancing the diffusion mixing and reaction of the two reaction solutions. Furthermore, the viscosity within the reactor is reduced through the heterogeneous system, thereby reducing the risk of microreactor blockage caused by excessive system viscosity and improving the operational stability of continuous preparation of polyamic acid solutions using a microreactor.

[0037] Specifically, introducing microbubbles into the microreactor's channels creates a complex flow field to enhance gas-liquid phase mixing. When the gas and liquid phases are injected at the microreactor inlet, the liquid phase, with its much higher viscosity than the gas phase, is broken into uniformly shaped bubbles that exist as the dispersed phase within the channel. By controlling the gas flow rate to be greater than the liquid flow rate, a Taylor flow is formed within the microreactor channel. This allows the gas phase to exist as a dispersed phase in the form of bubbles, while the liquid phase exists as a continuous phase in the form of liquid blasts. Adjacent liquid blasts are connected by a liquid film between the bubbles and the channel wall. The alternation of bubbles and liquid blasts creates an internal circulation, further enhancing the mixing of reactants within the liquid blasts. During continuous flow, the liquid blasts, serving as reaction sites, are dispersed and do not form a connected whole, reducing the polymer viscosity within the liquid blasts and thus lowering the overall viscosity of the reaction system to prevent blockage.

[0038] According to the present invention, Taylor flow is formed in the microreactor channel by controlling the gas phase flow rate to be greater than the liquid phase flow rate. Furthermore, the specific flow rates of the gas and liquid phases can be selected based on the volume of the microreactor; generally, given the same material residence time, the volume of the microreactor is positively correlated with the flow rate (the sum of the gas and liquid phase flow rates).

[0039] In some embodiments, the gas flow rate is 0.01 mL / min to 10 mL / min. Examples include 0.01 mL / min, 0.11 mL / min, 0.12 mL / min, 0.14 mL / min, 0.17 mL / min, 0.23 mL / min, 0.3 mL / min, 0.36 mL / min, 1 mL / min, 2 mL / min, 3 mL / min, 5 mL / min, 8 mL / min, and 10 mL / min. Optionally, the gas flow rate is 0.10 mL / min to 3.5 mL / min.

[0040] In some embodiments, the flow rates of solution A and solution B are independently from 0.005 mL / min to 4.9 mL / min. Examples include 0.005 mL / min, 0.015 mL / min, 0.04 mL / min, 0.05 mL / min, 0.08 mL / min, 0.11 mL / min, 0.15 mL / min, 0.165 mL / min, 1.14 mL / min, 1.4 mL / min, 2 mL / min, 4 mL / min, and 4.9 mL / min. Optionally, the flow rates of solution A and solution B are independently from 0.01 mL / min to 1.4 mL / min.

[0041] In some embodiments, the ratio of gas flow rate to the sum of the flow rates of solution A and solution B is (1.05–10):1. When the gas flow rate is greater than the total liquid flow rate, a heterogeneous Taylor flow can be formed in the channels of the microreactor, which can enhance the mixing degree between the reactants in the liquid phase, thereby facilitating the stable progress of the polymerization process.

[0042] Optionally, the ratio of gas flow rate to the sum of the flow rates of solution A and solution B is (1.05–5):1, for example, 1.05:1, 1.06:1, 1.2:1, 1.75:1, 2.3:1, 3:1, 4:1, 5:1, etc. This further ensures that the gas phase exists as a dispersed phase in the form of bubbles, while solutions A and B, after mixing, exist as a liquid phase in the form of liquid boulders, enhancing the mixing degree between the reactants in the liquid phase and facilitating the stable progress of the polymerization process.

[0043] In some embodiments, the inner diameter of the pipe is 0.5 mm to 2 mm, for example, 0.5 mm, 1 mm, 1.5 mm, 2 mm, etc. Therefore, the excellent mass and heat transfer characteristics of the microreactor can be utilized within the pipe, and the pressure drop within the pipe is moderate, requiring less driving force from the feed pump.

[0044] In some embodiments, the length of the pipe can be customized according to actual needs, such as reaction time, for example, 5m, 11.1m, 25m, 50m, 100m, etc.

[0045] In step (2), the dianhydride provided by solution A and the diamine provided by solution B flow continuously in the pipeline and react to form polyamic acid, thus obtaining the polyamic acid solution.

[0046] In some embodiments, the reaction temperature is -10°C to 40°C, for example -10°C, 10°C, 20°C, 30°C, 40°C, etc.

[0047] Optionally, the reaction temperature is between 20°C and 40°C. This reduces both the viscosity of the system and energy consumption.

[0048] In some embodiments, the predetermined dwell time is 10 min to 3 h, for example 10 min, 20 min, 30 min, 60 min, 90 min, 2 h, or 3 h.

[0049] According to the present invention, the first solvent and the second solvent can be selected from solvents in existing synthetic polyamic acid solutions. Generally, the first solvent and the second solvent can be polar aprotic solvents, respectively.

[0050] In some embodiments, the first solvent and the second solvent may be the same or different, and each independently includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone (NMP), and dimethyl sulfoxide.

[0051] Optionally, the first solvent and the second solvent are the same.

[0052] According to the present invention, the dianhydride and diamine can be selected from the reaction raw materials in existing synthetic polyamic acid solutions. In some embodiments, the dianhydride includes at least one of 1,2,4,5-pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-diphenyl ether dianhydride (ODPA), and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA). This is beneficial for reducing system viscosity and production costs.

[0053] In some embodiments, the diamine includes at least one of 4,4'-diaminodiphenyl ether (ODA), 4,4'-diaminodiphenylmethane (MDA), p-phenylenediamine (PPD), and m-phenylenediamine (MPD). This is beneficial for reducing system viscosity and production costs.

[0054] In some embodiments, the molar ratio of the diamine to the dianhydride is 1:(1 to 1.1), for example, 1:1, 1:1.05, 1:1.1, etc. This is beneficial for improving the reaction conversion rate and the product yield.

[0055] Optionally, the mass concentration of the dianhydride in solution A is 5% to 20%, such as 5%, 10%, 15%, or 20%. This improves synthesis efficiency while reducing the excessively high viscosity of the system caused by excessively high solid content in the product.

[0056] According to the present invention, the inert gas can be any gas that does not participate in the reaction. As some examples, the inert gas includes nitrogen (N2) and helium (He).

[0057] In some embodiments, solutions A and B can be obtained by dissolving diamine and dianhydride in NMP solvent under inert gas protection, respectively.

[0058] As an example, the diamine is 4,4'-diaminodiphenyl ether, and the dianhydride is 1,2,4,5-pyromellitic dianhydride.

[0059] As an example, the diamine is 4,4'-diaminodiphenyl ether, and the dianhydride is 4,4'-biphenyl ether dianhydride.

[0060] As an example, the diamine is 4,4'-diaminodiphenyl ether and p-phenylenediamine, and the dianhydride is 4,4'-biphenyl ether dianhydride.

[0061] As an example, the diamine is 4,4'-diaminodiphenyl ether, and the dianhydride is 4,4'-biphenyl ether dianhydride and 1,2,4,5-pyromellitic dianhydride.

[0062] In this invention, when solution A contains two dianhydride materials, the two materials can be formulated to form the same solution A.

[0063] Similarly, when solution B contains two diamine materials, the two materials are prepared to form the same solution B.

[0064] In some embodiments, the polyamic acid has a number-average molecular weight of 8 × 10⁻⁶. 3 g / mol ~ 50 × 10 3 g / mol, with a molecular weight distribution coefficient of 2 to 5, which can be selected as 2 to 4.

[0065] The preparation of polyamic acid solution according to this invention is a continuous production process, which can be carried out in a production apparatus including the microreactor. In some embodiments, such as Figure 1 As shown, in addition to the microreactor 5, the production device also includes a solution A feed pump 1, a solution B feed pump 2, and an inert gas storage tank 3, wherein...

[0066] The outlet pipes of solution A feed pump 1 and solution B feed pump 2 are connected to the inlet of microreactor 5 via a tee and a main pipeline;

[0067] The main pipeline is also equipped with a tee, through which the outlet pipeline of the inert gas storage tank 3 is connected to the main pipeline, so that the inert gas can enter and connect to the microreactor 5 through the main pipeline, and a gas flow meter is provided on the outlet pipeline.

[0068] Optionally, the production device may also be equipped with a high-speed camera 4 to observe the material flow pattern in the microreactor.

[0069] Optionally, the inlet pipes of solution A feed pump 1 and solution B feed pump 2 are respectively connected to solution A storage tank and solution B storage tank.

[0070] Alternatively, the feed pumps may each independently include an injection pump, a peristaltic pump, a plunger pump, or a horizontal flow pump.

[0071] Optionally, the gas flow meter includes a mass flow meter or a volumetric flow meter.

[0072] In some embodiments, the microreactor may be made of a metal or a polymer. Metals may be, for example, stainless steel or titanium alloys. Polymers may be fluoropolymers such as PFA, PTFE, FEP, or ETFE.

[0073] According to the present invention, the number of pipelines in the microreactor can be selected according to the production scale. In some embodiments, the microreactor includes a tubular microreactor, a plate microreactor, and a chip microreactor.

[0074] In some specific embodiments, reference is made to Figure 1 Step (2) includes the following process flow:

[0075] Solution A, solution B, and inert gas are combined and fed into the pipeline of microreactor 5 via the main pipeline. The flow pattern is observed through high-speed camera 4 to ensure that the gas-liquid dispersion flow pattern in the pipeline of the microreactor is Taylor flow, so that there is internal circulation in the liquid bomb to enhance mixing. The flow rate is controlled to allow the material to stay in the reactor for a period of time to react, thus obtaining a polyamic acid solution.

[0076] The method of this invention is simple to operate and has a certain degree of universality. By introducing an inert gas into the inlet of the microreactor pipe and matching its flow rate with the reaction solution to form a gas-liquid slug flow (Taylor flow), this heterogeneous flow pattern can enhance the mixing process of the reactants within the liquid slug, thereby promoting polymer chain growth and avoiding pipe blockage caused by the high viscosity of the homogeneous system when the polymer molecular weight increases. Furthermore, applying the microreactor method to the controllable preparation of polyamic acid solutions establishes a universal method for the mass synthesis of high molecular weight functional polymers.

[0077] The present invention will be described below through specific embodiments. It should be noted that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0078] Example 1

[0079] 4,4'-Diaminodiphenyl ether (ODA) was dissolved in N2-protected N-methylpyrrolidone solvent to obtain solution B with an ODA mass content of 15%. 1,2,4,5-pyromellitic dianhydride (PMDA) was dissolved in N2-protected N-methylpyrrolidone solvent to obtain solution A. Under equal volume conditions, the molar ratio of diamine in solution B to dianhydride in solution A was 1:1.

[0080] Solutions A and B were separately pumped into a PFA capillary microreactor with an inner diameter of 1 mm and a length of 25 m using a syringe pump at a flow rate of 0.08 mL / min. Simultaneously, the gas flow meter was adjusted to ensure a nitrogen inlet flow rate of 0.17 mL / min. This allowed the two solutions to form a Taylor flow with the gas in the microreactor, resulting in a reaction. The individual residence time was 60 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0081] Example 2

[0082] 4,4'-Diaminodiphenyl ether (ODA) was dissolved in He-protected N-methylpyrrolidone solvent to obtain solution B with an ODA mass content of 15%. 1,2,4,5-pyromellitic dianhydride (PMDA) was dissolved in He-protected N-methylpyrrolidone solvent to obtain solution A. Under the condition of equal volume, the molar ratio of diamine in solution B to dianhydride in solution A was 1:1.

[0083] Solutions A and B were separately pumped into a PFA capillary microreactor with an inner diameter of 1.5 mm and a length of 11.1 m using a syringe pump at a flow rate of 0.08 mL / min. Simultaneously, the gas flow meter was adjusted to ensure a He inlet flow rate of 0.17 mL / min. This allowed the two solutions to form a Taylor flow with the gas in the microreactor, resulting in mixing and reaction. The individual residence time was 60 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0084] Example 3

[0085] 4,4'-Diaminodiphenyl ether (ODA) was dissolved in N2-protected N-methylpyrrolidone solvent to obtain solution B with an ODA mass content of 10%. 4,4'-Biphenyl ether dianhydride (ODPA) was dissolved in N2-protected N-methylpyrrolidone solvent to obtain solution A. Under controlled equal volume conditions, the molar ratio of diamine in solution B to dianhydride in solution A was 1:1.05.

[0086] Solutions A and B were separately pumped into a PTFE microreactor with an inner diameter of 1 mm and a length of 25 m using a syringe pump at a flow rate of 0.05 mL / min. Simultaneously, the gas flow meter was adjusted to ensure an N2 inlet flow rate of 0.12 mL / min. This allowed the two solutions to form Taylor flows with the gas in the microreactor, resulting in a reaction. The individual residence time was 90 min, and the reaction temperature was 40 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0087] Example 4

[0088] 4,4'-Diaminodiphenyl ether (ODA) was dissolved in He-protected N-methylpyrrolidone solvent to obtain solution B with an ODA content of 10% by mass. 4,4'-Biphenyl ether dianhydride (ODPA) was dissolved in He-protected N-methylpyrrolidone solvent to obtain solution A. Under equal volume conditions, the molar ratio of diamine in solution B to dianhydride in solution A was 1:1.1. Solutions A and B were separately pumped into a PFA microreactor with an inner diameter of 1 mm and a length of 25 m using a syringe pump at a flow rate of 0.15 mL / min. Simultaneously, the gas flow meter was adjusted to maintain an N2 inlet flow rate of 0.36 mL / min. The two solutions formed a Taylor flow with the gas in the microreactor, and after mixing, a reaction occurred. The individual residence time was 30 min, and the reaction temperature was 40 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0089] Example 5

[0090] 4,4'-Diaminodiphenyl ether (ODA) and p-phenylenediamine were dissolved together in an N2-protected N-methylpyrrolidone solvent at a molar ratio of 1:1 to obtain solution B, which has a total diamine content of 10% by mass. 4,4'-Biphenyl ether dianhydride (ODPA) was dissolved in an N2-protected N-methylpyrrolidone solvent to obtain solution A. Under the condition of equal volume, the molar ratio of ODPA in solution A to diamine in solution B was 1:1.

[0091] Solutions A and B were separately pumped into a stainless steel microreactor with an inner diameter of 1 mm and a length of 25 m using a syringe pump at a flow rate of 0.04 mL / min. Simultaneously, the gas flow meter was adjusted to ensure an N2 inlet flow rate of 0.14 mL / min. This allowed the two solutions to form Taylor flows with the gas in the microreactor, where they mixed and reacted. The individual residence time was 90 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0092] Example 6

[0093] 4,4'-Diaminodiphenyl ether (ODA) was dissolved in N2-protected N-methylpyrrolidone solvent to obtain solution B with an ODA mass content of 10%. 4,4'-Biphenyl ether dianhydride (ODPA) and 1,2,4,5-pyromellitic dianhydride (PMDA) were co-dissolved in N2-protected N-methylpyrrolidone solvent at a molar ratio of 1:1 to obtain solution A. Under controlled equal volume conditions, the molar ratio of diamine in solution B to dianhydride in solution A was 1:1.05.

[0094] Solutions A and B were separately pumped into a 25m long, 1mm inner diameter FEP microreactor using a syringe pump at a flow rate of 0.05 mL / min. Simultaneously, the gas flow meter was adjusted to ensure an N2 inlet flow rate of 0.12 mL / min. This allowed the two solutions to form Taylor flows with the gas in the microreactor, resulting in mixing and reaction. The individual residence time was 90 min, and the reaction temperature was 20℃. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0095] Example 7

[0096] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both fed into a PFA tube microreactor with an inner diameter of 1 mm and a length of 25 m at a flow rate of 0.05 mL / min. At the same time, the gas flow meter was adjusted to make the inlet flow rate of N2 0.23 mL / min, the single residence time was 60 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0097] Example 8

[0098] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both fed into a PFA capillary microreactor with an inner diameter of 1 mm and a length of 25 m at a flow rate of 0.015 mL / min. At the same time, the gas flow meter was adjusted to make the inlet flow rate of N2 0.3 mL / min, the single residence time was 60 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0099] Example 9

[0100] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both fed into a PFA microreactor with an inner diameter of 2 mm and a length of 50 m at a flow rate of 1.14 mL / min. At the same time, the gas flow meter was adjusted to make the inlet flow rate of N2 3 mL / min, the single residence time was 30 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0101] Example 10

[0102] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both fed into a PFA microreactor with an inner diameter of 2 mm and a length of 100 m at a flow rate of 1.14 mL / min. At the same time, the gas flow meter was adjusted to make the inlet flow rate of N2 3 mL / min, the single residence time was 60 min, the reaction temperature was 20 °C, and after 2 residence times, the stable polyamic acid product solution was collected at the outlet.

[0103] Comparative Example 1

[0104] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both delivered at a flow rate of 0.165 mL / min into a PFA microreactor with an inner diameter of 1 mm and a length of 25 m. The two solutions formed a Taylor flow with the gas in the microreactor, and after mixing, a reaction occurred. The individual residence time was 60 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0105] Comparative Example 2

[0106] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both delivered to a PFA microreactor with an inner diameter of 1 mm and a length of 25 m at a flow rate of 0.165 mL / min. At the same time, the microreactor was immersed in an ultrasonic instrument with a working power of 100 W and a working frequency of 30 kHz so that the two solutions were mixed and reacted in the microreactor. The residence time for each solution was 60 min, and the reaction temperature was 20 °C. After two residence times, the stable polyamic acid product solution was collected at the outlet.

[0107] Comparative Example 3

[0108] The polyamic acid solution was prepared according to the method in Example 1, except that the solution A containing dianhydride and the solution B containing diamine were both fed into a PFA microreactor with an inner diameter of 1 mm and a length of 25 m at a flow rate of 0.11 mL / min. At the same time, the gas flow meter was adjusted so that the inlet flow rate of N2 was 0.11 mL / min, the single residence time was 60 min, the reaction temperature was 20 °C, and after 2 residence times, the stable polyamic acid product solution was collected at the outlet.

[0109] Test case

[0110] The polyamic acid collected in the examples and comparative examples was subjected to gel permeation chromatography (GPC) to obtain the number-average molecular weight and its molecular weight distribution. Specifically, using THF as the mobile phase, the polyamic acid solution was precipitated with ethanol, dried under vacuum, and characterized at 40°C and a flow rate of 1.0 mL / min using a Tosoh EcoSC HLC-8320GPC instrument.

[0111] NMR testing: The NMR was performed at room temperature using a Bruke 400MHz 1H NMR spectrometer with deuterated chloroform as the solvent.

[0112] The test results are shown in Table 1.

[0113] Table 1

[0114]

[0115] As can be seen from the table above, the flow pattern in the microreactors in Examples 1-10 is Taylor flow, the enhanced mixing in the pipe is obvious, the molecular weight of the obtained product is large, and the continuous and stable operation time is relatively long.

[0116] Compared with Example 1, Example 8 has a larger gas-liquid phase flow ratio and unstable flow pattern during operation, resulting in a reduced stable operation time.

[0117] Compared with Example 1, no gas was introduced into the system of Comparative Example 1. Instead, monomer polycondensation was carried out in a homogeneous solution. During the reaction, polymer gel blocks were formed at the tail end of the microreactor pipe. This was because the local molecular weight was too high and the viscosity of the homogeneous system was too high, making the continuous process unstable.

[0118] Compared with Example 1, no gas was introduced into the system of Comparative Example 2. Instead, a homogeneous solution was used for monomer polycondensation. Ultrasound was added during the polycondensation process. During the reaction, polymer gel blocks were also formed at the tail end of the microreactor pipe. This was because the local molecular weight was too high. Even with the help of ultrasound, the viscosity of the homogeneous system was too high, which made the continuous process unstable. In other words, ultrasound could not solve the problem of pipe blockage in the homogeneous system.

[0119] Compared with Comparative Example 3 and Example 1, the molecular weight of the product is significantly reduced under the same residence time because the internal circulation of the bubbly flow is weaker than that of the slub flow. It can be seen that under the same device running time, the bubbly flow cannot obtain high molecular weight polyamic acid.

[0120] Figure 2 The figure shows the 1H NMR spectrum of the polyamic acid from Example 1. As can be seen from the figure, it has characteristic peaks of benzene rings and hydrogen atoms of -NH2 on the monomers ODA and PMDA, indicating that the synthesized sample is a copolymer of dianhydride and diamine.

[0121] Figure 3 The figure shows the GPC spectrum of the polyamic acid from Example 1. As can be seen from the figure, the molecular weight distribution curve is a single peak, which is consistent with the typical molecular weight distribution of polycondensation products in the range of 2 to 5.

[0122] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0123] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for continuously preparing a polyamic acid solution, characterized in that, Includes the following steps: (1) Provide reaction solution The reaction solution includes solution A and solution B, wherein solution A contains dianhydride and a first solvent, and solution B contains diamine and a second solvent; (2) The solution A, the solution B and the inert gas are respectively introduced into the pipeline of the microreactor to mix the gas and liquid phases, and the gas flow rate is controlled to be greater than the sum of the flow rates of the solution A and the solution B, so that the gas-liquid mixture in the pipeline forms a Taylor flow, and the dianhydride and the diamine react to form polyamic acid within a predetermined residence time to obtain the polyamic acid solution. The ratio of the gas flow rate to the sum of the flow rates of solution A and solution B is (1.05~10):

1.

2. The method according to claim 1, characterized in that, The gas flow rate is 0.01 mL / min to 10 mL / min.

3. The method according to claim 1, characterized in that, The flow rates of solution A and solution B are independently 0.005 mL / min to 4.9 mL / min.

4. The method according to any one of claims 1-3, characterized in that, The ratio of the gas flow rate to the sum of the flow rates of solution A and solution B is (1.05~5):

1.

5. The method according to any one of claims 1-3, characterized in that, The inner diameter of the pipe is 0.5mm to 2mm.

6. The method according to any one of claims 1-3, characterized in that, The first solvent and the second solvent may be the same or different, and each independently includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The method according to any one of claims 1-3, characterized in that, The dianhydride comprises at least one of 1,2,4,5-pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-biphenyl ether dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride; and / or The diamine includes at least one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, p-phenylenediamine, and m-phenylenediamine.

8. The method according to any one of claims 1-3, wherein the method is characterized in that, The molar ratio of the diamine to the dianhydride is 1:(1~1.1).

9. The method according to any one of claims 1-3, characterized in that, In solution A, the mass concentration of the dianhydride is 5% to 20%.

10. The method according to any one of claims 1-3, characterized in that, The reaction temperature is -10℃ to 40℃; The predetermined residence time of the gas-liquid mixture in the pipeline is 10 min to 3 h.

11. The method according to claim 10, characterized in that, The reaction temperature is 20℃~40℃.

12. The method according to any one of claims 1-3, characterized in that, The polyamic acid has a number-average molecular weight of 8 × 10⁻⁶. 3 g / mol ~50×10 3 g / mol, with a molecular weight distribution coefficient of 2~5.

Images