System and method for preparing polyamic acid by continuous polymerization

Abstract

The present invention provides a system and method for preparing polyamic acid by continuous polymerization. The system for preparing polyamic acid by continuous polymerization provided by the present application controls the flow rate of the first part of dianhydride solution by a dianhydride feed controller A so that the diamine solution and the first part of dianhydride solution are mixed and then subjected to a first prepolymerization reaction in a first microchannel reactor to obtain a first prepolymer; then the flow rate of the second part of dianhydride solution is controlled by a dianhydride feed controller B so that the first prepolymer and the second part of dianhydride solution are mixed and then subjected to a second prepolymerization reaction in a second microchannel reactor to obtain a second prepolymer; finally, the flow rate of the remaining dianhydride solution is controlled by a dianhydride feed controller C so that the remaining dianhydride solution and the second prepolymer are mixed and then subjected to a final polymerization reaction in a twin-screw reactor, and the feeding molar ratio of diamine and dianhydride monomers can be controlled to be close to 1:1, and a polyamide with high molecular weight, narrow distribution and ultra-high viscosity is obtained, and no pipeline blockage is caused.

Description

Technical Field

[0001] The invention relates to the field of preparation of polyamic acid, and in particular to a system and method for preparing polyamic acid by continuous polymerization. Background Art

[0002] Polyimide (PI) is a polymer compound containing imide groups (-CO-N-CO) in its molecular structure. It is known for its excellent comprehensive performance and is listed as one of the most promising engineering plastics in the 21st century. Polyimide is widely used in high-tech fields such as aviation, aerospace, microelectronics, liquid crystal, laser, etc., and is known as the top material of the polymer material pyramid.

[0003] The common synthesis method of polyimide is to obtain polyamic acid by polycondensation of monomers in a non-protonic polar solvent, and then obtain it by high-temperature imidization or chemical imidization. At present, the mainstream polyimide products on the market are all processed by polycondensation of dianhydride and diamine monomers into polyamic acid, so how to produce stable and high-performance polyamic acid has become a key step in the preparation of polyimide. At present, the process used in the industry to prepare polyamic acid is still a single-pot intermittent polymerization method. This process has the disadvantages of poor mass and heat transfer, low production efficiency, poor batch stability, and wide molecular weight distribution. Continuous production is more conducive to the production of products with stable performance than intermittent production. The existing continuous production equipment mainly includes: tubular reactors, kettle reactors in series, microreactors, etc. However, since polyamic acid will generate a large amount of heat as the polymerization reaction proceeds and its viscosity continues to increase, the use of tubular reactors for continuous production is prone to blockage, leading to production stagnation; the mass transfer and heat transfer efficiency of kettle reactors is poor, resulting in a wide molecular weight distribution of the generated product, large fluctuations in product viscosity, long polymerization time, and low production efficiency; the microchannel reactor has high heat exchange efficiency, but when the molar ratio of the two monomers is close to 1:1, the viscosity increases instantly, which can easily cause pipeline blockage.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The main purpose of the present invention is to provide a system and method for preparing polyamic acid by continuous polymerization, so as to solve the problems in the prior art that in the process of continuous production of polyamic acid, a large amount of heat is released as the polymerization reaction proceeds, the viscosity increases, and the tubular reactor is easily blocked, resulting in production stagnation; the kettle reactor has poor mass transfer and heat transfer efficiency, resulting in a wide molecular weight distribution of the generated product and low production efficiency; and the viscosity of the microchannel reactor increases instantly when the feed ratio of diamine and dianhydride monomers is close to 1:1, which easily causes pipeline blockage and makes it impossible to achieve industrial continuous production.

[0006] In order to achieve the above-mentioned object, according to one aspect of the present invention, a system for preparing polyamic acid by continuous polymerization is provided, the system comprising a raw material supply unit, a feed control unit and a reaction unit, the raw material supply unit comprising a diamine supply unit and a dianhydride supply unit, the feed control unit comprising a diamine feed controller, a dianhydride feed controller A, a dianhydride feed controller B and a dianhydride feed controller C, wherein the inlet of the diamine feed controller is connected to the outlet of the diamine supply unit, and the inlets of the dianhydride feed controller A, the dianhydride feed controller B and the dianhydride feed controller C are respectively connected to the outlet of the dianhydride supply unit; the reaction unit comprises a first prepolymerization unit, a second prepolymerization unit and a final polymerization reaction unit connected in sequence, wherein the first prepolymerization reaction unit The prepolymerization reaction unit comprises a first mixer and a first microchannel reactor, the inlet of the first mixer is connected to the outlet of the diamine feed controller and the outlet of the dianhydride feed controller A respectively, and the outlet of the first mixer is connected to the inlet of the first microchannel reactor; the second prepolymerization reaction unit comprises a second mixer and a second microchannel reactor, the inlet of the second mixer is connected to the outlet of the first microchannel reactor and the outlet of the dianhydride feed controller B respectively, and the outlet of the second mixer is connected to the inlet of the second microchannel reactor; the final polymerization reaction unit comprises a third mixer and a twin-screw reactor, the inlet of the third mixer is connected to the outlet of the second microchannel reactor and the outlet of the dianhydride feed controller C respectively, and the outlet of the third mixer is connected to the inlet of the twin-screw reactor.

[0007] Furthermore, the dianhydride supply unit includes a dianhydride supply storage tank A, a dianhydride supply storage tank B and a dianhydride supply storage tank C, the outlet of the dianhydride supply storage tank A is connected to the inlet of the dianhydride feed controller A, the outlet of the dianhydride supply storage tank B is connected to the inlet of the dianhydride feed controller B, and the outlet of the dianhydride supply storage tank C is connected to the inlet of the dianhydride feed controller C.

[0008] Furthermore, the system for preparing polyamic acid by continuous polymerization also includes a product receiving unit, which includes a product storage tank, and an inlet of the product storage tank is connected to an outlet of the twin-screw reactor.

[0009] According to another aspect of the present invention, a method for preparing polyamic acid by continuous polymerization is provided, and the method comprises the following steps: step S1, providing a diamine solution and a dianhydride solution, wherein the molar ratio of the diamine in the diamine solution to the dianhydride in the dianhydride solution is 1:(0.9-1.2), the dianhydride solution is divided into a dianhydride solution A, a dianhydride solution B and a dianhydride solution C, and the molar ratio of the dianhydride in the dianhydride solution A, the dianhydride solution B and the dianhydride solution C is (0.6-0.8):(0.2-0.4):(0.01-0.2); step S2, mixing the diamine solution and the dianhydride solution A in a first mixer and conveying the mixture to a first microchannel reactor for a first prepolymerization reaction to obtain a first prepolymer; step S3, mixing the first prepolymer and the dianhydride solution B in a second mixer and conveying the mixture to a second microchannel reactor for a second prepolymerization reaction to obtain a second prepolymer; step S4, mixing the second prepolymer and the dianhydride solution C in a third mixer and conveying the mixture to a twin-screw reactor for a final polymerization reaction to obtain a polyamic acid reaction liquid.

[0010] Furthermore, the molar ratio of the diamine in the diamine solution to the dianhydride in the dianhydride solution is 1:(1.0-1.05).

[0011] Furthermore, the molar ratio of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C is (0.6-0.8):(0.2-0.4):(0.01-0.15).

[0012] Furthermore, the reaction temperature of the first prepolymerization reaction, the second prepolymerization reaction and the final polymerization reaction is -40°C to 60°C, preferably -20°C to 30°C.

[0013] Furthermore, the rotation speed of the twin-screw reactor is 100-150 rpm.

[0014] Furthermore, the residence time of the first microchannel reactor for the first prepolymerization reaction is 1-20 min.

[0015] Furthermore, the residence time of the second prepolymerization reaction in the second microchannel reactor is 1-10 min.

[0016] Furthermore, the residence time of the final polymerization reaction in the twin-screw reactor is 1-60 min.

[0017] Furthermore, the material flow rate in the first microchannel reactor, the second microchannel reactor and the twin-screw reactor is 0.1-50 g / min, preferably 0.2-30 g / min.

[0018] Furthermore, the solvents of the diamine solution and the dianhydride solution are respectively selected from at least one of dimethyl sulfoxide, N,N'-dimethylacetamide, and N,N'-dimethylformamide.

[0019] Furthermore, the diamine in the diamine solution is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine or 4,4'-diaminodiphenylmethane; the dianhydride in the dianhydride solution is selected from at least one of isobenzoic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bisphenol A diether dianhydride or hexafluoroisopropylphthalic anhydride.

[0020] By applying the technical solution of the present application, the system for preparing polyamic acid by continuous polymerization provided by the present application adopts a dianhydride feed controller A to control the flow rate of the first part of the dianhydride solution so that the diamine solution is first mixed with the first part of the dianhydride solution in a first mixer and then introduced into a first microchannel reactor for a first prepolymerization reaction to obtain a first prepolymer with a lower molecular weight and a lower viscosity; then, the flow rate of the second part of the dianhydride solution is controlled by controlling the dianhydride feed controller B so that the first prepolymer and the second part of the dianhydride solution are mixed in a second mixer and then introduced into a second microchannel reactor for a second prepolymerization reaction to obtain a second prepolymer with a higher molecular weight and a higher viscosity; finally, the flow rate of the remaining dianhydride solution is controlled by the dianhydride feed controller C so that the remaining dianhydride solution and the second prepolymer are mixed in a third mixer and then introduced into a twin-screw reactor for a final polymerization reaction. The system for preparing polyamic acid by continuous polymerization provided in the present application can not only control the feeding molar ratio of diamine and dianhydride monomers to be close to 1:1, thereby obtaining polyamide with high molecular weight, narrow distribution and ultra-high viscosity, but also will not cause pipeline blockage, and can realize industrial continuous production. At the same time, the product has high production efficiency and good batch stability, and has broad application prospects in the field of high-viscosity polyamide products. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 A schematic flow chart of a system for preparing polyamic acid by continuous polymerization provided in some embodiments of the present application is shown.

[0023] The above drawings include the following reference numerals:

[0024] 101. diamine supply storage tank; 102. dianhydride supply storage tank A; 103. dianhydride supply storage tank B; 104. dianhydride supply storage tank C; 105. diamine feed controller; 106. dianhydride feed controller A; 107. dianhydride feed controller B; 108. dianhydride feed controller C; 109. first mixer; 110. second mixer; 111. third mixer; 112. first microchannel reactor; 113. second microchannel reactor; 114. twin-screw reactor; 115. product storage tank. DETAILED DESCRIPTION

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0026] As described in the background technology of this application, the process currently used in the industrial preparation of polyamic acid is still a single-pot intermittent polymerization method, which has the disadvantages of poor mass transfer and heat transfer, low production efficiency, poor batch stability, and wide molecular weight distribution. Continuous production is more conducive to the production of products with stable performance than intermittent production. However, the continuous preparation of polyamic acid using a tubular reactor is prone to blockage of the tubular reactor as the polymerization reaction proceeds, resulting in production stagnation; and the continuous preparation of polyamic acid using a series of kettle reactors has poor mass transfer and heat transfer efficiency, which will lead to a wide molecular weight distribution of the generated product, large fluctuations in product viscosity, and a long polymerization time, and low production efficiency; although the microchannel reactor has high heat exchange efficiency, in the continuous preparation of polyamic acid, when the molar ratio of diamine monomers to dianhydride monomers is close to 1:1, there will be a situation where the viscosity increases instantly, which is easy to cause pipeline blockage. In order to solve these problems, the present application provides a system and method for preparing polyamic acid through continuous polymerization.

[0027] In a first typical embodiment of the present application, a system for preparing polyamic acid by continuous polymerization is provided, the system comprising a raw material supply unit, a feed control unit and a reaction unit connected in sequence; the raw material supply unit comprises a diamine supply unit and a diamine supply unit; the feed control unit comprises a diamine feed controller 105, a dianhydride feed controller A106, a dianhydride feed controller B107 and a dianhydride feed controller C108, wherein the inlet of the diamine feed controller 105 is connected to the outlet of the diamine supply unit, and the inlets of the dianhydride feed controller A106, the dianhydride feed controller B107 and the dianhydride feed controller C108 are respectively connected to the outlet of the dianhydride supply unit; the reaction unit comprises a first prepolymerization reaction unit, a second prepolymerization reaction unit and a final polymerization reaction unit connected in sequence, wherein the first prepolymerization reaction unit comprises a first mixer 109 and a first The microchannel reactor 112, the inlet of the first mixer 109 is respectively connected to the outlet of the diamine feed controller 105 and the outlet of the dianhydride feed controller A106, the outlet of the first mixer 109 is connected to the inlet of the first microchannel reactor 112, the second prepolymerization reaction unit includes a second mixer 110 and a second microchannel reactor 113, the inlet of the second mixer 110 is respectively connected to the outlet of the first microchannel reactor 112 and the outlet of the dianhydride feed controller B107, the outlet of the second mixer 110 is connected to the inlet of the second microchannel reactor 113, the final polymerization reaction unit includes a third mixer 111 and a twin-screw reactor 114, the inlet of the third mixer 111 is respectively connected to the outlet of the second microchannel reactor 113 and the outlet of the dianhydride feed controller C108; the outlet of the third mixer 111 is connected to the inlet of the twin-screw.

[0028] The system for preparing polyamic acid by continuous polymerization provided by the present application controls the flow of dianhydride in the first prepolymerization reaction, the second prepolymerization reaction and the final polymerization reaction respectively by means of dianhydride controller A, dianhydride controller B and dianhydride controller C, and controls the flow of dianhydride solution by means of dianhydride feed controller A106 so that the diamine solution is first mixed with the first part of dianhydride solution in the first mixer 109 and then introduced into the first microchannel reactor 112 for the first prepolymerization reaction to obtain the first prepolymer with lower molecular weight and lower viscosity; and then controls the flow of dianhydride feed controller so that the first prepolymer and the second part of dianhydride solution are mixed in the second mixer 110. The mixture is then introduced into the second microchannel reactor 113 for a second prepolymerization reaction to obtain a second prepolymer with a higher molecular weight and a higher viscosity. Finally, the flow rate of the remaining dianhydride solution is controlled so that the remaining dianhydride solution and the second prepolymer are mixed in the third mixer 111 and then introduced into the twin-screw reactor 114 for a final polymerization reaction. This can not only control the feeding molar ratio of the diamine and dianhydride monomers to be close to 1:1 to obtain a polyamide with a high molecular weight, a narrow distribution and an ultra-high viscosity, but also will not cause pipeline blockage, and can realize industrial continuous production. At the same time, the product has high production efficiency and good batch stability, and has broad application prospects in the field of high-viscosity polyamide products.

[0029] In the present application, the dianhydride supply unit includes a dianhydride supply storage tank, which is respectively input into the first mixer 109, the second mixer 110 and the third mixer 111 through the dianhydride flow controller A, the dianhydride flow controller B and the dianhydride flow controller C, so that the dianhydride stage enters the polymerization process in stages, thereby not only avoiding the violent polymerization phenomenon when the molar ratio of dianhydride and diamine monomer is close to 1:1, but also enabling timely mass transfer and heat transfer, so that the polyamic acid obtained by polymerization not only has high viscosity and large molecular weight, but also narrow molecular weight distribution, and higher product quality.

[0030] In the present application, the diamine supply unit includes a diamine supply storage tank 101 for storing diamine.

[0031] In some specific embodiments, the dianhydride supply unit includes a dianhydride supply tank A102, a dianhydride supply tank B103 and a dianhydride supply tank C104, wherein the outlet of the dianhydride supply tank A102 is connected to the inlet of the dianhydride feed controller A106, the outlet of the dianhydride supply tank B103 is connected to the inlet of the dianhydride feed controller B107, and the outlet of the dianhydride supply tank C104 is connected to the inlet of the dianhydride feed controller C108, thereby storing the dianhydride solution in different dianhydride supply tanks, which is more conducive to the feed control of the dianhydride solution.

[0032] In the process of preparing polyamic acid disclosed at present, in order to avoid excessive viscosity, it adds dianhydride solution in batches, but the concentration of the dianhydride solution added successively is not the same, and the concentration of the dianhydride solution added thereafter is significantly reduced, so as to reduce the viscosity of the product generated in the polymerization reaction process by increasing the consumption of the solvent in the dianhydride solution, avoid pipeline clogging, so that the solvent content in the product produced can be significantly improved, so that its post-processing difficulty is increased. Meanwhile, it needs to prepare the dianhydride solution of different concentrations in the dianhydride solution preparation process, which increases the cumbersomeness of operation. The system of preparing polyamic acid by continuous polymerization provided by the application is arranged by the first mixing vessel 109, the first micro passage reactor 112, the second mixing vessel 110, the second micro passage reactor 113, the third mixing vessel 111 and the twin screw reactor 114 connected in sequence, not only can realize that mixing between raw materials is more uniform, and mass transfer and heat transfer efficiency is high, adopting the dianhydride solution of same concentration, by controlling the addition of the dianhydride solution in different stages of polymerization, high viscosity can be prepared, high solid content, high molecular weight and the polyamic acid reaction solution of narrow molecular weight distribution.

[0033] In order to facilitate the collection of products, the system for preparing polyamic acid by continuous polymerization provided in the present application preferably also includes a product receiving unit, which includes a product storage tank 115, and the inlet of the product storage tank 115 is connected to the outlet of the twin-screw reactor 114 to facilitate the storage of the generated polyamic acid product.

[0034] It should be noted that if the dianhydride raw material used in the system for preparing polyamic acid by continuous polymerization provided in the present application is solid, the first mixer 109, the first microchannel reactor 112, the second mixer 110, the second microchannel reactor 113 and the third mixer 111 may not be used, and the diamine solution may be passed into the twin-screw reactor 114 through the diamine flow controller A, and the solid dianhydride may be directly added into the twin-screw reactor 114 for polymerization.

[0035] In some embodiments, the continuous polymerization system for preparing polyamic acid performs a continuous reaction process as follows:

[0036] (1) Preparation of reaction device: Use inert gas to purge and solvent to clean the reaction equipment to ensure that the equipment is free of water and oxygen. Set the diamine supply tank 101, the dianhydride supply tank A102, the dianhydride supply tank B103, the dianhydride supply tank C104, the first microchannel reactor 112, the second microchannel reactor 113 and the twin-screw reactor 114 to the target temperature, set the twin-screw reactor 114 to a predetermined speed, and start.

[0037] (2) Preparation of monomer solution: Under the protection of inert gas, the dianhydride monomer is mixed with the solvent in proportion to prepare a homogeneous solution of the same or different concentrations, and the diamine monomer is mixed with the solvent to prepare a homogeneous solution.

[0038] (3) Raw material feeding: Control the flow rate of dianhydride feed controller A106, dianhydride feed controller B107 and dianhydride feed controller C108, and start feeding at a certain flow rate.

[0039] (4) Polymerization: The dianhydride monomer and the diamine monomer flow through the first mixer 109, the second mixer 110 and the third mixer 111, and undergo multi-step polymerization reactions in the first microchannel reactor 112, the second microchannel reactor 113 and the twin-screw reactor 114, respectively.

[0040] (5) Product collection: After the viscosity of the polyamic acid reaction liquid in the twin-screw reactor 114 reaches a preset viscosity, it can enter the product receiving unit for storage.

[0041] (6) Cleaning: After the polymerization reaction is completed, the pump sucks in the solvent to clean the first mixer 109, the second mixer 110, the third mixer 111, the first microchannel reactor 112, the second microchannel reactor 113 and the twin-screw reactor 114. After cleaning, turn off the instrument and the power supply.

[0042] In a second typical embodiment of the present application, a method for preparing polyamic acid by continuous polymerization is also provided, the method comprising the following steps: step S1, providing a diamine solution and a dianhydride solution, wherein the molar ratio of the diamine in the diamine solution to the dianhydride in the dianhydride solution is 1:(0.9-1.2); dividing the dianhydride solution into dianhydride solution A, dianhydride solution B and dianhydride solution C, and the molar ratio of the dianhydride in the dianhydride solution A, dianhydride solution B and dianhydride solution C is (0.6-0.8)(0.2-0.4):(0.01-0.2); step S2, The diamine solution and the dianhydride solution A are mixed in the first mixer 109 and then conveyed to the first microchannel reactor 112 for a first prepolymerization reaction to obtain a first prepolymer; in step S3, the first prepolymer and the dianhydride solution B are mixed in the second mixer 110 and then conveyed to the second microchannel reactor 113 for a second prepolymerization reaction to obtain a second prepolymer; in step S4, the second prepolymer and the dianhydride solution C are mixed in the third mixer 111 and then conveyed to the twin-screw reactor 114 for a final polymerization reaction to obtain a polyamic acid reaction liquid.

[0043] The method for preparing polyamic acid by continuous polymerization provided in the present application controls the molar ratio of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C, so that the diamine solution is first mixed with dianhydride solution A in the first mixer 109 and then introduced into the first microchannel reactor 112 for a first prepolymerization reaction to obtain a first prepolymer with a lower molecular weight and a lower viscosity; then the first prepolymer and dianhydride solution B are mixed in the second mixer 110 and then introduced into the second microchannel reactor 113 for a second prepolymerization reaction to obtain a second prepolymer with a higher molecular weight and a higher viscosity. Finally, by controlling the flow rate of the remaining dianhydride solution, the dianhydride solution C and the second prepolymer are mixed in the third mixer 111 and then introduced into the twin-screw reactor 114 for final polymerization. This can not only control the feeding molar ratio of diamine and dianhydride monomers to be 1: (0.9-1.2), close to 1: 1, to obtain a polyamide with high molecular weight, narrow molecular weight distribution and ultra-high viscosity, but also will not cause pipeline blockage, and can realize industrial continuous production. At the same time, the product has high production efficiency and good batch stability, and has broad application prospects in the field of high-viscosity polyamide products.

[0044] In addition, the continuous polymerization method for preparing polyamic acid provided by the present application can effectively regulate the viscosity of the first prepolymer and the second prepolymer by adding the dianhydride solution in batches according to the proportion, avoiding clogging of the first microchannel reactor 112 and the second microchannel reactor 113, and the continuous reaction has high heat exchange efficiency, and can achieve accurate regulation of the viscosity and molecular weight distribution of the polyamide product, and the quality of the product is more stable. At the same time, compared with the traditional autoclave process, the reaction time is shortened and the production efficiency is improved.

[0045] Typically but not limiting, in the present application, based on the molar amount of the diamine monomer in the diamine solution, the amount of dianhydride in the dianhydride solution is 0.9, 0.95, 1.00, 1.05, 1.014, 1.15, 1.2 moles or a range consisting of any two values. In the present application, the molar ratio of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C is (0.6-0.8) (0.2-0.4): (0.01-0.2) means that, based on the total amount of diamine in the diamine solution as 1 mole, the molar amount of dianhydride in dianhydride solution A is 0.6, 0.65, 0.7, 0.75, 0.8 or a range consisting of any two values; the molar amount of dianhydride in dianhydride solution B is 0.2, 0.25, 0.3, 0.35, 0.4 or a range consisting of any two values; the molar amount of dianhydride in dianhydride solution C is 0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.2 or a range consisting of any two values.

[0046] In order to further increase the weight average molecular weight of the generated polyamide product, preferably in step S1, the molar ratio of diamine in the diamine solution and dianhydride in the dianhydride solution is 1:1.0-1.05, such as 1:1.0, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, etc. In particular, when the molar ratio of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C is (0.6-0.8): (0.2-0.4): (0.01-0.05), it is more conducive to increasing the weight average molecular weight of the polyamide acid product and reducing the molecular width of the molecular weight, so that the weight average molecular weight of the product is more uniform and the performance is more superior.

[0047] There is no special restriction on the polymerization temperature in the method for preparing polyamic acid by continuous polymerization provided in the present application, and heating or cooling is not required. In some embodiments, the reaction temperature of the first prepolymerization reaction, the second prepolymerization reaction, and the final polymerization reaction is preferably -40°C to 60°C, especially when the temperature is -20°C to 30°C, it is more conducive to controlling the polymerization reaction to proceed smoothly, and thus more conducive to the generation of a polyamic acid product with a high weight average molecular weight and higher viscosity.

[0048] Typically but not limitatively, the reaction temperatures for the first prepolymerization, the second prepolymerization and the final polymerization are -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C or a range consisting of any two of these values.

[0049] The method for preparing polyamic acid by continuous polymerization provided in the present application has high production efficiency, and the preparation of the polyamic acid reaction liquid can be completed within a few minutes to a few hours. In order to reduce the risk of microchannel blockage, in some embodiments, the residence time of the first prepolymerization reaction in the first channel reactor is 1-20min (such as 1min, 2min, 5min, 8min, 10min, 12min, 15min, 18min, 20min), and the residence time is adjusted according to the different types of dianhydride monomers and diamine monomers used. Preferably, the viscosity of the first prepolymer is controlled at 0-100cps. Similarly, in order to avoid the viscosity of the generated second prepolymer being too high and clogging the second microchannel reactor 113, the residence time of the second prepolymerization reaction in the second microchannel reactor 113 is controlled to be shorter, preferably 1-10min (such as 1min, 2min, 4min, 5min, 8min, 10min), so that the viscosity of the second prepolymer is controlled at 50-300cps. In view of the high viscosity of the second prepolymer and the large stirring capacity of the twin-screw reactor 114, the residence time for the final polymerization reaction in the twin-screw reactor 114 is preferably 1-60 min (e.g., 1 min, 2 min, 5 min, 8 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 60 min) to facilitate the preparation of a polyamic acid product with higher viscosity, larger weight average molecular weight and narrower molecular weight distribution.

[0050] The viscosity of the first prepolymer, the second prepolymer and the polyamic acid reaction solution is the viscosity measured at 25° C. using a NDJ-8T viscometer produced by Shanghai Nirun Intelligent Technology Co., Ltd.

[0051] In the method for preparing polyamic acid by continuous polymerization provided in the present application, the material flow rates in the first microchannel reactor 112, the second microchannel reactor 113 and the twin screw reactor 114 are not limited, and the material flow rates commonly used in the art can be used. In some specific embodiments, the logistics flow rates in the first microchannel reactor 112, the second microchannel reactor 113 and the twin screw reactor 114 are each independently 0.1-50 g / min (such as 0.1 min, 0.2 min, 0.5 min, 0.8 min, 1 min, 2 min, 5 min, 8 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min), and more preferably 0.1~40 g / min.

[0052] In the present application, the solvents used in the diamine solution and the dianhydride solution are both organic solvents, so as to improve the efficiency of the polymerization reaction and reduce the molecular weight distribution width of the generated polymer. The organic solvent is not specifically limited, and any organic solvent commonly used in the art can be used. Specifically, the organic solvents used in the diamine solution and the dianhydride solution are independently selected from any one or more of dimethyl sulfoxide, N,N'-dimethylacetamide, and N,N'-dimethylformamide.

[0053] The method for preparing polyamic acid by continuous polymerization provided in the present application is applicable to a variety of different types of diamine monomers and dianhydride monomers, especially for diamine monomers and dianhydride monomers with stronger rigidity, and is more conducive to the preparation of polyamic acid products with high viscosity, higher weight-average molecular weight and narrower molecular weight distribution.

[0054] In some specific embodiments, the diamine in the diamine solution is selected from any one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine or 4,4'-diaminodiphenylmethane, and the dianhydride in the dianhydride solution is selected from any one or more of isobenzoic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bisphenol A diether dianhydride or hexafluoroisopropylphthalic anhydride.

[0055] The beneficial effects of the present application will be further illustrated below in combination with embodiments and comparative examples.

[0056] Example 1

[0057] like Figure 1As shown, this embodiment provides a system for preparing polyamic acid by continuous polymerization, which includes a raw material supply unit, a feed control unit and a reaction unit connected in sequence; the raw material supply unit includes a diamine supply unit and a diamine supply unit; the feed control unit includes a diamine feed controller 105, a dianhydride feed controller A106, a dianhydride feed controller B107 and a dianhydride feed controller C108, wherein the inlet of the diamine feed controller 105 is connected to the outlet of the diamine supply unit, and the inlets of the dianhydride feed controller A106, the dianhydride feed controller B107 and the dianhydride feed controller C108 are respectively connected to the outlet of the dianhydride supply unit; the reaction unit includes a first prepolymerization reaction unit, a second prepolymerization reaction unit and a final polymerization reaction unit connected in sequence, wherein the first prepolymerization reaction unit includes a first mixer 109 and a first microchannel reaction The inlet of the first mixer 109 is connected to the outlet of the diamine feed controller 105 and the outlet of the dianhydride feed controller A106 respectively, the outlet of the first mixer 109 is connected to the inlet of the first microchannel reactor 112, the second prepolymerization reaction unit includes a second mixer 110 and a second microchannel reactor 113, the inlet of the second mixer 110 is connected to the outlet of the first microchannel reactor 112 and the outlet of the dianhydride feed controller B107 respectively, the outlet of the second mixer 110 is connected to the inlet of the second microchannel reactor 113, the final polymerization reaction unit includes a third mixer 111 and a twin-screw reactor 114, the inlet of the third mixer 111 is connected to the outlet of the second microchannel reactor 113 and the outlet of the dianhydride feed controller B107 respectively; the outlet of the third mixer 111 is connected to the inlet of the twin screw.

[0058] The system for preparing polyamic acid by continuous polymerization provided by the present application controls the flow of dianhydride in the first prepolymerization reaction, the second prepolymerization reaction and the final polymerization reaction respectively by means of dianhydride controller A, dianhydride controller B and dianhydride controller C, and controls the flow of dianhydride solution by means of dianhydride feed controller A106 so that the diamine solution is first mixed with the first part of dianhydride solution in the first mixer 109 and then introduced into the first microchannel reactor 112 for the first prepolymerization reaction to obtain the first prepolymer with lower molecular weight and lower viscosity; and then controls the flow of dianhydride feed controller so that the first prepolymer and the second part of dianhydride solution are mixed in the second mixer 110. The mixture is then introduced into the second microchannel reactor 113 for a second prepolymerization reaction to obtain a second prepolymer with a higher molecular weight and a higher viscosity. Finally, the flow rate of the remaining dianhydride solution is controlled so that the remaining dianhydride solution and the second prepolymer are mixed in the third mixer 111 and then introduced into the twin-screw reactor 114 for a final polymerization reaction. This can not only control the feeding molar ratio of the diamine and dianhydride monomers to be close to 1:1 to obtain a polyamide with a high molecular weight, a narrow distribution and an ultra-high viscosity, but also will not cause pipeline blockage, and can realize industrial continuous production. At the same time, the product has high production efficiency and good batch stability, and has broad application prospects in the field of high-viscosity polyamide products.

[0059] In the present embodiment, the dianhydride supply unit includes dianhydride supply storage tank A102, dianhydride supply storage tank B103 and dianhydride supply storage tank C104, wherein the outlet of dianhydride supply storage tank A102 is connected to the inlet of dianhydride feed controller A106, the outlet of dianhydride supply storage tank B103 is connected to the inlet of dianhydride feed controller B107, and the outlet of dianhydride supply storage tank C104 is connected to the inlet of dianhydride feed controller C108, thereby by storing the dianhydride solution in different dianhydride supply storage tanks respectively, it is more conducive to the feed control of the dianhydride solution. The diamine supply unit includes a diamine supply storage tank 101 for storing diamines.

[0060] In order to facilitate the collection of products, the system for preparing polyamic acid by continuous polymerization provided in the present application also includes a product receiving unit, which includes a product storage tank 115. The inlet of the product storage tank 115 is connected to the outlet of the twin-screw reactor 114 to facilitate the storage of the generated polyamic acid product.

[0061] Example 2

[0062] This embodiment provides a method for preparing polyamic acid by continuous polymerization using 4,4'-diaminodiphenyl ether as a diamine monomer and pyromellitic dianhydride as a dianhydride monomer, which is carried out in the system for preparing polyamic acid by continuous polymerization provided in Example 1, and comprises the following steps:

[0063] (1) Preparation of reaction device: Use nitrogen to purge and use N,N'-dimethylacetamide to clean the reaction equipment to ensure that the equipment is free of water and oxygen. Set the diamine supply tank 101, dianhydride supply tank A102, dianhydride supply tank B103, dianhydride supply tank C104, first microchannel reactor 112, second microchannel reactor 113, and twin-screw reactor 114 to 20°C, set the speed of the twin-screw reactor 114 to 100 rpm, and start.

[0064] (2) Preparation of diamine monomer solution: Under nitrogen protection, 30.0 g of 4,4'-diaminodiphenyl ether monomer (purity 98%) and 112.44 g of N,N'-dimethylacetamide were mixed in a diamine supply tank 101 to prepare a homogeneous solution.

[0065] (3) Preparation of dianhydride solution A: Under nitrogen protection, 22.63 g of pyromellitic dianhydride monomer (purity 99%) and 254.549 g of N,N'-dimethylacetamide were mixed in dianhydride supply tank A102 to prepare a homogeneous solution, thereby obtaining dianhydride solution A.

[0066] (4) Preparation of dianhydride solution B: Under nitrogen protection, 6.468 g of pyromellitic dianhydride monomer (purity 99%) and 72.726 g of N,N'-dimethylacetamide were mixed in dianhydride supply tank B103 to prepare a homogeneous solution.

[0067] (5) Preparation of dianhydride solution C: Under nitrogen protection, 3.234 g of pyromellitic dianhydride monomer (purity 99%) and 36.363 g of N,N'-dimethylacetamide were mixed in dianhydride supply tank C104 to prepare a homogeneous solution.

[0068] (6) Polymerization: The diamine solution is delivered to the first mixer 109 through the diamine feed controller 105, and the dianhydride solution A is delivered to the first mixer 109 through the dianhydride feed controller A106, so that the diamine solution and the dianhydride solution A are evenly mixed in the first mixer 109 and then delivered to the first microchannel reactor 112 for a first prepolymerization reaction, and the residence time of the materials is 8 minutes, thereby obtaining a first prepolymer with a viscosity of 80 cps; the first prepolymer is delivered to the second mixer 110, and the dianhydride solution B is delivered to the second mixer 110 and mixed with the first prepolymer by the dianhydride feed controller B107. After the materials are mixed evenly, they are transported to the second microchannel reactor 113 for a second prepolymerization reaction, and the residence time of the materials in the second microchannel reactor 113 is 4 minutes, and a second prepolymer with a viscosity of 150 cps is obtained; the second prepolymer is transported to the third mixer 111, and the dianhydride solution C is transported to the third mixer 111 through the dianhydride feed controller C108, mixed with the second prepolymer, and then transported to the twin-screw reactor 114 for final polymerization, and the residence time of the materials in the twin-screw reactor 114 is 8 minutes, and a polyamic acid reaction liquid with a viscosity of 10100 cps is obtained. Among them, the feeding rate of the diamine solution is 1.58 g / min; the feeding rate of the dianhydride solution A is 3.07 g / min; the feeding rate of the dianhydride solution B is 0.88 g / min, and the feeding rate of the dianhydride solution C is 0.43 g / min, and the total polymerization time is 20 minutes.

[0069] (7) Product collection: The polyamic acid reaction liquid is discharged from the twin-screw reactor 114 into the product storage tank 115 for storage.

[0070] (8) Cleaning: After the polymerization reaction is completed, the pump sucks N,N'-dimethylacetyl to clean the first mixer 109, the second mixer 110, the third mixer 111, the first microchannel reactor 112, the second microchannel reactor 113 and the twin-screw reactor 114. After cleaning, turn off the instrument and the power supply.

[0071] Example 3

[0072] The difference between this embodiment and embodiment 2 is that in step (6), the residence time of the material in the first microchannel reactor 112 is 15 minutes, the residence time in the second microchannel reactor 113 is 10 minutes, the residence time in the twin-screw reactor 114 is 15 minutes, and the total polymerization time is 40 minutes.

[0073] Example 4

[0074] The difference between this embodiment and embodiment 2 is that in step (1), the diamine supply tank 101, the dianhydride supply tank A102, the dianhydride supply tank B103, the dianhydride supply tank C104, the first microchannel reactor 112, the second microchannel reactor 113, and the twin-screw reactor 114 are respectively set to 10°C.

[0075] Example 5

[0076] The difference between this embodiment and embodiment 2 is that in step (1), the rotation speed of the twin-screw reactor 114 is set to 150 rpm.

[0077] Example 6

[0078] The difference between this embodiment and embodiment 2 is that in steps (3) to (5), the amounts of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C are adjusted so that the molar ratio of the three is 0.8:0.2:0.1, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.1.

[0079] Example 7

[0080] The difference between this embodiment and embodiment 2 is that in (3)-(5), the amount of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C is adjusted so that the molar ratio of the three is 0.8:0.2:0.15, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.15.

[0081] Example 8

[0082] The difference between this embodiment and embodiment 2 is that in (3)-(5), the amounts of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C are adjusted so that the molar ratio of the three is 0.8:0.2:0.2, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.2.

[0083] Example 9

[0084] The difference between this embodiment and embodiment 2 is that in (3)-(5), the amount of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C is adjusted so that the molar ratio of the three is 0.6:0.4:0.05, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.05.

[0085] Example 10

[0086] The difference between this embodiment and embodiment 2 is that in (3)-(5), the amounts of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C are adjusted so that the molar ratio of the three is 0.8:0.2:0.01, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.01.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing polyamic acid, comprising the following steps:

[0089] (1) Preparation of the kettle reactor: At 75°C, the reaction equipment was evacuated for 1 hour, during which nitrogen was replaced three times to ensure that the equipment was anhydrous and oxygen-free. After the replacement was completed, the reaction equipment was connected to the temperature control system and the temperature was set to 20°C;

[0090] (2) Preparation of diamine solution: Under nitrogen protection, add 4.21 g of 4,4'-diaminodiphenyl ether (purity 98%) into a kettle reactor, quickly pump out and replace nitrogen three times, then add 30 mL of N,N'-dimethylacetamide and stir until the solid is dissolved to obtain a diamine solution;

[0091] (3) Preparation of dianhydride solution: Weigh 4.68 g of dry pyromellitic dianhydride (purity 99%) into a single-necked bottle, add 55 mL of N,N'-dimethylacetamide under nitrogen protection, and stir until the solid is dissolved to obtain a dianhydride solution;

[0092] (4) Polymerization reaction: transfer the dianhydride solution to a constant pressure dropping funnel and start to slowly add the solution at a rate of 0.5 mL / s. Continue the reaction for 4 h. After the polymerization is completed, remove the polymerization product, clean the polymerization equipment, and turn off the instrument and power supply.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 2 is that the twin-screw reactor 114 is not used for final polymerization, and the second prepolymer is the final product polyamic acid reaction liquid obtained.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 2 is that in step (6), the diamine solution and the dianhydride solution A are directly transported to the first microchannel reactor 112 for a first prepolymerization reaction, and then the first prepolymer and the dianhydride solution B are directly transported to the second microchannel reactor 113 for a second prepolymerization reaction, and finally the second prepolymer and the dianhydride solution C are transported to the twin-screw reactor 114 for a final polymerization reaction.

[0097] Comparative Example 4

[0098] The difference between this comparative example and Example 2 is that the amounts of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C are adjusted so that the molar ratio of the three is 0.7:0.3:0.25, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.25.

[0099] Comparative Example 5

[0100] The difference between this comparative example and Example 2 is that the amounts of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C are adjusted so that the molar ratio of the three is 0.55:0.45:0.1, and the molar ratio of diamine monomer to dianhydride monomer in the twin-screw reactor 114 is 1:1.1.

[0101] Test example

[0102] The dynamic viscosities of the first prepolymer, the second prepolymer and the obtained polyamic acid product in the example were measured respectively, and the weight average molecular weight and molecular weight distribution width of the polyamic acid product obtained after extracting the polyamic acid reaction solution were measured. The results are shown in Table 1 below.

[0103] Table 1

[0104]

[0105] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0106] The method for preparing polyamic acid by continuous polymerization provided in the present application controls the molar ratio of dianhydride in dianhydride solution A, dianhydride solution B and dianhydride solution C, so that the diamine solution is first mixed with dianhydride solution A in the first mixer 109 and then introduced into the first microchannel reactor 112 for a first prepolymerization reaction to obtain a first prepolymer with a lower molecular weight and a lower viscosity; then the first prepolymer and dianhydride solution B are mixed in the second mixer 110 and then introduced into the second microchannel reactor 113 for a second prepolymerization reaction to obtain a second prepolymer with a higher molecular weight and a higher viscosity. Finally, by controlling the flow rate of the remaining dianhydride solution, the dianhydride solution C and the second prepolymer are mixed in the third mixer 111 and then introduced into the twin-screw reactor 114 for final polymerization. This can not only control the feeding molar ratio of diamine and dianhydride monomers to be 1: (0.9-1.2), close to 1: 1, to obtain a polyamide with high molecular weight, narrow molecular weight distribution and ultra-high viscosity, but also will not cause pipeline blockage, and can realize industrial continuous production. At the same time, the product has high production efficiency and good batch stability, and has broad application prospects in the field of high-viscosity polyamide products.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing polyamic acid by continuous polymerization, characterized in that: The method comprises the following steps: Step S1, providing a diamine solution and a dianhydride solution, wherein the molar ratio of the diamine in the diamine solution to the dianhydride in the dianhydride solution is 1:(1.0-1.05); dividing the dianhydride solution into dianhydride solution A, dianhydride solution B and dianhydride solution C, and the molar ratio of the dianhydride in the dianhydride solution A, the dianhydride solution B and the dianhydride solution C is (0.6-0.8):(0.2-0.4):(0.01-0.15); Step S2, mixing the diamine solution and the dianhydride solution A in a first mixer (109), and then transporting the mixture to a first microchannel reactor (112) for a first prepolymerization reaction to obtain a first prepolymer; Step S3, mixing the first prepolymer and the dianhydride solution B in a second mixer (110) and then transporting the mixture to a second microchannel reactor (113) for a second prepolymerization reaction to obtain a second prepolymer; Step S4, mixing the second prepolymer and the dianhydride solution C in a third mixer (111), and then conveying the mixture to a twin-screw reactor (114) for final polymerization to obtain a polyamic acid reaction liquid; The diamine in the diamine solution is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dihydroxybenzidine or 4,4'-diaminodiphenylmethane; The dianhydride in the dianhydride solution is selected from at least one of benzoic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, bisphenol A type diether dianhydride or hexafluoroisopropylphthalic anhydride; The reaction temperature of the first prepolymerization reaction, the second prepolymerization reaction and the final polymerization reaction is -10°C to 20°C; The rotation speed of the twin-screw reactor (114) is 100-150 rpm; The residence time of the first microchannel reactor (112) for the first prepolymerization reaction is 1-20 min; the viscosity of the first prepolymer is 0-100 cps; The residence time of the second prepolymerization reaction in the second microchannel reactor (113) is 1-10 min, and the viscosity of the second prepolymer is 50-300 cps; The residence time of the final polymerization reaction in the twin-screw reactor (114) is 1-60 min; The method is carried out in a system for preparing polyamic acid by continuous polymerization, wherein the system comprises: A raw material supply unit, wherein the raw material supply unit comprises a diamine supply unit and a dianhydride supply unit; A feed control unit, the feed control unit comprising a diamine feed controller (105), a dianhydride feed controller A (106), a dianhydride feed controller B (107) and a dianhydride feed controller C (108), wherein the inlet of the diamine feed controller (105) is connected to the outlet of the diamine supply unit; the inlets of the dianhydride feed controller A (106), the dianhydride feed controller B (107) and the dianhydride feed controller C (108) are respectively connected to the outlet of the dianhydride supply unit; A reaction unit, wherein the reaction unit comprises a first prepolymerization reaction unit, a second prepolymerization reaction unit and a final polymerization reaction unit connected in sequence, wherein the first prepolymerization reaction unit comprises a first mixer (109) and a first microchannel reactor (112), the inlet of the first mixer (109) is respectively connected to the outlet of the diamine feed controller (105) and the outlet of the dianhydride feed controller A (106), and the outlet of the first mixer (109) is connected to the inlet of the first microchannel reactor (112); the second prepolymerization reaction unit comprises a second mixer (110) and a second microchannel reactor (113), the The inlet of the second mixer (110) is respectively connected to the outlet of the first microchannel reactor (112) and the outlet of the dianhydride feed controller B (107), and the outlet of the second mixer (110) is connected to the inlet of the second microchannel reactor (113); the final polymerization reaction unit comprises a third mixer (111) and a twin-screw reactor (114), the inlet of the third mixer (111) is respectively connected to the outlet of the second microchannel reactor (113) and the outlet of the dianhydride feed controller C (108), and the outlet of the third mixer (111) is connected to the inlet of the twin-screw reactor (114).

2. The method according to claim 1, characterized in that the material flow rate in the first microchannel reactor (112), the second microchannel reactor (113), and the twin-screw reactor (114) is 0.1-50 g / min.

3. The method according to claim 1 or 2, characterized in that: The solvents of the diamine solution and the dianhydride solution are respectively selected from at least one of dimethyl sulfoxide, N,N'-dimethylacetamide and N,N'-dimethylformamide.

4. The method according to claim 1, characterized in that: In the system, the dianhydride supply unit includes a dianhydride supply storage tank A (102), a dianhydride supply storage tank B (103) and a dianhydride supply storage tank C (104), wherein the outlet of the dianhydride supply storage tank A (102) is connected to the inlet of the dianhydride feed controller A (106), the outlet of the dianhydride supply storage tank B (103) is connected to the inlet of the dianhydride feed controller B (107), and the outlet of the dianhydride supply storage tank C (104) is connected to the inlet of the dianhydride feed controller C (108).

5. The method according to claim 1, characterized in that The system further comprises a product receiving unit, wherein the product receiving unit comprises a product storage tank (115), wherein an inlet of the product storage tank (115) is connected to an outlet of the twin-screw reactor (114).

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