A process for the continuous production of high performance polyimide precursor polyamic acid

Abstract

The application provides a process for continuously preparing high-performance polyimide precursor polyamic acid, and a device used in the process comprises a feeding device, a reaction system and a temperature control system. The amount of heat released in the whole reaction process is controlled through two measures of regulating the flow of a metering pump at a feeding port and stepwise temperature control; the mixing section, the prepolymerization section and the tackification section in a transparent kettle body can all achieve ideal stirring effects by using a coaxial asynchronous motor, so that the molar ratio of amine and anhydride functional groups at any position in the reactor remains consistent at the same time, thereby obtaining a polymer with extremely narrow molecular weight distribution; and the above measures fundamentally solve the problems of mass transfer and heat transfer, so that the polymerization process and the polymerization reaction mechanism are fully matched, and polyamic acid with good performance, good storage stability and narrower molecular weight distribution is prepared.

Description

Technical Field

[0001] This invention relates to polyamic acid, specifically to the apparatus and process for synthesizing polyamic acid. Background Technology

[0002] Polyimide is a class of polymers containing imide rings in its main chain, and it is one of the best-performing organic polymer materials. Polyimide possesses excellent insulation properties (F to H class insulation) and superior mechanical properties over a wide temperature range (-200 to 300°C). As a top-tier specialty engineering plastic among polymer synthetic materials, it has been widely used in aerospace, microelectronics, and other fields since its first commercialization by DuPont in the 1960s. Due to its excellent overall performance, it is hailed as a problem-solving expert and one of the most promising engineering plastics of the 21st century.

[0003] After more than half a century of development, my country's polyimide industry has achieved self-sufficiency in electrical insulation applications. However, domestically produced polyimide films lag significantly behind their foreign counterparts in dimensional stability, mechanical properties, coefficient of thermal expansion, and hygroscopicity, particularly exhibiting substantial batch-to-batch stability variations. This hinders their application in high-end fields such as microelectronics and aerospace, severely limiting the development of these sectors in my country. The booming development of smart terminals like mobile phones and new energy vehicles has created an increasingly urgent demand for high-end polyimide products, further highlighting the weaknesses of my country's polyimide industry. These issues urgently require breakthroughs and solutions from industry professionals.

[0004] Currently, the industrial-scale preparation process of polyimide in my country involves dissolving the monomer diamine in a polar solvent, then slowly adding solid dianhydride to the diamine solution for slow polymerization to obtain the polyimide precursor polyamic acid. The polyamic acid is then processed into various polyimide products such as films, fibers, foams, composite materials, and engineering plastics through chemical or thermal methods. Currently, mainstream polyimide products on the market are all derived from dianhydride and diamine monomers through polymerization and processing into polyamic acid. Therefore, how to stably prepare high-performance polyamic acid is one of the key points for polyimide products. Polyamic acid, the polyimide precursor, is commonly known in the industry as polyimide slurry, and its English name is PI varnish. The polyamic acid described in this article is consistent with the industry's generally accepted definition.

[0005] To successfully prepare high-performance and batch-stable polyimide products, solutions need to be found in three aspects: formulation, polymerization process, and processing. Regarding formulation, Chinese companies and research institutions have conducted in-depth research and published numerous papers and patents, showing a relatively small gap with leading international companies such as DuPont, Ube, and Kaneka. However, research reports on polymerization processes are scarce, and the published reports have not addressed the fundamental problems of polyimide polymerization. Currently, the industrially used polymerization process is still single-reactor batch polymerization. This process is highly incompatible with the polymerization mechanism of polyamic acid, the precursor of polyimide, resulting in serious defects such as poor mass and heat transfer, low production efficiency, and poor batch stability. This makes it difficult to prepare high-performance and stable polyamic acid precursors, leading to my country's continued heavy reliance on imports for mid-to-high-end polyimide products. Therefore, innovative development of new polyamic acid precursor polymerization technology is a key factor in breaking through the bottleneck of polyimide as a high-end strategic material and promoting the high-quality development of my country's polyimide industry.

[0006] Because the reaction between dianhydrides and diamines is extremely rapid, with a rate constant reaching up to 0.6 L / mol·s, and is accompanied by intense exothermic reactions, the preparation of high-performance and stable polyamic acids requires addressing two major challenges: mass transfer and heat transfer. Current polymerization processes employ two main methods: low-temperature polymerization and single-reactor batch polymerization with slow, solid-state feeding. These methods present several problems.

[0007] 1. Because the polymerization mechanism of polyamic acid, the precursor of polyimide, is intermolecular bifunctional ring-opening addition polymerization, rather than the condensation polymerization seen on the surface of the polymer structure, if the polymerization reactor is divided into countless infinitely small polymerization units, the intermolecular bifunctional polymerization mechanism requires that the molar ratio of amine and anhydride functional groups that can participate in the reaction in each tiny polymerization unit be as equal as possible at the same time point. Only in this way can the polymerization reaction mechanism be closely approximated, and high-performance polyamic acid with high molecular weight, narrow distribution, and good storage stability be prepared efficiently and stably, and the structural characteristics of different formulations be maximized. In reality, existing single-reactor batch polymerization processes are characterized by the following: First, the designed amount of diamine monomer is dissolved, and then the dianhydride monomer is added in solid form from the top of the reactor in multiple batches. As a result, the molar ratio of dianhydride to diamine at any point in time from the start to the end of the reaction differs significantly from the molar ratio of dianhydride to diamine at points farther from the addition point. Although the total molar ratio after addition is relatively controllable, in reality, from a microscopic perspective, the molar ratio at every moment and at every location during the reaction is uncontrollable. Furthermore, as the reaction proceeds, the system viscosity gradually increases, and the difficulty of mass and heat transfer gradually increases. Combined with the different end-group reactivity at different degrees of polymerization, this causes a severe imbalance in the molar ratio throughout the reaction process. From a macroscopic perspective, the viscosity increase within the reaction system is extremely uneven. The final result is a wider molecular weight distribution, longer feeding time, and lower production efficiency.

[0008] 2. As it is a solid-liquid two-phase reaction, the dissolution and polymerization of dianhydride occur simultaneously. At this time, the polymerization reaction occurs on the surface of the solid particles of dianhydride, and the polymerization rate is very fast. As a result, the dianhydride is easily encapsulated by the polymer and is difficult to dissolve. In severe cases, it may even clump, adhere to the stirring paddle, reaction vessel wall or bottom, causing some dianhydride monomers to be unable to continue to participate in the reaction. The molar ratio deviates significantly from the formula design value, and polyamic acid with the required viscosity cannot be obtained.

[0009] 3. Because the dianhydride is added from the top, the heat release is too concentrated at the local contact point between the dianhydride and the reaction system, which often easily leads to side reactions and causes polyamic acid gelation. Macroscopically, this results in transparent particles with significantly different refractive indices appearing in the polyamic acid solution.

[0010] 4. Due to the wide molecular weight distribution, low molecular weight polyamic acid has high end group reactivity, which can lead to degradation of polyamic acid during storage and reduce storage stability.

[0011] 5. Due to the poor batch-to-batch reproducibility of the dianhydride dissolution and polymerization rates resulting from this polymerization process, the viscosity often deviates from the target value after the final batch is fed. Operators need to rely on experience to add dianhydride or diamine monomers to increase or decrease the viscosity to achieve the target value. This results in very poor batch stability, further amplifying the defects of this polymerization process.

[0012] 6. Since the mass and heat transfer problems in the reaction process cannot be fundamentally solved, the only solution is to add materials in batches and extend the reaction time to slow down the exothermic reaction and avoid agglomeration. This results in a long single-reactor reaction cycle, which fails to take advantage of the fast polymerization speed and makes it difficult to scale up further. This greatly limits the production efficiency per unit time and per unit space and increases production costs.

[0013] In summary, the existing single-reactor batch polymerization process has the following drawbacks: the prepared polyamic acid has a wide molecular weight distribution, poor batch stability, low production efficiency, and poor storage stability.

[0014] Therefore, fundamentally solving the mass and heat transfer problems and developing polymerization equipment and processes that conform to the polymerization reaction mechanism of polyamic acid, the precursor of polyimide, and fully utilize the characteristics of the polymerization reaction are the keys to overcoming the above problems. Summary of the Invention

[0015] This invention overcomes the shortcomings of the traditional polymerization process and independently developed a polymerization device and process for the continuous preparation of high-performance polyimide precursor polyamic acid, filling a gap in the domestic polyimide field.

[0016] To achieve the effects of this invention, the following technical solution is provided:

[0017] A continuous process for preparing high-performance polyimide precursor polyamic acid, the apparatus for continuous preparation of high-performance polyimide precursor polyamic acid includes a feeding device, a reaction system, and a temperature control system. The feeding device includes a first dissolving vessel, a second dissolving vessel, a third dissolving vessel, a first metering pump, a second metering pump, a third metering pump, and a fourth metering pump. The reaction system includes a transparent vessel body and a discharge port. The transparent vessel body includes a mixing section, a prepolymerization section, and a thickening section. The prepolymerization section is located above the thickening section, and the mixing section is located above the prepolymerization section. The mixing section is equipped with... It has a first inlet, a second inlet, and a third inlet, and a fourth inlet is provided on the thickening section; the first dissolving vessel is connected to the first inlet provided on the mixing section of the transparent vessel through the first metering pump, the second dissolving vessel is connected to the second inlet provided on the mixing section of the transparent vessel through the second metering pump, the third dissolving vessel is connected to the third inlet provided on the mixing section of the transparent vessel through the third metering pump, and the first dissolving vessel is connected to the fourth inlet provided on the thickening section of the transparent vessel through the fourth metering pump;

[0018] A first partition is provided between the mixing section and the prepolymerization section, and a first check valve is provided on the first partition. A second partition is provided between the prepolymerization section and the thickening section, and a second check valve is provided on the second partition.

[0019] The temperature control system includes a first temperature control device, a second temperature control device, and a third temperature control device; the mixing section is connected to the first temperature control device, the prepolymerization section is connected to the second temperature control device, and the thickening section is connected to the third temperature control device;

[0020] The transparent vessel is equipped with a high-speed stirring motor and a low-speed stirring motor, which are connected by a stirring shaft that runs through the mixing section, the prepolymerization section, and the thickening section.

[0021] The stirring shaft is equipped with a stirrer. A first stirrer is provided on the stirring shaft that passes through the mixing section and the prepolymerization section. The first stirrer is a three-blade or four-blade oblique-blade stirrer and is driven by the high-speed stirring motor. A second stirrer is provided on the stirring shaft that passes through the thickening section. The second stirrer is a double-ribbon stirrer and is driven by the low-speed stirring motor.

[0022] The continuous preparation process for high-performance polyimide precursor polyamic acid includes the following steps:

[0023] S1: Add 100 parts of dianhydride monomer to the first dissolving vessel by molar ratio, then add 400 parts of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0024] S2: Add 99.5 parts of diamine monomer to the second dissolving vessel by molar ratio, then add 400 parts of N,N-dimethylformamide to the second dissolving vessel and mix evenly;

[0025] S3: Add 0.1 parts of additive to the third dissolving vessel by molar ratio, then add 2 parts of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0026] S4: Set the high-speed stirring motor speed to 300~1000rpm and the low-speed stirring motor speed to 50~500rpm;

[0027] S5: Set the first temperature control device to -50~-10℃, the second temperature control device to -30~0℃, and the third temperature control device to -10~40℃;

[0028] S6: Using a meter, simultaneously start the first, second, and third feed pumps to begin feeding. Set the flow rate of the first feed pump to 1~10 parts / min, the flow rate of the second feed pump to 1.5~15 parts / min, and the flow rate of the third feed pump to 0.001~0.005 parts / min.

[0029] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.45~5 parts / min;

[0030] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0031] Preferably, the dianhydride monomer in step S1 is one or two of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-oxobisphthalic anhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0032] Preferably, the diamine monomer in step S2 is one or two of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, and 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0033] Preferably, the additive in step S3 is one of the following: dicalcium phosphate, nano alumina, nano silica, nano titanium dioxide, and nano carbon black.

[0034] The beneficial effects of this invention are as follows:

[0035] 1. The transparent reactor of the continuous polymerization apparatus designed in this invention is divided into a mixing section, a prepolymerization section, and a thickening section. The dianhydride and diamine monomer are first mixed in the mixing section, which greatly inhibits the monomer reactivity and reduces the reaction rate. At the same time, high-speed stirring ensures thorough mixing and solves the mass transfer problem.

[0036] 2. The reaction temperature of the prepolymerization section is controlled by two measures: adjusting the molar ratio using a metering pump and using a temperature control system. After thorough mixing in the mixing section, the materials enter the prepolymerization section. At this point, the temperature in the prepolymerization section is higher than in the mixing section, allowing the polymerization reaction to proceed rapidly while simultaneously enabling the rapid transfer of heat through the temperature control system, thus stabilizing the polymerization reaction at a specific temperature. Before the reaction in the prepolymerization section, the materials have been thoroughly mixed, ensuring a consistent molar ratio of amine and anhydride functional groups throughout the transparent reactor, resulting in a prepolymer with a very narrow molecular weight distribution. This stage primarily controls the exothermic reaction. The prepolymer then enters the thickening section, where it reacts with the remaining... The remaining monomers, dianhydrides or diamines, are mixed at the inlet of the thickening section and continue to react, further increasing the molecular weight until the designed value is reached. Since the viscosity of the polymer in the thickening section increases rapidly, the stirring speed used in the thickening section cannot be kept consistent with that in the prepolymerization section. This application achieves this function by using a coaxial asynchronous motor. Because the end-group reactivity of the prepolymer in the thickening section is relatively weak, and the remaining monomers are fed in solution, the reaction is a homogeneous reaction. The molar ratio of monomers to prepolymer end-groups can quickly reach the equilibrium molar ratio. At the same time, because the amount of this monomer added accounts for a small proportion of the total amount, the heat release is very small. Therefore, the temperature can be further increased to accelerate the reaction, promote the reaction, and improve production efficiency.

[0037] 3. This invention spatially separates mass and heat transfer. First, mixing is performed to achieve the designed molar ratio of reactive functional groups. Then, a prepolymerization reaction is carried out, controlling the exothermic reaction. Finally, a further feedstock reaction is conducted to achieve the designed molecular weight and molecular weight distribution of the polymer. This ensures that the reaction process is consistent with the theoretical reaction mechanism.

[0038] 4. The tubular reactor of the present invention can realize continuous feeding and discharging, giving full play to the advantage of the fast polymerization reaction of polyamic acid, improving production efficiency, and improving the overall performance and batch stability of the product. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the apparatus used for the continuous preparation of polyamic acid, a high-performance polyimide precursor.

[0040] The reference numerals in the attached diagrams are as follows: First dissolving vessel 1-11, Second dissolving vessel 1-21, Third dissolving vessel 1-31, First metering pump 1-12, Second metering pump 1-22, Third metering pump 1-32, Fourth metering pump 1-13, First feed inlet 6-1, Second feed inlet 6-2, Third feed inlet 6-3, Fourth feed inlet 6-4, Mixing section 4-1, Prepolymerization section 4-2, Thickening section 4-3, First baffle 4-41, Second baffle 4-42, First check valve 4-51, Second check valve 4-52, High-speed stirring motor 4-61, Low-speed stirring motor 4-62, First stirrer 4-71, Second stirrer 4-72, First temperature control device 5-51, Second temperature control device 5-52, Third temperature control device 5-53, Discharge port 7, Stirring shaft 8. Detailed Implementation

[0041] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0042] Example 1

[0043] The apparatus for continuous preparation of high-performance polyimide precursor polyamic acid includes a feeding device, a reaction system, and a temperature control system. The reaction system includes an outlet 8 and a transparent vessel. The feeding device includes a first dissolving vessel 1-11, a second dissolving vessel 1-21, a third dissolving vessel 1-31, a first metering pump 1-12, a second metering pump 1-22, a third metering pump 1-32, and a fourth metering pump 1-13. The transparent vessel includes a mixing section 4-1, a prepolymerization section 4-2, and a thickening section 4-3. The prepolymerization section 4-2 is located above the thickening section 4-3, and the mixing section 4-1 is located above the prepolymerization section 4-2. The mixing section 4-1 is provided with a first inlet 6-1, a second inlet 6-2, and a third inlet 6-3. A fourth inlet 6-4 is provided on the thickening section 4-3, and a first dissolving vessel 1-11 is connected to the first inlet 6-1 on the mixing section 4-1 in the transparent vessel body via a first metering pump 1-12. A second dissolving vessel 1-21 is connected to the second inlet 6-2 on the mixing section 4-1 in the transparent vessel body via a second metering pump 1-22. A third dissolving vessel 1-31 is connected to the third inlet 6-3 on the mixing section 4-1 in the transparent vessel body via a third metering pump 1-32. The first dissolving vessel 1-11 is connected to the fourth inlet 6-4 on the thickening section 4-3 in the transparent vessel body via a fourth metering pump 1-13. The metering pumps are used to control the feed rate, and the dissolving vessels are used to dissolve the reactants.

[0044] A first partition 4-41 is provided between the mixing section 4-1 and the prepolymerization section 4-2, and a first check valve 4-51 is provided on the first partition 4-41. A second partition 4-42 is provided between the prepolymerization section 4-2 and the thickening section 4-3, and a second check valve 4-52 is provided on the second partition 4-42. In this embodiment, the volume of the transparent vessel is 1000ml. Preferably, the aspect ratio of the transparent vessel is set to 6, wherein the aspect ratio of the mixing section 4-1 is set to 1; the aspect ratio of the prepolymerization section 4-2 is set to 1; and the aspect ratio of the thickening section 4-3 is set to 4. This invention separates the mixing section, prepolymerization section, and thickening section with partitions, and at the same time, provides one-way flow check valves on the partitions to ensure that the materials inside the reaction system are always in one-way flow between the functional areas. The temperature control system includes a first temperature control device 5-51, a second temperature control device 5-52, and a third temperature control device 5-53. In this embodiment, the temperature control device is a refrigeration-heating circulator used to control the temperature inside the transparent reactor, which is existing technology. The mixing section 4-1 is connected to the first temperature control device 5-51 via a circulation pipe, the prepolymerization section 4-2 is connected to the second temperature control device 5-52 via a circulation pipe, and the thickening section 4-3 is connected to the third temperature control device 5-53 via a circulation pipe. The first temperature control device is used to suppress the reaction in the mixing section, ensuring that the materials are only physically mixed without chemical reaction at this stage. The second temperature control device is used to remove the heat generated by the prepolymerization reaction in a timely manner, preventing overheating and side reactions that could reduce the effectiveness of the invention. The purpose of the third temperature control is to enhance the reactivity of the polymer end groups in the thickening section, accelerate the reaction, obtain polymers with larger molecular weights, shorten the reaction time, and improve production efficiency.

[0045] The transparent vessel is equipped with a high-speed stirring motor 4-61 and a low-speed stirring motor 4-62. The high-speed stirring motor 4-61 and the low-speed stirring motor 4-62 are connected by a stirring shaft 8 that runs through the mixing section 4-1, the prepolymerization section 4-2, and the thickening section 4-3.

[0046] A stirrer is installed on the stirring shaft 8. A first stirrer 4-71, a three-bladed oblique-blade stirrer, is installed on the stirring shaft 8 that passes through the mixing section 4-1 and the prepolymerization section 4-2. The first stirrer 4-71 is driven by the high-speed stirring motor 4-61. A second stirrer 4-72, a double-ribbon stirrer, is installed on the stirring shaft 8 that passes through the thickening section 4-3. The second stirrer 4-72 is driven by the low-speed stirring motor 4-62. Because the viscosity of the mixing and prepolymerization sections is low, a high-speed stirrer can quickly achieve the desired mixing effect, which is beneficial for mass transfer. The viscosity of the thickening section is higher, making it difficult to use the same speed as the mixing and prepolymerization sections. Therefore, a coaxial asynchronous stirring system is adopted to ensure that the materials in the mixing, prepolymerization, and thickening sections can achieve the desired mixing effect in a short time.

[0047] Example 2

[0048] This embodiment provides a continuous process for preparing high-performance polyimide precursor polyamic acid, which is implemented using the apparatus provided in Example 1. The process specifically includes the following steps:

[0049] S1: Add 10 mol of pyromellitic anhydride to the first dissolving vessel, then add 40 mol of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0050] S2: Add 9.95 mol of p-phenylenediamine to the second dissolving vessel, then add 40 mol of N,N-dimethylformamide to the second dissolving vessel and mix evenly;

[0051] S3: Add 0.01 mol of dicalcium phosphate to the third dissolving vessel, then add 0.2 mol of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0052] S4: Set the high-speed mixing motor speed to 300 rpm and the low-speed mixing motor speed to 50 rpm;

[0053] S5: Set the first temperature control device to -50℃, the second temperature control device to -30℃, and the third temperature control device to -10℃;

[0054] S6: Simultaneously start the first, second, and third feed pumps to begin feeding. Set the flow rate of the first feed pump to 0.1 mol / min, the flow rate of the second feed pump to 0.15 mol / min, and the flow rate of the third feed pump to 0.0001 mol / min.

[0055] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.045 mol / min;

[0056] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0057] Example 3

[0058] This embodiment provides a continuous process for preparing high-performance polyimide precursor polyamic acid, which is implemented using the apparatus provided in Example 1. The process specifically includes the following steps:

[0059] S1: Add 10 mol of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride to the first dissolving vessel, then add 40 mol of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0060] S2: Add 9.95 mol of m-phenylenediamine to the second dissolving vessel, then add 40 mol of N,N-dimethylformamide to the second dissolving vessel and mix evenly;

[0061] S3: Add 0.01 mol of nano-alumina to the third dissolving vessel, then add 0.2 mol of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0062] S4: Set the high-speed mixing motor speed to 1000 rpm and the low-speed mixing motor speed to 500 rpm;

[0063] S5: Set the first temperature control device to -10℃, the second temperature control device to 0℃, and the third temperature control device to 40℃;

[0064] S6: Simultaneously start the first feed pump, the second feed pump, and the third feed pump to begin feeding. Set the flow rate of the first feed pump to 1 mol / min, the flow rate of the second feed pump to 1.5 mol / min, and the flow rate of the third feed pump to 0.0005 mol / min.

[0065] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.5 mol / min;

[0066] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0067] Example 4

[0068] This embodiment provides a continuous process for preparing high-performance polyimide precursor polyamic acid, which is implemented using the apparatus provided in Example 1. The process specifically includes the following steps:

[0069] S1: Add 10 mol of 4,4'-oxophthalic anhydride to the first dissolving vessel, then add 40 mol of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0070] S2: Add 9.95 mol of 4,4'-diaminodiphenyl ether to the second dissolving vessel, then add 40 mol of N,N-dimethylformamide to the second dissolving vessel and mix evenly;

[0071] S3: Add 0.01 mol of nano-silica to the third dissolving vessel, then add 0.2 mol of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0072] S4: Set the high-speed mixing motor speed to 650 rpm and the low-speed mixing motor speed to 275 rpm;

[0073] S5: Set the first temperature control device to -30℃, the second temperature control device to -15℃, and the third temperature control device to 15℃;

[0074] S6: Simultaneously start the first feed pump, the second feed pump, and the third feed pump to begin feeding. Set the flow rate of the first feed pump to 0.55 mol / min, the flow rate of the second feed pump to 0.825 mol / min, and the flow rate of the third feed pump to 0.0003 mol / min.

[0075] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.2725 mol / min;

[0076] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0077] Example 5

[0078] This embodiment provides a continuous process for preparing high-performance polyimide precursor polyamic acid, which is implemented using the apparatus provided in Example 1. The process specifically includes the following steps:

[0079] S1: Add 10 mol of 3,3',4,4'-benzophenone tetracarboxylic dianhydride to the first dissolving vessel, then add 40 mol of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0080] S2: Add 9.95 mol of 1,3-bis(4'-aminophenoxy)benzene to the second dissolving vessel, then add 40 mol of N,N-dimethylformamide to the second dissolving vessel and mix evenly;

[0081] S3: Add 0.01 mol of nano-silica to the third dissolving vessel, then add 0.2 mol of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0082] S4: Set the high-speed mixing motor speed to 400 rpm and the low-speed mixing motor speed to 250 rpm;

[0083] S5: Set the first temperature control device to -25℃, the second temperature control device to -20℃, and the third temperature control device to 20℃;

[0084] S6: Simultaneously start the first feed pump, the second feed pump, and the third feed pump to begin feeding. Set the flow rate of the first feed pump to 0.5 mol / min, the flow rate of the second feed pump to 0.7 mol / min, and the flow rate of the third feed pump to 0.0002 mol / min.

[0085] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.45 mol / min;

[0086] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0087] Example 6

[0088] This embodiment provides a continuous process for preparing high-performance polyimide precursor polyamic acid, which is implemented using the apparatus provided in Example 1. The process specifically includes the following steps:

[0089] S1: Add 10 mol of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride to the first dissolving vessel, then add 40 mol of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0090] S2: Add 9.95 mol of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane to the second dissolving vessel, then add 40 mol of N,N-dimethylformamide to the second dissolving vessel and mix evenly;

[0091] S3: Add 0.01 mol of nano-titanium dioxide to the third dissolving vessel, then add 0.2 mol of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0092] S4: Set the high-speed mixing motor speed to 900 rpm and the low-speed mixing motor speed to 400 rpm;

[0093] S5: Set the first temperature control device to -8℃, the second temperature control device to -12℃, and the third temperature control device to -18℃;

[0094] S6: Simultaneously start the first feed pump, the second feed pump, and the third feed pump to begin feeding. Set the flow rate of the first feed pump to 0.6 mol / min, the flow rate of the second feed pump to 1.2 mol / min, and the flow rate of the third feed pump to 0.0004 mol / min.

[0095] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.06 mol / min;

[0096] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0097] Example 7

[0098] This embodiment provides a continuous process for preparing high-performance polyimide precursor polyamic acid, which is implemented using the apparatus provided in Example 1. The process specifically includes the following steps:

[0099] S1: Add 5 mol of pyromellitic anhydride and 5 mol of 4,4'-oxophthalic anhydride to the first dissolving vessel, then add 40 mol of N,N-dimethylformamide to the first dissolving vessel and mix evenly;

[0100] S2: Add 5 mol of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 4.95 mol of 2,2'-bis(trifluoromethyl)diaminobiphenyl to the second dissolving vessel, then add 40 mol of N,N-dimethylformamide to the second dissolving vessel and mix evenly.

[0101] S3: Add 0.01 mol of nano carbon black to the third dissolving vessel, then add 0.2 mol of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension;

[0102] S4: Set the high-speed mixing motor speed to 850 rpm and the low-speed mixing motor speed to 320 rpm;

[0103] S5: Set the first temperature control device to -30℃, the second temperature control device to -15℃, and the third temperature control device to 0℃;

[0104] S6: Simultaneously start the first feed pump, the second feed pump, and the third feed pump to begin feeding. Set the flow rate of the first feed pump to 0.9 mol / min, the flow rate of the second feed pump to 1.4 mol / min, and the flow rate of the third feed pump to 0.0002 mol / min.

[0105] S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.2 mol / min;

[0106] S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

[0107] Comparative Example 1

[0108] The equipment uses a traditional polymerization apparatus. The batching process is as follows: 9.95 mol of p-phenylenediamine is added to a dissolving vessel, followed by 40 mol of N,N-dimethylformamide. The reactor temperature is set to -10℃, and the rotation speed is set to its maximum limit of 200 rpm. 10 mol of pyromellitic anhydride is added in four portions, the first 95% in solid form, in four separate additions at proportions of 40%, 30%, 20%, and 10%, respectively. Each addition is allowed to complete the solid phase before adding new solid to prevent clumping and excessive exothermic reactions that could lead to localized gelation. As the system viscosity increases, the stirring speed is gradually reduced to prevent motor overload and seizing. The motor load is maintained at 90% throughout the feeding process to ensure optimal mixing. After all solids have been added, the remaining 5% of pyromellitic anhydride is dissolved in 2 LDMF and slowly added to the system using a peristaltic pump to continue the reaction. The final product is a polyamic acid solution.

[0109] Comparative Example 2

[0110] The equipment uses a traditional polymerization apparatus. The batching process is as follows: 9.95 mol of p-phenylenediamine is added to a dissolving vessel, followed by 40 mol of N,N-dimethylformamide. The reactor temperature is set to -10°C, and the rotation speed is set to its maximum limit of 200 rpm. 10 mol of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is added in four portions, the first 95% in solid form, in four separate additions at proportions of 40%, 30%, 20%, and 10%, respectively. Each addition is allowed to proceed only after the solid has completely dissipated to prevent clumping and excessive exothermic reactions that could lead to localized gelation. As the system viscosity increases, the stirring speed is gradually reduced to prevent motor overload and seizure. The motor load is maintained at 90% throughout the entire feeding process to ensure optimal mixing. After all solids have been added, the remaining 5% of pyromellitic dianhydride is dissolved in 2 LDMF and slowly added to the system using a peristaltic pump to continue the reaction. The final product is a polyamic acid solution.

[0111] The polyamic acid solutions obtained in Example 2 and Comparative Example 1 were used to prepare polyamic acid films by thermal imidization. The process conditions were as follows: the polyamic acid solution was cast through a die onto a steel belt dryer for drying to prepare a polyimide gel film. The process conditions were 150°C, 180°C, 180°C, 160°C, and 100°C for 10 min. The obtained polyimide gel film was then placed in a high-temperature drying tunnel for further imidization. The process conditions were 200°C, 350°C, 500°C, 350°C, 210°C, and 120°C for 5 min to obtain a fully imidized polyimide film.

[0112] The polyimide films prepared in Example 2 and Comparative Example 1 were subjected to performance tests.

[0113] Molecular weight distribution was determined using a Waters 1515 gel permeation chromatograph.

[0114] Tensile strength, tensile modulus, and elongation were tested using an Instron 3369 universal testing machine, and the test methods were in accordance with GB / T 13542.2-2009.

[0115] The intrinsic viscosity was determined by diluting polyamic acid to 0.5 g / L with DMF and measuring it at 25°C using an Ubbelohde viscometer, specifically the Hangzhou Zhuoxiang Technology IV8200X model.

[0116] The coefficient of thermal expansion (CTE) was tested using a Waters TMA450 thermomechanical analyzer, with the testing standard referring to ISO11359-2:1999.

[0117] Dynamic viscosity was tested using a Brookfield DVNXHBCP cone-plate viscometer rheometer with a cone rotor model of CPA-52Z and a test temperature of 25℃.

[0118] The test results are shown in Table 1:

[0119]

[0120] As shown in Table 1, the polyamic acid prepared by the continuous polymerization apparatus and process of this invention has a narrower molecular weight distribution and higher intrinsic viscosity compared to polyamic acid obtained by the traditional single-reactor batch polymerization method. The advantages of this polyamic acid lie in the fact that, at the microscopic level, there are fewer low-polymerization-degree polyamic acids and stronger intermolecular interactions; at the macroscopic level, the same molar ratio can produce polyamic acids with high dynamic viscosity and high intrinsic viscosity, resulting in polyimide films with superior physical and mechanical properties such as tensile strength, tensile modulus, and elongation. Similarly, due to the smaller quantity of low-polymerization-degree polyamic acids, the molecular chains are more difficult to move thermally after heating, resulting in a lower coefficient of thermal expansion (CTE) value for the material.

[0121] Traditional single-reactor batch polymerization methods produce polyamic acid with more low-polymerization degree molecular chains and a wider molecular weight distribution, resulting in lower dynamic viscosity and even lower intrinsic viscosity. Consequently, the polyimide films prepared by this method have poor physical and mechanical properties such as tensile strength, elongation, and tensile modulus; and higher thermal properties such as the coefficient of thermal expansion (CTE).

[0122] The polyamic acid obtained in Example 2 and Comparative Example 1 was wet-spun into polyamic acid fibers, which were then imidized and thermally drawn to obtain polyimide fibers. The resulting polyimide fibers were subjected to modulus and strength tests. The tensile modulus of the polyamic acid obtained in Example 2 was 158 GPa, while that of the polyimide fiber obtained in Comparative Example 1 was 128 GPa. This demonstrates that, due to the narrow molecular weight distribution of the polyamic acid obtained in this invention, the polyimide fibers made from polyamic acid have a higher tensile modulus.

[0123] The polyamic acids prepared in Examples 3-7 and Comparative Example 2 were subjected to performance tests.

[0124] Molecular weight distribution was determined using a Waters 1515 gel permeation chromatograph.

[0125] The intrinsic viscosity was determined by diluting polyamic acid to 0.5 g / L with DMF and measuring it at 25°C using an Ubbelohde viscometer, specifically the Hangzhou Zhuoxiang Technology IV8200X model.

[0126] Storage stability testing methods:

[0127] After polymerization, the dynamic viscosity of the prepared polyamic acid was tested and denoted as η1.

[0128] Then, after storing the polyamic acid at 25°C for 10 days, the dynamic viscosity was measured and denoted as η2.

[0129] Storage stability is measured as a percentage change in dynamic viscosity relative to the initial viscosity. .

[0130] The test data is shown in Table 2:

[0131]

[0132] Because polyamic acid (PA) molecules are polymers with carboxyl groups at the ortho positions of the amide bonds, the presence of these ortho-carboxyl groups reduces the stability of the amide bonds. Water and reactive end groups such as amine or carboxyl groups in the system can attack the amide bonds in the main chain, causing polymer chain breakage and degradation. According to activation energy theory, the larger the polymer molecular weight, the weaker the end group reactivity, making it less likely to cause chain breakage and degradation, and consequently, the more stable the polyamic acid molecular weight. Therefore, to prepare polyamic acid with good storage stability, in addition to controlling the water content and increasing the degree of polymerization, it is even more important to control the molecular weight distribution to be narrower and reduce the content of low-polymerization-degree molecular chains. This will result in better storage stability of the polyamic acid.

[0133] As can be seen from Examples 3-7, the polyamic acid produced by this invention has a narrow molecular weight distribution and a high intrinsic viscosity. This indicates that there is less low molecular weight polyamic acid, resulting in lower end-group reactivity and better storage stability. In contrast, the polyamic acid prepared by the traditional single-reactor batch polymerization process in Comparative Example 2 has a wide molecular weight distribution and a high proportion of low-polymerization-degree polyamic acid, resulting in higher polymer end-group reactivity and poor storage stability. Furthermore, its intrinsic viscosity and dynamic viscosity are also relatively low.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A process for continuous preparation of high-performance polyimide precursor polyamic acid, characterized in that, The apparatus for continuous preparation of high-performance polyimide precursor polyamic acid includes a feeding device, a reaction system, and a temperature control system. The feeding device includes a first dissolving vessel, a second dissolving vessel, a third dissolving vessel, a first metering pump, a second metering pump, a third metering pump, and a fourth metering pump. The reaction system includes a transparent vessel and a discharge port. The transparent vessel includes a mixing section, a prepolymerization section, and a thickening section. The prepolymerization section is located above the thickening section, and the mixing section is located above the prepolymerization section. The mixing section has a first inlet, a second inlet, and a third inlet, and the thickening section has a fourth inlet. The first dissolving vessel is connected to the first inlet in the mixing section of the transparent vessel via the first metering pump. The second dissolving vessel is connected to the second inlet in the mixing section of the transparent vessel via the second metering pump. The third dissolving vessel is connected to the third inlet in the mixing section of the transparent vessel via the third metering pump. The first dissolving vessel is connected to the fourth inlet in the thickening section of the transparent vessel via the fourth metering pump. A first partition is provided between the mixing section and the prepolymerization section, and a first check valve is provided on the first partition. A second partition is provided between the prepolymerization section and the thickening section, and a second check valve is provided on the second partition. The temperature control system includes a first temperature control device, a second temperature control device, and a third temperature control device; the mixing section is connected to the first temperature control device, the prepolymerization section is connected to the second temperature control device, and the thickening section is connected to the third temperature control device; The transparent vessel is equipped with a high-speed stirring motor and a low-speed stirring motor, which are connected by a stirring shaft that runs through the mixing section, the prepolymerization section, and the thickening section. The stirring shaft is equipped with a stirrer. A first stirrer is provided on the stirring shaft that passes through the mixing section and the prepolymerization section. The first stirrer is a three-blade or four-blade oblique-blade stirrer and is driven by the high-speed stirring motor. A second stirrer is provided on the stirring shaft that passes through the thickening section. The second stirrer is a double-ribbon stirrer and is driven by the low-speed stirring motor. The continuous preparation process for high-performance polyimide precursor polyamic acid includes the following steps: S1: Add 100 parts of dianhydride monomer to the first dissolving vessel by molar ratio, then add 400 parts of N,N-dimethylformamide to the first dissolving vessel and mix evenly; S2: Add 99.5 parts of diamine monomer to the second dissolving vessel by molar ratio, then add 400 parts of N,N-dimethylformamide to the second dissolving vessel and mix evenly; S3: Add 0.1 parts of additive to the third dissolving vessel by molar ratio, then add 2 parts of N,N-dimethylformamide to the third dissolving vessel and mix to prepare a suspension. The additive is one of dicalcium phosphate, nano alumina, nano silica, nano titanium dioxide, and nano carbon black. S4: Set the high-speed stirring motor speed to 300~1000rpm and the low-speed stirring motor speed to 50~500rpm; S5: Set the first temperature control device to -50~-10℃, the second temperature control device to -30~0℃, and the third temperature control device to -10~40℃; S6: Using a meter, simultaneously start the first, second, and third feed pumps to begin feeding. Set the flow rate of the first feed pump to 1~10 parts / min, the flow rate of the second feed pump to 1.5~15 parts / min, and the flow rate of the third feed pump to 0.001~0.005 parts / min. S7: Once the mixture enters the thickening section, start the fourth metering pump and set the flow rate to 0.45~5 parts / min; S8: Once the mixture fills the thickening section, a polyamic acid solution is discharged from the outlet.

2. The process for continuous preparation of high-performance polyimide precursor polyamic acid according to claim 1, characterized in that, The dianhydride monomer in step S1 is one or two of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 4,4'-oxobisphthalic anhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

3. The process for continuous preparation of high-performance polyimide precursor polyamic acid according to claim 1, characterized in that, The diamine monomer in step S2 is one or two of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, and 2,2'-bis(trifluoromethyl)diaminobiphenyl.

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