A process for the synthesis of a thermoplastic polyimide resin

Abstract

The application belongs to the field of high polymer materials, and discloses a thermoplastic polyimide resin and a preparation method thereof. The thermoplastic polyimide resin is prepared by using pyromellitic dianhydride (PMDA) and p-phenylenediamine (p-PDA) as main raw materials, using the combination of benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-diaminodiphenyl methane (MDA) and 1,3-bis(4-aminophenoxy) benzene (APB) as a modified material, using N-methyl pyrrolidone as a reaction solvent, and completing polymerization and imidization reaction in a low water content nitrogen protective atmosphere. 1-Chloro phthalic anhydride is used as a molecular chain end capping agent, and cyclopentane is used for assisting resin crystallization. The high-purity thermoplastic polyimide resin is obtained after purification and drying. The problems of the traditional PMDA / p-PDA based polyimide, such as heat resistance, poor melt processability, easy hydrolysis of dianhydride, many side reactions, wide molecular weight distribution of products, high impurity content and poor processability, are solved. The thermoplastic polyimide resin has excellent heat resistance, electrical insulation, chemical corrosion resistance and melt processability, and can be widely applied in the fields of electronic appliances, flexible circuit boards, lithium batteries, aerospace, military equipment and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology. In particular, it relates to a synthesis process for thermoplastic polyimide resin. Background Technology

[0002] With the advancement of science and technology and the development of society, people are developing and applying new technologies and materials more and more widely, and the requirements for electronic and electrical insulation materials are getting higher and higher, especially electrical insulation materials with high temperature resistance and hydrolysis resistance, and especially new materials with very low water absorption and moisture absorption.

[0003] In recent years, electrical insulation materials for electric motors, capacitors, and lithium-ion batteries have increasingly demanded properties such as heat resistance at high temperatures, hydrolysis resistance, low moisture absorption, high electrical insulation, and resistance to chemical corrosion. As an electrical insulation material for electric motors used in refrigerators and air conditioners, considering environmental concerns, and as a separator and encapsulation material for capacitors and lithium-ion batteries, a chemically resistant electrical insulation material has been proposed. This material requires not only heat resistance but also hydrolysis resistance. Furthermore, as an electrical insulation material for electric motors used in hybrid vehicles, and for the ultra-high-capacity batteries required for pure electric vehicles, in addition to heat resistance, the electrical insulation material also needs to be resistant to chemical corrosion.

[0004] Thermoplastic polyimide (TPI) resin possesses heat resistance, flame retardancy, high rigidity, chemical corrosion resistance, low moisture absorption, and excellent electrical insulation properties, making it widely applicable in electronic instruments, machinery, automotive parts, electronic seals, and mechanical seals. The polyimide backbone contains an imide ring structure, and based on its structure, it can be classified into aliphatic, semi-aromatic, and aromatic polyimides. Based on its thermal properties, it can be classified into thermoplastic and thermosetting polyimides. Its unique alternating structure of benzene rings and five-membered nitrogen rings endows the material with excellent high and low temperature performance, mechanical properties, dielectric properties, low expansion, flame retardancy, and radiation resistance. It is widely used in aerospace, microelectronics, and separation membranes, and is also a common substrate for motors, cables, flexible substrates, solar panels, and flexible displays.

[0005] Chinese patent application number 200380103395.8 discloses a thermoplastic polyimide resin and its manufacturing method. This invention provides a thermoplastic polyimide resin with biaxial optical anisotropy and excellent durability. A polyimide solution with an imidization rate of 98-100% is coated onto a plastic substrate, and then the solution is dried to form a polyimide coating. Although this patent obtains the thermoplastic polyimide resin through a biaxial orientation manufacturing method, the thermoplastic polyimide resin is produced using a coating molding process, not a melt extrusion process. Therefore, problems such as toughness and tear elongation of the thermoplastic polyimide resin manufactured using this method are not fundamentally solved.

[0006] Chinese Patent Application No. 200580032118.1 discloses a method for manufacturing a thermoplastic polyimide resin with high adhesion. This invention provides a non-biaxially oriented film with excellent tear elongation and planarity. The method describes a non-thermoplastic polyimide resin exhibiting high storage stability of the precursor solution and high adhesion without costly surface treatment. However, this patent reveals that the polyimide resin is thermosetting, which is not conducive to the production of biaxially stretched thermoplastic polyimide resins. Although the production process is simple, it is not beneficial for the application of thermoplastic polyimide resins.

[0007] The purpose of this invention is to manufacture a thermoplastic polyimide resin with excellent performance in all aspects, especially in terms of heat resistance, dimensional stability, electrical insulation, and chemical resistance. This material can be used in electric motors, transformers, insulating cables, battery separator materials, loudspeakers, etc.

[0008] Given that most polyimide films on the market are thermosetting products with poor reprocessing performance, and considering the limitations of this type of polyimide resin application, this patent selects commercially available monomers dianhydride and diamine with higher rigidity segments to replace the original monomers. At the same time, it selects readily available chemical raw materials and adopts corresponding polyimide resin synthesis and purification processes to manufacture inexpensive and high-performance thermoplastic polyimide resin.

[0009] To address the aforementioned deficiencies in existing technologies, this invention aims to provide a thermoplastic polyimide resin with superior overall performance, exhibiting excellent heat resistance, dimensional stability, electrical insulation, and chemical resistance. This resin is suitable for various applications, including motors, transformers, cables, and battery separators. This invention utilizes readily available rigid-chain dianhydrides and diamine monomers, and through optimized synthesis and purification processes, prepares a high-performance thermoplastic polyimide resin that is high-performance, low-cost, and suitable for large-scale production, thus overcoming the shortcomings of existing technologies. Summary of the Invention

[0010] This invention employs multi-monomer copolymerization modification combined with optimized polymerization and purification processes, effectively overcoming the drawbacks of thermosetting polyimide resins such as non-melt processing, easy decomposition at high temperatures, and narrow applicability, thereby improving the application and processing performance of thermoplastic polyimide resins.

[0011] To achieve the above-mentioned objectives, the following technical solution is provided: According to one embodiment of the present invention, a thermoplastic polyimide resin comprises the following raw materials: This thermoplastic polyimide resin uses pyromellitic dianhydride (PMDA) and p-phenylenediamine (p-PDA) as the main raw materials, and a combination of benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-diaminodiphenylmethane (MDA) and 1,3-bis(4-aminophenoxy)benzene (APB) as the modifying materials, with N-methylpyrrolidone (NMP) as the solvent. The molar ratio of mixed dianhydride PMDA+BTDA to mixed diamine p-PDA+MDA+APB is 1:1~2, wherein the molar ratio of PMDA+BTDA is 60~80%:20~40%; and the molar ratio of p-PDA+MDA+APB is 50~60%:20~30%:20~30%.

[0012] According to one embodiment of the present invention, the total molar ratio of the mixed dianhydride to the mixed diamine is 1.0:1.001 to 1.03.

[0013] The present invention also aims to provide a preparation process for the thermoplastic polyimide resin, characterized by comprising the following steps: (1) Under nitrogen protection, the mixed diamines were dissolved in NMP solvent, dehydrated, and then cooled for later use; (2) Mixed dianhydrides were continuously added to the above diamine solution, and prepolymerization was carried out under low temperature conditions. Then, 1-chlorophthalic anhydride was added to carry out the end-capping reaction. (3) Add cyclopentane to the reaction system for azeotropic reflux imidization. After the reaction is complete, put it into acetone solvent to precipitate resin. After cooling and solid-liquid separation, obtain resin filter cake. (4) The resin filter cake was repeatedly suspended and refluxed and washed with acetone; (5) The filter cake obtained from washing is dried under vacuum to obtain thermoplastic polyimide resin powder.

[0014] According to one embodiment of the present invention, the reaction is protected by nitrogen gas throughout, the water content of the protective nitrogen gas is less than 10 ppm, and the water content of the reaction system is controlled below 50 ppm.

[0015] According to one embodiment of the present invention, the purity of the NMP solvent is ≥99.8% and the water content is less than 2wt%.

[0016] According to one embodiment of the present invention, before the polymerization reaction, the mixed diamine monomers are prepared into an NMP solution with a mass fraction of 10-20%, which is then heated and dehydrated before being cooled to room temperature for later use.

[0017] According to one embodiment of the present invention, the mixed dianhydride monomers are fed uniformly through a single-screw extruder at a feeding speed of 10-18 kg / min; the system temperature is controlled at -6 to 0°C during the polymerization reaction stage, the stirring speed is 100-300 rpm, and the polymerization reaction time is 3-6 h.

[0018] According to one embodiment of the present invention, after the polymerization reaction is completed, 1-chlorophthalic anhydride accounting for 1-3% of the total molar amount of dianhydride is added as a capping agent, and the reaction is stirred continuously for 6-8 hours; then cyclopentane is added, the temperature is raised to 170-180°C, and the reaction is carried out under constant temperature reflux for 5-7 hours.

[0019] According to one embodiment of the present invention, during the resin crystallization purification process, the resin is cooled and crystallized at a cooling rate of 10-20°C / min; during the multi-stage acetone washing process, an acetone suspension with a resin solid content of 10-20 wt% is prepared and refluxed at 60-80°C for 5-8 hours, and the washing filtrate of each stage is reused step by step.

[0020] According to one embodiment of the present invention, a scraped evaporator is used for vacuum drying, the drying temperature is controlled at 240-280°C, and the vacuum drying time is 2-6 hours, to obtain high-purity thermoplastic polyimide resin.

[0021] The core technical solution of this invention is as follows: using a multi-component compound dianhydride and diamine raw material system, with high-purity N-methylpyrrolidone as the reaction solvent, and under a high-purity nitrogen inert protective atmosphere, the polymerization reaction, molecular chain end capping, resin crystallization precipitation, multi-stage purification and impurity removal and high-temperature vacuum drying processes are completed sequentially to prepare a high-purity thermoplastic polyimide resin with a narrow molecular weight distribution.

[0022] This invention uses pyromellitic dianhydride (PMDA) and p-phenylenediamine (p-PDA) as basic polymerization raw materials, supplemented by benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-diaminodiphenylmethane (MDA), and 1,3-bis(4-aminophenoxy)benzene (APB) as modifying comonomers, N-methylpyrrolidone (NMP) as the reaction solvent, and 1-chlorophthalic anhydride as the molecular chain end-capping agent. The molar ratio of the total dianhydride component (PMDA+BTDA) to the total diamine component (p-PDA+MDA+APB) is 1.0:1-2.

[0023] The specific molar ratios of the components in this invention are defined as follows: (1) Dianhydride system: PMDA accounts for 60% to 80%, BTDA accounts for 20% to 40%; (2) Diamine system: p-PDA accounts for 50% to 60%, MDA accounts for 20% to 30%, and APB accounts for 20% to 30%; (3) End-capping agent: The amount of 1-chlorophthalic anhydride added is 1% to 3% of the total molar amount of dianhydride; (4) Reaction solvent: NMP organic solvent with a purity of ≥99.8% and an initial moisture content of ≤2wt% is selected.

[0024] This invention employs low-moisture, high-purity nitrogen for inert protection throughout the entire process, ensuring that the moisture content of the nitrogen is ≤10ppm. The specific synthesis process steps are as follows: (1) System dehydration pretreatment: A quantitative amount of NMP solvent was added to a 500L jacketed reactor, and each diamine monomer was added according to the preset molar ratio to prepare an NMP mixed solution with a diamine monomer mass fraction of 10% to 20%. Medium-pressure steam was used to heat and dehydrate the material in the reactor to remove free water from the system until the overall water content of the reaction system was ≤50ppm. After dehydration was completed, heating was stopped, and the material in the reactor was cooled to room temperature with cooling water, sealed and kept for later use to completely eliminate the adverse effects of water on the polymerization reaction.

[0025] (2) Low-temperature polymerization reaction: The compounded dianhydride monomers are uniformly added to the above diamine mixed solution at a constant rate of 10-18 kg / min using a single-screw extruder; at the same time, ammonium nitrate freezing brine at -6 to 0℃ is introduced into the jacket of the reactor to strictly control the polymerization reaction temperature. After the dianhydride monomers are added, the stirring speed of the reactor is adjusted to 100-300 rpm, and the reaction is carried out at a constant temperature for 3-6 hours to complete the prepolymerization reaction.

[0026] (3) Molecular chain end-capping modification: After the prepolymerization reaction is completed, a measured amount of 1-chlorophthalic anhydride end-capping agent is added to the reaction system and the reaction is continuously stirred at a constant temperature for 6-8 hours to end-cap the resin molecular chain and precisely control the resin molecular weight and molecular weight distribution.

[0027] (4) High-temperature closed-loop reflux reaction: After the end-capping reaction is completed, add 100L of cyclopentane into the reactor, close the jacket low-temperature cooling valve, turn on the medium-pressure steam heating, raise the temperature of the material in the reactor to 110-170℃, and reflux at a constant temperature for 5-7 hours to promote the full copolymerization of monomers and complete the resin imidization reaction.

[0028] (5) Resin crystallization and solid-liquid separation: After the reflux reaction is completed, the reaction material in the reactor is transferred to a washing reactor containing acetone solvent to promote the crystallization of polyimide resin from the NMP solvent system; the mixture is cooled to room temperature at a cooling rate of 10-20°C, and then solid-liquid separation is performed; the filtrate obtained by separation is sent to the solvent recovery process for recycling, and the solid resin filter cake is retained for purification.

[0029] (6) Three-stage acetone purification: The obtained resin filter cake is subjected to three independent acetone reflux purification treatments, and the purification process parameters are kept consistent for each batch: acetone solvent is added to the resin filter cake to prepare a suspension with a resin solid content of 10% to 20%, and the temperature is raised to 60 to 80℃ and refluxed for 5 to 8 hours to fully remove small molecule impurities, unreacted monomers and polymerization by-products wrapped on the surface and inside of the resin; after the reaction is completed, the mixture is cooled to room temperature and the solid-liquid separation is completed. The purified filtrates at each stage are reused in stages as resin crystallization diluent and washing solvent, respectively, to achieve closed-loop recycling of solvent. The purified resin filter cake is kept for later use.

[0030] (7) High-temperature vacuum drying and devolatification: The resin filter cake after multi-stage purification is put into a scraped evaporator and dried for 2-6 hours at a temperature of 240-280℃ and under vacuum conditions to completely remove residual solvent, volatile matter and trace impurities from the resin, and finally obtain high-purity thermoplastic polyimide resin powder.

[0031] Key process control principles and functions of this invention (1) Precise control of low moisture content system: This invention strictly limits the overall moisture content of the reaction system to ≤50ppm and the moisture content of the protective nitrogen gas to ≤10ppm. If the moisture content of the system exceeds the limit, it will cause hydrolysis of dianhydride monomer, disrupt the theoretical ratio balance between dianhydride and diamine monomer, resulting in excessive enrichment of diamine monomer and diazo side reaction, which in turn leads to discoloration of the system materials and an increase in the content of small molecule impurities. This not only degrades the purity and processing performance of the resin, but also increases raw material loss, solvent distillation residue, and subsequent wastewater treatment load. This invention stabilizes the polymerization reaction ratio through dual moisture control measures, inhibits the occurrence of side reactions from the source, and ensures that the reaction system is stable and controllable.

[0032] (2) Flexible monomer copolymerization modification: The present invention introduces MDA and APB diamine modified monomers containing flexible ether bonds and alkyl links, which can effectively improve the thermosetting properties of traditional all-aromatic rigid polyimide, realize the thermoplastic modification of polyimide resin, reduce the crystallinity of the resin body and the melt viscosity, significantly improve the melt flowability and molding process adaptability of the resin, and effectively improve the yield of finished products.

[0033] (3) Mono-anhydride end capping molecular weight control: Using 1-chlorophthalic anhydride as a molecular chain end capping agent can effectively terminate the growth of resin molecular chains, accurately control the molecular chain length, reduce the polydispersity index of resin molecular weight, and obtain resin products with narrow molecular weight distribution; at the same time, this end capping modification method can effectively improve the oxygen index of resin, optimize the flame retardant performance of materials, reduce the difficulty of subsequent purification and impurity removal of resin, and take into account both product processing performance and overall quality.

[0034] (4) Multi-stage low-boiling-point solvent purification: Low-boiling-point acetone solvent is used for multiple high-temperature reflux purification, which can efficiently remove unreacted monomers, small molecule polymers and polymerization by-products in the resin system, and strictly control the content of volatile components of the resin to below 0.3%, which meets the high purity index requirements of high-end precision processing of thermoplastic polyimide resin.

[0035] (5) Post-processing auxiliary modification process: The present invention can perform forced filtration treatment on the prepared resin melt to completely remove mechanical impurities introduced during the synthesis process, eliminate surface defects of the product, and effectively improve the flatness, appearance quality and mechanical properties of the molded product; at the same time, for the precision processing scenario of thin film, an anti-static treatment process is set up to eliminate the problem of static electricity accumulation caused by material friction during the processing, avoid the interference of static electricity on the production rhythm, and significantly improve the product processing efficiency.

[0036] Technical advantages and product performance of this invention

[0037] (1) Uniform and controllable molecular weight distribution: Through precise end-capping modification with 1-chlorophthalic anhydride, the excessive entanglement and uneven growth of resin molecular chains are effectively suppressed. The resin has a narrow molecular weight distribution and excellent polydispersity index, which solves the defect of poor melt flow of traditional linear polyimide. The resin melt flow index can be stably maintained at more than 180g / 10min, which can be adapted to various precision processing conditions.

[0038] (2) Wide processing adaptability: The melt flow index of the resin of this invention can be controlled within the range of 150-200 g / 10 min, which is compatible with mainstream thermoplastic material processing technology. Among them, the high flowability resin specification can meet the molding requirements of high-end cast films, improve the uniformity of film molding and production efficiency; the conventional specification can be applied to precision injection molding and modified composite material preparation, with a wide processing technology window and strong adaptability.

[0039] (3) Excellent product purity and stability: Relying on the system's low moisture control, three-stage multi-stage purification and high-temperature vacuum devolatilization coupling process, the content of volatiles, small molecule impurities and by-products inside the resin is extremely low, the product batch stability is good and the overall quality is excellent.

[0040] (4) Excellent process economy and environmental protection: This invention reduces raw material loss by using solvent closed-loop recycling and suppressing side reactions at the source, which greatly reduces raw material consumption, solvent distillation costs and the pressure of waste treatment. The overall process has low production cost, is green and environmentally friendly, and has industrial mass production value.

[0041] The high-purity thermoplastic polyimide resin prepared by this invention has excellent melt flowability, high purity, good flame retardancy and stable molding performance. It can be widely used in high-end polyimide functional films, precision engineering injection molded parts, high-performance polymer modified composite materials and other technical fields. It effectively solves the industry technical pain points of traditional polyimide resin, such as high processing difficulty, many molding defects, low mass production efficiency and poor product consistency. Detailed Implementation

[0042] The present invention will be described below through specific embodiments to make the technical solution of the present invention easier to understand and master, but the present invention is not limited thereto. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are all commercially available. Example

[0043] This embodiment provides a high-purity thermoplastic polyimide resin, which uses pyromellitic dianhydride (PMDA) and p-phenylenediamine (p-PDA) as the main polymerizing monomers, and a modified diamine system composed of benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-diaminodiphenylmethane (MDA), and 1,3-bis(4-aminophenoxy)benzene (APB) as the modifying component, and N-methylpyrrolidone (NMP) as the polymerization reaction solvent.

[0044] The raw material molar ratios in this embodiment are as follows: the molar ratio of total acid anhydride components (PMDA+BTDA) to total diamine components (p-PDA+MDA+APB) is 1.0:1.001; wherein, the molar ratio of PMDA to BTDA is 60%:40%, and the molar ratio of p-PDA, MDA, and APB is 50%:30%:20%. High-purity nitrogen inert protection is used throughout the process, and the moisture content of the NMP solvent system is strictly controlled to ≤50ppm. After solution polymerization, crystallization separation, multi-stage purification, and vacuum drying, high-purity thermoplastic polyimide resin is obtained.

[0045] The specific synthesis process steps are as follows: (1) Raw material pretreatment and system dehydration: Under a high-purity nitrogen inert atmosphere with a moisture content ≤10ppm, the mixed diamine monomers of a predetermined molar amount were accurately weighed and added to a jacketed reactor containing 500L of NMP solvent; the NMP solvent used had a purity ≥99.8% and a moisture content ≤2wt%, and was stirred and dispersed to prepare a diamine / NMP mixed solution with a mass fraction of 10wt%. Medium-pressure steam was used to heat the material in the reactor to remove residual moisture from the system. Heating was stopped when the moisture content of the system dropped below 50ppm as detected online. Cooling water was introduced to cool the material in the reactor to room temperature, and the reactor was sealed and left to stand for later use.

[0046] (2) Low-temperature polymerization and end-capping reaction: The mixed dianhydride monomers were uniformly added to the diamine reaction solution at a constant conveying rate of 10 kg / min using a single-screw extruder; simultaneously, -6℃ cold ammonium nitrate brine was introduced into the jacket of the reactor to achieve low-temperature constant temperature stirring. After the dianhydride monomers were added, the stirring speed was increased to 300 rpm, and the reaction was carried out at a constant temperature for 3 hours; then, 1 mol% of the end-capping agent 1-chlorophthalic anhydride based on the total amount of dianhydride was added, and the reaction was continued at a constant temperature for 8 hours. Then, 100 L of cyclopentane was added to the reaction system. The jacket ice water circulation valve was closed, and the medium-pressure steam heating valve was opened to raise the temperature of the material in the reactor to 170℃. The reaction was carried out at a constant temperature reflux for 7 hours to complete the polymerization and end-capping process.

[0047] (3) Crystallization and solid-liquid separation: After the polymerization reaction is completed, the mixture in the reactor is transferred to a jacketed washing reactor containing acetone solvent, so that the polyimide resin crystallizes out from the NMP / acetone mixture. The material in the washing reactor is cooled to room temperature at a constant cooling rate of 10℃ / min to complete the solid-liquid separation operation; the filtrate obtained by separation is sent to the solvent recovery process for recycling, and the solid resin filter cake is kept for later use.

[0048] (4) Multi-stage acetone purification and washing: The above resin filter cake is mixed with acetone solvent to prepare an acetone suspension with a resin solid content of 10 wt%, and transferred to a jacketed washing vessel. Medium-pressure steam is introduced to raise the temperature to 60°C, and the mixture is refluxed at a constant temperature for 8 hours. After natural cooling to room temperature, solid-liquid separation is performed. The separated filtrate is sent to the next purification process and used as a diluent for resin crystallization. The solid filter cake is retained for later use. The above constant temperature reflux washing process is repeated twice. The filtrate obtained from both washings is used as a special washing agent for resin crystallization and recycled. The solid filter cake after each washing is retained for later use.

[0049] (5) Vacuum drying and performance characterization: The resin filter cake after multi-stage purification and washing was fed into a scraped evaporator and heated to 240°C under vacuum negative pressure. It was then dried at a constant temperature for 6 hours to remove residual solvent and trace amounts of moisture, finally obtaining polyimide resin powder. The thermal properties of the finished resin were tested. The test results showed that the resin began to melt when the ambient temperature rose to 340°C. As the temperature continued to rise, the resin could be completely melted and plasticized, exhibiting typical thermoplastic polyimide resin melt processing characteristics. Example

[0050] This embodiment uses PMDA and p-PDA as the main monomers, BTDA, MDA, and APB as diamine modifying components, and NMP as the polymerization solvent to prepare thermoplastic polyimide resin. The molar ratio of raw materials in this embodiment is as follows: the total anhydride component (PMDA+BTDA) to the total diamine component (p-PDA+MDA+APB) is 1.0:1.01; wherein the molar ratio of PMDA to BTDA is 80%:20%, and the molar ratio of p-PDA, MDA, and APB is 60%:20%:20%. The entire process is under nitrogen inert protection, and the moisture content of the NMP solvent in the reaction system is controlled to ≤50ppm. The finished thermoplastic polyimide resin is obtained after polymerization, purification, and drying. The specific process steps are as follows: (1) Raw material pretreatment and system dehydration: Under a high-purity nitrogen protective atmosphere with a moisture content ≤10ppm, accurately weigh and mix the diamine monomers, add them to 500L of NMP solvent with a purity ≥99.8% and a moisture content ≤2wt%, and stir to prepare a 20wt% diamine / NMP solution. Remove residual moisture from the system by heating with medium-pressure steam. Stop heating when the moisture content of the system is <50ppm, and cool water is introduced to cool the material to room temperature for later use.

[0051] (2) Low-temperature polymerization and end-capping reaction: The mixed dianhydride monomers were fed into the diamine reaction solution at a constant rate of 18 kg / min using a single-screw extruder. The reaction vessel jacket was circulated with 0°C cold ammonium nitrate brine for constant temperature stirring. After the feeding was completed, the stirring speed was adjusted to 100 rpm, and the reaction was maintained at a constant temperature for 3 hours. 1-Chlorophthalic anhydride was added at 3 mol% based on the total amount of dianhydride, and the reaction was continued for 6 hours. Then, 100 L of cyclopentane was added to the system. The ice water circulation valve was closed, and the medium-pressure steam was turned on to raise the temperature to 180°C. The reaction was carried out at a constant temperature under reflux for 5 hours.

[0052] (3) Crystallization and solid-liquid separation: After the reaction is completed, the material in the reactor is transported to the acetone washing reactor for crystallization treatment. The material is cooled to room temperature at a cooling rate of 20℃ / min to complete the solid-liquid separation. The filtrate is sent to the solvent recovery process for recycling, and the solid resin filter cake is kept for later use.

[0053] (4) Multi-stage acetone purification and washing: The resin filter cake is mixed with acetone solvent to prepare an acetone suspension with a resin solid content of 10-20 wt%. The suspension is heated to 80°C and refluxed for 5 hours. After cooling to room temperature, the solid and liquid are separated. The obtained filtrate is recycled as a resin crystallization diluent. The above washing process is repeated twice. The filtrate after washing is recycled as a crystallization washing agent. For the last washing, a 20 wt% resin acetone suspension is prepared. The same washing temperature and reaction time are maintained. The filter cake is retained for later use after each washing.

[0054] (5) Vacuum drying and performance characterization: The purified resin filter cake was placed in a scraped evaporator and dried at a constant temperature of 280℃ for 2 hours under vacuum to obtain the polyimide resin product. The thermal performance test results showed that the resin initially melted at 360℃ and could completely melt after continuous heating, which is consistent with the performance characteristics of thermoplastic polyimide resin. Example

[0055] In this embodiment, PMDA and p-PDA are used as the main polymer monomers, BTDA, MDA, and APB are used as diamine modifying components, and NMP is used as the polymerization solvent to prepare thermoplastic polyimide resin.

[0056] In this embodiment, the molar ratio of raw materials is as follows: the total anhydride component to the total diamine component is 1.0:1.02; the molar ratio of PMDA to BTDA is 70%:30%, and the molar ratio of p-PDA, MDA, and APB is 50%:30%:20%. High-purity nitrogen is used throughout the process, and the moisture content of the system is strictly controlled below 50 ppm. The specific synthesis process is as follows: (1) Raw material pretreatment and system dehydration: Under a low-moisture nitrogen inert atmosphere, a quantitative mixture of diamine monomers was added to 500L of high-purity NMP solvent to prepare a 13wt% diamine / NMP mixed solution. The system moisture was removed by medium-pressure steam heating. After the system moisture content dropped to below 50ppm, heating was stopped and the system was cooled to room temperature for later use.

[0057] (2) Low-temperature polymerization and end-capping reaction: The mixed dianhydride monomers were added at a rate of 12 kg / min using a single-screw extruder. The reaction vessel jacket was circulated with -4℃ cold ammonium nitrate brine for constant temperature control. After the addition was completed, the stirring speed was increased to 150 rpm and the reaction was continued for 4 h. Then, 1.3 mol% of 1-chlorophthalic anhydride based on the total molar amount of dianhydride was added, and the reaction was continued with stirring for 7.5 h. Finally, 100 L of cyclopentane was added. The temperature was raised to 173℃ and refluxed for 6.0 h.

[0058] (3) Crystallization and solid-liquid separation: The polymer material is transferred to an acetone washing tank and cooled to room temperature at a cooling rate of 15℃ / min to complete the resin crystallization and solid-liquid separation. The filtrate is recycled and reused, and the solid filter cake is kept for later use.

[0059] (4) Multi-stage acetone purification and washing: The resin filter cake was prepared into a 13wt% acetone suspension and washed under constant temperature reflux at 68℃ for 7.5h, followed by cooling and separation. The washing process was repeated 3 times. The filtrate from the first washing was used as a resin crystallization diluent, and the filtrate from the last two washings was used as a crystallization washing agent. All of the filtrate was recycled, and the solid filter cake was continuously stored for later use.

[0060] (5) Vacuum drying and performance characterization: The purified filter cake was dried in a scraped evaporator at 260°C under vacuum for 4 hours to obtain the polyimide resin product. Thermal performance tests showed that the resin began to melt at 350°C and could be completely melted and plasticized, exhibiting stable thermoplastic characteristics. Example

[0061] In this embodiment, high-purity thermoplastic polyimide resin is prepared using PMDA and p-PDA as the main raw materials, BTDA, MDA, and APB as compounding and modifying components, and NMP as the solvent.

[0062] In this embodiment, the molar ratio of raw materials is as follows: the total anhydride component to the total diamine component is 1.0:1.015; the molar ratio of PMDA to BTDA is 65%:35%, and the molar ratio of p-PDA, MDA, and APB is 55%:25%:20%. The entire process is under nitrogen inert protection, and the moisture content of the system is ≤50ppm. The specific synthesis process is as follows: (1) Raw material pretreatment and system dehydration: Under a nitrogen protective atmosphere, a quantitative mixture of diamine monomers was added to 500L of high-purity NMP solvent to prepare a 16wt% diamine / NMP solution. The system was heated to remove moisture until the content was <50ppm, cooled to room temperature, and sealed for later use.

[0063] (2) Low-temperature polymerization and end-capping reaction: The mixed dianhydride monomers were fed at a uniform rate of 15 kg / min, and the jacket of the reactor was circulated with -2℃ cold brine for constant temperature control. After the feeding was completed, the reaction was stirred at 180 rpm for 4.5 h; 1-chlorophthalic anhydride of 2.0 mol% based on the total amount of dianhydride was added, and the reaction was stirred for 6.5 h. Then 100 L of cyclopentane was added, and the temperature was raised to 175℃ and refluxed for 6.5 h.

[0064] (3) Crystallization and solid-liquid separation: The polymer material is fed into the acetone washing kettle and cooled to room temperature at a rate of 15℃ / min to complete the resin crystallization and solid-liquid separation. The filtrate is recovered and the solid filter cake is kept for later use.

[0065] (4) Multi-stage acetone purification and washing: The resin filter cake was prepared into a 16wt% acetone suspension and washed under reflux at 73℃ for 6.5h, followed by cooling and separation. The washing was repeated 3 times, and the filtrate was used as a crystallization diluent and crystallization washing agent for graded recycling, while the filter cake was retained for later use.

[0066] (5) Vacuum drying and performance characterization: The filter cake was vacuum dried at 275℃ for 5 hours to obtain the finished polyimide resin. The thermal performance test results showed that the resin began to melt at 363℃ and could be completely melted and plasticized, which is a typical thermoplastic polyimide resin. Example

[0067] In this embodiment, a thermoplastic polyimide resin is prepared using PMDA and p-PDA as the main polymer monomers, BTDA, MDA, and APB as modifying components, and NMP as the polymerization solvent.

[0068] In this embodiment, the molar ratio of raw materials is as follows: the total anhydride component to the total diamine component is 1.0:1.008; the molar ratio of PMDA to BTDA is 63%:37%, and the molar ratio of p-PDA, MDA, and APB is 58%:21%:21%. The entire process is under high-purity nitrogen protection, and the moisture content of the system is ≤50ppm. The specific synthesis process is as follows: (1) Raw material pretreatment and system dehydration: Under a low moisture nitrogen atmosphere, prepare an 18wt% diamine / NMP mixed solution, heat to remove moisture from the system until the content is <50ppm, and cool to room temperature for later use.

[0069] (2) Low-temperature polymerization and end-capping reaction: The mixed dianhydride monomers were fed at a rate of 15 kg / min, and the jacket was circulated with -1℃ cold brine for constant temperature control. After the feeding was completed, the mixture was stirred at 230 rpm for 5.3 h, and 1-chlorophthalic anhydride of 2.2 mol% based on the total amount of dianhydride was added. After stirring for 6.1 h, 100 L of cyclopentane was added, and the temperature was raised to 178℃ and refluxed for 6.8 h.

[0070] (3) Crystallization and solid-liquid separation: The polymer material is transferred to an acetone washing tank and cooled to crystallize at a rate of 18℃ / min. Solid-liquid separation is completed at room temperature, the filtrate is recycled, and the filter cake is used for later use.

[0071] (4) Multi-stage acetone purification and washing: The resin filter cake was prepared into an 18wt% acetone suspension, and washed under constant temperature reflux at 75℃ for 8 hours. The washing was repeated 3 times. The filtrate was recycled in stages, and the solid filter cake was kept for later use.

[0072] (5) Vacuum drying and performance characterization: The purified filter cake was vacuum dried at 280℃ for 6 hours to obtain the polyimide resin product. Thermal performance tests showed that the resin started to melt at 368℃ and could be completely melted, exhibiting excellent thermoplastic properties. Example

[0073] In this embodiment, thermoplastic polyimide resin is prepared using PMDA and p-PDA as the main raw materials, BTDA, MDA, and APB compound system as the modifying components, and NMP as the solvent.

[0074] In this embodiment, the molar ratio of raw materials is as follows: the total anhydride component to the total diamine component is 1.0:1.03; the molar ratio of PMDA to BTDA is 80%:20%, and the molar ratio of p-PDA, MDA, and APB is 60%:20%:20%. The entire process is under nitrogen inert protection, and the moisture content of the system is ≤50ppm. The specific synthesis process is as follows: (1) Raw material pretreatment and system dehydration: Prepare a 10wt% diamine / NMP solution under nitrogen protection, heat to remove residual moisture from the system to a content ≤50ppm, and cool to room temperature for later use.

[0075] (2) Low-temperature polymerization and end-capping reaction: The mixed dianhydride monomers were fed at a rate of 18 kg / min, and the jacket was circulated with cold brine at 0℃ for constant temperature control. After the feeding was completed, the mixture was stirred at 300 rpm for 6 h, and 1 mol% of 1-chlorophthalic anhydride based on the total amount of dianhydride was added. After stirring for 8 h, 100 L of cyclopentane was added, and the mixture was heated to 180℃ and refluxed for 7 h.

[0076] (3) Crystallization and solid-liquid separation: The polymer material is fed into the acetone washing kettle and cooled to room temperature at a rate of 10℃ / min for crystallization and separation. The filtrate is recycled and the solid filter cake is used for later use.

[0077] (4) Multi-stage acetone purification and washing: The filter cake was prepared into a 10wt% acetone suspension and washed under constant temperature reflux at 80℃ for 8 hours. The washing was repeated 3 times. The filtrate was recycled in stages and the filter cake was kept for later use.

[0078] (5) Vacuum drying and performance characterization: The purified filter cake was vacuum dried at 240℃ for 2h to obtain the polyimide resin product. Thermal performance tests showed that the resin initially melted at 361℃ and could be completely melted and plasticized after heating, which is consistent with the performance characteristics of thermoplastic polyimide resin.

[0079] Comparative Example 1

[0080] This comparative example uses a pure monomer polymerization system without the addition of BTDA, MDA, or APB modifying components. Only PMDA and p-PDA are used as monomers, and NMP is used as the reaction solvent. The monomer molar ratio is PMDA:p-PDA = 1.0:1.001. Nitrogen inert protection is maintained throughout the process, and the moisture content of the NMP system is controlled to ≤50ppm. All other synthesis, purification, and drying process parameters are completely consistent with Example 1. The specific process is as follows:

[0081] (1) Raw material pretreatment: Under the protection of high-purity nitrogen with a moisture content of ≤10ppm, a quantitative amount of p-PDA monomer was added to 500L of NMP solvent with a purity of ≥99.8% and a moisture content of ≤2wt% to prepare a 10wt% diamine solution. The moisture in the system was removed by heating with medium-pressure steam. After the moisture content dropped to below 50ppm, the system was cooled to room temperature with cooling water for later use.

[0082] (2) Polymerization reaction: PMDA monomer was added at a rate of 10 kg / min, and the jacket was circulated with cold ammonium nitrate brine at -6℃ for constant temperature control. After the addition was completed, the mixture was stirred at 100 rpm for 6 h, 1 mol% of 1-chlorophthalic anhydride was added and stirring was continued for 8 h, 100 L of cyclopentane was added and the temperature was raised to 170℃ and refluxed for 7 h.

[0083] (3) Post-processing: After the material is crystallized in acetone solvent, cooled at a constant rate of 10℃ / min, and separated into solid and liquid, it is treated with the same three-stage acetone washing and vacuum drying at 240℃ for 6 hours as in Example 1.

[0084] (4) Performance test results: The thermal performance test results of the finished resin show that when the ambient temperature rises to 370℃, the resin does not melt; after continuous heating, the resin undergoes thermal degradation, and when the temperature reaches 520℃, the thermal decomposition rate of the resin is significantly accelerated, exhibiting the typical performance characteristics of thermosetting polyimide resin, which does not melt and is easily thermally decomposed.

[0085] Comparative Example 2

[0086] The total proportion of raw materials, solvent system, and basic process parameters of this comparative example are completely consistent with those of Example 2. The molar ratio of total acid anhydride components to total diamine components is 1.0:1.01. Nitrogen protection is maintained throughout the process, and the moisture content of the system is ≤50ppm. The synthesis, purification, and drying processes are completely matched with those of Example 2.

[0087] (1) Raw material pretreatment: Prepare a 20wt% diamine / NMP solution under nitrogen protection, heat to remove water until the water content of the system is <50ppm, and cool to room temperature for later use.

[0088] (2) Polymerization reaction: The dianhydride monomer was fed at a rate of 18 kg / min, the temperature was controlled by cold brine at 0℃, and the reaction was stirred at 100 rpm for 3 h; 3 mol% of 1-chlorophthalic anhydride was added and stirred for 6 h, and 100 L of cyclopentane was added and refluxed at 180℃ for 5 h.

[0089] (3) Post-processing: The crystallization separation was carried out by cooling at a rate of 20℃ / min, followed by three-stage washing with acetone at 80℃ and vacuum drying at 280℃ for 2 hours to complete the preparation. The process parameters were exactly the same as those in Example 2.

[0090] (4) Performance test results: The resin does not melt when heated to 370℃, but thermal degradation occurs after continuous heating. The thermal decomposition rate of the resin increases significantly at 530℃, exhibiting typical thermosetting polyimide resin performance.

[0091] Comparative Example 3

[0092] The overall synthesis and post-processing of this comparative example are consistent with those of Example 3, except that the molar ratio of monomer components is adjusted and the molar ratio of total acid anhydride components to total diamine components remains unchanged at 1.0:1.03. Among them, PMDA:BTDA=50%:50%, p-PDA:MDA:APB=40%:30%:30%, nitrogen protection is maintained throughout the process, and the moisture content of the system is ≤50ppm.

[0093] (1) Raw material pretreatment: Prepare a 20wt% diamine / NMP solution under nitrogen protection, heat to remove moisture until it meets the standard, and cool to room temperature for later use.

[0094] (2) Polymerization reaction: The dianhydride monomer was fed at a rate of 18 kg / min, the temperature was controlled by cold brine at 0℃, and the reaction was stirred at 300 rpm for 6 h; 3 mol% of 1-chlorophthalic anhydride was added and stirred for 8 h, and 100 L of cyclopentane was added and refluxed at 170℃ for 5 h.

[0095] (3) Post-processing: Crystallize by cooling at a rate of 10-20℃ / min, wash with three-stage acetone reflux at 60℃ and vacuum dry at 280℃ for 6h to complete the preparation. The process is completely consistent with that in Example 3.

[0096] (4) Performance test results: Thermal performance test results show that the resin starts to melt at 353.2℃ and can be completely melted and plasticized as the temperature rises, exhibiting stable thermoplastic polyimide resin characteristics.

[0097] Based on the results of the examples and comparative examples, it can be seen that the present invention, by employing multi-monomer copolymerization modification combined with optimized polymerization and purification processes, effectively overcomes the drawbacks of traditional pure monomer polyimide resins, such as non-meltability, easy decomposition at high temperatures, and narrow applicability. It achieves controllable modification of the thermoplasticity of polyimide, breaking through processing bottlenecks. By adjusting the ratio of acid anhydride and diamine, the resin melting temperature gradient can be adjusted, adapting to different molding processes and heat resistance requirements. This copolymer system exhibits good formulation tolerance and process stability, and can stably prepare high-performance thermoplastic polyimide resins, demonstrating significantly better versatility than traditional single-formulation systems.

[0098] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A thermoplastic polyimide resin, characterized in that, Including the following raw materials: This thermoplastic polyimide resin uses pyromellitic dianhydride and p-phenylenediamine as the main raw materials, and a combination of benzophenone tetracarboxylic dianhydride, 4,4'-diaminodiphenylmethane and 1,3-bis(4-aminophenoxy)benzene as the modifying material, with N-methylpyrrolidone as the solvent. The molar ratio of the total molar amount of the mixed dianhydrides pyromellitic dianhydride and benzophenone tetracarboxylic dianhydride to the total molar amount of the mixed diamines p-phenylenediamine, 4,4'-diaminodiphenylmethane and 1,3-bis(4-aminophenoxy)benzene is 1:1 to 2. The molar ratio of pyromellitic dianhydride to benzophenone tetracarboxylic dianhydride is 60-80%:20-40%; the molar ratio of p-phenylenediamine:4,4'-diaminodiphenylmethane:1,3-bis(4-aminophenoxy)benzene is 50-60%:20-30%:20-30%.

2. The thermoplastic polyimide resin according to claim 1, characterized in that: The total molar ratio of mixed dianhydrides to mixed diamines is 1.0:1.001 to 1.

03.

3. The method for preparing the thermoplastic polyimide resin according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Under nitrogen protection, the mixed diamines were dissolved in NMP solvent, dehydrated, and then cooled for later use; (2) Mixed dianhydrides were continuously added to the above diamine solution, and prepolymerization was carried out under low temperature conditions. Then, 1-chlorophthalic anhydride was added to carry out the end-capping reaction. (3) Add cyclopentane to the reaction system for azeotropic reflux imidization. After the reaction is complete, put it into acetone solvent to precipitate resin. After cooling and solid-liquid separation, obtain resin filter cake. (4) The resin filter cake was repeatedly suspended and refluxed and washed with acetone; (5) The filter cake obtained from washing is dried under vacuum to obtain thermoplastic polyimide resin powder.

4. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: The entire reaction is protected by nitrogen, and the water content of the protective nitrogen is less than 10 ppm. The water content of the reaction system is controlled below 50 ppm.

5. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: The NMP solvent has a purity of ≥99.8% and a water content of less than 2wt%.

6. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: Before the polymerization reaction, the mixed diamines are prepared into an NMP solution with a mass fraction of 10-20%, and after being heated and dehydrated, the solution is cooled to room temperature for later use.

7. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: The mixed dianhydrides are fed uniformly through a single-screw extruder at a feeding speed of 10–18 kg / min; the system temperature is controlled at -6–0℃ during the polymerization reaction stage, the stirring speed is 100–300 rpm, and the polymerization reaction time is 3–6 h.

8. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: After the polymerization reaction is completed, 1-chlorophthalic anhydride, accounting for 1-3% of the total molar amount of dianhydride, is added as a capping agent, and the reaction is stirred continuously for 6-8 hours; then cyclopentane is added, the temperature is raised to 170-180℃, and the reaction is carried out under constant temperature reflux for 5-7 hours.

9. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: During the resin crystallization purification process, the resin is cooled and crystallized at a cooling rate of 10-20℃ / min. During the multi-stage acetone washing process, an acetone suspension with a resin solid content of 10-20wt% is prepared and refluxed at 60-80℃ for 5-8 hours. The washing filtrate from each stage is reused step by step.

10. The method for preparing the thermoplastic polyimide resin according to claim 3, characterized in that: Vacuum drying was performed using a scraped evaporator, with the drying temperature controlled at 240–280℃ and the vacuum drying time at 2–6 hours, to obtain high-purity thermoplastic polyimide resin.