Polyoxazolidinones prepared by a heterogeneous catalytic mass polymerization and methods

Abstract

The application discloses a polyoxazolidinone prepared by heterogeneous catalytic bulk polymerization and a method, and belongs to the technical field of polymer material synthesis. The method comprises the following steps: uniformly mixing an antioxidant and a polyisocyanate, vacuum drying to obtain a mixed solution; uniformly mixing cardanol diglycidyl ether and bisphenol F diglycidyl ether, vacuum drying to form an epoxide composition; adding 1-butyl-3-methyl imidazole chloride and aluminum trioxide into mesoporous silica, and baking to obtain a supported heterogeneous catalyst; fully dispersing the composition and the catalyst, and then gradually adding the mixed solution under temperature rising, so that the conversion rate of an epoxy group reaches 68-72%; then, the mixed solution is gradually added under temperature rising, so that the conversion rate of the epoxy group is improved; finally, the mixed solution is gradually added under temperature rising, so that the reaction is completed; the filtered filtrate is degassed and granulated, and polyoxazolidinone particles are obtained, so that the purity, mechanical property and thermal stability of the polyoxazolidinone are improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization. Background Technology

[0002] Polyoxazolidinones (POPs) are a class of polymeric materials containing oxazolidinone rings (five-membered heterocycles containing oxygen and nitrogen atoms) in their main chain or side chains. POPs are resistant to acid, alkali, and organic solvent corrosion, making them suitable for harsh chemical environments. They are also stable below 300°C, have a high decomposition temperature, and are suitable for high-temperature environments, such as engine parts, high-temperature seals, and electronic component packaging. The rigid heterocyclic structure in the molecular chain significantly improves the material's strength, modulus, and impact resistance. Their dense molecular structure provides excellent electrical insulation properties, making them suitable for the electronics and electrical fields, such as transformer windings, motor insulation layers, and printed circuit board (PCB) substrates. Some modified POPs (such as those containing phosphorus or halogen groups) are self-extinguishing, meeting flame-retardant material standards, and can be used in fire-retardant coatings for buildings and cable sheaths.

[0003] Current methods for preparing polyoxazolidinones primarily involve the bulk polymerization of diisocyanates and diepoxides using homogeneous ionic liquid catalysis. This process requires staged temperature control, and the homogeneous ionic liquid catalysts used are difficult to separate. Residual catalyst can negatively impact the thermal stability and mechanical properties of the final polyoxazolidinone. Furthermore, these processes often involve continuous sample addition, which can lead to excessively high local reactant concentrations, triggering side reactions and increasing the polydispersity of the polyoxazolidinone product.

[0004] To address the aforementioned issues, researchers have further developed new catalysts, such as magnetic MOF-confined ionic liquid sub-nanostructure catalysts. These catalysts confine catalytically active ionic liquids within the nanopores of magnetic metal-organic frameworks (MOFs). After the reaction, the catalyst can be separated from the reaction system using a magnet, solving the problem of separating homogeneous catalysts. However, this approach yields small-molecule aryl oxazolidinones. Patent CN112996835 A, entitled "Method for Producing Thermoplastic Polyoxazolidinone Polymers," proposes using diisocyanate compounds and diepoxide compounds (such as isosorbide diglycidyl ether), with tetraphenylphosphonium salts (such as tetraphenylphosphonium chloride) as catalysts, to prepare thermoplastic polyoxazolidinones through copolymerization with the assistance of monofunctional isocyanates and / or monofunctional epoxides. This method reduces reaction time and achieves high selectivity for thermoplastic polyoxazolidinones, but it still cannot overcome the problems of homogeneous catalyst residue and product performance in existing polyoxazolidinone bulk polymerization, as well as the defects of side reactions caused by local uneven concentration and difficulty in controlling polydispersity in traditional staged temperature control processes. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization. It solves the problems of homogeneous catalyst residue and product performance impairment in the existing polyoxazolidinone bulk polymerization, and overcomes the defects of side reactions caused by local uneven concentration and difficulty in controlling polydispersity in the traditional staged temperature control process. It also realizes the recyclability and reuse of catalyst and improves the purity and batch stability of polyoxazolidinone.

[0006] This invention is achieved through the following technical solution: A method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization specifically includes the following steps: Step 1: Mix the antioxidant and polyisocyanate evenly, then vacuum dry to obtain a mixture; mix cashew phenol diglycidyl ether and bisphenol F diglycidyl ether evenly, then vacuum dry to form an epoxide composition; add the active component suspension composed of 1-butyl-3-methylimidazolium chloride, aluminum oxide and anhydrous ethanol to mesoporous silica, remove the anhydrous ethanol, calcine at a constant temperature and then sieve to obtain a supported heterogeneous catalyst; Step 2: The epoxide composition and the supported heterogeneous catalyst are fully dispersed to obtain a suspension premixed system. The suspension premixed system is then heated to 151~153℃, and the mixture is added dropwise and dispersed evenly so that the molar ratio of the isocyanate group of the polyisocyanate to the epoxy group of the epoxide composition is (0.723~0.727):(0.975~0.985). The isothermal reaction is carried out to achieve an epoxy group conversion rate of 68~72%, and the first reaction system is obtained. Step 3: The temperature of the first reaction system is raised from 151~153℃ to 177~179℃, and then the mixed liquid is added dropwise and dispersed evenly so that the molar ratio of the isocyanate group of the polyisocyanate to the epoxy group of the epoxide composition is (0.201~0.205):(0.975~0.985). The reaction is carried out at a constant temperature until the epoxy group conversion rate reaches 92~95%, and the second reaction system is obtained. Step 4: The temperature of the second reaction system is increased from 177~179℃ to 214~216℃. Then, equal amounts of the mixed liquid are added dropwise in three separate steps to disperse the mixture evenly, so that the molar ratio of the total isocyanate groups of the polyisocyanate to the epoxy groups of the epoxide composition in the mixed liquid added in steps 2, 3 and 3 is 1:(0.975~0.985). The reaction is carried out at a constant temperature to allow the remaining epoxy groups to react completely with the isocyanate groups, resulting in the third reaction system. The third reaction system is then filtered, and the filtrate is degassed and granulated sequentially to obtain polyoxazolidinone particles.

[0007] A further improvement of the present invention is that: The antioxidant mentioned in step 1 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], the polyisocyanate is tetramethylene xylene 2,4-diisocyanate with a functionality of 1.99±0.03, and the pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 0.075~0.085% of the mass of tetramethylene xylene 2,4-diisocyanate.

[0008] Step 1: Mix cashew phenol diglycidyl ether and bisphenol F diglycidyl ether evenly at a mass ratio of 3:7.

[0009] The supported heterogeneous catalyst described in step 1 is obtained as follows: Mesoporous silica with a pore size of 12.3–12.9 nm, a specific surface area of ​​323–333 m² / g, and an average particle size of 45–55 μm is heated to 540–560 °C at a rate of 3–7 °C / min, then calcined at this temperature for 3–5 h, and naturally cooled to room temperature to obtain pretreated mesoporous silica; 1-Butyl-3-methylimidazolium chloride is dissolved in anhydrous ethanol at a ratio of 1 g:5 mL to form a transparent ionic liquid ethanol solution, and then aluminum oxide with an average particle size of 2 μm is added and ultrasonically dispersed. The mass ratio of butyl-3-methylimidazolium chloride to alumina is 4:1 to form a uniform suspension of active components. Under stirring conditions, the suspension of active components is dropped into pretreated mesoporous silica at a dropping rate of 0.4~0.6 mL / min. The active component suspension accounts for 15.5~16% of the mass of pretreated mesoporous silica. After standing for 25~35 min, anhydrous ethanol is removed. Finally, the temperature is raised to 210~230℃ at a rate of 2~4℃ / min and calcined at a constant temperature for 1.5~2.5 h. After cooling, the catalyst is passed through 200 mesh and 400 mesh standard sieves to obtain a supported heterogeneous catalyst with a particle size of 38~74 μm.

[0010] Step 2: The epoxide composition is heated to 127~129°C at a temperature not lower than 75°C. Then, within 5 minutes, 2.25~2.35% of the total mass of the epoxide composition is added and fully dispersed to obtain a suspension premixed system.

[0011] Step 2: Using a stirring speed of 275-285 rpm, raise the temperature of the suspension premixed system to 151-153℃ at a rate of 1.8-2.2℃ / min. Then, add the mixture dropwise and disperse it evenly until the viscosity is 850-1200 mPa. s, thus obtaining the first reaction system.

[0012] Step 3: Using a stirring speed of 315-325 rpm and a shear frequency of 19-25 Hz, the temperature of the first reaction system is increased from 151-153℃ to 177-179℃ at a rate of 1.7-1.9℃ / min. Then, the mixture is added dropwise at a rate of 1.4-1.6 mL / min to disperse it evenly, so that the viscosity is 2500-3200 mPa. For the first 20 minutes of the isothermal reaction, the stirring speed was 345-355 rpm and the shear frequency was 29-31 Hz. During the remaining time, the shear frequency was gradually reduced to 14-16 Hz at a rate of 1 Hz / 5 min, and the stirring speed was 315-325 rpm to obtain the second reaction system.

[0013] Step 4: Using a stirring speed of 375-385 rpm and a shear frequency of 24-26 Hz, the temperature of the second reaction system is increased from 177-179℃ to 214-216℃ at a rate of 2.0-2.4℃ / min. Then, equal volumes of the mixture are added dropwise in three separate additions, with an interval of 7.5-8.5 min between each addition. The mixture is then dispersed thoroughly until the viscosity reaches 8000-8500 mPa. s, the isothermal reaction allows the remaining epoxy groups to react completely with the isocyanate groups, yielding the third reaction system.

[0014] Step 4: Reduce the temperature of the third reaction system to 164-166℃ and the viscosity to 6000-6500 mPa. The catalyst is filtered at a pressure of 0.25~0.37MPa through a filter with a precision of 7.8~8.2μm to obtain filtrate and filter cake. The filtrate is degassed under vacuum and stirring, and then granulated by twin-screw extrusion to obtain uniform polyoxazolidinone particles of 2.0~4.0mm. The filter cake is washed with anhydrous ethanol and then vacuum dried to obtain a supported heterogeneous catalyst.

[0015] The polyoxazolidinone obtained by the heterogeneous catalytic bulk polymerization method described in any one of the above claims.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention provides a method for preparing polyoxazolidinone via heterogeneous catalytic bulk polymerization. Isothermal calcination allows the active component to form stable bonds with the surface of the mesoporous silica support. The resulting supported heterogeneous catalyst replaces the traditional homogeneous ionic liquid, and an antioxidant inhibits the oxidation of polyisocyanates. The method involves pre-dispersing an epoxide composition with the supported heterogeneous catalyst, followed by the staged addition of a mixture containing polyisocyanates. The initial polymerization reaction of polyoxazolidinone is completed at a first polymerization temperature (151-153°C), achieving the preliminary polymerization of most of the polyisocyanates and efficient oxazolidinone ring formation, while avoiding excessively high local concentrations. The process avoids side reactions such as isocyanate trimerization. In the intermediate temperature range (second polymerization temperature 177~179℃), polyisocyanate is added, representing the intermediate growth stage of the polymerization reaction. By raising the temperature to the second polymerization temperature, the monomer conversion rate is further improved, while balancing melt viscosity growth and material mixing uniformity, avoiding excessive polymer chain entanglement, and laying the foundation for subsequent high-temperature post-polymerization. Post-polymerization in the high-temperature range (214~216℃) is the final stage of the polymerization reaction, also enabling the separation of the supported heterogeneous catalyst. High-temperature post-polymerization achieves complete reaction of the remaining monomers and directional growth of polymer chains, allowing the product to reach the target molecular weight. This invention combines gradient temperature control and shear enhancement to achieve bulk polymerization of diisocyanate and diepoxide, ensuring a stable and controllable polymerization reaction throughout, avoiding side reactions and product performance deviations caused by parameter fluctuations, achieving batch stability ≥98%, and successfully solving the problems of catalyst residue and high product polydispersity in existing processes. The resulting polyoxazolidinone has narrow distribution and high molecular weight characteristics, suitable for injection molding, extrusion and other molding processes, as well as thermoplastic material modification. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0018] This invention provides a method for preparing polyoxazolidinones via heterogeneous catalytic bulk polymerization, the specific steps of which are as follows: Step 1. Dehydration and impurity removal of the polyisocyanate and epoxide compositions, and preparation of the supported heterogeneous catalyst. All raw material processing was carried out in a dust-free, dry operating environment, with humidity controlled below 35% and temperature at 25±2℃. All containers in contact with the raw materials were dried at 120℃ for 2 hours and then cooled to room temperature for later use to ensure no moisture or impurities were introduced. The specific process is as follows: 1.1 Pretreatment of the polyisocyanate composition: Tetramethylene xylene 2,4-diisocyanate (TMXDI) with a functionality of 1.99±0.03 was selected as the polyisocyanate. Its isocyanate group content was determined to be 31.2±0.2% according to DIN EN ISO 14896. There were no other isocyanate impurities with a functionality greater than 2.0, and the purity was ≥99.5%.

[0019] Weigh antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) precisely at 0.08±0.005% of the polyisocyanate mass. It is used only as a trace additive to inhibit isocyanate oxidation. Excessive addition will leave residues in the product and affect its mechanical properties. When adding, use a micro-syringe to add it precisely to ensure uniform dissolution. Slowly add the antioxidant to the three-necked flask containing the polyisocyanate, turn on the magnetic stirrer, stir at 300 rpm, and stir at room temperature for 15 minutes until the antioxidant is completely dissolved and there are no visible particles.

[0020] The above mixture was transferred to a pear-shaped vacuum drying flask, and the vacuum system was connected to a constant temperature water bath. The water bath temperature was set to 65°C, and the vacuum was turned on. The vacuum degree was gradually increased to -0.093±0.002MPa to avoid the material from boiling over due to a sudden increase in vacuum. The material was dried at a constant temperature for 2.5 hours. During the drying process, the drying flask was gently shaken once every 30 minutes to ensure that the material inside the flask was heated evenly and to remove trace amounts of moisture (the moisture content was ultimately controlled to ≤0.03%).

[0021] After drying, transfer the drying bottle to a constant temperature insulated container at 72±1℃ while maintaining a vacuum. After releasing the vacuum, quickly seal the insulated container to keep the polyisocyanate in a liquid state. During the standby period, protect it with a slight positive pressure (0.005MPa) of argon gas in the insulated container to prevent side reactions from contacting air. The standby time should not exceed 8 hours.

[0022] Step 1.2 Pretreatment of the epoxide composition: Cashew phenol diglycidyl ether (epoxy equivalent weight 286±5 g / eq) and bisphenol F diglycidyl ether (epoxy equivalent weight 168±3 g / eq) were accurately weighed at a mass ratio of 3:7. The two diepoxides were added to a double-walled glass reactor equipped with a mechanical stirrer. The stirrer was turned on at 250 rpm and stirred at room temperature for 20 min until the two materials were completely mixed and homogeneous, forming an aliphatic-aromatic composite epoxide composition with an overall functionality of 1.98±0.02 and no epoxide impurities with a functionality greater than 2.0. The final epoxy equivalent weight was 188±4 g / eq, and the epoxy value was determined to be 8.52±0.1% according to DIN EN ISO 3001.

[0023] The above-mentioned compounded epoxide composition was kept under stirring, and hot oil was introduced into the jacket of the double-layered glass reactor to gradually raise the material temperature to 115±2℃. At the same time, the vacuum system was turned on and the vacuum degree was slowly increased to -0.097±0.001MPa. Under these conditions, the material was vacuum dried at a constant temperature for 3 hours to remove trace amounts of moisture (final moisture content ≤0.02%) and low molecular weight volatiles. During the drying process, the stirring speed was kept at 200 rpm to avoid local overheating of the material.

[0024] After drying, maintain a vacuum state and reduce the material temperature to 85±1℃ at a rate of 3℃ / min. Then release the vacuum and introduce 99.99% pure argon gas into the reactor to a slightly positive pressure (0.008MPa). Seal the reactor and store the material at this temperature for no more than 12 hours. During the storage period, turn on the stirrer for 5 minutes (200rpm) every 2 hours to prevent the material from separating.

[0025] Step 1.3 Preparation of Supported Heterogeneous Catalysts Mesoporous silica was selected as the carrier, with a pore size of 12.6±0.3nm, a specific surface area of ​​328±5m² / g, and an average particle size of 50±5μm. The carrier was placed in a muffle furnace and heated to 550℃ at a rate of 5℃ / min, and calcined at a constant temperature for 4h to remove hydroxyl groups, moisture, and impurities from the surface of the carrier. After calcination, the carrier was naturally cooled to room temperature and transferred to a desiccator for later use, ensuring that there was no residual moisture (moisture content ≤0.01%).

[0026] Weigh 1-butyl-3-methylimidazolium chloride (BMIM-Cl, purity ≥99%) and aluminum oxide (Al2O3, analytical grade, average particle size 2μm) precisely at a mass ratio of 4:1. Add 1-butyl-3-methylimidazolium chloride to anhydrous ethanol and stir to dissolve (solid-liquid ratio 1:5, g / mL) to form a transparent ionic liquid ethanol solution. Then slowly add aluminum oxide to the above solution and start ultrasonic dispersion at 300W for 25min until the aluminum oxide is completely dispersed, forming a uniform suspension of active components with no obvious sedimentation.

[0027] The above-mentioned active component suspension was accurately measured according to the carrier absorption capacity (preliminary experimental determination of 1.2 mL / g). The pretreated mesoporous silica carrier was added to a rotary evaporation flask. Under the conditions of room temperature and low-speed stirring (150 rpm), the active component suspension was added dropwise to the carrier at a dropping rate of 0.5 mL / min to ensure that the carrier fully and uniformly adsorbed the suspension without excess liquid residue. The total loading was 15.8 ± 0.2% of the carrier mass.

[0028] The impregnated carrier was placed in a rotary evaporation flask and allowed to stand for 30 minutes to allow the active components to fully diffuse into the mesopores of the carrier. Then, it was connected to a rotary evaporator, and the water bath temperature was set to 80℃ and the vacuum degree to -0.085MPa. The carrier was then rotary evaporated for 1.5 hours to remove anhydrous ethanol. The carrier was then transferred to a muffle furnace and heated to 220℃ at a rate of 3℃ / min. The carrier was then calcined at this temperature for 2 hours to allow the active components to form stable bonds with the surface of the carrier. After calcination, the carrier was allowed to cool naturally to room temperature.

[0029] The calcined catalyst was passed through standard sieves of 200 mesh and 400 mesh in sequence to remove coarse particles larger than 74 μm and fine powder smaller than 38 μm, resulting in a supported heterogeneous catalyst with a particle size of 38~74 μm. The catalyst appeared as a white powder without agglomeration. The catalyst was then placed in a sealed, dry sample bottle and stored in a desiccator for no more than 30 days. Before use, it was dried again under vacuum at 100℃ for 1 hour to ensure no moisture adsorption.

[0030] Step 2. Construct the pre-polymerization system, focusing on achieving uniform pre-dispersion of the epoxide composition and the supported heterogeneous catalyst. The entire process is carried out under argon protection to prevent the introduction of oxygen and moisture. The reaction equipment is a 5L stainless steel reactor with jacketed temperature control, mechanical stirring, built-in shear impeller, and argon inlet and outlet. The reactor body is dried at 150℃ for 3 hours and then cooled to room temperature. After being evacuated to -0.095MPa, the pressure is maintained for 30 minutes to ensure there are no leaks before proceeding with the operation. All material transfers are carried out using positive pressure argon delivery, with no open contact. The specific process is as follows: 2.1 Pre-processing and inertization of the reaction vessel: Inspect the reactor's jacket temperature control system, mechanical stirring system, shearing system, argon inlet and outlet valves, and pressure monitoring device to ensure all systems are operating normally, valves are leak-free, pressure monitoring accuracy is ±0.001 MPa, stirring speed adjustment range is 0~500 rpm, shearing frequency adjustment range is 0~50 Hz, and jacket temperature control accuracy is ±1℃. Introduce 99.999% pure argon gas into the reactor until the pressure reaches 0.1 MPa. Close the argon inlet valve, start stirring (100 rpm), maintain this for 5 minutes, then open the bottom vent valve to slowly release pressure to atmospheric pressure, completing the first purging. Repeat this operation three times. The final oxygen content in the reactor, measured by an online oxygen analyzer, should be ≤50 ppm, ensuring no residual oxygen in the reaction system. After purging, introduce high-purity argon gas into the reactor until the pressure reaches 0.012 ± 0.001 MPa. Close all inlet and outlet valves, maintaining a slight positive pressure of argon gas inside the reactor to prevent external air and moisture from entering.

[0031] 2.2 Addition of epoxide composition and temperature control: The pretreated epoxide composition (85±1℃) is transferred from the double-layered glass reactor to the inertized 5L stainless steel reactor using argon positive pressure feeding. The feeding pressure is 0.05MPa. During the transfer, the temperature of the epoxide composition is kept not lower than 75℃ to prevent a sudden increase in the viscosity of the material. After the transfer is completed, the mass of the added epoxide composition is accurately measured and recorded as M1 (2.5kg is fixed in this process).

[0032] Turn on the mechanical stirring system of the reactor and set the stirring speed to 280±5 rpm. The stirring paddle is a double-layered inclined blade paddle to ensure that there is no material sedimentation at the bottom of the reactor or material adhering to the reactor wall. At the same time, hot oil is introduced into the reactor jacket, and the material temperature is gradually raised to the first premixing temperature T0=128±1℃ through the temperature control system at a heating rate of 2℃ / min to avoid local overheating of the material due to a sudden temperature rise. During the heating process, the actual temperature of the material in the reactor is monitored in real time. After the temperature stabilizes at 128±1℃, it is kept constant for 10 minutes to ensure that the material temperature in the reactor is uniform and there is no temperature difference.

[0033] 2.3 Addition and Pre-dispersion of Supported Heterogeneous Catalysts: The catalyst is precisely supported at 2.3 ± 0.05% of the total mass M1 of the epoxide composition. Insufficient addition will result in a slow reaction rate and insufficient monomer conversion; excessive addition will trigger side reactions such as isocyanate trimerization, leading to increased polydispersity of the product. Precise weighing with an electronic balance (accuracy ± 0.001 g) is used during addition to ensure the actual addition deviates from the theoretical value by ≤ ± 0.05%. The catalyst is added to the solid feed port of the reactor, which has been pre-purged with argon gas three times. The feed port valve is then opened, and the catalyst is slowly added to the reactor under slight positive pressure protection of argon gas. The addition time is controlled within 5 minutes to avoid local agglomeration caused by adding the catalyst all at once. After addition is complete, the feed port valve is closed, and argon gas is introduced again to restore slight positive pressure to the feed port.

[0034] After the catalyst is added, the material temperature in the reactor is maintained at 128±1℃ and the stirring speed is 280±5rpm. The built-in shearing paddle is turned on and the shearing frequency is set to 15±1Hz. The shearing paddle is a toothed dispersion paddle located 5cm below the stirring paddle to ensure that the catalyst is fully dispersed in the epoxide composition. Under these conditions, the material is pre-dispersed at a constant temperature for 35±2min. During the pre-dispersion process, the material state is observed through the sight glass of the reactor every 10min to ensure that there are no catalyst agglomerates and no material adhering to the reactor wall. Finally, a uniform light white suspension premixed system is formed, and the catalyst does not settle significantly in the system.

[0035] After pre-dispersion, turn off the shear paddle and maintain the stirring speed at 280 rpm. Use a sampler to take samples from different locations in the reactor (upper, middle, and lower layers, with 3 sampling points per layer). Use a laser particle size analyzer to determine the dispersed particle size of the catalyst in the sample, ensuring that the dispersed particle size is 45~70 μm and there are no agglomerates with a particle size greater than 100 μm. After passing the test, maintain the premixed system at 128±1℃ and under a slightly positive argon pressure, waiting for the subsequent polymerization reaction to begin. The interval should not exceed 10 minutes to avoid catalyst sedimentation.

[0036] Step 3. The initial reaction stage of polyoxazolidinone polymerization. The core is to complete the dropwise addition and preliminary polymerization of most of the polyisocyanates at the first polymerization temperature. By precisely controlling the dropwise acceleration rate, stirring-shear coordination, and reaction time, the efficient formation of the oxazolidinone ring is achieved, while avoiding side reactions such as isocyanate trimerization caused by excessively high local concentrations. Throughout the process, a slight positive pressure of argon gas (0.012±0.001MPa) is maintained in the reactor, with an oxygen content ≤50ppm, and material temperature fluctuations are controlled within ±2℃. All operations are adjusted based on real-time monitoring data from online viscometers and temperature sensors. The specific process is as follows: Step 3.1 Raise the reaction temperature to the first polymerization temperature T1 Based on the premixed system obtained in step 2.3, maintain the stirring speed at 280±5 rpm, turn off the shear paddle, and introduce hot oil into the reactor jacket. Raise the temperature of the material inside the reactor from 128℃ to the first polymerization temperature T1=152±1℃ at a rate of 2.0±0.2℃ / min. During the heating process, monitor the temperature at different locations (upper, middle, and lower layers) inside the reactor in real time to ensure that the temperature difference is ≤1℃ and there are no local overheating areas.

[0037] After the temperature reaches 152±1℃, keep the jacket temperature constant and continue stirring for 10 minutes to make the temperature of the material in the reactor completely uniform. After confirming that the value displayed by the online temperature sensor is stable at 151~153℃, prepare for the first drop of polyisocyanate.

[0038] Step 3.2 First addition of polyisocyanate Transfer the polyisocyanate, which was kept at a constant temperature of 72±1℃ in step 1.1, to the insulated dropping vessel. After the dropping vessel was purged with argon three times, it was kept under a slight positive pressure (0.008MPa). The dropping pipeline was designed with heat tracing and insulation, and the temperature was controlled at 70±2℃ to prevent the polyisocyanate from condensing and sticking to the wall. Turn on the metering pump between the dropping vessel and the reaction vessel, calibrate the dropping rate, and ensure that the accuracy is ±0.1mL / min.

[0039] The amount of polyisocyanate used must be guaranteed. The molar ratio of epoxy groups in the diepoxide to isocyanate groups in the diisocyanate must be strictly controlled at 1:0.98±0.005. The amount of feed is calculated based on the actual content of the two functional groups: the epoxy group content is determined according to DIN EN ISO 3001 with an accuracy of ±0.5%, and the isocyanate group content is determined according to DIN EN ISO 14896 with an accuracy of ±0.01%. The content of each batch of raw materials is tested before feeding, and the amount of feed is adjusted according to the test results to ensure that the molar ratio deviation is ≤±0.005, so as to avoid the excessive or insufficient residue of a single functional group, which would limit the growth of polymer chains.

[0040] The initial addition amount was determined to be 72.5 ± 0.2% of the polyisocyanate mass. The mechanical stirrer and built-in shear impeller of the reactor were turned on, and the stirring speed was adjusted to 320 ± 5 rpm and the shear frequency was adjusted to 25 ± 1 Hz. After the stirring and shearing system had been running stably for 5 minutes, the metering pump was started for dropping. The dropping rate was controlled at 2.8 ± 0.1 mL / min. The dropping port was located 10 cm below the liquid surface of the reactor and directly opposite the center of the flow field of the stirring impeller to ensure that the added polyisocyanate was dispersed instantly.

[0041] During the dropping process, the viscosity of the melt in the reactor is monitored in real time using an online rotary viscometer, and the viscosity range is controlled to be 850~1200 mPa. s, if the viscosity is below 850 mPa Increase the dropping rate by 0.2~0.3 mL / min; if the viscosity is higher than 1200 mPa Reduce the dropping rate by 0.2~0.3 mL / min while maintaining the material temperature at 151~153℃. If the temperature deviation exceeds ±2℃, adjust the jacket temperature promptly.

[0042] When the added amount reaches the preset 72.5%, turn off the metering pump and the heating of the adding pipeline. Record the actual adding time and amount, and ensure that the deviation between the actual added amount and the theoretical value is ≤0.5%. After the addition is completed, keep the stirring speed at 320±5 rpm and the shear frequency at 25±1 Hz, and continue the reaction for 5 minutes to fully disperse the unreacted isocyanate groups in the system.

[0043] Step 3.3 Low-temperature isothermal polymerization reaction After the dropwise addition is complete, reduce the shear frequency from 25Hz to 20±1Hz, maintain the stirring speed at 320±5rpm, and keep the reactor temperature at 152±1℃ for isothermal polymerization. The isothermal reaction time is 42±1min. Monitor the melt viscosity in real time throughout the process; the viscosity should increase slowly (20mPa). (s / min) to 1800~2200 mPa s, if the viscosity increases too rapidly (more than 20 mPa per minute) (s), appropriately increase the shear frequency to 22~23Hz.

[0044] After reacting at a constant temperature for 42±1 min, stop the shearing paddle and maintain the stirring speed at 200 rpm. Use a sampler preheated to 150℃ to take a sample from the middle layer of the reactor, with a sample size of about 5g. Seal the sample quickly and determine the epoxy value of the sample according to DIN EN ISO 3001. Calculate the epoxy group conversion rate and ensure that the conversion rate reaches 68~72%. If the conversion rate is lower than 68%, extend the constant temperature reaction time and take a sample every 5 min until the conversion rate reaches the target. Keep the temperature and stirring parameters constant during the extended reaction process.

[0045] After the conversion rate reaches the target, observe the state of the material in the reactor. It should be a uniform, light white, viscous suspension with no obvious clumping or stratification, and no bubbles should be generated. Once it is confirmed to be qualified, prepare to enter the medium-temperature reaction stage.

[0046] Step 4. Mid-temperature stage addition and viscosity control: This is the intermediate growth stage of the polymerization reaction. The core process involves gradient heating to the second polymerization temperature to complete the second addition of polyisocyanate, further improving monomer conversion. Simultaneously, dynamic control of stirring and shear parameters balances melt viscosity growth with material mixing uniformity, preventing excessive polymer chain entanglement and laying the foundation for subsequent high-temperature polymerization. Throughout the process, a slight positive pressure of argon gas (0.012±0.001MPa) is maintained inside the reactor. All parameter adjustments follow the principles of slow gradient and real-time monitoring to prevent sudden changes in the system state. The specific process is as follows: Step 4.1 Raise the reaction temperature to the second polymerization temperature T2 Based on the reaction system obtained in step 3.3, maintain a stirring speed of 320±5 rpm and a shear frequency of 20±1 Hz, and introduce hot oil into the reactor jacket to raise the temperature of the material inside the reactor from 152℃ to the second polymerization temperature T2=178±1℃ at a rate of 1.8±0.1℃ / min. During the heating process, monitor the melt viscosity in real time, and the viscosity increase should be controlled within 15~20 mPa per minute. If the increase is too rapid, the shear frequency should be appropriately increased to 22~25Hz.

[0047] After the temperature reaches 178±1℃, maintain a constant jacket temperature and continue stirring and shearing for 10 minutes to ensure uniform material temperature within the reactor. The temperature difference between the three monitoring points should be ≤1℃, and the online viscometer should display a stable viscosity between 2200~2400 mPa. After s, prepare for the second addition of polyisocyanate.

[0048] Step 4.2 Second addition of polyisocyanate Recalibrate the heating temperature (70±2℃) of the remaining polyisocyanate in the insulated dropping vessel. Determine the amount to be added for the second time based on 20.3±0.2% of the mass of polyisocyanate. Start the metering pump and adjust the dropping rate to 1.5±0.1mL / min. During the dropping process, maintain the stirring speed at 350±5rpm (appropriately increase it in the lower temperature range to enhance mixing). Adjust the shear frequency to 30±1Hz (high shear reduces local viscosity and avoids agglomeration).

[0049] During the dropwise addition process, the melt viscosity is strictly controlled within the range of 2500~3200 mPa by real-time monitoring with an online viscometer. s, if the viscosity is close to 3200 mPa For s, reduce the dropping rate by 0.1~0.2 mL / min, while increasing the shear frequency to 32~33 Hz; if the viscosity is below 2500 mPa Increase the dropping rate by 0.1~0.2 mL / min, maintain the shearing frequency at 30 Hz, and keep the material temperature at 177~179℃ throughout the process.

[0050] After the addition is complete, turn off the metering pump, maintain the stirring speed at 350±5 rpm and the shear frequency at 30±1 Hz, and continue the reaction for 5 minutes to ensure sufficient contact between the isocyanate groups and epoxy groups in the system. At this point, the melt viscosity should stabilize at 3000~3200 mPa. s, no local viscosity anomaly region.

[0051] Step 4.3 Isothermal polymerization and viscosity control in the intermediate temperature range After the addition is complete, a constant temperature polymerization reaction is started for 42±1 min. For the first 20 min, the stirring speed is maintained at 350±5 rpm and the shear frequency at 30±1 Hz to allow the monomer to react quickly. For the remaining time, the shear frequency is gradually reduced to 15±1 Hz at a rate of 1 Hz / 5 min, while the stirring speed is maintained at 320±5 rpm to slowly reduce the shear force, avoid polymer chain breakage, and promote moderate chain growth.

[0052] During the isothermal reaction, the melt viscosity should rise slowly and steadily to 4500~5000 mPa. s, if the viscosity rise rate exceeds 30 mPa per minute s, pause reducing the shear frequency and maintain the current shear parameters until the viscosity stabilizes; if the viscosity increases too slowly (the increase is less than 10 mPa per minute). (s), appropriately reduce the shearing frequency to 12~13Hz to promote chain growth.

[0053] After reacting at a constant temperature for 38 minutes, sample and test the epoxy group conversion rate according to the method in step 3.3 to ensure that the conversion rate reaches 92-95%. If the conversion rate does not meet the standard, continue the reaction at a constant temperature, and take samples for testing every 4 minutes. During the extension, maintain a stirring speed of 320 rpm and a shear frequency of 15 Hz until the conversion rate meets the standard. After meeting the standard, the melt viscosity should be controlled at 4800-5000 mPa. The system is a uniform, viscous suspension with no particulate matter.

[0054] Step 4.4 Preparation of the intermediate temperature end-point system After the conversion rate reaches the target, maintain the temperature inside the reactor at 178±1℃, the stirring speed at 320±5rpm, and the shear frequency at 15±1Hz for 5 minutes. Confirm that the temperature, viscosity, and pressure parameters monitored online are stable and there are no fluctuations, and that there are no bubbles or lumps inside the reactor. Then, prepare to start the high-temperature section heating program. Before heating, restore the shear frequency to 25±1Hz to prepare for the high-temperature section melt mixing.

[0055] Step 5. High-temperature post-polymerization and catalyst separation is the final stage of the polymerization reaction and the catalyst separation process. The core of this step is to achieve complete reaction of the remaining monomers and directional growth of the polymer chains through high-temperature post-polymerization, ensuring the product reaches the target molecular weight. Simultaneously, precise cooling and pressure filtration operations achieve efficient separation and recovery of the supported heterogeneous catalyst. The melt viscosity is controlled throughout the process to avoid excessive equipment load. The catalyst separation process ensures no material loss and no catalyst residue. The purity of the resulting crude polyoxazolidinone melt meets the requirements for subsequent post-processing. The specific process is as follows: Step 5.1 Raise the reaction temperature to the final polymerization temperature T3 Based on the reaction system obtained in step 4.4, maintain a stirring speed of 380±5 rpm (the melt viscosity is high in the high-temperature section, so increasing the speed enhances mixing) and a shear frequency of 25±1 Hz. Introduce hot oil into the reactor jacket and raise the temperature of the material inside the reactor from 178℃ to the final polymerization temperature T3=215±1℃ at a rate of 2.2±0.2℃ / min. Monitor the melt viscosity in real time during the heating process, and control the viscosity increase to 40~50 mPa per minute. s, if the viscosity exceeds 5500 mPa s, increasing the shear frequency to 28~30Hz.

[0056] After the temperature reaches 215±1℃, maintain a constant jacket temperature and continue stirring and shearing for 10 minutes to ensure uniform material temperature within the reactor. The temperature difference between the three monitoring points should be ≤1℃, and the online viscometer should display a stable viscosity of 6000~6500 mPa. After s, preparations will be made to add the remaining polyisocyanate.

[0057] Step 5.2 Add the remaining polyisocyanate in batches. The remaining amount to be added is determined as 7.2±0.4% of the total mass of polyisocyanate. The addition is carried out in batches instead of continuous dripping to avoid local side reactions caused by continuous dripping at high temperature. The addition is completed in 3 batches, with each addition being of equal amount and an interval of 8±0.5 min between adjacent additions.

[0058] For the first addition, turn on the metering pump and rapidly add the corresponding amount of polyisocyanate at a rate of 3.0 mL / min. After the addition is complete, turn off the metering pump and maintain the stirring speed at 380±5 rpm and the shear frequency at 25±1 Hz for 8 minutes. During this period, the viscosity should rise to 7000~7500 mPa. s; After repeating the above operation, add the mixture twice, reacting for 8 minutes after each addition. After the third addition, the melt viscosity should stabilize at 8000~8500 mPa. s.

[0059] After all the remaining polyisocyanate was added, the dripping line was checked and found to be free of residue, and there was no localized clumping of the material in the reactor. The online monitoring showed a temperature of 214~216℃ and a viscosity of 8000~8500 mPa. After the parameters stabilize, the process enters the high-temperature isothermal polymerization stage.

[0060] Step 5.3 Polymerization after isothermal treatment in the high-temperature section Maintain the temperature inside the reactor at 215±1℃, the stirring speed at 380±5rpm, and the shear frequency at 25±1Hz for 55±1min of isothermal post-polymerization reaction. The core of this stage is to achieve the complete reaction of the remaining epoxy groups and isocyanate groups, as well as the moderate growth of the polymer chain, so that the number average molar mass reaches the target range.

[0061] During post-polymerization, the melt viscosity should slowly increase to 8500~9800 mPa. s, if the viscosity exceeds 9800 mPa The shearing frequency was increased to 30-32 Hz, while the stirring speed was reduced to 360 rpm to reduce the equipment load without changing the reaction temperature. The state of the material in the reactor was observed throughout the process. There were no bubbles or stratification, and the catalyst was still uniformly suspended in the melt without sedimentation or agglomeration.

[0062] After reacting at a constant temperature for 55 min, samples were taken to test the content of free isocyanate groups, ensuring that the content is ≤0.1%. At the same time, the number-average molar mass was rapidly determined by gel permeation chromatography (GPC), ensuring that it is ≥20000 g / mol with an accuracy of ±500 g / mol, and the polydispersity is ≤2.8 with an accuracy of ±0.1. If the content of free isocyanate groups exceeds the standard, the number-average molar mass is too low, or the polydispersity is too high, the reaction time at a constant temperature is extended, and samples are taken for testing every 5 min until the standard is met.

[0063] Step 5.4 Preparations before cooling the polymerization system and separating the catalyst After the post-polymerization endpoint is reached, turn off the shear impeller, maintain the stirring speed at 380 rpm, and circulate cooling oil into the reactor jacket to reduce the temperature of the material inside the reactor from 215℃ to 165±1℃ at a rate of 3.0±0.3℃ / min. During the cooling process, monitor the melt viscosity in real time; the viscosity should slowly decrease to 6000~6500 mPa. If the viscosity increases sharply during the cooling process, increase the stirring speed to 400 rpm.

[0064] A precision filter device is connected to the bottom of the reactor. The filter device is a plate and frame filter press structure. The filter membrane is made of stainless steel sintered filter plate with a pore size of 8±0.2μm to ensure complete retention of the catalyst (particle size 38~74μm) and no catalyst residue in the filtrate (residual amount ≤10ppm). After drying at 150℃ and purging with argon, the filter device is sealed to the reactor. The filter pipeline is heated to 160±2℃ to prevent the melt from condensing and sticking to the wall. Prepare a filter press argon tank and adjust the pressure to 0.4MPa for standby.

[0065] After the temperature drops to 165±1℃, reduce the stirring speed to 150±5 rpm and maintain this position for 10 minutes to ensure the melt is homogeneous and the catalyst suspension is stable. This prevents high-speed stirring from clogging the filter membrane during filtration. At this point, the melt viscosity should be stable between 6000 and 6500 mPa. s.

[0066] Step 5.5 Supported heterogeneous catalyst pressure filtration separation Open the valve between the reactor and the filter device, start the pressure filter argon tank, and press the polyoxazolidinone melt in the reactor into the filter device at a constant pressure of 0.35±0.02MPa. Too high a pressure will cause the filter membrane to break and the catalyst to leak, while too low a pressure will cause the filtration speed to be too slow and the material to stagnate. During the pressure filter process, maintain the melt temperature at 163~167℃ and the stirring speed at 150rpm to ensure that the melt flows smoothly without turbulence.

[0067] Observe the filtration status through the sight glass of the filtration device. The filtrate should be a colorless, transparent to pale yellow viscous melt without solid particles, and the filter cake should be a supported catalyst without melt entrainment. If the filtrate is observed to be turbid, immediately reduce the filtration pressure to 0.25 MPa and continue filtration until the filtrate is clear.

[0068] After the pressure filtration is completed, first close the argon pressure tank, then close the valve between the reactor and the filtration device, collect the filtrate in the filtration device, which is the crude polyoxazolidinone melt. Accurately measure the mass of the filtrate to ensure that the material yield is ≥99%. Open the filtration device and collect the filter cake (the recovered supported catalyst), with a catalyst recovery rate of ≥95%.

[0069] Step 5.6 Preliminary treatment of recovered catalyst The collected recovered catalyst was transferred to a dry container, and anhydrous ethanol was added at 5 times the mass of the catalyst. The mixture was stirred and washed for 10 min to remove the polymer melt adhering to the surface. Then, it was filtered. The washed catalyst was placed in a vacuum drying oven at 105±2℃ with a vacuum degree of -0.095MPa and dried for 2 h to remove the ethanol. The dried catalyst was placed in a desiccator for later use. The recovery rate was ≥95%, and it could be directly reused in the next batch of polymerization reaction. The number of reuses was ≥5 times, and the catalytic efficiency decreased by ≤10% after reuse (based on the epoxy group conversion rate within the same reaction time). No re-calcination was required before reuse.

[0070] Step 5.7 Temporary storage of crude polyoxazolidinone melt The crude polyoxazolidinone melt obtained from filtration was transferred to a constant temperature storage tank at 160±2℃. After being purged with argon gas, the storage tank was kept under a slight positive pressure (0.008MPa) for no more than 30 minutes. Then, it immediately entered the melt post-processing stage to avoid thermal degradation caused by prolonged placement of the melt at high temperature.

[0071] Step 6. Melt post-treatment is the final stage in the preparation of the polyoxazolidinone finished product. The core process involves degassing and granulating the crude polyoxazolidinone melt obtained in Step 5.7 to thoroughly remove trace amounts of low-molecular-weight byproducts and dissolved gases, preventing defects such as bubbles and shrinkage cavities in the finished product. Simultaneously, precise control of extrusion granulation parameters ensures the production of polyoxazolidinone granules with uniform particle size and good flowability. The melt temperature is maintained within the process range throughout to prevent thermal degradation and chain segment breakage. All equipment undergoes drying and inertization treatment, ensuring no moisture or oxygen is introduced. The specific process is as follows: Step 6.1 Preparation of crude melt transfer and degassing equipment The crude polyoxazolidinone melt in the 160±2℃ constant temperature temporary storage tank was transferred to a 5L vacuum degassing reactor by argon positive pressure conveying at a pressure of 0.06±0.01MPa. The transfer pipeline was designed with heat tracing and insulation, and the temperature was controlled at 158±2℃ to prevent the melt from condensing and sticking to the wall. During the transfer process, the melt was kept in contact with no open parts. The transfer was completed under argon protection. The mass of the transferred melt was accurately measured to ensure a material yield of ≥99.5%.

[0072] The vacuum degassing vessel is a stainless steel reactor equipped with a jacketed temperature control, anchor stirring, vacuum system, and tail gas collection device. Before use, it is dried at 150°C for 3 hours, cooled to room temperature, and then evacuated to -0.098MPa and held for 30 minutes to ensure no leakage. High-purity argon gas is introduced into the vessel to atmospheric pressure, and then evacuated again to -0.098MPa to complete the inertization process and ensure that the oxygen content in the vessel is ≤50ppm.

[0073] Turn on the hot oil circulation in the jacket of the degassing vessel to preheat the temperature inside the vessel to 158±1℃. Turn on the anchor stirring and adjust the speed to 120±5rpm. The gap between the stirring paddle and the bottom and wall of the vessel should be ≤5mm to ensure that there are no dead corners or local stagnation in the melt stirring.

[0074] Step 6.2 Vacuum degassing treatment After adding the crude melt to the degassing vessel, maintain the stirring speed at 120±5 rpm and the temperature at 158±1℃, turn on the vacuum system, and use a gradient vacuum method to avoid the melt from boiling and spraying due to a sudden increase in vacuum: first increase the vacuum to -0.03MPa and hold for 5 minutes; then increase it to -0.06MPa and hold for 5 minutes; finally slowly increase it to -0.098±0.001MPa, taking a total of 10 minutes, with a vacuum control accuracy of ±0.002MPa.

[0075] After the vacuum degree reaches -0.098MPa, the jacket temperature is maintained at 158±1℃ and the stirring speed is 120±5rpm for 28±1min of constant temperature vacuum degassing to remove dissolved argon gas and trace amounts of low molecular weight byproducts generated in the reaction (such as a small amount of isocyanate oligomers). During the degassing process, the low molecular weight substances are collected by the tail gas collection device to ensure that no harmful gas is emitted.

[0076] During degassing, observe the melt state in real time. It should be a uniform viscous melt without bubbles or boiling. If small bubbles are observed to precipitate on the surface of the melt, reduce the stirring speed to 100 rpm and restore it to 120 rpm after the bubbles disappear. Monitor the vacuum and temperature throughout the process, and control the fluctuations within ±0.002 MPa and ±1℃, respectively.

[0077] After degassing for 28 minutes, turn off the vacuum system and slowly introduce high-purity argon into the reactor to a slight positive pressure (0.005 MPa). Take a sample to observe the state of the melt. There should be no visible bubbles. After the melt stands for 1 minute, no bubbles should precipitate on the surface, indicating that the degassing is qualified. If it does not meet the standard, continue degassing at -0.098 MPa for 5 minutes until it is qualified.

[0078] Step 6.3 Preparations before extrusion granulation A twin-screw extruder (screw diameter 20mm, length-to-diameter ratio 30:1) was selected. Before granulation, the extruder barrel, screw, and die were preheated in sections: Zone 1 155℃, Zone 2 158℃, Zone 3 160℃, and die 158±1℃, for a preheating time of 30 minutes, ensuring that the temperature of each section was stable within ±1℃. The vacuum exhaust port of the extruder was evacuated to -0.095±0.002MPa, and the die orifice diameter was 2.0±0.1mm, with a total of 12 orifices, and there was no blockage.

[0079] The degassed polyoxazolidinone melt is transported to the extruder hopper via a melt pump at the bottom of the degassing reactor. The melt pump speed is 20±2 r / min, the conveying pressure is 0.2±0.02 MPa, the hopper is kept at a constant temperature of 155±1℃, and argon gas is introduced under slight positive pressure (0.005 MPa) for protection to prevent the melt from contacting air, cooling down and forming a crust.

[0080] Step 6.4 Twin-screw extrusion granulation Start the twin-screw extruder and adjust the screw speed to 80±5 rpm. Match the feeding rate with the melt pump delivery rate to ensure that the melt filling rate in the barrel is 70~80%, without idling or bridging. If the screw torque exceeds 80% of the rated value, immediately reduce the feeding rate to prevent melt from sticking to the wall and causing equipment overload. If the die head becomes clogged, immediately stop feeding and heat to 165℃ to clean it, avoiding high-temperature degradation of the melt. The extruder vacuum exhaust port should be kept at -0.095MPa to further remove trace gases dissolved in the melt during transportation.

[0081] The melt is extruded through the die to form a strip with a diameter of 2.0±0.1mm. The strip immediately enters the water bath cooling tank, which adopts multi-stage temperature control: zone 1 45±2℃, zone 2 30±2℃, and zone 3 25±2℃. The strip stays in the cooling tank for 15±2s to ensure rapid and uniform cooling and avoid the strip sticking and deformation. After cooling, the strip temperature is ≤30℃.

[0082] After cooling, the material strips are fed into the pelletizer by a traction machine. The pelletizer rotates at 300±10 rpm and the pellet length is 3.0±0.2 mm. After pelleting, the pellets are fed into a vibrating screen with a double-layer screen: the upper screen has a mesh size of 4.0 mm to remove excessively long and agglomerated particles; the lower screen has a mesh size of 2.0 mm to remove excessively fine and broken particles. The vibration frequency of the screen is 50±2 Hz and the amplitude is 3±0.5 mm.

[0083] Step 6.5 Finished Product Drying and Packaging The sieved polyoxazolidinone particles were sent into a vacuum drying oven, and the temperature was set at 60±2℃ and the vacuum degree at -0.085±0.002MPa for 2 hours to remove the moisture adsorbed on the particle surface. The moisture content of the dried particles was ≤0.02%.

[0084] Randomly sample and test the performance of the finished product. The number average molar mass should be ≥20000g / mol, the polydispersity should be ≤2.8, the melt flow rate should be determined according to GB / T3682 (230℃ / 2.16kg) as 8.5±0.5g / 10min with an accuracy of ±0.2g / 10min, and the appearance should be white and uniform granules, without yellowing, bubbles, or adhesion. Only after passing the test can the product be packaged.

[0085] The dried finished product is packaged in a dust-free environment with humidity below 35% and temperature of 25±2℃ using aluminum-plastic composite bags, each weighing 25±0.1kg. Before packaging, high-purity argon gas is introduced into the bag to replace the air. After sealing, a label is affixed, indicating the product batch, production date, and performance indicators. The product is then stored in a dry and ventilated warehouse at a temperature ≤30℃, avoiding direct sunlight.

[0086] The above polymerization reaction (including pretreatment, pre-configuration, and post-treatment) is protected by 99.999% high-purity argon gas throughout. All reaction equipment, storage containers, and delivery pipelines are purged with argon gas at least 3 times, and the final oxygen content is ≤50ppm. During the reaction, a slight positive pressure of argon gas is maintained inside the equipment to prevent outside air from seeping in. The slight positive pressure is automatically controlled by a pressure regulating valve with a deviation of ±0.001MPa.

[0087] The moisture content of all raw materials, equipment, and pipelines is controlled to be ≤0.03%, of which the epoxide composition is ≤0.02%, the polyisocyanate is ≤0.03%, and the catalyst is ≤0.01%. Before use, the equipment is dried at 120~150℃ for 2~3 hours, and the pipelines are dried with hot air (100℃, drying time 1 hour). Contact with water is avoided throughout the process to prevent isocyanate from reacting with water to form urea bonds and trigger cross-linking side reactions.

[0088] All raw material pretreatment, catalyst preparation, and material transfer operations are carried out in a dust-free and dry environment with an ambient humidity of ≤35% and a temperature of 25±2℃. The work surface is covered with waterproof and non-stick polytetrafluoroethylene board. Glassware and metal tools are dried and cooled before use to avoid the introduction of impurities and moisture.

[0089] The above reaction temperature has the following gradient and precision control: The polymerization reaction adopts a three-stage gradient heating, with the heating rate controlled at 1.8~2.2℃ / min. The temperature of each stage strictly follows the following: premixing temperature 128±1℃ → low temperature polymerization temperature 152±1℃ → medium temperature polymerization temperature 178±1℃ → high temperature polymerization temperature 215±1℃ → cooling and filtration temperature 165±1℃ (cooling rate 3.0℃ / min) → degassing temperature 158±1℃, to avoid local overheating or sudden changes in melt viscosity caused by sudden temperature rises and drops.

[0090] The actual temperature deviation of materials in all reaction stages is ≤±1℃, and the temperature deviation of the equipment jacket is ≤±0.5℃. The intelligent temperature control system monitors and regulates the temperature in real time. Three layers of temperature sensors are installed inside the reactor, with a detection accuracy of ±0.1℃. If the temperature deviation at a certain monitoring point exceeds ±2℃, the jacket temperature is adjusted to ensure that the temperature of the materials inside the reactor is uniform and the temperature difference is ≤1℃.

[0091] Previously, we explained the main viscosity adjustments. For situations not previously addressed, if the viscosity deviates from the threshold, we can adjust the dropping rate, stirring speed, and shear frequency in a coordinated manner. Prioritize adjusting the dropping rate ± (0.1~0.3 mL / min), then adjust the shear frequency ± (1~5 Hz), and finally fine-tune the stirring speed ± (10~20 rpm). This avoids abrupt changes in the system state due to large adjustments to a single parameter, ensuring the melt viscosity remains within the process range. This prevents excessive equipment load due to excessively high viscosity or incomplete reaction due to excessively low viscosity. In the low viscosity stage, shear-enhanced dispersion is the primary method, while in the high viscosity stage, stirring-enhanced mixing is the primary method. Furthermore, the relationship between viscosity and shear frequency ensures that the hydrodynamic state is adapted to the reaction requirements.

[0092] When the slight positive pressure inside the reactor exceeds the set value during the polymerization reaction, the vent valve is opened to slowly release the pressure. When the pressure falls below the set value, argon gas is added in time to prevent air from seeping in. The pressure detection accuracy is ±0.001MPa.

[0093] This invention covers all dimensions of material proportioning, reaction environment, fluid dynamics, equipment operation, and quality monitoring. All parameters are set with precise control ranges and deviation thresholds. Through online monitoring, real-time adjustment, and staged detection, the entire polymerization reaction is ensured to be stable and controllable, avoiding side reactions and product performance deviations caused by parameter fluctuations. Simultaneously, it guarantees equipment operational safety and achieves batch stability of ≥98%. Due to the extensive content of the above scheme and the fact that most reagents and parameters are already clearly defined, subsequent examples only list specific details not previously addressed to avoid unnecessary repetition.

[0094] Example 1 1. Experimental materials and process parameters Polyisocyanates: TMXDI 1.872 kg (isocyanate group content 31.1%), antioxidant 1010 added 1.498 g.

[0095] Epoxide composition: 0.75 kg of cashew phenol diglycidyl ether + 1.75 kg of bisphenol F diglycidyl ether (final epoxy equivalent weight is 186 g / eq, epoxy value is 8.58%).

[0096] Supported catalyst: BMIM-Cl / Al2O3 supported on a mesoporous silica support, with an addition amount of 57.43 g (2.297% of the mass of the epoxide composition).

[0097] Core ratio: Molar ratio of epoxy groups to isocyanate groups 1:0.978.

[0098] Reaction temperature: premix 127.8℃ → low temperature section 151.6℃ → medium temperature section 177.9℃ → high temperature section 214.8℃.

[0099] Dropping parameters: First drop volume 1.357 kg (72.5%), dropping rate 2.76 mL / min; Second drop volume 0.380 kg (20.3%), dropping rate 1.48 mL / min; The remaining 0.135 kg (7.2%) was added in 3 separate drops of 0.045 kg each.

[0100] 2. Experimental Results Epoxy group conversion rate: 70.3% at the end of the low temperature range and 93.7% at the end of the medium temperature range.

[0101] Free isocyanate group content: 0.087%.

[0102] Product properties: Number average molar mass 21460 g / mol, polydispersity 2.63; melt flow rate (230℃ / 2.16 kg) 8.32 g / 10 min.

[0103] Material yield: 99.2%.

[0104] Catalyst recovery rate: 95.8%, catalytic efficiency decreased by 7.2% after reuse (70.3% for the first epoxy group conversion, 65.3% after 5 reuses).

[0105] Example 2 1. Experimental materials and process parameters Polyisocyanates: TMXDI 1.865 kg (isocyanate group content 31.3%), antioxidant 1010 added 1.492 g.

[0106] Epoxide composition: 0.75 kg of cashew phenol diglycidyl ether + 1.75 kg of bisphenol F diglycidyl ether (final epoxy equivalent weight is 189 g / eq, epoxy value is 8.47%).

[0107] Supported catalyst: 57.68 g (2.307% of the mass of the epoxide composition).

[0108] Core ratio: Molar ratio of epoxy groups to isocyanate groups 1:0.982.

[0109] Reaction temperature: premix 128.3℃ → low temperature section 152.4℃ → medium temperature section 178.2℃ → high temperature section 215.3℃.

[0110] Dropping parameters: First drop volume 1.351 kg (72.4%), dropping rate 2.83 mL / min; second drop volume 0.379 kg (20.4%), dropping rate 1.52 mL / min; the remaining 0.135 kg (7.2%) was added in 3 separate drops of 0.045 kg each.

[0111] 2. Experimental Results Epoxy group conversion rate: 69.5% at the end of the low temperature range and 94.2% at the end of the medium temperature range.

[0112] Free isocyanate group content: 0.093%.

[0113] Product properties: Number average molar mass 22180 g / mol, polydispersity 2.71; melt flow rate (230℃ / 2.16 kg) 8.67 g / 10 min.

[0114] Material yield: 99.1%.

[0115] Catalyst recovery rate: 96.3%, catalytic efficiency decreased by 8.5% after reuse (initial epoxy group conversion rate 69.5%, 63.7% after 5 reuses).

[0116] Example 3 1. Experimental materials and process parameters Polyisocyanates: TMXDI 1.881 kg (isocyanate group content 31.0%), antioxidant 1010 added 1.505 g.

[0117] Epoxide composition: 0.75 kg of cashew phenol diglycidyl ether + 1.75 kg of bisphenol F diglycidyl ether (final epoxy equivalent weight is 189 g / eq, epoxy value is 8.45%).

[0118] Supported catalyst: 57.28 g (2.291% of the mass of the epoxide composition).

[0119] Core ratio: Molar ratio of epoxy groups to isocyanate groups 1:0.976.

[0120] Reaction temperature: premix 127.6℃ → low temperature section 151.8℃ → medium temperature section 177.7℃ → high temperature section 214.6℃.

[0121] Dropping parameters: First drop volume 1.364 kg (72.6%), dropping rate 2.78 mL / min; second drop volume 0.383 kg (20.4%), dropping rate 1.47 mL / min; the remaining 0.134 kg (7.1%) was added in 3 portions of 0.045 kg each (the third portion was 0.044 kg).

[0122] 2. Experimental Results Epoxy group conversion rate: 71.2% at the end of the low temperature range and 94.5% at the end of the medium temperature range.

[0123] Free isocyanate group content: 0.082%.

[0124] Product properties: Number average molar mass 20850 g / mol, polydispersity 2.68; melt flow rate (230℃ / 2.16 kg) 8.45 g / 10 min.

[0125] Material yield: 99.3%.

[0126] Catalyst recovery rate: 95.5%, catalytic efficiency decreased by 6.8% after reuse (71.2% for the first epoxy group conversion, 66.4% after 5 reuses).

[0127] Example 4 1. Experimental materials and process parameters Polyisocyanates: TMXDI 1.869 kg (isocyanate group content 31.2%), antioxidant 1010 added 1.495 g.

[0128] Epoxide composition: 0.75 kg of cashew phenol diglycidyl ether + 1.75 kg of bisphenol F diglycidyl ether (final epoxy equivalent weight is 187 g / eq, epoxy value is 8.54%).

[0129] Supported catalyst: 57.55 g (2.302% of the mass of the epoxide composition).

[0130] Core ratio: Molar ratio of epoxy groups to isocyanate groups 1:0.980.

[0131] Reaction temperature: premix 128.1℃ → low temperature section 152.2℃ → medium temperature section 178.1℃ → high temperature section 215.1℃.

[0132] Dropping parameters: First drop volume 1.354 kg (72.5%), dropping rate 2.81 mL / min; second drop volume 0.378 kg (20.2%), dropping rate 1.51 mL / min; the remaining 0.137 kg (7.3%) was added in 3 portions of 0.046 kg each (the third portion was 0.045 kg).

[0133] 2. Experimental Results Epoxy group conversion rate: 68.9% at the end of the low temperature range and 92.8% at the end of the medium temperature range.

[0134] Free isocyanate group content: 0.096%.

[0135] Product properties: Number average molar mass 21730 g / mol, polydispersity 2.75; melt flow rate (230℃ / 2.16 kg) 8.72 g / 10 min.

[0136] Material yield: 99.0%.

[0137] Catalyst recovery rate: 96.1%, catalytic efficiency decreased by 9.1% after reuse (initial epoxy group conversion rate 68.9%, 62.6% after 5 reuses).

[0138] Experimental results from four examples demonstrate that the process is stable and reliable: the number-average molar mass of the product reaches over 20,000 g / mol (20,850~22,180 g / mol), the polydispersity is controlled between 2.63 and 2.75 (≤2.8), and the free isocyanate group content is ≤0.096%, meeting the requirements for high molecular weight and narrow distribution products; the overall material yield is ≥99.0%, the supported catalyst recovery rate is ≥95.5%, and the catalytic efficiency decreases by ≤9.1% after 5 reuses, achieving efficient recovery and recycling of the catalyst. The obtained polyoxazolidinone particles have a uniform appearance and good melt flow properties (8.32~8.72 g / 10 min), making them fully suitable for injection molding, extrusion, and other molding processes, as well as for the modification of thermoplastic materials. The product batch stability is high, indicating promising prospects for industrial application.

Claims

1. A method for preparing polyoxazolidinone via heterogeneous catalytic bulk polymerization, characterized in that, Includes the following steps: S1, antioxidant and polyisocyanate are mixed evenly and then vacuum dried to obtain a mixture; cashew phenol diglycidyl ether and bisphenol F diglycidyl ether are mixed evenly and then vacuum dried to form an epoxide composition; an active component suspension consisting of 1-butyl-3-methylimidazolium chloride, aluminum oxide and anhydrous ethanol is added to mesoporous silica, anhydrous ethanol is removed, and after constant temperature calcination and sieving, a supported heterogeneous catalyst is obtained; S2, the epoxide composition and the supported heterogeneous catalyst are fully dispersed to obtain a suspension premix system. The suspension premix system is then heated to 151~153℃, and then a mixture is added dropwise and dispersed evenly so that the molar ratio of the isocyanate group of the polyisocyanate to the epoxy group of the epoxide composition is (0.723~0.727):(0.975~0.985). The isothermal reaction is carried out to achieve an epoxy group conversion rate of 68~72%, and the first reaction system is obtained. S3, the temperature of the first reaction system is raised from 151~153℃ to 177~179℃, and then a mixed liquid is added dropwise and dispersed evenly so that the molar ratio of the isocyanate group of the polyisocyanate to the epoxy group of the epoxide composition is (0.201~0.205):(0.975~0.985). The reaction is carried out at a constant temperature until the epoxy group conversion rate reaches 92~95%, and the second reaction system is obtained. S4, the second reaction system is heated from 177~179℃ to 214~216℃, and then equal amounts of mixed liquid are added dropwise in three batches to disperse evenly, so that the molar ratio of total isocyanate groups of polyisocyanate to epoxy groups of epoxide composition in S2, S3 and the three added mixed liquids is 1:(0.975~0.985). The reaction is carried out at a constant temperature to allow the remaining epoxy groups to react completely with the isocyanate groups, resulting in a third reaction system. The third reaction system is filtered, and the filtrate is degassed and granulated in sequence to obtain polyoxazolidinone particles.

2. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, The antioxidant described in S1 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], the polyisocyanate is tetramethylene xylene 2,4-diisocyanate with a functionality of 1.99±0.03, and the pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is 0.075~0.085% of the mass of tetramethylene xylene 2,4-diisocyanate.

3. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, S1 mixes cashew phenol diglycidyl ether and bisphenol F diglycidyl ether evenly at a mass ratio of 3:

7.

4. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, The supported heterogeneous catalyst described in S1 is obtained through the following process: Mesoporous silica with a pore size of 12.3~12.9nm, a specific surface area of ​​323~333m² / g, and an average particle size of 45~55μm was heated to 540~560℃ at a rate of 3~7℃ / min, then calcined at a constant temperature for 3~5h, and naturally cooled to room temperature to obtain pretreated mesoporous silica. 1-Butyl-3-methylimidazolium chloride was dissolved in anhydrous ethanol at a ratio of 1 g to 5 mL to form a transparent ionic liquid ethanol solution. Then, aluminum oxide with an average particle size of 2 μm was added and ultrasonically dispersed at a mass ratio of 4:1 to form a uniform suspension of active components. Under stirring conditions, the active component suspension was dropped into the pretreated mesoporous silica at a dropping rate of 0.4–0.6 mL / min. The active component suspension accounted for 15.5–16% of the mass of the pretreated mesoporous silica. After standing for 25–35 min, anhydrous ethanol was removed. Finally, the temperature was increased to 210–230 °C at a rate of 2–4 °C / min and calcined at a constant temperature for 1.5–2.5 h. After cooling, the sample was passed through standard sieves of 200 mesh and 400 mesh to obtain a supported heterogeneous catalyst with a particle size of 38–74 μm.

5. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, S2 raises the epoxide composition to 127~129℃ at a temperature not lower than 75℃, and then within 5 minutes, adds 2.25~2.35% of the total mass of the epoxide composition of a supported heterogeneous catalyst to fully disperse it, thus obtaining a suspension premixed system.

6. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, S2 stirs the suspension premixed system at a speed of 275-285 rpm and raises the temperature to 151-153℃ at a rate of 1.8-2.2℃ / min. Then, the mixture is added dropwise and dispersed evenly to achieve a viscosity of 850-1200 mPa. s, thus obtaining the first reaction system.

7. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, S3, using a stirring speed of 315-325 rpm and a shear frequency of 19-25 Hz, heated the first reaction system from 151-153℃ to 177-179℃ at a rate of 1.7-1.9℃ / min. Then, the mixture was added dropwise at a rate of 1.4-1.6 mL / min to disperse it evenly, achieving a viscosity of 2500-3200 mPa. For the first 20 minutes of the isothermal reaction, the stirring speed was 345-355 rpm and the shear frequency was 29-31 Hz. During the remaining time, the shear frequency was gradually reduced to 14-16 Hz at a rate of 1 Hz / 5 min, and the stirring speed was 315-325 rpm to obtain the second reaction system.

8. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, S4 uses a stirring speed of 375-385 rpm and a shear frequency of 24-26 Hz to raise the temperature of the second reaction system from 177-179°C to 214-216°C at a rate of 2.0-2.4°C / min. Then, equal amounts of the mixture are added dropwise in three separate additions, with an interval of 7.5-8.5 min between each addition. The mixture is then dispersed until it is homogeneous and the viscosity is adjusted to 8000-8500 mPa. s, the isothermal reaction allows the remaining epoxy groups to react completely with the isocyanate groups, yielding the third reaction system.

9. The method for preparing polyoxazolidinone by heterogeneous catalytic bulk polymerization according to claim 1, characterized in that, S4 lowers the temperature of the third reaction system to 164-166℃ and the viscosity to 6000-6500 mPa. The catalyst is filtered at a pressure of 0.25~0.37MPa through a filter with a precision of 7.8~8.2μm to obtain filtrate and filter cake. The filtrate is degassed under vacuum and stirring, and then granulated by twin-screw extrusion to obtain uniform polyoxazolidinone particles of 2.0~4.0mm. The filter cake is washed with anhydrous ethanol and then vacuum dried to obtain a supported heterogeneous catalyst.

10. A polyoxazolidinone obtained by the heterogeneous catalytic bulk polymerization method for preparing polyoxazolidinone according to any one of claims 1 to 9.