Anhydrous hydrophilic polyacrylamide polymer powder and its preparation method

Abstract

This invention belongs to the field of polyacrylamide polymer preparation technology, and particularly relates to an anhydrous hydrophilic polyacrylamide polymer powder and its preparation method, comprising: (1) purifying acrylamide monomers; (2) mixing the purified acrylamide monomers, organic solvent, RAFT reagent, and free radical initiator uniformly under an inert atmosphere, reacting at 50-75°C for 12-20 hours to form a polymer reaction solution or to allow the polymer to precipitate naturally in the system; (3) recrystallizing and separating the polymer reaction solution in an antisolvent to obtain a crude product; or filtering the naturally precipitated polymer to obtain a crude product; (4) removing impurities from the crude product and drying it under vacuum to obtain an anhydrous polymer powder. This invention can not only prepare high-purity anhydrous polymer powder with strong controllability of molecular weight and narrow molecular weight distribution, but also the method has mild reaction conditions, high production efficiency, and a monomer conversion rate of 97% or higher.

Description

Technical Field

[0001] This invention belongs to the field of polyacrylamide polymer preparation technology, and particularly relates to anhydrous hydrophilic polyacrylamide polymer powder and its preparation method. Background Technology

[0002] Acrylamide-based hydrophilic polymers exhibit broad application potential in various fields due to their unique temperature sensitivity and water solubility. The following is a brief introduction to their properties and application areas:

[0003] 1. Temperature sensitivity and water solubility

[0004] The thermosensitivity of acrylamide polymers stems from the synergistic effect of hydrophilic groups (such as amide groups) and hydrophobic groups (such as isopropyl or ethyl groups) in their molecular structure. When the temperature rises to the critical dissolution temperature (LCST), the polymer chains transition from a hydrophobic state to a hydrophilic state, resulting in a significant phase transition. For example, poly(N-isopropylacrylamide) undergoes a phase transition at around 32°C, exhibiting good temperature responsiveness.

[0005] 2. Drug delivery system

[0006] Thermosensitive polymers have particularly prominent applications in drug delivery. Polyacrylamide-based polymer hydrogels are used as sustained-release drug carriers. Studies have shown that these thermosensitive gels can control the drug release rate at different temperatures, thereby mimicking temperature changes within the human body to achieve precise delivery. Furthermore, poly(N-isopropylacrylamide)-based nanogels have also been used for gene delivery and cell culture, demonstrating their potential in the biomedical field.

[0007] 3. Biomedical Materials

[0008] Acrylamide polymers are widely used in the development of biomedical materials due to their excellent biocompatibility and temperature sensitivity, such as wound healing, tissue engineering, and cell immobilization. These materials can adjust their physical properties according to changes in external temperature, thereby regulating cell growth and function.

[0009] 4. Sensors and Smart Materials

[0010] Thermosensitive polymers are also used in the fields of sensors and smart materials. For example, hydrogels based on poly(N-isopropylacrylamide) can be used for chemical analysis and surface wettability studies, achieving rapid response through temperature stimulation; in addition, poly(N-isopropylacrylamide) nanoparticles are used to construct thermoresponsive electrochemical sensors for detecting biomolecules and environmental pollutants.

[0011] 5. Environmental and Industrial Applications

[0012] In the industrial sector, acrylamide polymers are used for petroleum recovery and wastewater treatment. For example, modified acrylamide copolymers improve petroleum recovery efficiency through host-guest interactions; furthermore, poly(N-isopropylacrylamide) polymers are used to develop novel smart composite materials for wastewater treatment and industrial wastewater reuse.

[0013] 6. Other special applications

[0014] Regarding gel permeation chromatography (GPC) standards, acrylamide polymers offer advantages in controlling molecular weight distribution and can be used as GPC standards. Polyacrylamide hydrogels are also used in the fabrication of electronic skin due to their high extensibility and capacitive touch properties.

[0015] Currently, the preparation of acrylamide-based hydrophilic polymers mostly employs free radical polymerization. However, traditional solution polymerization often requires an aqueous medium, resulting in products containing a large amount of water and easily introducing impurities. The water content in the product is difficult to adjust, significantly increasing the difficulty of using the product. Complex post-processing (such as drying and purification) is required to prepare anhydrous powder. This not only increases the complexity of the process but also raises energy consumption and production costs.

[0016] Traditional aqueous polymerization methods are difficult to use to prepare anhydrous polymer powders, often requiring complex post-processing steps, resulting in high energy consumption and low efficiency. Furthermore, because acrylamide monomers are sensitive to humidity and oxygen, controlling the reaction environment during polymerization is crucial.

[0017] Therefore, it is particularly important to develop a method for the efficient production of anhydrous acrylamide-based hydrophilic polymer powders. Summary of the Invention

[0018] The purpose of this invention is to address the problems of easy introduction of impurities, difficulty in controlling moisture content, and complex post-processing in existing processes. It provides an anhydrous hydrophilic polyacrylamide polymer powder and its efficient preparation method. This method employs RAFT controlled free radical polymerization combined with vacuum drying technology, or RAFT controlled free radical polymerization combined with anti-solvent recrystallization and vacuum drying technology. High-purity anhydrous polymer powder can be prepared without complex post-processing. Furthermore, this method features mild reaction conditions, high production efficiency, strong controllability of the molecular weight and molecular weight distribution of the obtained product, and uniform product performance; the anhydrous polymer powder is also less prone to water absorption.

[0019] To achieve the above objectives, the present invention adopts the following technical solution:

[0020] This invention provides a method for preparing anhydrous powder of hydrophilic polyacrylamide polymers, comprising the following steps:

[0021] (1) Purify acrylamide monomers;

[0022] (2) Under an inert atmosphere (such as nitrogen), add purified acrylamide monomers, organic solvents, RAFT reagents and free radical initiators to the reactor and mix them. Control the system temperature at 50-75℃ (e.g., 55℃, 60℃, 65℃, 70℃) and react for 12-20 hours (e.g., 13 hours, 14 hours, 15 hours, 16 hours). After the reaction is completed, a polymer reaction solution is formed or polymer is naturally precipitated in the system.

[0023] (3) The obtained polymer reaction solution is slowly poured into an antisolvent under an inert atmosphere (such as nitrogen) and under vigorous stirring to recrystallize and precipitate. The resulting crystallized product is then separated to obtain the crude product.

[0024] Alternatively, the naturally precipitated polymer can be filtered to obtain a crude product.

[0025] (4) Remove impurities from the crude product and dry it under vacuum to obtain anhydrous powder of hydrophilic polyacrylamide polymer.

[0026] In this article, the acrylamide monomers may include, but are not limited to, acrylamide, N,N-dimethylacrylamide, N,N-diethyl-2-acrylamide, N-ethyl-N-methylacrylamide, N-isopropylacrylamide, etc.

[0027] According to the preparation method provided by the present invention, in some embodiments, the acrylamide monomer is selected from at least one of the compounds shown in Formula I, Formula II, Formula III, Formula IV, and Formula V:

[0028]

[0029] In some embodiments, the organic solvent is selected from one or more of toluene, tetrahydrofuran, dioxane, and acetonitrile. This organic solvent has excellent solubility and reaction stability, and is easily removed in subsequent processes.

[0030] In some embodiments, the RAFT reagent is selected from at least one of the compounds shown in Formula I, Formula II, Formula III, Formula IV, Formula V, and Formula VI:

[0031]

[0032] That is, in this paper, the RAFT reagent can be selected from one or more of 2-phenyl-2-propylbenzodisulfide, 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropionic acid, 2-cyanopropyl-2-ylbenzodisulfide, 4-((((2-carboxyethyl)thio)thiocarbonyl)thio)-4-cyanopentanoic acid, cyanomethyl (3,5-dimethyl-1H-pyrazole)-dithioester and 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]pentanoic acid.

[0033] In some embodiments, the free radical initiator is an azo initiator or an organic peroxide initiator, preferably azobisisobutyronitrile (AIBN).

[0034] In this article, the free radical initiator may also be other free radical initiators commonly used in the field, which will not be elaborated here.

[0035] In some embodiments, the mass ratio of the organic solvent to the acrylamide monomer is 2:1 to 10:1, for example, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2.5:1, 2:1.

[0036] In the reaction system of this invention, the amount of RAFT reagent added can be determined and adjusted according to the molecular weight of the target polymer. In some embodiments, the molar ratio of the RAFT reagent to the acrylamide monomer is 1:50-1:2500, for example, 1:55, 1:60, 1:80, 1:100, 1:150, 1:200, 1:300, 1:400, 1:500, 1:600, 1:800, 1:1000, 1:1200, 1:1500, 1:2000, 1:2400.

[0037] In some embodiments, the molar ratio of the free radical initiator to the RAFT reagent is 1:1 to 0.5:10, for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, 1:4.5, 1:5, 1:6, 1:7, 1:8, 1:10, 1:12, 1:14, 1:15, 1:16, 1:18, 1:19, 1:20.

[0038] In this document, the purification can be performed using conventional methods in the art. In some embodiments, the purification in step (1) can be achieved by purifying the liquid polymer monomer through a vacuum chromatography column packed with basic alumina, or by recrystallizing the solid polymer monomer and drying it to a water content of <0.1 wt% to remove impurities. The process conditions for purification using a vacuum chromatography column packed with basic alumina and the process conditions for drying after recrystallization are both conventional operations in the art and will not be described in detail here.

[0039] The purification and removal of impurities from the monomer raw materials in step (1) is the basis for ensuring the efficient progress of the polymerization reaction. The purpose of purification is to remove polymerization inhibitors (such as hydroquinone, p-benzoquinone, p-tert-butylcatechol, etc.) added to the monomer raw materials for long-term preservation.

[0040] In this study, the polymerization inhibitors in the monomer feedstock are removed by reacting them with alkaline alumina in a vacuum chromatography column or by recrystallizing and drying them, thus eliminating their influence on the polymerization reaction. The purified monomers can be stored sealed at -20°C for 1-7 days.

[0041] According to the preparation method of the present invention, before heating the system in step (2), an inert gas can be introduced into the reaction device under constant pressure to remove oxygen from the system.

[0042] In some implementations, in step (3), the amount of antisolvent used is 3-10 times the volume of the reaction system (e.g., 3.5 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 9.5 times) to ensure crystallization effect.

[0043] In some implementations, in step (3), the antisolvent is selected from one or more of petroleum ether, n-hexane, and cyclohexane.

[0044] During recrystallization precipitation in an antisolvent, to ensure the polymer reaction solution is slowly poured into the antisolvent under vigorous stirring conditions for precipitation, the stirring speed can be controlled, for example. In some embodiments, the recrystallization precipitation process conditions in step (3) include: a stirring speed of 200-1000 rpm (e.g., 250 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 800 rpm, 900 rpm) and a stirring time of 5-20 min (e.g., 6 min, 8 min, 10 min, 12 min, 15 min, 18 min). Maintaining uniform stirring during recrystallization precipitation can prevent polymer agglomeration and water absorption for dissolution.

[0045] By controlling the stirring speed and stirring time during the recrystallization and sedimentation process, it is possible to ensure that the polymer is evenly dispersed in the antisolvent, resulting in good crystallinity and making the anhydrous polymer powder less prone to water absorption.

[0046] In step (4), the obtained crude product can be washed several times in the antisolvent and / or subjected to reflux pulping to remove residual solvent and residual initiator, etc., and then filtered and vacuum dried.

[0047] In some embodiments, the crude product obtained by recrystallization of the polymer reaction solution can be washed in an antisolvent, stirred and slurried at reflux temperature (e.g., 60-90°C) (e.g., 6-24 hours) to remove residual solvent and residual initiator, and then filtered and vacuum dried.

[0048] In some implementations, the crude product obtained by natural precipitation of polymer in the system can be stirred and pulped in an antisolvent at a reflux temperature (e.g., 60-90°C) for 6-24 hours to completely remove the solvent and residual initiator coated in the polymer, and then filtered and vacuum dried.

[0049] In step (4), the drying process under vacuum conditions can be a conventional choice in the art. In some embodiments, the drying process conditions in step (4) include: a drying temperature of 30-65°C (e.g., 35°C, 40°C, 50°C, 60°C), and a drying time of 1-8 hours (e.g., 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours). The vacuum conditions can be parameters known to those skilled in the art, and will not be elaborated here.

[0050] According to the preparation method provided by the present invention, in some embodiments, the weight-average molecular weight of the finally obtained hydrophilic polyacrylamide polymer is controlled between 0.5 million and 250,000 (e.g., 0.8 million, 1.0 million, 1.5 million, 2.0 million, 3.0 million, 5.0 million, 6.0 million, 8.0 million, 10.0 million, 12.0 million, 15.0 million, 18.0 million, 200,000, 220,000, 240,000), and the molecular weight distribution index (PDI) is less than or equal to 1.5 (e.g., less than or equal to 1.5, less than or equal to 1.4, less than or equal to 1.3, less than or equal to 1.2, less than or equal to 1.1, less than or equal to 1.0).

[0051] According to the preparation method provided by the present invention, in some embodiments, the hydrophilic polyacrylamide polymer finally obtained is selected from one or more of the following: homopolymers of acrylamide, homopolymers of N,N-dimethylacrylamide, homopolymers of N,N-diethyl-2-acrylamide, homopolymers of N-ethyl-N-methylacrylamide, and homopolymers of N-isopropylacrylamide.

[0052] The present invention also provides a hydrophilic polyacrylamide polymer prepared by the preparation method described above.

[0053] In some embodiments, the weight-average molecular weight of the hydrophilic polyacrylamide polymer is controlled between 0.5 million and 250,000, and the molecular weight distribution index (PDI) is less than or equal to 1.5. According to the present invention, the polyacrylamide polymer can be anhydrous powder of a CTA-terminated acrylamide polymer.

[0054] Compared to traditional free radical polymerization, RAFT controlled radical polymerization technology achieves precise control over the molecular weight and molecular weight distribution of polymers by introducing specific chain transfer agents (i.e., RAFT reagents, such as thiocarbonyl thio compounds) and initiators, thus enabling the subsequent synthesis of polymers with complex structures. The advantages of this technology are mainly reflected in the following aspects:

[0055] (1) Precise control of molecular weight and distribution: RAFT polymerization can achieve strict control of polymer molecular weight through reversible addition-fragmentation chain transfer mechanism, thereby obtaining a uniform molecular weight distribution, which is crucial for the preparation of high-performance materials;

[0056] (2) Ability to synthesize complex structures: Hydrophilic polyacrylamide polymer anhydrous powder obtained by RAFT controlled free radical polymerization technology can be used to prepare block copolymers, star polymers and polymer materials with specific functional groups; for example, by adjusting the type and amount of chain transfer agent, the precise distribution of different monomers in block copolymers can be achieved; the polymer prepared according to the technical solution of this application has the potential to prepare block copolymers.

[0057] (3) Mild reaction conditions: RAFT polymerization is usually carried out at a low temperature, avoiding side reactions caused by high temperature. At the same time, it has low requirements for solvent selectivity, which makes it more flexible in industrial applications.

[0058] Compared with the prior art, the beneficial effects of the technical solution of the present invention are at least as follows:

[0059] 1. The reaction conditions are mild and the process is simple.

[0060] 2. The obtained anhydrous polymer products have high purity (>96%), monomer conversion rates of 97% and above, strong controllability of molecular weight and narrow molecular weight distribution, and uniform product properties; furthermore, the polymer has good crystallinity, making the anhydrous polymer powder less prone to water absorption.

[0061] 3. Applicable to the industrial production of hydrophilic polyacrylamide polymer anhydrous powders using acrylamide monomers. Attached Figure Description

[0062] Figure 1a The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 1;

[0063] Figure 1b The image shown is a GPC report graph of the product obtained in Example 1.

[0064] Figure 2a The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 2;

[0065] Figure 2b The image shown is a GPC report graph of the product obtained in Example 2.

[0066] Figure 3a The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 3;

[0067] Figure 3b The image shown is a GPC report graph of the product obtained in Example 3;

[0068] Figure 4a The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 4;

[0069] Figure 4b The image shown is a GPC report graph of the product obtained in Example 4;

[0070] Figure 5a The hydrogen nuclear magnetic resonance spectrum of the product obtained in Example 5;

[0071] Figure 5b The image shown is a GPC report graph of the product obtained in Example 5.

[0072] Figure 6a This is a GPC report graph of the product obtained in Example 6.

[0073] It should be noted that the GPC report graphs of the products provided in each embodiment may differ slightly, but this does not affect the information they provide about the molecular weight and distribution of the products. Detailed Implementation

[0074] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Unless otherwise specified, the raw materials used in the examples are commercially available.

[0075] Example 1:

[0076] Table 1. Reactant materials and their amounts

[0077]

[0078] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0079] (1) Monomer pretreatment: The DMAA monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified DMAA monomer was stored at low temperature (-20℃) for later use.

[0080] (2) Feeding and polymerization reaction: Add 545g of purified DMAA monomer, 3g of 2-phenyl-2-propylbenzodisulfide, 0.2g of AIBN and 2500mL of toluene to a 5L reactor and stir (at 180rpm) until the mixture is homogeneous.

[0081] Under constant pressure, nitrogen gas was bubbled into the reactor at a flow rate of 400 mL / min for 30 minutes to remove oxygen; the reactor was heated to 50°C, kept at that temperature, and stirred for 16 hours to ensure that the monomer conversion rate reached more than 95%; after the reaction was completed, the polymer reaction solution was obtained.

[0082] (3) Antisolvent recrystallization: The obtained polymer reaction solution was slowly poured into 25L of n-hexane under nitrogen protection and stirred rapidly (stirring speed of 700rpm) for 15min to promote polymer recrystallization and precipitation; after standing and allowing the solid phase to disperse, the supernatant was removed to obtain crude product.

[0083] (4) Post-processing: The crude product was transferred to a reactor, and 2L of n-hexane was added to the reactor. Stirring was started (stirring speed 180rpm) and the temperature was raised to 70℃ and refluxed for 12 hours to remove low molecular weight impurities and solvent residues. The solid was filtered under nitrogen atmosphere and finally vacuum dried at 40℃ for 2 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0084] Product performance testing: ¹H NMR analysis showed a product NMR purity of 97% with no obvious side peaks; GPC analysis showed a product molecular weight (Mw) of 0.5 million and a PDI of 1.12; the conversion rate was 98%. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 1a This demonstrates that the synthesized polymer is poly(N,N-dimethylacrylamide); as shown in the GPC report graph ( Figure 1b This provides information about the molecular weight of the polymer.

[0085] Example 2:

[0086] Table 2. Reaction raw materials and their amounts

[0087]

[0088] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0089] (1) Monomer pretreatment: The acrylamide monomer raw material is recrystallized and dried to a water content of <0.1wt% to fully remove the reaction inhibitors contained therein; the purified acrylamide monomer is stored at low temperature (-20℃) under nitrogen protection for later use.

[0090] (2) Feeding and polymerization reaction: Add 600g of purified acrylamide monomer, 22g of 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropionic acid and 7.5g of ABVN to a 5L reactor and mix them evenly with 3,000mL of dioxane solvent under stirring (200rpm).

[0091] Under constant pressure, nitrogen gas was bubbled into the reactor at a flow rate of 200 mL / min for 60 minutes to raise the temperature inside the reactor to 60°C. The reactor was kept at this temperature and stirred for 12 hours to ensure that the monomer was basically converted. After the reaction was completed, the polymer reaction solution was cooled to room temperature.

[0092] (3) Antisolvent recrystallization: The obtained polymer reaction solution was slowly poured into 15L of petroleum ether under nitrogen protection and stirred rapidly (stirring speed 600rpm) for 10min to promote polymer recrystallization and precipitation. The solid was collected and vacuum filtered to obtain crude product.

[0093] (4) Post-processing: Under nitrogen protection, the crude product was washed three times with clean petroleum ether and filtered. Then, it was vacuum dried at 60°C for 4 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0094] Product performance testing: ¹H NMR analysis showed a product purity of 97%, with trace impurity peaks; GPC analysis showed a molecular weight (Mw) of 0.7 million and a PDI of 1.11; the conversion rate was 98%. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 2a This proves that the synthesized polymer is polyacrylamide; as shown in the GPC report graph ( Figure 2b This provides information about the molecular weight of the polymer.

[0095] Example 3:

[0096] Table 3. Reaction raw materials and their amounts

[0097]

[0098]

[0099] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0100] (1) Monomer pretreatment: The N-isopropylacrylamide monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified N-isopropylacrylamide monomer was stored at low temperature (-20℃) for later use.

[0101] (2) Feeding and polymerization reaction: Add 550g of purified N-isopropylacrylamide monomer, 1.2g of 2-cyanopropyl-2-ylbenzodisulfide, 0.3g of AIBN and 2500mL of acetonitrile to a 5L reactor with stirring, and stir (at 180rpm) to mix them evenly.

[0102] Under constant pressure, nitrogen gas was introduced into the reactor system at a flow rate of 400 mL / min for 30 minutes; after the reactor was heated to 55°C, it was kept at a constant temperature and the reaction was continued with stirring for 16 hours. Stirring was carried out to ensure uniform polymerization and that the monomer conversion rate reached more than 95%. After the reaction was completed, the polymer reaction solution was obtained.

[0103] (3) Recrystallization of the antisolvent: The obtained polymer reaction solution was slowly poured into 20L of ice-cold n-hexane under nitrogen protection and stirred rapidly (stirring speed 700rpm) for 6min to promote polymer recrystallization and precipitation. The solid precipitated out rapidly, and after standing and separation, the supernatant was removed to obtain the crude product.

[0104] (4) Post-processing: The crude product was washed three times with clean n-hexane, the sample was collected, and then placed in a reaction vessel and pure n-hexane was added and heated to 70°C and refluxed for 16 hours to remove initiator residues; then the solid was filtered under nitrogen atmosphere and vacuum dried at 45°C for 2 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0105] Product performance testing: ¹H NMR analysis showed a product NMR purity of 98%; GPC analysis showed a product molecular weight (Mw) of 80,000 and a PDI of 1.21; the conversion rate was 97%. The ¹H NMR spectrum... Figure 3a This demonstrates that the synthesized polymer is poly-N-isopropylacrylamide; as shown in the GPC report graph ( Figure 3b This provides information about the molecular weight of the polymer.

[0106] Example 4:

[0107] Table 4. Reaction raw materials and their amounts

[0108]

[0109] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0110] (1) Monomer pretreatment: The N-ethyl-N-methylacrylamide monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified N-ethyl-N-methylacrylamide monomer was stored at low temperature (-20℃) for later use.

[0111] (2) Feeding and polymerization reaction: Add 500g of purified N-ethyl-N-methylacrylamide monomer, 1g of 4-((((2-carboxyethyl)thio)thiocarbonyl)thio)-4-cyanopentanoic acid, and 0.5g of ABVN to a 5L reactor and mix them evenly with 3,000mL of dioxane solvent under stirring (200rpm).

[0112] Under constant pressure, nitrogen gas was introduced into the reactor system at a flow rate of 400 mL / min for 30 minutes; the temperature inside the reactor was raised to 60°C, and the reaction was maintained and stirred for 12 hours to ensure that the monomer was basically converted. After the reaction was completed, the polymer reaction solution was cooled to room temperature.

[0113] (3) Antisolvent recrystallization: The obtained polymer reaction solution was slowly poured into 15L of petroleum ether under nitrogen protection and stirred rapidly (stirring speed 1000rpm) for 10min to promote polymer recrystallization and precipitation. The solid was collected and vacuum filtered to obtain crude product.

[0114] (4) Post-processing: Under nitrogen protection, the crude product was washed three times with clean petroleum ether, filtered, and then vacuum dried at 60°C for 4 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0115] Product performance testing: ¹H NMR analysis showed a product purity of 97%, with trace impurity peaks; GPC analysis showed a molecular weight (Mw) of 75,000 and a PDI of 1.44; the conversion rate was 98%. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 4a This demonstrates that the synthesized polymer is poly(N-ethyl-N-methylacrylamide); as shown in the GPC report graph ( Figure 4b This provides information about the molecular weight of the polymer.

[0116] Example 5:

[0117] Table 5. Reaction raw materials and their amounts

[0118]

[0119] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0120] (1) Monomer pretreatment: The N,N-diethyl-2-acrylamide monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified N,N-diethyl-2-acrylamide monomer was stored at low temperature (-20℃) for later use.

[0121] (2) Feeding and polymerization reaction: Add 550g of purified N,N-diethyl-2-acrylamide monomer, 0.7g of cyanomethyl (3,5-dimethyl-1H-pyrazole)-dithioester, 0.4g of AIBN and 2750mL of acetonitrile to a 5L reactor with stirring, and stir (at 180rpm) to mix it evenly.

[0122] Under constant pressure, nitrogen gas was introduced into the reactor system at a flow rate of 400 mL / min for 30 minutes; after the reactor was heated to 55°C, it was kept at a constant temperature and the reaction was continued with stirring for 16 hours. Stirring was carried out thoroughly to ensure uniform polymerization and to ensure that the monomer conversion rate reached more than 95%. After the reaction was completed, the polymer reaction solution was obtained.

[0123] (3) Recrystallization of the antisolvent: The obtained polymer reaction solution was slowly poured into 20L of ice-cold n-hexane under nitrogen protection and stirred rapidly (stirring speed 200rpm) for 20min to promote polymer recrystallization and precipitation. The solid precipitated out rapidly, and after standing and separation, the supernatant was removed to obtain the crude product.

[0124] (4) Post-processing: The crude product was washed three times with clean n-hexane, the sample was collected, and then placed in a reaction vessel and pure n-hexane was added and refluxed at 70°C for 16 hours to remove initiator residues; then the solid was filtered under nitrogen atmosphere and vacuum dried at 45°C for 2 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0125] Product performance testing: ¹H NMR analysis showed a product NMR purity of 98%; GPC analysis showed a product molecular weight (Mw) of 143,000 and a PDI of 1.4; the conversion rate was 97%. The ¹H NMR spectrum... Figure 5a This demonstrates that the synthesized polymer is poly(N,N-diethyl-2-acrylamide); as shown in the GPC report graph ( Figure 5b This provides information about the molecular weight of the polymer.

[0126] Example 6:

[0127] Table 6. Reaction raw materials and their amounts

[0128]

[0129] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0130] (1) Monomer pretreatment: The N,N-dimethylacrylamide monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified N,N-dimethylacrylamide monomer was stored at low temperature (-20℃) for later use.

[0131] (2) Feeding and polymerization reaction: Add 550g of purified N,N-dimethylacrylamide monomer, 1.1g of 4-cyano-4-[[(dodecylthio)thionylmethyl]thio]valeric acid, 0.4g of AIBN and 2750mL of acetonitrile to a 5L reactor with stirring, and stir (at 180rpm) to mix it evenly;

[0132] Under constant pressure, nitrogen gas was introduced into the reactor system at a flow rate of 400 mL / min for 30 minutes; after the reactor was heated to 55°C, it was kept at a constant temperature and the reaction was continued with stirring for 16 hours. Stirring was carried out thoroughly to ensure uniform polymerization and to ensure that the monomer conversion rate reached more than 95%. After the reaction was completed, the polymer reaction solution was obtained.

[0133] (3) Recrystallization of the antisolvent: The obtained polymer reaction solution was slowly poured into 20L of ice-cold n-hexane under nitrogen protection and stirred rapidly (stirring speed 200rpm) for 10min to promote polymer recrystallization and precipitation. The solid precipitated out rapidly, and after standing and separation, the supernatant was removed to obtain the crude product.

[0134] (4) Post-processing: The crude product was washed three times with clean n-hexane, the sample was collected, and then placed in a reaction vessel and pure n-hexane was added and heated to 70°C and refluxed for 16 hours to remove initiator residues; then the solid was filtered under nitrogen atmosphere and vacuum dried at 45°C for 2 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0135] Product performance testing: HNMR analysis showed that the product's NMR purity was 98%; GPC analysis showed that the product's molecular weight (Mw) was 215,000, PDI was 1.47, and the conversion rate was 97%. (GPC report graph...) Figure 6a This provides information about the molecular weight of the polymer.

[0136] Example 7:

[0137] Table 7. Reaction raw materials and their amounts

[0138]

[0139] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0140] (1) Monomer pretreatment: The acrylamide monomer raw material is recrystallized and dried to a water content of <0.1wt% to fully remove the reaction inhibitors contained therein; the purified acrylamide monomer is stored at low temperature (-20℃) under nitrogen protection for later use.

[0141] (2) Feeding and polymerization reaction: Add 600g of purified acrylamide monomer, 22g of 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropionic acid and 7.5g of ABVN to a 5L reactor and mix them evenly with 3,000mL of acetonitrile solvent under stirring (200rpm).

[0142] Under constant pressure, nitrogen gas was bubbled into the reactor at a flow rate of 200 mL / min for 60 minutes to raise the temperature inside the reactor to 60°C. The reactor was kept at this temperature and stirred for 12 hours. During this period, polymers were continuously precipitated. After the reaction was completed, the reaction solution was filtered to obtain the crude product.

[0143] (3) Post-processing: The crude product was transferred to a reaction vessel, and 2L of n-hexane was added to the vessel. Stirring was started (stirring speed 180rpm) and the temperature was raised to 70℃ and refluxed for 12 hours to remove low molecular weight impurities and solvent residues. Then, the solid was filtered under a nitrogen atmosphere and finally vacuum dried at 40℃ for 2 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0144] Product performance testing: HNMR analysis showed that the product's NMR purity was 97%, with trace impurity peaks; GPC analysis showed that the product's molecular weight (Mw) was 0.8 million, PDI was 1.15, and the conversion rate was 98%.

[0145] Comparative Example 1 (mechanical dehydration compared to Example 1):

[0146] Table 8. Reaction raw materials and their amounts

[0147]

[0148] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0149] (1) Monomer pretreatment: The DMAA monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified DMAA monomer was stored at low temperature (-20℃) for later use.

[0150] (2) Feeding and polymerization reaction: Add 545g of purified DMAA monomer, 3g of 2-phenyl-2-propylbenzodisulfide, 0.2g of AIBN and 2500mL of toluene to a 5L reactor and stir (at 180rpm) until the mixture is homogeneous.

[0151] Under constant pressure, nitrogen gas was bubbled into the reactor at a flow rate of 400 mL / min for 30 minutes to remove oxygen; the reactor was heated to 50°C, kept at that temperature, and stirred for 16 hours to ensure that the monomer conversion rate reached more than 95%; after the reaction was completed, the polymer reaction solution was obtained.

[0152] (3) Mechanical dehydration: The obtained polymer reaction solution is removed by vacuum evaporation to remove the solvent, degassed, extruded and granulated to obtain agglomerated polymer particles, which are then powdered and sent to a forced-air drying oven and dried at 60°C for 2 hours to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0153] Product performance testing: HNMR analysis showed that the product's NMR purity was 93% (with obvious H2O peak and toluene solvent peak); GPC analysis showed that the product's molecular weight (Mw) was 67,000, PDI was 1.3, and the conversion rate was 98%.

[0154] Comparative Example 2 (compared to Example 1, general free radical polymerization):

[0155] Table 9. Reaction raw materials and their amounts

[0156]

[0157] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0158] (1) Monomer pretreatment: The DMAA monomer raw material was purified by passing it through a vacuum chromatography column packed with alkaline alumina to remove the reaction inhibitors contained therein. The purified DMAA monomer was stored at low temperature (-20℃) for later use.

[0159] (2) Feeding and polymerization reaction: Add 545g of purified DMAA monomer, 3.67g of n-dodecyl mercaptan and 2,250mL of toluene to a 5L reactor and stir (180rpm) until well mixed; dissolve AIBN in 250mL of toluene and place the dissolved AIBN solution in a dropping funnel for later use.

[0160] Under constant pressure, nitrogen gas was bubbled into the reactor at a flow rate of 400 mL / min for 30 minutes to remove oxygen; the reactor was heated to 50°C, and the prepared AIBN solution was added dropwise evenly within 1 hour; after the addition was completed, the reaction was stirred for 16 hours to ensure that the monomer conversion rate reached more than 95%; after the reaction was completed, the polymer reaction solution was obtained.

[0161] (3) Antisolvent recrystallization: The obtained polymer reaction solution was slowly poured into 25L of n-hexane under nitrogen protection and stirred rapidly (stirring speed of 700rpm) for 15min to promote polymer recrystallization and precipitation; after standing and allowing the solid phase to disperse, the supernatant was removed to obtain crude product.

[0162] (4) Post-processing: The crude product was transferred to a reactor, and 2L of n-hexane was added to the reactor. Stirring was started (stirring speed 180rpm) and the temperature was raised to 70℃ and refluxed for 12 hours to remove low molecular weight impurities and solvent residues. The solid was filtered under a nitrogen atmosphere and finally vacuum dried at 40℃ for 2 hours to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0163] Product performance testing: HNMR analysis showed that the product's NMR purity was 97%, with no obvious side peaks; GPC analysis showed that the product's molecular weight (Mw) was 62,000, PDI was 2.9, and the conversion rate was 97%.

[0164] Comparative Example 3 (compared to Example 2)

[0165] Table 10 Reactant materials and their amounts

[0166]

[0167]

[0168] The preparation process of anhydrous hydrophilic polyacrylamide polymer powder is as follows:

[0169] (1) Monomer pretreatment: The acrylamide monomer raw material is recrystallized and dried to a water content of <0.1wt% to fully remove the reaction inhibitors contained therein; the purified acrylamide monomer is stored at low temperature (-20℃) under nitrogen protection for later use.

[0170] (2) Feeding and polymerization reaction: Add 600g of purified acrylamide monomer, 22g of 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropionic acid and 7.5g of ABVN to a 5L reactor and mix them evenly with 3,000mL of dioxane solvent under stirring (200rpm).

[0171] Under constant pressure, nitrogen gas was bubbled into the reactor at a flow rate of 200 mL / min for 60 minutes to raise the temperature inside the reactor to 60°C. The reactor was kept at this temperature and stirred for 12 hours to ensure that the monomer was basically converted. After the reaction was completed, the polymer reaction solution was cooled to room temperature.

[0172] (3) Antisolvent recrystallization: The obtained polymer reaction solution was poured into 15L of petroleum ether under nitrogen protection for 1 minute and maintained for 10 minutes to promote polymer recrystallization and precipitation. The solid was collected and vacuum filtered to obtain crude product.

[0173] (4) Post-processing: Under nitrogen protection, the crude product was washed three times with clean petroleum ether, filtered, and then vacuum dried at 60°C for 4 hours to constant weight to obtain hydrophilic polyacrylamide polymer anhydrous powder.

[0174] Product performance testing: HNMR analysis showed that the product's NMR purity was 90%, with a clear solvent peak; GPC analysis showed that the product's molecular weight (Mw) was 13,000, PDI was 1.22, and the conversion rate was 98%.

[0175] Table 11 Performance test results of the products obtained from each embodiment and comparative example.

[0176]

[0177]

[0178] Hygroscopicity test of anhydrous polymer powder under atmospheric conditions:

[0179] The anhydrous polymer powders prepared in the above examples and the mechanically dehydrated and pulverized powders were tested for moisture content (wt%) by heating weight loss (TGA) before and after placement under different humidity atmospheric environments; the test results are shown in the table below.

[0180] Table 12. TGA test of water absorption of anhydrous powders of hydrophilic polyacrylamide polymers (at 25℃ and 60% relative humidity in air).

[0181]

[0182] In this example, Example 1 and Comparative Example 1 are poly(N,N-dimethylacrylamide), and Example 2 and Comparative Example 3 are polyacrylamide.

[0183] The test results in Table 12 demonstrate that the anhydrous polymer powder obtained by the technical solution of this invention is less prone to water absorption. It should be noted that due to the molecular characteristics of polymers, these polymers inherently possess strong hygroscopic capacity, which increases with relative humidity and is unavoidable. The advantage of the anhydrous powder prepared by this invention is that it absorbs water more slowly in the initial stages of environmental exposure, facilitating transfer and packaging, thus providing operational convenience. However, in actual storage scenarios, sealing and protection with dry inert gas are still required.

[0184] Based on the experimental data from various embodiments and comparative examples, this invention employs a RAFT controlled radical polymerization process combined with vacuum drying technology. Through this process, anhydrous CTA-terminated acrylamide polymer powders are obtained. This allows for precise control of the polymer's molecular weight and distribution, enabling subsequent synthesis of polymers with complex structures. The resulting hydrophilic polymer anhydrous powders exhibit higher purity and more uniform performance, along with milder reaction conditions and higher production efficiency. Alternatively, the RAFT controlled radical polymerization process can be combined with an antisolvent recrystallization treatment and vacuum drying technology. The antisolvent recrystallization treatment ensures uniform dispersion of the polymer in the antisolvent, resulting in good crystallinity and making the anhydrous polymer powder less prone to water absorption. Using the technical solution of this invention, the molecular weight of the product can be precisely controlled over a wide range, achieving a narrower molecular weight distribution and yielding hydrophilic polymer anhydrous powders with higher purity, more uniform performance, and even less water absorption.

[0185] Compared to the mechanical dehydration method used in Comparative Example 1 to treat the polymerization reaction solution, the anhydrous polymer powder product obtained by the present invention has higher purity. Compared to the traditional free radical polymerization process used in Comparative Example 2, the anhydrous polymer powder obtained by the present invention shows significant improvements in both product purity and polymer molecular weight distribution. Compared to the inferior sedimentation process used in Comparative Example 3, the anhydrous polymer powder product obtained by the present invention has higher purity.

[0186] As can be seen from the test results in Table 12, compared with the comparative examples, Examples 1-6 adopted the RAFT controlled free radical polymerization process combined with the antisolvent recrystallization process and vacuum drying technology. Because the combination of the antisolvent recrystallization process can ensure that the polymer is evenly dispersed in the antisolvent, resulting in good crystallinity, and thus the anhydrous polymer powder is not easy to absorb water.

[0187] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. A method for preparing anhydrous powder of hydrophilic polyacrylamide polymer, characterized in that, Includes the following steps: (1) Purify acrylamide monomers; (2) Under an inert atmosphere, add purified acrylamide monomers, organic solvents, RAFT reagents and free radical initiators to the reactor and mix them. Control the system temperature at 50-75℃ and react for 12-20 hours. After the reaction is completed, a polymer reaction solution is formed or polymer is naturally precipitated in the system. (3) The obtained polymer reaction solution is poured into an antisolvent under stirring conditions under an inert atmosphere to recrystallize and precipitate. The resulting crystallized product is then separated to obtain a crude product. Alternatively, the naturally precipitated polymer can be filtered to obtain a crude product. (4) Remove impurities from the crude product and dry it under vacuum to obtain anhydrous powder of hydrophilic polyacrylamide polymer.

2. The preparation method according to claim 1, characterized in that, The acrylamide monomer is selected from at least one of the compounds shown in Formula I, Formula II, Formula III, Formula IV, and Formula V: The organic solvent is selected from one or more of toluene, tetrahydrofuran, dioxane, and acetonitrile.

3. The preparation method according to claim 1 or 2, characterized in that, The RAFT reagent is selected from at least one of the compounds shown in Formula I, Formula II, Formula III, Formula IV, Formula V, and Formula VI: The free radical initiator is an azo initiator or an organic peroxide initiator, preferably azobisisobutyronitrile (AIBN).

4. The preparation method according to any one of claims 1-3, characterized in that, The mass ratio of the organic solvent to the acrylamide monomer is 2:1 to 10:

1.

5. The preparation method according to any one of claims 1-4, characterized in that, The molar ratio of the RAFT reagent to the acrylamide monomer is 1:50 to 1:2500.

6. The preparation method according to any one of claims 1-5, characterized in that, The molar ratio of the free radical initiator to the RAFT reagent is 1:1 to 0.5:

10.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (3), the amount of the antisolvent used is 3-10 times the volume of the reaction system; In step (3), the antisolvent is selected from one or more of petroleum ether, n-hexane and cyclohexane.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (3), the process conditions for recrystallization include: a stirring speed of 200-1000 rpm and a stirring time of 5-20 min.

9. The preparation method according to any one of claims 1-8, characterized in that, The final hydrophilic polyacrylamide polymer has a weight-average molecular weight of 0.5 million to 250,000 and a molecular weight distribution index (PDI) of less than or equal to 1.

5. The hydrophilic polyacrylamide polymer finally obtained is selected from one or more of the following: homopolymers of acrylamide, homopolymers of N,N-dimethylacrylamide, homopolymers of N,N-diethyl-2-acrylamide, homopolymers of N-ethyl-N-methylacrylamide, and homopolymers of N-isopropylacrylamide.

10. The hydrophilic polyacrylamide polymer prepared by any one of claims 1-9.

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