A method for preparing polyacrylonitrile and polyacrylonitrile

Abstract

The present application relates to polyacrylonitrile polymerization technical field, specifically to a kind of preparation method of polyacrylonitrile and polyacrylonitrile, method includes: polyacrylonitrile, comonomer, chain transfer agent and organic solvent are mixed to form polymerization system;Oxygen concentration in polymerization system is adjusted after adding initiator and carries out polymerization, and polymerization includes initiation stage, chain growth stage and ripening stage, and the polymerization temperature of initiation stage is lower than the polymerization temperature of chain growth stage, and the polymerization temperature of chain growth stage is lower than the polymerization temperature of ripening stage;Initiation stage lasts 1~3h, and chain growth stage lasts 8~12h, and ripening stage lasts 3~5h;Polymerization is carried out under the state of stirring, and the stirring speed of initiation stage is lower than the stirring speed of chain growth stage, and the stirring speed of chain growth stage is lower than the stirring speed of ripening stage;After polymerization, polyacrylonitrile is obtained;The preparation method of the present application improves the molecular weight of polyacrylonitrile and the uniformity of molecular weight distribution.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile polymerization technology, specifically to a method for preparing polyacrylonitrile and polyacrylonitrile itself. Background Technology

[0002] Polyacrylonitrile (PAN) is an important precursor for the preparation of high-performance carbon fibers. The molecular weight and molecular weight distribution of the polymer directly affect the subsequent spinning process and the properties of the carbon fibers.

[0003] Polyacrylonitrile (PA) is typically prepared using free radical solution polymerization. The polymerization process generally includes an initiation stage, a chain growth stage, and a maturation stage. The initiation stage requires the formation of stable free radicals, the chain growth stage is necessary to maintain the stability of the polymerization reaction, and the maturation stage is used to improve monomer conversion and stabilize the polymerization system. Therefore, the reaction conditions at each polymerization stage directly affect the molecular weight and molecular weight distribution of the PA polymer.

[0004] In existing technologies, isothermal polymerization is typically employed to achieve polyacrylonitrile polymerization, often accompanied by conventional nitrogen sealing or inert gas protection. However, in actual polymerization processes, on the one hand, the decomposition rate of the initiator is significantly affected by temperature, while the polymerization reaction is continuously exothermic, leading to fluctuations in the temperature of the polymerization system. On the other hand, as the polymerization reaction proceeds, the viscosity of polyacrylonitrile increases, its free radical diffusion capacity gradually decreases, and oxygen has a quenching effect on free radicals, easily inhibiting free radical polymerization reactions.

[0005] Therefore, during the polymerization process, problems such as fluctuations in free radical concentration, unstable polymerization reaction rate, and large differences in the growth process of polymer chains are likely to occur, making it difficult to stably control the molecular weight and molecular weight distribution of polyacrylonitrile polymers, which will reduce the performance consistency of polyacrylonitrile precursors and carbon fiber products.

[0006] In summary, how to achieve stable polyacrylonitrile polymerization and improve the molecular weight and molecular weight distribution uniformity of polyacrylonitrile polymers has become a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0007] In order to overcome the above-mentioned defects and deficiencies in the prior art, the present invention aims to provide a method for preparing polyacrylonitrile and polyacrylonitrile, so as to achieve stable polyacrylonitrile polymerization process and improve the molecular weight and molecular weight distribution uniformity of polyacrylonitrile polymer. In a first aspect, the present invention provides a method for preparing polyacrylonitrile, comprising: Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed in a preset mass ratio to form a polymerization system; After adjusting the oxygen concentration in the polymerization system to 0.05%~0.15%, an initiator is added to initiate the polymerization reaction. The polymerization reaction includes an initiation stage, a chain growth stage, and a maturation stage. The polymerization temperature during the initiation stage is 60~70°C. The polymerization temperature during the chain growth stage is 70~75°C. The polymerization temperature during the maturation stage is 75~77°C. Furthermore, the polymerization temperature of the initiation stage is lower than the polymerization temperature of the chain growth stage, and the polymerization temperature of the chain growth stage is lower than the polymerization temperature of the maturation stage. The initiation phase lasts 1-3 hours, the chain growth phase lasts 8-12 hours, and the maturation phase lasts 3-5 hours. The polymerization reaction is carried out under stirring. The stirring speed during the initiation stage is 18~30 r / min, the stirring speed during the chain growth stage is 30~50 r / min, and the stirring speed during the maturation stage is 50~68 r / min. The stirring speed during the initiation stage is lower than the stirring speed during the chain growth stage, and the stirring speed during the chain growth stage is lower than the stirring speed during the maturation stage. After the polymerization reaction is complete, polyacrylonitrile is obtained.

[0008] According to the technical solution provided in the embodiments of the present invention, the oxygen concentration in the polymerization system is 0.10%.

[0009] According to the technical solution provided in the embodiment of the present invention, the polymerization temperature of the initiation stage is 65°C. The polymerization temperature during the chain growth stage is 72°C. The polymerization temperature during the maturation stage is 76°C. .

[0010] According to the technical solution provided in the embodiments of the present invention, the initiation stage lasts for 2 hours, the chain growth stage lasts for 10 hours, and the maturation stage lasts for 4 hours.

[0011] According to the technical solution provided by the embodiments of the present invention, the stirring speed during the initiation stage is 24 r / min, the stirring speed during the chain growth stage is 40 r / min, and the stirring speed during the maturation stage is 60 r / min.

[0012] According to the technical solution provided in the embodiments of the present invention, the components in the polymerization system are proportioned by weight, wherein acrylonitrile is the base component with a weight of 100 parts, comonomer is 0.8~1.2 parts, chain transfer agent is 0.05~0.3 parts, initiator is 0.5~0.8 parts, and organic solvent is 320~340 parts.

[0013] According to the technical solution provided in the embodiments of the present invention, the comonomer includes one or more of itaconic acid, acrylic acid, methacrylic acid, fumaric acid and maleic acid; And / or, the chain transfer agent includes one or more of n-octyl mercaptan, n-butyritin and dodecyl mercaptan; And / or, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisovalerate; And / or, the organic solvent includes one or more of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0014] According to the technical solution provided in the embodiments of the present invention, after the polymerization reaction is completed, the obtained polyacrylonitrile is subjected to post-treatment, the post-treatment including at least one of the following processes: (a) Removal of unreacted monomers from polyacrylonitrile; (b) Filter the polyacrylonitrile after removing unreacted monomers; (c) Removing air bubbles from polyacrylonitrile; and, (d) Adjust the pH value of polyacrylonitrile.

[0015] According to the technical solution provided in the embodiments of the present invention, the removal of unreacted monomers from polyacrylonitrile includes: at a temperature of 75~85°C Under pressure of -100~-95kPa, vacuum distillation is carried out for 0.5~1h to vaporize and separate the unreacted monomers in polyacrylonitrile from the polyacrylonitrile. And / or, the removal of bubbles from polyacrylonitrile includes: at a temperature of 75~85°C Vacuum degassing was performed on the filtered polyacrylonitrile under a pressure of -100~-95kPa. And / or, adjusting the pH value of the polyacrylonitrile includes: introducing ammonia gas into the degassed polyacrylonitrile to adjust the pH value of the polyacrylonitrile to 6.5~7.5.

[0016] Secondly, the present invention provides a polyacrylonitrile, which is obtained by the preparation method described above.

[0017] The beneficial effects of this invention are: Compared with the prior art, the polyacrylonitrile preparation method provided by the present invention constructs a polymerization system by mixing acrylonitrile, comonomer, chain transfer agent and organic solvent in a preset mass ratio. At the same time, the oxygen concentration in the polymerization system is adjusted to 0.05%~0.15% to reduce the quenching effect of oxygen on active free radicals, so that free radicals can continue to participate in the polymerization reaction and reduce the impact of oxygen inhibition and abnormal chain termination on the polymerization process. As the polymerization reaction proceeds, the monomer concentration in the polymerization system gradually decreases, the polymer content continuously increases, the system viscosity continuously increases, and the free radical diffusion capacity and reactivity change accordingly. The rate relationships between various reaction processes also continuously change. This invention addresses the evolution of the kinetic state of the polymerization system by using a 60-70% concentration during the initiation stage. The polymerization temperature, reaction time of 1-3 hours, and stirring speed of 18-30 r / min were adjusted to ensure stable decomposition of the initiator while forming a suitable free radical concentration; during the chain growth stage, a stirring speed of 70-75 μm was used. The polymerization temperature, reaction time of 8-12 hours, and stirring speed of 30-50 r / min ensure continuous chain growth and adaptability to the gradual increase in system viscosity; during the maturation stage, a stirring speed of 75-77°C is used. The polymerization temperature, reaction time of 3-5 hours, and stirring speed of 50-68 r / min promote the further polymerization of the remaining monomers and maintain the homogeneity of the polymerization system. By coordinating the polymerization temperature, reaction time, and stirring speed at each polymerization stage, the initiator decomposition rate, effective free radical concentration, and chain growth, chain transfer, and chain termination processes are adapted to the reaction state at each stage. This ensures that the polymerization system maintains a relatively stable kinetic equilibrium throughout the polymerization process, reduces the differences in the polymer chain growth process, and is beneficial to improving the molecular weight and molecular weight distribution uniformity of the polyacrylonitrile polymer. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are only for explaining the related invention and are not intended to limit the invention. Unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to embodiments.

[0019] Unless otherwise specified, the materials, reagents, and apparatus used in the following examples can be obtained commercially or prepared according to methods published in the literature.

[0020] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​falling within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0021] One objective of this invention is to provide a method for preparing polyacrylonitrile, comprising: Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed in a preset mass ratio to form a polymerization system; After adjusting the oxygen concentration in the polymerization system to 0.05%~0.15%, an initiator is added to initiate the polymerization reaction. The polymerization reaction includes an initiation stage, a chain growth stage, and a maturation stage. The polymerization temperature during the initiation stage is 60~70°C. The polymerization temperature during the chain growth stage is 70~75°C. The polymerization temperature during the maturation stage is 75~77°C. Furthermore, the polymerization temperature of the initiation stage is lower than the polymerization temperature of the chain growth stage, and the polymerization temperature of the chain growth stage is lower than the polymerization temperature of the maturation stage. The initiation phase lasts 1-3 hours, the chain growth phase lasts 8-12 hours, and the maturation phase lasts 3-5 hours. The stirring speed during the initiation stage is 18-30 r / min, the stirring speed during the chain growth stage is 30-50 r / min, and the stirring speed during the maturation stage is 50-68 r / min. The stirring speed during the initiation stage is lower than the stirring speed during the chain growth stage, and the stirring speed during the chain growth stage is lower than the stirring speed during the maturation stage. After the polymerization reaction is complete, polyacrylonitrile is obtained.

[0022] In this invention, the oxygen concentration refers to the volume fraction of oxygen in the gas phase space of the polymerization system relative to all gas components. The oxygen concentration can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%.

[0023] Specifically, before the polymerization reaction, the gas in the polymerization system is replaced with an inert gas to reduce the oxygen concentration to 0.05%~0.15% before adding the initiator for polymerization, and the above oxygen concentration is maintained during the polymerization process. When the oxygen concentration is higher than 0.15%, the quenching effect of oxygen on active free radicals is enhanced, resulting in a decrease in the effective concentration of free radicals, which easily leads to a decrease in the polymerization rate and increases the probability of oxygen inhibition and abnormal chain termination reactions. When the oxygen concentration is lower than 0.05%, the improvement effect on the polymerization reaction is limited, while increasing the deoxygenation cost, which is not conducive to industrial production. Maintaining the oxygen concentration within the range of 0.05%~0.15% can reduce the influence of oxygen on the free radical polymerization reaction and ensure that the polymerization reaction proceeds smoothly, so that the polymerization system maintains a relatively stable free radical concentration, which is beneficial to improving the molecular weight and molecular weight distribution uniformity of polyacrylonitrile polymer.

[0024] In this invention, the polymerization temperature during the initiation stage can be 60°C. 61 62 63 64 65 66 67 68 69 Or 70 .

[0025] In this invention, the polymerization temperature during the chain growth stage can be 70°C. 71 72 73 74 Or 75 .

[0026] In this invention, the polymerization temperature during the ripening stage can be 75°C. 76 Or 77 .

[0027] It should be noted that the polymerization temperatures of the initiation stage, chain growth stage, and maturation stage are not arbitrarily selected independently within their respective temperature ranges. Instead, they should simultaneously satisfy a progressively increasing relationship, meaning the polymerization temperature of the initiation stage is lower than that of the chain growth stage, and the polymerization temperature of the chain growth stage is lower than that of the maturation stage. Therefore, after determining the polymerization temperature of a certain stage, the polymerization temperature of the subsequent stage should be selected within its corresponding temperature range by a value higher than that of the previous stage. For example, when the polymerization temperature of the initiation stage is 70... At that time, the polymerization temperature during the chain growth stage cannot be 70°C. Instead, it should be greater than 70. and not higher than 75 The range is selected; when the polymerization temperature of the chain growth stage is 75... At that time, the polymerization temperature during the ripening stage cannot be 75°C. Instead, it should be greater than 75. and not higher than 77 Select from the range.

[0028] Specifically, the initiation phase uses 60-70 The temperature range is set to allow the initiator to decompose at a suitable rate and form stable active free radicals; the chain growth stage uses a temperature range of 70~75°C. The temperature range is adjusted to keep the free radical generation rate and chain growth rate compatible, reducing the impact of increased viscosity on the polymerization reaction; the maturation stage uses 75~77℃. The temperature range allows the remaining monomers to continue participating in polymerization, gradually bringing the polymerization system to a stable state. During the polymerization reaction, as monomers are continuously consumed and polymer content increases, the viscosity of the polymerization system gradually increases, and the free radical diffusion capacity, chain growth rate, and chain termination rate continuously change. The polymerization system has different requirements for reaction temperature at different stages. Based on the evolution law of the kinetic state of the polymerization system, this invention uses different polymerization temperatures in the initiation stage, chain growth stage, and maturation stage to adapt the initiator decomposition rate, effective free radical concentration, and chain growth, chain transfer, and chain termination processes to the reaction state at each stage. This avoids the increased fluctuation of free radical concentration and differences in the polymer chain growth process caused by the mismatch between reaction conditions and the state of the polymerization system during isothermal polymerization, thereby helping to improve the molecular weight and molecular weight distribution uniformity of polyacrylonitrile polymers.

[0029] In this invention, the initiation phase can last for 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0030] In this invention, the chain growth phase can last for 8h, 9h, 10h, 11h or 12h.

[0031] In this invention, the ripening stage can last for 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0032] Specifically, the initiation stage lasts 1-3 hours, allowing sufficient time for the initiator to decompose and form stable active free radicals; the chain growth stage lasts 8-12 hours, providing ample reaction time for the continuous growth of the polymer chain and increasing the polymer yield; the maturation stage lasts 3-5 hours, allowing the remaining monomers to further participate in the polymerization and gradually stabilizing the polymerization system; different reaction times are used for each polymerization stage to ensure that the polymerization reaction can fully complete the corresponding reaction process of each stage, avoiding incomplete polymerization due to too short a reaction time, or increased energy consumption and decreased polymerization efficiency due to too long a reaction time, which is beneficial for obtaining polyacrylonitrile with stable performance.

[0033] In this invention, the stirring speed during the initiation stage can be 18 r / min, 20 r / min, 22 r / min, 24 r / min, 26 r / min, 28 r / min or 30 r / min.

[0034] In this invention, the stirring speed during the chain growth stage can be 30 r / min, 32 r / min, 35 r / min, 37 r / min, 40 r / min, 45 r / min or 50 r / min.

[0035] In this invention, the stirring speed during the maturation stage can be 50 r / min, 52 r / min, 55 r / min, 58 r / min, 60 r / min, 65 r / min or 68 r / min.

[0036] It should be noted that the stirring speeds for the initiation, chain growth, and maturation stages are not arbitrarily selected independently within their respective speed ranges. Instead, they must simultaneously satisfy a progressively increasing relationship, meaning the stirring speed for the initiation stage is lower than that for the chain growth stage, and the stirring speed for the chain growth stage is lower than that for the maturation stage. Therefore, after determining the stirring speed for a certain stage, the stirring speed for the subsequent stage should be selected within its corresponding speed range by a value higher than that of the previous stage. For example, when the stirring speed for the initiation stage is 30 r / min, the stirring speed for the chain growth stage cannot be 30 r / min, but should be selected within a range greater than 30 r / min and not higher than 50 r / min; similarly, when the stirring speed for the chain growth stage is 50 r / min, the stirring speed for the maturation stage cannot be 50 r / min, but should be selected within a range greater than 50 r / min and not higher than 68 r / min. By gradually increasing the stirring speed in each of the three polymerization stages, the stirring intensity can be adapted to the changes in polymer content and system viscosity during polymerization, thus maintaining a relatively uniform mixing state in the polymerization system at different stages.

[0037] Specifically, the initiation stage uses a stirring speed of 18-30 r / min, which ensures uniform mixing of components when the viscosity of the polymerization system is low, avoiding the impact of excessively high speed on the initial free radical formation. The chain growth stage uses a stirring speed of 30-50 r / min to adapt to the gradual increase in viscosity during polymerization, keeping the polymerization system uniformly mixed. The maturation stage uses a stirring speed of 50-68 r / min to maintain the homogeneity of the polymerization system when the polymer content further increases and the system viscosity is higher, allowing the remaining monomers to fully participate in the polymerization reaction. As polymers are continuously generated during polymerization, the viscosity of the polymerization system gradually increases. If the same stirring speed is always used, it is easy to cause uneven mixing in some parts of the polymerization system, resulting in differences in monomer concentration, free radical concentration, and exothermic reaction distribution. This invention gradually increases the stirring speed at each polymerization stage according to the viscosity change law of the polymerization system, keeping the polymerization system uniformly mixed, which helps to reduce local reaction rate fluctuations, promotes the stable progress of the polymerization reaction, and thus helps to improve the molecular weight and molecular weight distribution uniformity of polyacrylonitrile polymer. In this invention, based on the evolution law of the kinetic state of the polymerization system, the polymerization temperature, reaction time and stirring speed of different polymerization stages are set in a coordinated manner so that the reaction conditions of each polymerization stage are adapted to the reaction state of the polymerization system at the corresponding stage. This allows the polymerization system to maintain a relatively stable reaction state throughout the polymerization process, reduces the fluctuation of the polymerization reaction rate and the difference in the polymerization chain growth process, and is beneficial to improving the molecular weight and molecular weight distribution uniformity of the polyacrylonitrile polymer.

[0038] In a preferred embodiment, the oxygen concentration in the polymerization system is 0.10%.

[0039] Specifically, by controlling the oxygen concentration in the polymerization system to 0.10%, the capturing effect of oxygen on the active centers of free radicals can be reduced, the occurrence of free radical chain termination reactions can be reduced, and the problem of uneven local chain growth rate caused by excessively low oxygen content in the early stage of polymerization reaction can be avoided. This keeps the free radical concentration stable during the polymerization reaction, which is beneficial to controlling the growth process of polyacrylonitrile molecular chains and improving the uniformity of polymer molecular weight distribution.

[0040] In a preferred embodiment, the polymerization temperature during the initiation stage is 65°C. The polymerization temperature during the chain growth stage is 72°C. The polymerization temperature during the maturation stage is 76°C. .

[0041] Specifically, 65 is used in the initiation phase. It can promote the decomposition of the initiator and generate a stable number of free radicals, avoiding excessively high initial free radical concentrations that could lead to rapid chain growth; the temperature is increased to 72°C during the chain growth stage. This allows for maintaining a suitable chain growth rate, ensuring continuous monomer participation in the polymerization reaction; the temperature is raised to 76°C during the ripening stage. This can promote further reaction of residual monomers, improve polymerization conversion, and reduce chain transfer and side reactions caused by excessively high temperatures, thereby obtaining a polyacrylonitrile polymer with a stable molecular structure.

[0042] In a preferred embodiment, the initiation phase lasts for 2 hours, the chain growth phase lasts for 10 hours, and the maturation phase lasts for 4 hours.

[0043] Specifically, by controlling the initiation stage to 2 hours, the initiator in the system is fully decomposed and a stable free radical concentration is formed, providing continuous reactivity for subsequent chain growth; by controlling the chain growth stage to 10 hours, acrylonitrile and comonomers can fully participate in chain segment extension, promoting uniform growth of polymer molecular chains; by controlling the maturation stage to 4 hours, unreacted active segments and residual monomers are further reacted, improving the degree of polymerization reaction and reducing the content of oligomers and residual monomers in polyacrylonitrile.

[0044] In a preferred embodiment, the stirring speed during the initiation stage is 24 r / min, the stirring speed during the chain growth stage is 40 r / min, and the stirring speed during the maturation stage is 60 r / min.

[0045] Specifically, using 24 r / min in the initiation stage can ensure uniform dispersion of the initiator and all reaction components, avoiding local differences in free radical concentration; increasing the speed to 40 r / min in the chain growth stage can enhance the mass transfer effect of the system, allowing monomers, free radicals and polymer segments to fully contact and promote uniform growth of molecular chains; increasing the speed to 60 r / min in the maturation stage can reduce the mass transfer obstacles caused by the increase in viscosity of the polymerization system, allowing residual monomers to further diffuse and participate in the reaction, and improving the compositional uniformity of polyacrylonitrile.

[0046] In a preferred embodiment, the oxygen concentration in the polymerization system is 0.10%; the polymerization temperature during the initiation stage is 65°C. The polymerization temperature during the chain growth stage is 72°C. The polymerization temperature during the maturation stage is 76°C. The initiation stage lasts for 2 hours, the chain growth stage lasts for 10 hours, and the maturation stage lasts for 4 hours. The stirring speed during the initiation stage is 24 r / min, the stirring speed during the chain growth stage is 40 r / min, and the stirring speed during the maturation stage is 60 r / min.

[0047] Specifically, in this preferred embodiment, the oxygen concentration, polymerization temperature, reaction time, and stirring speed adopt the above-mentioned preferred parameter combination. The parameters are coordinated with each other and adapted to the evolution law of the kinetic state of the polymerization system, so that the polymerization reaction is more stable, further reducing the fluctuation of the polymerization reaction rate and the difference in the polymerization chain growth process, which is more conducive to improving the molecular weight and molecular weight distribution uniformity of the polyacrylonitrile polymer.

[0048] In a preferred embodiment, the components in the polymerization system are proportioned by weight, wherein acrylonitrile is the base component with a weight of 100 parts, comonomer is 0.8 to 1.2 parts, chain transfer agent is 0.05 to 0.3 parts, initiator is 0.5 to 0.8 parts, and organic solvent is 320 to 340 parts.

[0049] In this invention, acrylonitrile is used as the base component, with a weight of 100 parts, and the weight of the comonomer can be 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, or 1.2 parts. In this invention, acrylonitrile is used as the base component, with a weight of 100 parts, and the weight of the chain transfer agent can be 0.05 parts, 0.10 parts, 0.15 parts, 0.20 parts, 0.25 parts, or 0.30 parts. In this invention, acrylonitrile is used as the base component, with a weight of 100 parts, and the weight of the initiator can be 0.50 parts, 0.55 parts, 0.60 parts, 0.65 parts, 0.70 parts, 0.75 parts, or 0.80 parts. In this invention, acrylonitrile is used as the base component, with a weight of 100 parts, and the weight of the organic solvent can be 320 parts, 325 parts, 330 parts, 335 parts, or 340 parts.

[0050] In this invention, the weight parts of each component in the polymerization system can be: 100 parts acrylonitrile, 0.8 parts comonomer, 0.05 parts chain transfer agent, 0.5 parts initiator, and 320 parts organic solvent. In this invention, the weight parts of each component in the polymerization system can be: 100 parts acrylonitrile, 1.0 part comonomer, 0.15 parts chain transfer agent, 0.65 parts initiator, and 330 parts organic solvent; In this invention, the weight parts of each component in the polymerization system may also be: 100 parts acrylonitrile, 1.2 parts comonomer, 0.3 parts chain transfer agent, 0.8 parts initiator, and 340 parts organic solvent; Specifically, when the weight percentages of comonomers, chain transfer agents, initiators, and organic solvents are below the aforementioned ranges, the coordination between monomer concentration, free radical generation, and chain transfer in the polymerization system is affected, easily leading to incomplete polymerization and limited chain growth. When the weight percentages of each component are above the aforementioned ranges, the balance between free radical generation, chain growth, and chain transfer processes is easily disrupted, resulting in increased fluctuations in the polymerization rate and an increased likelihood of side reactions. Limiting the weight percentages of each component within the aforementioned ranges ensures that the monomer concentration, free radical generation, and chain transfer capabilities in the polymerization system are matched, providing a basis for the stable evolution of the polymerization system's kinetic state. This facilitates smooth polymerization, reduces differences in the chain growth process, improves the molecular weight and molecular weight distribution uniformity of the polyacrylonitrile polymer, and stabilizes the viscosity and rheological properties of polyacrylonitrile.

[0051] In a preferred embodiment, the comonomer includes one or more of itaconic acid, acrylic acid, methacrylic acid, fumaric acid, and maleic acid; And / or, the chain transfer agent includes one or more of n-octyl mercaptan, n-butyritin and dodecyl mercaptan; And / or, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisovalerate; And / or, the organic solvent includes one or more of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0052] In this invention, the comonomer may be any one of itaconic acid, acrylic acid, methacrylic acid, fumaric acid, or maleic acid; it may also be a combination of itaconic acid and acrylic acid, a combination of itaconic acid and methacrylic acid, a combination of itaconic acid and fumaric acid, a combination of itaconic acid and maleic acid, a combination of acrylic acid and methacrylic acid, a combination of acrylic acid and fumaric acid, a combination of acrylic acid and maleic acid, a combination of methacrylic acid and maleic acid, or a combination of fumaric acid and maleic acid; it may also be any three or more combinations of itaconic acid, acrylic acid, methacrylic acid, fumaric acid, and maleic acid.

[0053] Specifically, the comonomer contains unsaturated groups that can participate in free radical polymerization reactions. During the polymerization process, it can undergo copolymerization with acrylonitrile monomers, introduce polar structural units, regulate the chemical structure and chain segment arrangement of polyacrylonitrile molecular chains, improve the inter-chain forces of polymer molecules, and thus improve the structural stability and subsequent processing performance of the polymer.

[0054] In this invention, the chain transfer agent may be any one of n-octyl mercaptan, n-butyl mercaptan, or dodecyl mercaptan; it may also be a combination of n-octyl mercaptan and n-butyl mercaptan, a combination of n-octyl mercaptan and dodecyl mercaptan, or a combination of n-butyl mercaptan and dodecyl mercaptan; or it may be a combination of n-octyl mercaptan, n-butyl mercaptan, and dodecyl mercaptan.

[0055] Specifically, the chain transfer agent contains active sulfur and hydrogen groups, which can undergo chain transfer reactions with growing free radicals during polymerization, regulate the growth rate of free radical chains, control the length of polyacrylonitrile molecular chains, reduce the fluctuation of molecular weight distribution caused by excessively rapid local chain growth, and thus improve the stability of polymer molecular weight and molecular weight distribution.

[0056] In this invention, the initiator may be any one of azobisisobutyronitrile, azobisisoheptanenitrile, or azobisisovaleratenitrile; it may also be a combination of azobisisobutyronitrile and azobisisoheptanenitrile, a combination of azobisisobutyronitrile and azobisisovaleratenitrile, or a combination of azobisisoheptanenitrile and azobisisovaleratenitrile; or it may be a combination of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisovaleratenitrile.

[0057] Specifically, the initiator can decompose to generate free radicals under polymerization temperature conditions, providing active centers for the polymerization reaction of acrylonitrile and comonomers. By controlling the free radical generation rate, the polymerization reaction initiation process and chain growth process can be affected, so that the polymerization reaction can be kept stable.

[0058] In this invention, the organic solvent may be any one of dimethyl sulfoxide, dimethylformamide, or dimethylacetamide; it may also be a combination of dimethyl sulfoxide and dimethylformamide, a combination of dimethyl sulfoxide and dimethylacetamide, or a combination of dimethylformamide and dimethylacetamide; or it may be a combination of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0059] Specifically, the organic solvent is used to dissolve acrylonitrile, comonomer, chain transfer agent and initiator, so that the reaction components are fully mixed, while adjusting the viscosity and mass transfer state of the polymerization system, reducing local concentration differences during polymerization, and promoting uniform polymerization reaction.

[0060] In a preferred embodiment, the comonomer is itaconic acid, the chain transfer agent is n-octyl mercaptan, the initiator is azobisisobutyronitrile, and the organic solvent is dimethyl sulfoxide.

[0061] Specifically, itaconic acid, as a comonomer, is introduced into the polyacrylonitrile molecular chain, which is beneficial to improving the polymer molecular structure; n-octyl mercaptan, as a chain transfer agent, is beneficial to regulating the growth length of the polymer chain; azobisisobutyronitrile, as an initiator, can stably decompose at the polymerization temperature to generate free radicals; dimethyl sulfoxide, as an organic solvent, can fully dissolve the raw materials and maintain the homogeneity of the polymerization system. The above components work together to ensure that the polymerization reaction proceeds smoothly, which is beneficial to obtaining polyacrylonitrile with a higher molecular weight and a narrower molecular weight distribution.

[0062] In a preferred embodiment, after the polymerization reaction is completed, the obtained polyacrylonitrile undergoes post-treatment, which includes at least one of the following processes: (a) Removal of unreacted monomers from polyacrylonitrile; (b) Filter the polyacrylonitrile after removing unreacted monomers; (c) Removing air bubbles from polyacrylonitrile; and, (d) Adjust the pH value of polyacrylonitrile.

[0063] Specifically, after the polymerization reaction is completed, unreacted monomers are first removed from the polyacrylonitrile to reduce the impact of residual monomers on the performance of polyacrylonitrile and subsequent processing. Then, the polyacrylonitrile is filtered to remove mechanical impurities and gel particles generated during polymerization, thereby improving the cleanliness of the polyacrylonitrile. The filtered polyacrylonitrile is further degassed to remove entrained gases and reduce the generation of bubble defects during subsequent spinning. Finally, the pH value of the polyacrylonitrile is adjusted to meet the requirements of subsequent storage and spinning processes.

[0064] In a preferred embodiment, the removal of unreacted monomers from polyacrylonitrile comprises: at a temperature of 75-85°C Under pressure of -100~-95kPa, vacuum distillation is carried out for 0.5~1h to vaporize and separate the unreacted monomers in polyacrylonitrile from the polyacrylonitrile. And / or, the removal of bubbles from polyacrylonitrile includes: at a temperature of 75~85°C Vacuum degassing was performed on the filtered polyacrylonitrile under a pressure of -100~-95kPa. And / or, adjusting the pH value of the polyacrylonitrile includes: introducing ammonia gas into the degassed polyacrylonitrile to adjust the pH value of the polyacrylonitrile to 6.5~7.5.

[0065] In this invention, the temperature of the vacuum distillation can be 75°C. 80 Or 85 ; In this invention, the pressure of the vacuum distillation can be -100 kPa, -98 kPa, or -95 kPa; In this invention, the distillation time for vacuum distillation can be 0.5h, 0.75h, or 1h.

[0066] Specifically, during vacuum distillation, by reducing the system pressure, the boiling points of unreacted acrylonitrile and comonomers in polyacrylonitrile are lowered, thereby enabling selective volatilization of monomer components at lower temperatures and reducing the residual monomer content in polyacrylonitrile; wherein, when the vacuum distillation temperature is controlled at 75°C... ~85 When the pressure is controlled at -100~-95kPa, the temperature required for monomer volatilization can be further reduced, the removal efficiency of unreacted monomers can be improved, and the impact of residual monomers on the subsequent spinning process of polyacrylonitrile can be reduced. When the pressure is controlled at 0.5h~1h, the residual monomers can have sufficient time to escape, ensuring the monomer removal effect while avoiding the decrease in polymer molecular weight caused by long-term heat treatment.

[0067] In a preferred embodiment, the temperature of the vacuum distillation is 80°C. The pressure was -98 kPa and the distillation time was 0.75 h.

[0068] Specifically, in 80 At a reduced pressure distillation temperature, the volatility difference between acrylonitrile and its comonomers and the polyacrylonitrile component in polyacrylonitrile is utilized to allow unreacted acrylonitrile and comonomers to rapidly vaporize and escape. Simultaneously, by reducing the system pressure to -98 kPa, the boiling point of the monomer components is lowered, enabling effective removal at lower temperatures and avoiding thermal degradation or structural changes in the polyacrylonitrile molecular chains caused by high-temperature treatment. Furthermore, by controlling the distillation time to 0.75 h, sufficient escape time is provided for the residual monomers, ensuring monomer removal efficiency while avoiding a decrease in polymer molecular weight and a broadening of molecular weight distribution due to prolonged heating. Therefore, at 80... Under reduced pressure distillation conditions of -98 kPa and 0.75 h, the residual monomer content in polyacrylonitrile can be effectively reduced, the purity and storage stability of polyacrylonitrile can be improved, and the molecular structure of polyacrylonitrile can be kept stable, which is beneficial to improving the processing stability in the subsequent spinning process to prepare carbon fiber precursor.

[0069] In this invention, the temperature of the vacuum degassing can be 75°C. 80 Or 85 .

[0070] In this invention, the pressure of vacuum degassing can be -95kPa, -98kPa, or -100kPa.

[0071] Specifically, in the vacuum degassing process, polyacrylonitrile is maintained at 75°C. ~85 Within a specific temperature range, the viscosity of polyacrylonitrile is reduced, which facilitates the escape of gases dissolved within the polyacrylonitrile and microbubbles encapsulated between polymer segments. Simultaneously, applying a negative pressure environment of -100 to -95 kPa reduces the gas partial pressure at the gas-liquid interface, promoting bubble expansion, rupture, and rapid expulsion. Specifically, when the vacuum degassing temperature is 80... At a pressure of -98 kPa, while ensuring the fluidity of polyacrylonitrile, the gas removal efficiency can be improved, reducing problems such as uneven local viscosity of polyacrylonitrile caused by residual bubbles, filament breakage or molding defects during spinning, thereby improving the uniformity and storage stability of polyacrylonitrile.

[0072] In a preferred embodiment, the vacuum degassing temperature is 80°C. The vacuum degassing pressure is -98 kPa.

[0073] Specifically, in this embodiment, the vacuum degassing temperature is controlled at 80°C. This method maintains a suitable flow viscosity for polyacrylonitrile (PAB), allowing for a high migration rate of internal bubbles. Simultaneously, controlling the vacuum degassing pressure to -98 kPa effectively reduces the internal gas dissolution equilibrium pressure of PAB, promoting the rupture and escape of microbubbles. Under these temperature and pressure conditions, both gas removal efficiency and PAB stability can be balanced, avoiding problems such as high PAB viscosity and insufficient bubble removal due to excessively low temperatures, and thermal degradation of polymer chains or changes in PAB properties due to excessively high temperatures. This results in PABs with low bubble content and good uniformity.

[0074] In this invention, the pH value of the polyacrylonitrile can be adjusted to 6.5, 7.0 or 7.5.

[0075] Specifically, ammonia gas is introduced into the polyacrylonitrile (PAB), and the ammonia gas neutralizes the residual acidic components in the PAB, adjusting the pH value of the PAB to 6.5-7.5, thus placing the PAB in a near-neutral stable environment. Within this pH range, the influence of residual comonomers, unreacted acidic groups, and trace acidic impurities on the PAB molecular chain structure can be reduced, minimizing the risk of molecular chain degradation, viscosity changes, and performance fluctuations during storage and transportation. Simultaneously, a suitable pH environment helps maintain the stability of the PAB molecular weight and molecular weight distribution, improving the uniformity of the PAB and providing a stable raw material basis for the subsequent wet spinning preparation of PAB fiber precursors.

[0076] In a preferred embodiment, ammonia gas is introduced into the polyacrylonitrile to adjust the pH value of the polyacrylonitrile to 7.0.

[0077] Specifically, under a pH value of 7.0, the acidic residual components in polyacrylonitrile can be fully neutralized, while avoiding changes in the state of polar groups in polyacrylonitrile due to excessive alkalinity. By adjusting polyacrylonitrile to a neutral environment, the possibility of the polymer molecular chain being affected by the acid and alkaline environment during storage can be effectively reduced, and the viscosity of polyacrylonitrile can be kept stable, thus taking into account both the stability of polyacrylonitrile and the performance of subsequent spinning processing.

[0078] In a preferred embodiment, the method for preparing polyacrylonitrile includes the following steps: S1. Weigh the organic solvent according to the preset weight ratio and add it to the mixing tank. Add the comonomer under stirring to fully dissolve the comonomer. Then add acrylonitrile and chain transfer agent and continue stirring to mix the components evenly and form a polymerization solution.

[0079] S2. The polymerization solution is transported to the polymerization reactor, and the air in the polymerization reactor is replaced with inert gas to reduce the oxygen concentration in the polymerization system to a preset oxygen concentration. Then, an initiator is added to carry out the polymerization reaction. The polymerization reaction includes an initiation stage, a chain growth stage, and a maturation stage. Each polymerization stage is completed by using the corresponding polymerization temperature, reaction time, and stirring speed.

[0080] S3. After the polymerization reaction is completed, the polyacrylonitrile is transported to the monomer removal unit, where unreacted monomers are removed under reduced pressure to separate the unreacted monomers from the polyacrylonitrile.

[0081] S4. The polyacrylonitrile after removing unreacted monomers is conveyed to a filtration device for filtration to remove mechanical impurities and gel particles from the polyacrylonitrile.

[0082] S5. The filtered polyacrylonitrile is conveyed to the degassing device, where it is degassed under reduced pressure to remove air bubbles from the polyacrylonitrile.

[0083] S6. Ammonia gas is introduced into the degassed polyacrylonitrile to adjust the pH value of the polyacrylonitrile, thus obtaining polyacrylonitrile.

[0084] A second objective of this invention is to provide a polyacrylonitrile, which is obtained by the preparation method described above.

[0085] Specifically, the polyacrylonitrile prepared by this invention can be used as a raw material for preparing carbon fiber precursors, and carbon fibers can be prepared through processes such as spinning, pre-oxidation and carbonization. Since the polyacrylonitrile prepared by this invention has a high molecular weight and a narrow molecular weight distribution, it is beneficial to improve the forming stability of precursor fibers and further improve the performance consistency of carbon fiber products.

[0086] Example 1 This embodiment provides a method for preparing polyacrylonitrile, the steps of which include: S1. Weigh 330 parts of dimethyl sulfoxide according to the weight ratio and add them to the mixing tank. Add 1.0 part of itaconic acid under stirring to fully dissolve the itaconic acid. Then add 100 parts of acrylonitrile and 0.15 parts of n-octyl mercaptan and continue stirring until all components are mixed evenly to form a polymerization solution. S2. The polymerization solution is transported to the polymerization reactor, and the air in the reactor is replaced with nitrogen to reduce the oxygen concentration in the polymerization system to 0.10%. Then, 0.65 parts of azobisisobutyronitrile are added as an initiator, and the polymerization reaction is started. Polymerization reactions include an initiation phase, a chain growth phase, and a maturation phase, among which: The initiation stage temperature is 65°C. The stirring was carried out for 2 hours at a speed of 24 r / min. The temperature rises to 72 during the chain growth phase. The stirring was carried out for 10 hours at a speed of 40 r / min. The temperature during the ripening stage rises to 76 degrees Celsius. The stirring was carried out for 4 hours at a speed of 60 r / min. S3. After polymerization, the polyacrylonitrile is transported to the depolymerization tower at 80°C. Unreacted acrylonitrile and comonomers in polyacrylonitrile were removed by vacuum distillation for 0.75 h under -98 kPa conditions. S4. The polyacrylonitrile after separation is transported to a closed filter for filtration to remove mechanical impurities and gel particles from the polyacrylonitrile. S5. The filtered polyacrylonitrile is then conveyed to the degassing tower at 80°C. Vacuum degassing was performed under -98 kPa conditions; S6. Ammonia gas is introduced into the degassed polyacrylonitrile to adjust the pH of the polyacrylonitrile to 7.0, thus obtaining polyacrylonitrile.

[0087] Example 2 This embodiment is basically the same as embodiment 1, except that: The oxygen concentration in the polymerization system was adjusted to 0.05%; All other process conditions are the same as in Example 1.

[0088] Example 3 This embodiment is basically the same as embodiment 1, except that: The oxygen concentration in the polymerization system was adjusted to 0.15%; All other process conditions are the same as in Example 1.

[0089] Example 4 This embodiment is basically the same as embodiment 1, except that: The initiation stage temperature is 60°C. ; The temperature rises to 70 during the chain growth phase. ; The temperature during the ripening stage rises to 75 degrees Celsius. ; All other process conditions are the same as in Example 1.

[0090] Example 5 This embodiment is basically the same as embodiment 1, except that: The initiation stage temperature is 70°C. ; The temperature rises to 75 during the chain growth phase. ; The temperature during the ripening stage rises to 77°C. ; All other process conditions are the same as in Example 1.

[0091] Example 6 This embodiment is basically the same as embodiment 1, except that: During the aggregation process: The trigger phase lasts for 1 hour; The chain growth phase lasted for 8 hours. The ripening stage lasts for 3 hours; All other process conditions are the same as in Example 1.

[0092] Example 7 This embodiment is basically the same as embodiment 1, except that: During the aggregation process: The trigger phase lasts for 3 hours; The chain growth phase lasts for 12 hours. The ripening stage lasts for 5 hours; All other process conditions are the same as in Example 1.

[0093] Example 8 This embodiment is basically the same as embodiment 1, except that: During the aggregation process: The stirring speed during the initiation stage is 18 r / min; The stirring speed during the chain growth stage is 30 r / min; The stirring speed during the maturation stage is 50 r / min; All other process conditions are the same as in Example 1.

[0094] Example 9 This embodiment is basically the same as embodiment 1, except that: During the aggregation process: The stirring speed during the initiation stage is 30 r / min; The stirring speed during the chain growth stage is 50 r / min; The stirring speed during the maturation stage is 68 r / min; All other process conditions are the same as in Example 1.

[0095] Example 10 This embodiment is basically the same as embodiment 1, except that: The components in the polymerization system, by weight, are: 100 parts acrylonitrile, 1.2 parts itaconic acid, 0.30 parts n-octyl mercaptan, 0.80 parts azobisisobutyronitrile, and 340 parts dimethyl sulfoxide; All other process conditions are the same as in Example 1.

[0096] Example 11 This embodiment is basically the same as embodiment 1, except that: The components in the polymerization system, by weight, are: 100 parts acrylonitrile, 0.8 parts itaconic acid, 0.05 parts n-octyl mercaptan, 0.50 parts azobisisobutyronitrile, and 320 parts dimethyl sulfoxide; All other process conditions are the same as in Example 1.

[0097] Example 12 This embodiment is basically the same as embodiment 1, except that: The components in the polymerization system, by weight, are: 100 parts acrylonitrile, 0.50 parts itaconic acid, 0.02 parts n-octyl mercaptan, 0.30 parts azobisisobutyronitrile, and 300 parts dimethyl sulfoxide; All other process parameters are the same as in Example 1.

[0098] Example 13 This embodiment is basically the same as embodiment 1, except that: The components in the polymerization system, by weight, are: 100 parts acrylonitrile, 2.0 parts itaconic acid, 0.50 parts n-octyl mercaptan, 1.20 parts azobisisobutyronitrile, and 360 parts dimethyl sulfoxide; All other process parameters are the same as in Example 1.

[0099] Comparative Example 1 This comparative example is basically the same as Example 1, except that: The polymerization process employs a constant temperature method, maintaining a temperature of 72°C throughout. The aggregation time is 16 hours.

[0100] All other process parameters are the same as in Example 1.

[0101] Comparative Example 2 This comparative example is basically the same as Example 1, except that: The oxygen concentration in the polymerization system is 0.50%.

[0102] Comparative Example 3 This comparative example is basically the same as Example 1, except that: During the aggregation process: The initiation, chain growth, and maturation stages were all stirred at 40 r / min.

[0103] All other process parameters are the same as in Example 1.

[0104] Comparative Example 4 This comparative example is basically the same as Example 1, except that: The oxygen concentration in the polymerization system was adjusted to 0.03%.

[0105] All other process parameters are the same as in Example 1.

[0106] Comparative Example 5 This comparative example is basically the same as Example 1, except that: The oxygen concentration in the polymerization system was adjusted to 0.20%; All other process parameters are the same as in Example 1.

[0107] Comparative Example 6 This comparative example is basically the same as Example 1, except that: During the aggregation process: The initiation stage temperature is 55°C. ; All other process parameters are the same as in Example 1.

[0108] Comparative Example 7 This comparative example is basically the same as Example 1, except that: During the aggregation process: The initiation stage temperature is 75°C. ; All other process parameters are the same as in Example 1.

[0109] Comparative Example 8 This comparative example is basically the same as Example 1, except that: During the aggregation process: The temperature during the chain growth phase is 80 degrees Celsius. ; All other process parameters are the same as in Example 1.

[0110] Comparative Example 9 This comparative example is basically the same as Example 1, except that: During the aggregation process: The ripening stage temperature is 85°C. ; All other process parameters are the same as in Example 1.

[0111] Performance testing The polyacrylonitrile prepared in the examples and comparative examples were subjected to performance tests, including tests on the molecular weight, molecular weight distribution, viscosity, and monomer conversion rate of the polyacrylonitrile polymer.

[0112] Specifically, the test items include: (1) Weight-average molecular weight (Mw) and number-average molecular weight (Mn) test The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of polyacrylonitrile polymers were determined by gel permeation chromatography (GPC), and the molecular weight distribution index (PDI) was calculated. =Mw / Mn.

[0113] (2) Polyacrylonitrile viscosity test Polyacrylonitrile at 25°C was determined using a rotational viscometer. The viscosity was measured to evaluate the flow properties of polyacrylonitrile.

[0114] (3) Monomer conversion rate test The contents of unreacted acrylonitrile and comonomers in polyacrylonitrile were determined by gas chromatography (GC), and the monomer conversion rate was calculated based on the feed amount.

[0115] The performance test results are shown in Table 1 below; Table 1

[0116] As shown in Table 1, the weight-average molecular weight and number-average molecular weight of the polyacrylonitrile obtained in Examples 1-13 were maintained at a high level, and the molecular weight distribution index was lower than that of Comparative Examples 1-9. Furthermore, the viscosity and monomer conversion rate of polyacrylonitrile maintained good stability. This indicates that by controlling the oxygen concentration of the polymerization system and combining it with the staged control of temperature, reaction time, and stirring speed in the initiation, chain growth, and maturation stages, the present invention can coordinate the free radical generation, molecular chain growth, and chain termination processes, which is beneficial to improving the molecular weight and molecular weight distribution uniformity of polyacrylonitrile.

[0117] In Example 1, using preferred oxygen concentration, raw material ratio, and polymerization process parameters, the resulting polyacrylonitrile had a molecular weight distribution index of 1.69 and a monomer conversion rate of 90.2%. While maintaining a high molecular weight, it also had a narrow molecular weight distribution, exhibiting superior overall performance.

[0118] In contrast, Comparative Example 1 used a constant-temperature polymerization method without adjusting the temperature according to the reaction characteristics of different polymerization stages, which led to a decrease in the matching of the polymerization process, resulting in a decrease in the weight-average molecular weight and number-average molecular weight of the obtained polyacrylonitrile, an increase in the molecular weight distribution index, and a decrease in the viscosity of polyacrylonitrile.

[0119] Comparative Examples 2, 4, and 5 altered the oxygen concentration in the polymerization system, causing it to deviate from the scope defined in this invention. This resulted in changes in the oxygen inhibition effect or free radical regulation effect, leading to a decrease in the stability of the polymerization process, a decrease in the molecular weight of the obtained polyacrylonitrile, and an increase in the molecular weight distribution index.

[0120] Comparative Example 3 used a fixed stirring speed and did not adjust the stirring conditions according to the reaction characteristics of the initiation stage, chain growth stage and maturation stage, which reduced the mixing and mass transfer effect of the polymerization system and led to a decrease in the uniformity of the polymerization reaction.

[0121] Comparative Examples 6 to 9 changed the temperature parameters at different polymerization stages, which affected the balance between initiator decomposition, molecular chain growth and chain termination processes, resulting in a decrease in the weight-average molecular weight and number-average molecular weight of the obtained polyacrylonitrile, an increase in the molecular weight distribution index and a decrease in the viscosity of polyacrylonitrile.

[0122] Therefore, it can be seen that the present invention makes the polymerization process more stable by synergistically controlling the low-oxygen polymerization environment and the phased polymerization process parameters, which is conducive to obtaining polyacrylonitrile with higher molecular weight, more uniform molecular weight distribution and stable performance.

[0123] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention is not limited to the specific combination of the above-described technical features, but also includes other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this invention.

Claims

1. A method for preparing polyacrylonitrile, characterized in that, include: Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed in a predetermined mass ratio to form a polymerization system; After adjusting the oxygen concentration in the polymerization system to 0.05%~0.15%, an initiator is added to initiate the polymerization reaction. The polymerization reaction includes an initiation stage, a chain growth stage, and a maturation stage. The polymerization temperature during the initiation stage is 60~70°C. The polymerization temperature during the chain growth stage is 70~75°C. The polymerization temperature during the maturation stage is 75~77°C. Furthermore, the polymerization temperature of the initiation stage is lower than the polymerization temperature of the chain growth stage, and the polymerization temperature of the chain growth stage is lower than the polymerization temperature of the maturation stage. The initiation phase lasts 1-3 hours, the chain growth phase lasts 8-12 hours, and the maturation phase lasts 3-5 hours. The polymerization reaction is carried out under stirring. The stirring speed during the initiation stage is 18~30 r / min, the stirring speed during the chain growth stage is 30~50 r / min, and the stirring speed during the maturation stage is 50~68 r / min. The stirring speed during the initiation stage is lower than the stirring speed during the chain growth stage, and the stirring speed during the chain growth stage is lower than the stirring speed during the maturation stage. After the polymerization reaction is complete, polyacrylonitrile is obtained.

2. The method for preparing polyacrylonitrile according to claim 1, characterized in that, The oxygen concentration in the polymerization system is 0.10%.

3. The method for preparing polyacrylonitrile according to claim 1, characterized in that, The polymerization temperature during the initiation stage is 65°C. The polymerization temperature during the chain growth stage is 72°C. The polymerization temperature during the maturation stage is 76°C. .

4. The method for preparing polyacrylonitrile according to claim 1, characterized in that, The initiation phase lasts for 2 hours, the chain growth phase lasts for 10 hours, and the maturation phase lasts for 4 hours.

5. The method for preparing polyacrylonitrile according to claim 1, characterized in that, The stirring speed during the initiation stage is 24 r / min, the stirring speed during the chain growth stage is 40 r / min, and the stirring speed during the maturation stage is 60 r / min.

6. The method for preparing polyacrylonitrile according to claim 1, characterized in that, The components in the polymerization system are proportioned by weight, wherein acrylonitrile is the base component with a weight of 100 parts, comonomer is 0.8 to 1.2 parts, chain transfer agent is 0.05 to 0.3 parts, initiator is 0.5 to 0.8 parts, and organic solvent is 320 to 340 parts.

7. The method for preparing polyacrylonitrile according to claim 1, characterized in that, The comonomers include one or more of itaconic acid, acrylic acid, methacrylic acid, fumaric acid, and maleic acid. And / or, the chain transfer agent includes one or more of n-octyl mercaptan, n-butyritin and dodecyl mercaptan; And / or, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisovalerate; And / or, the organic solvent includes one or more of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

8. The method for preparing polyacrylonitrile according to claim 1, characterized in that, After the polymerization reaction is completed, the obtained polyacrylonitrile is subjected to post-treatment, which includes at least one of the following processes: (a) Removal of unreacted monomers from polyacrylonitrile; (b) Filter the polyacrylonitrile after removing unreacted monomers; (c) Remove air bubbles from polyacrylonitrile; and, (d) Adjust the pH value of polyacrylonitrile.

9. The method for preparing polyacrylonitrile according to claim 8, characterized in that, The removal of unreacted monomers from polyacrylonitrile includes: at a temperature of 75-85°C. Under pressure of -100~-95kPa, vacuum distillation is carried out for 0.5~1h to vaporize and separate the unreacted monomers in polyacrylonitrile from the polyacrylonitrile. And / or, the removal of bubbles from polyacrylonitrile includes: at a temperature of 75~85°C Vacuum degassing was performed on the filtered polyacrylonitrile under a pressure of -100~-95kPa. And / or, adjusting the pH value of the polyacrylonitrile includes: introducing ammonia gas into the degassed polyacrylonitrile to adjust the pH value of the polyacrylonitrile to 6.5~7.

5.

10. A polyacrylonitrile, characterized in that, The polyacrylonitrile is obtained by the preparation method described in any one of claims 1 to 9.

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