Polyacrylonitrile polymerization solution, method for preparing the same, and use thereof

Abstract

The present application relates to polyacrylonitrile polymerization technical field, specifically relates to a kind of polyacrylonitrile polymerization liquid, its preparation method and purpose, the polyacrylonitrile polymerization liquid is mainly by including acrylonitrile, comonomer, chain transfer agent, initiator and organic solvent polymerization system is prepared by polymerization reaction, by controlling the proportion of each component in polymerization system, optimize the balance between radical generation rate, chain growth process and chain transfer behavior.The copolymer is 0.8~1.2 parts, chain transfer agent is 0.05~0.3 parts, initiator is 0.5~0.8 parts, organic solvent is 320~340 parts with acrylonitrile mass fraction is 100 parts, and the mass ratio of chain transfer agent and initiator is (1:10)~(1:2).The present application can improve polyacrylonitrile polymer molecular weight, improve molecular weight distribution width, improve polymerization liquid viscosity stability and spinning forming performance, can be used for preparing carbon fiber material.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile polymerization technology, specifically to a polyacrylonitrile polymerization solution, its preparation method, and its uses. Background Technology

[0002] In existing technologies, polyacrylonitrile (PAN) polymerization solutions are typically prepared by free radical polymerization of acrylonitrile and comonomers and used as spinning solutions for carbon fibers. However, during the polymerization process, the ratio of components such as acrylonitrile, comonomers, initiators, and chain transfer agents directly affects the free radical generation rate, chain growth process, and chain transfer behavior.

[0003] Because the proportions of each component in the polymerization system are not precisely controlled in the existing technology, the chain growth rate and chain termination rate are easily mismatched during the polymerization process, resulting in polyacrylonitrile polymers with insufficient molecular weight, wide molecular weight distribution, and poor viscosity stability of the polymerization liquid.

[0004] Molecular weight and molecular weight distribution affect the rheological properties, spinning properties, and uniformity of the internal structure of polyacrylonitrile polymerization solutions. This makes it difficult for existing polyacrylonitrile polymerization solutions to simultaneously achieve high molecular weight, narrow molecular weight distribution, and suitable spinning viscosity, thus limiting their application as spinning dopes for carbon fiber spinning. Summary of the Invention

[0005] In order to overcome the above-mentioned defects and deficiencies in the existing technology, the present invention aims to provide a polyacrylonitrile polymerization solution, its preparation method and application. By optimizing the proportion of each component in the polymerization system, the molecular weight and molecular weight distribution of polyacrylonitrile in the polyacrylonitrile polymerization solution can be effectively controlled, thereby improving the stability and spinning applicability of the polyacrylonitrile polymerization solution.

[0006] In a first aspect, the present invention provides a polyacrylonitrile polymerization liquid, which is mainly prepared by a polymerization reaction of a polymerization system comprising acrylonitrile, comonomer, chain transfer agent, initiator and organic solvent; In the polymerization system, the mass fraction of acrylonitrile is 100 parts. The comonomer is in the form of 0.8 to 1.2 parts by mass. The chain transfer agent is present in a mass fraction of 0.05 to 0.3 parts; The initiator is present in a mass fraction of 0.5 to 0.8 parts; The organic solvent is in the form of 320-340 parts by mass. The mass ratio of the chain transfer agent to the initiator is (1:10) to (1:2).

[0007] According to the technical solution provided in the embodiments of this application, the mass ratio of the chain transfer agent to the initiator in the polymerization system is (1:8) to (1:3).

[0008] According to the technical solution provided in the embodiments of this application, the mass ratio of the chain transfer agent to the initiator in the polymerization system is 3:13.

[0009] According to the technical solution provided in the embodiments of this application, the mass ratio of the comonomer to the acrylonitrile in the polymerization system is (1:125) to (1:83).

[0010] According to the technical solution provided in the embodiments of this application, the mass ratio of the comonomer to the acrylonitrile in the polymerization system is 1:100.

[0011] According to the technical solution provided in the embodiments of this application, 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.

[0012] According to the technical solution provided in the embodiments of this application, the comonomer is itaconic acid, the chain transfer agent is n-octyl mercaptan, the initiator is azobisisobutyronitrile, and the organic solvent is dimethyl sulfoxide.

[0013] According to the technical solution provided in the embodiments of this application, the components in the polymerization system, by mass parts, include: Acrylonitrile 100 parts, itaconic acid 1.0 part, n-octyl mercaptan 0.15 parts, azobisisobutyronitrile 0.65 parts, and dimethyl sulfoxide 330 parts.

[0014] According to the technical solution provided in the embodiments of this application, the chain transfer agent includes n-octyl mercaptan and n-butyrithiol, and the mass ratio of n-octyl mercaptan to n-butyrithiol is (1:3) to (1:1).

[0015] According to the technical solution provided in the embodiments of this application, the chain transfer agent includes n-octyl mercaptan and dodecyl mercaptan, and the mass ratio of n-octyl mercaptan and dodecyl mercaptan is (2:2) to (2:1).

[0016] Secondly, the present invention provides a method for preparing the polyacrylonitrile polymerization solution as described above, comprising: Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed according to the preset mass ratio to form a polymerization system; The initiator is added to the polymerization system at a mass ratio of (1:10) to (1:2) of the chain transfer agent to the initiator; Under preset polymerization conditions, the acrylonitrile and the comonomer undergo a polymerization reaction to obtain the polyacrylonitrile polymer solution.

[0017] Thirdly, the present invention provides an application of the polyacrylonitrile polymerization solution as described above, comprising: using the polyacrylonitrile polymerization solution as a spinning dope to prepare polyacrylonitrile-based carbon fibers by a dry-jet wet spinning process.

[0018] The beneficial effects of this invention are: This invention achieves synergistic regulation of the proportions of acrylonitrile, comonomer, chain transfer agent, initiator, and organic solvent in the polymerization system, enabling each component to play a complementary role in the free radical polymerization process. Specifically, the initiator generates initiating free radicals, controlling the initiation rate and concentration of the polymerization reaction; the chain transfer agent regulates the growth length of the polymer molecular chain and inhibits excessive chain growth by undergoing a chain transfer reaction with the growing chain free radicals; the comonomer participates in the regulation of the molecular chain structure, improving the polymer chain segment composition and interchain interactions; and the organic solvent provides a suitable polymerization reaction environment, regulating the viscosity and mass transfer state of the reaction system.

[0019] By limiting the mass ratio of chain transfer agent to initiator to (1:10) to (1:2), the chain transfer intensity is matched with the free radical generation rate. This avoids excessive chain growth and widening of molecular weight distribution due to excessive free radical concentration caused by excessive initiator content, and also avoids excessive restriction of chain growth and reduction of molecular weight due to excessive chain transfer agent ratio. Thus, the chain growth and chain termination are kept in relative balance during the polymerization reaction.

[0020] Meanwhile, by controlling the addition ratio of comonomers, chain transfer agents and initiators in the polymerization system, the formation process of polyacrylonitrile molecular chains is made more stable, which is beneficial to improve the molecular weight stability of polyacrylonitrile polymerization solution, reduce the dispersion of molecular weight distribution, improve the uniformity of polymerization solution and spinning processing performance, thereby meeting the requirements of high molecular weight and narrow molecular weight distribution polymerization solution in the preparation of high-performance polyacrylonitrile-based carbon fibers. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] One of the objectives of this invention is to provide a polyacrylonitrile polymerization solution, which is mainly prepared by a polymerization reaction of a polymerization system containing acrylonitrile, comonomer, chain transfer agent, initiator and organic solvent; In the polymerization system, the mass fraction of acrylonitrile is 100 parts. The comonomer is in the form of 0.8 to 1.2 parts by mass. The chain transfer agent is present in a mass fraction of 0.05 to 0.3 parts; The initiator is present in a mass fraction of 0.5 to 0.8 parts; The organic solvent is in the form of 320-340 parts by mass. The mass ratio of the chain transfer agent to the initiator is (1:10) to (1:2).

[0025] In this invention, the mass fraction of the comonomer in the polymerization system is 0.8 to 1.2 parts, for example: 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts or 1.2 parts, based on 100 parts by mass of the acrylonitrile. Specifically, the addition of the comonomer can participate in the acrylonitrile free radical copolymerization reaction, and improve the stability of molecular chain formation during the polymerization reaction by adjusting the copolymer structure in the polymer molecular chain. When the amount of the comonomer added is less than 0.8 parts, the comonomer's regulatory effect on the polymer chain structure is insufficient, and it is difficult to effectively improve the regularity of polymer chain segments. When the amount of the comonomer added is more than 1.2 parts, the excessive comonomer may lead to an increase in the proportion of copolymer chain segments, affecting the continuous growth of acrylonitrile chain segments, which is not conducive to obtaining a polyacrylonitrile polymerization solution with suitable molecular weight and molecular weight distribution.

[0026] In this invention, the mass fraction of the chain transfer agent in the polymerization system is 0.05 to 0.3 parts, for example: 0.05 parts, 0.10 parts, 0.15 parts, 0.20 parts, 0.25 parts or 0.30 parts, based on 100 parts by mass of the acrylonitrile. Specifically, the chain transfer agent can undergo a chain transfer reaction with the active free radicals formed during polymerization, causing the growing polymer free radicals to transfer chains, thereby regulating the growth length of the polymer molecular chain and controlling the molecular weight and molecular weight distribution of polyacrylonitrile. By controlling the chain transfer agent within the above-mentioned range, the chain transfer effect is matched with the rate of free radical generation by the initiator, which is beneficial to maintaining the balance between chain growth and chain termination during polymerization. When the amount of the chain transfer agent added is less than 0.05 parts, the chain transfer effect is weak, the continuous growth time of the polymer active chain is prolonged, which can easily lead to excessively high polymer molecular weight or a widened molecular weight distribution. When the amount of the chain transfer agent added is more than 0.3 parts, the excessively strong chain transfer effect will cause the active chain to terminate prematurely, limiting the growth of the polymer molecular chain and making it difficult to obtain a polyacrylonitrile polymerization solution with a high molecular weight.

[0027] In this invention, the polymer system comprises 100 parts by mass of acrylonitrile, and the initiator comprises 0.5 to 0.8 parts by mass, for example: 0.5, 0.6, 0.65, 0.7 or 0.8 parts. Specifically, the initiator is used to decompose and generate free radicals in the polymerization system to initiate a free radical polymerization reaction between acrylonitrile and the comonomer. The amount added affects the free radical concentration and polymerization rate in the polymerization system. When the amount of initiator is within the aforementioned range, the free radical generation rate can be matched with the chain transfer reaction rate, which is beneficial for controlling the growth process of the polymer molecular chain and improving the stability of the polyacrylonitrile molecular weight and molecular weight distribution. When the amount of initiator is less than 0.5 parts, the free radical concentration in the polymerization system is low, the polymerization reaction initiation and chain growth rate decrease, easily leading to incomplete polymerization and affecting the increase of polyacrylonitrile molecular weight. When the amount of initiator is greater than 0.8 parts, the free radical concentration in the polymerization system is too high, easily causing an increase in termination reactions between active chains, resulting in uneven molecular chain length distribution and a wider molecular weight distribution, which is not conducive to obtaining a polyacrylonitrile polymerization solution with a high molecular weight and narrow molecular weight distribution.

[0028] In this invention, the polymer system comprises 320 to 340 parts by mass of the organic solvent, with 100 parts by mass of the acrylonitrile, for example: 320 parts, 325 parts, 330 parts, 335 parts or 340 parts by mass.

[0029] Specifically, the organic solvent is used to dissolve acrylonitrile, comonomers, chain transfer agents, and initiators, and to provide a uniform liquid-phase reaction environment for the free radical polymerization reaction. By controlling the amount of the organic solvent added within the above-mentioned range, the viscosity and component diffusion capacity of the polymerization system can be adjusted, allowing the reactants to fully contact each other. This is beneficial for improving the stability of free radical transport and chain growth during the polymerization reaction, thereby improving the molecular weight distribution of the polyacrylonitrile polymerization solution. When the amount of the organic solvent added is less than 320 parts, the concentration of the polymerization system is high, the viscosity of the system increases, and the diffusion and mass transfer capacity of the reactants decreases, which can easily cause uneven local polymerization reactions and affect the molecular weight distribution of the polymer. When the amount of the organic solvent added is greater than 340 parts, the concentration of the polymerization system decreases, the effective collision probability between active free radicals and monomer molecules decreases, the polymerization reaction rate decreases, and it is not conducive to obtaining a polyacrylonitrile polymerization solution with a high molecular weight.

[0030] In this invention, the mass ratio of the chain transfer agent to the initiator is (1:10) to (1:2), for example: (1:10), (1:8), (1:6), (1:4), (1:3) or (1:2).

[0031] Specifically, the mass ratio of the chain transfer agent to the initiator is used to adjust the matching relationship between the chain transfer reaction rate and the free radical generation rate during polymerization. The initiator generates free radicals through decomposition, providing active centers for the chain growth reaction of acrylonitrile and comonomers. The chain transfer agent regulates the active chain length by undergoing a chain transfer reaction with the growing chain free radicals, thereby controlling the molecular weight and molecular weight distribution of polyacrylonitrile. By controlling the mass ratio of the chain transfer agent to the initiator within the aforementioned range, a balance can be maintained between the free radical generation rate and the chain transfer regulation capability, promoting the synergistic occurrence of the chain growth reaction and the chain transfer reaction, thereby improving the molecular weight stability and molecular weight distribution of polyacrylonitrile. When the mass ratio of the chain transfer agent to the initiator is less than 1:10... When the chain transfer agent content relative to the initiator in the polymerization system is low, the chain transfer reaction control ability is insufficient, the continuous growth time of the active chain is prolonged, which can easily lead to excessive growth of some polymer molecular chains, resulting in a wider molecular weight distribution of the obtained polyacrylonitrile and affecting the performance stability of the polymerization solution. When the mass ratio of the chain transfer agent to the initiator is higher than 1:2, the chain transfer agent content relative to the initiator in the polymerization system is too high, the chain transfer reaction is too strong, and the active chain is prone to premature chain transfer during the growth process, which leads to limited growth of polymer molecular chains, resulting in a decrease in the molecular weight of the obtained polyacrylonitrile, which is not conducive to obtaining a high molecular weight polyacrylonitrile polymerization solution.

[0032] In a preferred embodiment, the mass ratio of the chain transfer agent to the initiator in the polymerization system is (1:8) to (1:3).

[0033] In this embodiment, the mass ratio of the chain transfer agent to the initiator in the polymerization system is (1:8) to (1:3), for example, (1:8), (1:6), (1:4) or (1:3).

[0034] More preferably, the mass ratio of the chain transfer agent to the initiator in the polymerization system is 3:13.

[0035] Specifically, by further limiting the mass ratio of the chain transfer agent to the initiator to (1:8) to (1:3), the matching relationship between the chain transfer reaction and the free radical generation reaction can be further optimized, so that the concentration of active free radicals during the polymerization process is maintained within a suitable range. This avoids disordered growth of molecular chains due to insufficient chain transfer and also avoids limited growth of molecular chains due to excessive chain transfer, thereby facilitating the acquisition of polyacrylonitrile polymerization liquid with higher molecular weight and narrower molecular weight distribution.

[0036] Furthermore, when the mass ratio of the chain transfer agent to the initiator is 3:13, the regulating effect of the chain transfer agent on the active chain length and the rate at which the initiator generates free radicals are optimally matched, so that the chain growth reaction, chain transfer reaction and chain termination reaction are maintained in a good dynamic balance. This is beneficial to improving the uniformity of the polyacrylonitrile molecular chain structure, reducing the dispersion of molecular weight distribution, and improving the spinning adaptability of the polymerization solution.

[0037] In a preferred embodiment, the mass ratio of the comonomer to the acrylonitrile in the polymerization system is (1:125) to (1:83).

[0038] In this embodiment, the mass ratio of the comonomer to the acrylonitrile in the polymerization system is (1:125) to (1:83), for example, (1:125), (1:100), (1:90) or (1:83).

[0039] Specifically, the comonomer and acrylonitrile are blended in the aforementioned ratio to allow the comonomer to be appropriately introduced into the polymer molecular chain during acrylonitrile polymerization, thereby regulating the molecular chain structure and preventing the continuous chain growth of acrylonitrile from being affected by an excessively high comonomer ratio. By controlling the mass ratio of the comonomer to acrylonitrile, the uniformity of polymer chain composition is improved, making the molecular chain growth more stable during the polymerization reaction, thus regulating the molecular weight and molecular weight distribution of polyacrylonitrile. When the mass ratio of the comonomer to acrylonitrile is less than 1:125, i.e., the comonomer addition ratio is too low, the comonomer's regulatory effect on the polymer molecular chain structure is insufficient, making it difficult to effectively improve the differences between molecular chains, which may lead to a wider molecular weight distribution of polyacrylonitrile. When the mass ratio of the comonomer to acrylonitrile is greater than 1:83, i.e., the comonomer addition ratio is too high, the excess comonomer will increase the proportion of comonomer segments, reduce the proportion of acrylonitrile repeating units in the molecular chain, affect the polymer chain growth process, and is not conducive to obtaining a polyacrylonitrile polymerization solution with a high molecular weight.

[0040] More preferably, the mass ratio of the comonomer to the acrylonitrile in the polymerization system is 1:100.

[0041] Specifically, when the mass ratio of the comonomer to the acrylonitrile is 1:100, the comonomer can effectively regulate the molecular chain structure while ensuring the formation of the acrylonitrile main chain segment, so that the chain growth stability, molecular chain structure uniformity and molecular weight distribution control effect during the polymerization reaction can achieve a better balance.

[0042] 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.

[0043] In the embodiments, 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.

[0044] 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.

[0045] In this embodiment, 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.

[0046] 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.

[0047] In this embodiment, 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.

[0048] 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.

[0049] In this embodiment, 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.

[0050] 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, which is conducive to the uniform polymerization reaction and improving the stability of the polymerization liquid.

[0051] 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.

[0052] In this embodiment, itaconic acid is used as the comonomer, n-octyl mercaptan as the chain transfer agent, azobisisobutyronitrile as the initiator, and dimethyl sulfoxide as the organic solvent. The components exhibit good synergistic effects. Specifically, itaconic acid contains unsaturated double bonds and polar groups that can participate in free radical polymerization, introducing appropriate polar structural units during acrylonitrile polymerization, which is beneficial for regulating the polyacrylonitrile molecular chain structure. n-Octayl mercaptan has high chain transfer activity, which can regulate the growth process of active free radical chains, keeping the molecular chain growth rate stable. Azobisisobutyronitrile can stably generate free radicals under polymerization conditions, providing continuous active centers for the polymerization reaction. Dimethyl sulfoxide can simultaneously dissolve all reaction components, providing a uniform reaction environment for the polymerization reaction. Through the synergistic effect of the above components, the rate at which the initiator generates free radicals, the ability of the chain transfer agent to regulate the length of the active chain, and the regulatory effect of the comonomer on the molecular chain structure are matched with each other. This is conducive to achieving a balance between chain growth, chain transfer, and chain termination reactions during the polymerization process, thereby obtaining a polyacrylonitrile polymerization solution with a higher molecular weight and a narrower molecular weight distribution, and improving the stability of the polymerization solution and its subsequent spinning adaptability.

[0053] In a preferred embodiment, the components in the polymerization system, by mass parts, include: Acrylonitrile 100 parts, itaconic acid 1.0 part, n-octyl mercaptan 0.15 parts, azobisisobutyronitrile 0.65 parts, and dimethyl sulfoxide 330 parts.

[0054] Specifically, under the above-mentioned formulation conditions, itaconic acid, as a comonomer, participates in the free radical polymerization reaction of acrylonitrile, introducing an appropriate amount of polar structural units into the polyacrylonitrile molecular chain to regulate the molecular chain structure; n-octyl mercaptan, as a chain transfer agent, controls the growth length of the active chain by undergoing a chain transfer reaction with the growing free radicals; azobisisobutyronitrile, as an initiator, can stably generate free radicals, providing a continuous active center for the polymerization reaction; dimethyl sulfoxide, as an organic solvent, provides a uniform reaction environment for each reaction component and regulates the viscosity and mass transfer state of the polymerization system; wherein, the mass ratio of n-octyl mercaptan to azobisisobutyronitrile is 3:13, so that the chain transfer rate and the free radical generation rate are optimally matched; at the same time, the mass ratio of itaconic acid to acrylonitrile is 1:100, so that the copolymer structure regulation effect and the growth process of the acrylonitrile main chain segment are balanced. By synergistically regulating the proportions of the above components, the generation of free radicals, chain growth, chain transfer, and chain termination reactions during the polymerization process can be kept relatively stable, which is beneficial to obtaining polyacrylonitrile polymerization solutions with high molecular weight, narrow molecular weight distribution, and suitable viscosity.

[0055] In a preferred embodiment, the chain transfer agent comprises n-octyl mercaptan and n-butyritin, wherein the mass ratio of n-octyl mercaptan to n-butyritin is (1:3) to (1:1).

[0056] In this invention, the mass ratio of n-octyl mercaptan to n-butyric acid is (1:3) to (1:1), for example: 1:3, 1:2.5, 1:2, 1:1.8, 1:1.5, 1:1.2 or 1:1.

[0057] Specifically, by compounding n-octyl mercaptan and n-butyl mercaptan, two chain transfer agents with different chain transfer activities work synergistically during polymerization. n-Butyl mercaptan has high chain transfer activity, promoting timely chain transfer reactions in active chains and inhibiting excessively rapid chain growth; n-octyl mercaptan's chain transfer effect is relatively mild, buffering and regulating the chain growth process. By adjusting the mass ratio of the two, the free radical chain growth rate and chain transfer rate in the polymerization system are matched, thereby reducing the molecular weight distribution width of polyacrylonitrile and improving the uniformity and stability of the polyacrylonitrile polymerization solution. When the mass ratio of n-octyl mercaptan to n-butyl mercaptan is greater than 1:1, the proportion of n-octyl mercaptan is too high, the chain transfer reaction rate in the system decreases, the active chain growth time is prolonged, and it is easy to lead to an increase in the molecular weight of polyacrylonitrile and a wider molecular weight distribution. When the mass ratio of n-octyl mercaptan to n-butyl mercaptan is less than 1:3, the proportion of n-butyl mercaptan is too high, the chain transfer reaction is too active, and it is easy to cause premature termination of the molecular chain, resulting in a decrease in the molecular weight of polyacrylonitrile and affecting the mechanical properties of the subsequent carbon fibers.

[0058] In a preferred embodiment, the chain transfer agent comprises n-octyl mercaptan and dodecyl mercaptan, wherein the mass ratio of n-octyl mercaptan to dodecyl mercaptan is (2:2) to (2:1).

[0059] In this invention, the mass ratio of n-octyl mercaptan to dodecyl mercaptan is (2:2) to (2:1), for example: 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1.

[0060] Specifically, by compounding n-octyl mercaptan and dodecyl mercaptan, thiol chain transfer agents with different carbon chain lengths work synergistically during polymerization. N-octyl mercaptan has moderate chain transfer activity, effectively regulating the free radical chain growth process; dodecyl mercaptan has a longer molecular chain, resulting in a relatively milder chain transfer effect, reducing drastic fluctuations during chain growth. By adjusting the mass ratio of the two, the chain transfer reaction rate is matched with the polymerization rate of acrylonitrile and comonomers, thereby reducing differences in molecular chain length during polymerization, improving the uniformity of the molecular weight distribution of the resulting polyacrylonitrile, and enhancing the stability of the polyacrylonitrile polymerization solution. When the mass ratio of n-octyl mercaptan to dodecyl mercaptan is greater than 2:1, the excessively high proportion of n-octyl mercaptan enhances the chain transfer effect in the system, easily causing some molecular chains to have limited growth, reducing the molecular weight of polyacrylonitrile, and affecting the mechanical properties of carbon fibers. When the mass ratio of n-octyl mercaptan to dodecyl mercaptan is less than 1:1, the excessively high proportion of dodecyl mercaptan weakens the chain transfer effect, prolongs the active chain growth time, easily leading to an increase in the molecular weight of polyacrylonitrile and a wider molecular weight distribution, reducing the uniformity of the polymerization solution.

[0061] A second objective of this invention is to provide a method for preparing the polyacrylonitrile polymerization solution as described above, comprising: Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed according to the preset mass ratio to form a polymerization system; The initiator is added to the polymerization system at a mass ratio of (1:10) to (1:2) of the chain transfer agent to the initiator; Under preset polymerization conditions, the acrylonitrile and the comonomer undergo a polymerization reaction to obtain the polyacrylonitrile polymer solution.

[0062] In one specific embodiment, the method for preparing the polyacrylonitrile polymerization solution includes: S1. Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed according to the preset mass ratio to form a polymerization system; Specifically, each component is weighed according to the mass ratio of 100 parts acrylonitrile, 0.8-1.2 parts comonomer, 0.05-0.3 parts chain transfer agent, and 320-340 parts organic solvent, and added to the reaction vessel. Under stirring conditions, the components are thoroughly mixed so that acrylonitrile, comonomer, and chain transfer agent are uniformly dispersed in the organic solvent to form a homogeneous and stable polymerization system.

[0063] S2. Add the initiator to the polymerization system at a mass ratio of (1:10) to (1:2) of the chain transfer agent to the initiator; Specifically, the amount of initiator added is determined based on the amount of chain transfer agent added, maintaining a preset mass ratio between the chain transfer agent and the initiator. The initiator is then added to the polymerization system to ensure uniform dispersion within the system. The initiator generates free radicals under polymerization conditions, providing active centers for the polymerization reaction of acrylonitrile and comonomers. The chain transfer agent regulates the growth process of the active chain; by controlling the ratio between the chain transfer agent and the initiator, the free radical generation rate is matched with the chain transfer regulation capability.

[0064] S3. Under preset polymerization conditions, the acrylonitrile and the comonomer undergo a polymerization reaction to obtain the polyacrylonitrile polymer solution.

[0065] Specifically, the polymerization system with the initiator added is subjected to polymerization under an inert gas atmosphere, and the polymerization temperature is 65-76°C. The reaction time is 12-20 hours, and the stirring speed is 20-60 r / min.

[0066] A third objective of this invention is to provide the use of the polyacrylonitrile polymerization solution as described above, including: using the polyacrylonitrile polymerization solution as a spinning dope to prepare polyacrylonitrile-based carbon fibers through a dry-jet wet spinning process.

[0067] Specifically, the polyacrylonitrile polymer solution has a high molecular weight and a narrow molecular weight distribution, which enables it to maintain good molecular chain continuity and orientation during spinning, thus improving the spinnability of the spinning solution and the stability of fiber formation. When using the polyacrylonitrile polymer solution as the spinning solution for dry-jet wet spinning, it can promote the alignment of polymer molecular chains along the fiber axis, reduce the fiber structure inhomogeneity caused by an excessively wide molecular weight distribution, and thereby obtain polyacrylonitrile-based carbon fibers with uniform structure and stable performance.

[0068] Example 1 This embodiment provides a method for preparing a polyacrylonitrile polymerization solution, including: S1. Weigh out 100 parts of acrylonitrile, 1.0 part of itaconic acid, 0.15 parts of n-octyl mercaptan, and 330 parts of dimethyl sulfoxide according to the mass ratio and add them to the reactor. Mix them evenly under stirring to form a polymerization system. S2. Add 0.65 parts of azobisisobutyronitrile to the polymerization system, wherein the mass ratio of n-octyl mercaptan to azobisisobutyronitrile is 3:13; S3. The polymerization reaction is carried out under nitrogen protection at a polymerization temperature of 70°C. The reaction time was 16 hours, and the stirring speed was 45 r / min to obtain a polyacrylonitrile polymerization solution.

[0069] Example 2 This embodiment is basically the same as embodiment 1, except that: Itaconic acid 0.8 parts; The remaining preparation conditions were the same as in Example 1.

[0070] Example 3 This embodiment is basically the same as embodiment 1, except that: Itaconic acid 1.2 parts; The remaining preparation conditions were the same as in Example 1.

[0071] Example 4 This embodiment is basically the same as embodiment 1, except that: 0.05 parts of n-octyl mercaptan and 0.50 parts of azobisisobutyronitrile; The mass ratio of n-octyl mercaptan to the azobisisobutyronitrile is 1:10; The remaining preparation conditions were the same as in Example 1.

[0072] Example 5 This embodiment is basically the same as embodiment 1, except that: 0.30 parts of n-octyl mercaptan and 0.60 parts of azobisisobutyronitrile; The mass ratio of n-octyl mercaptan to the azobisisobutyronitrile is 1:2; The remaining preparation conditions were the same as in Example 1.

[0073] Example 6 This embodiment is basically the same as embodiment 1, except that: 0.10 parts of n-octyl mercaptan and 0.50 parts of azobisisobutyronitrile; The mass ratio of n-octyl mercaptan to the azobisisobutyronitrile is 1:5; The remaining preparation conditions were the same as in Example 1.

[0074] Example 7 This embodiment is basically the same as embodiment 1, except that: 0.20 parts of n-octyl mercaptan and 0.80 parts of azobisisobutyronitrile; The mass ratio of n-octyl mercaptan to the azobisisobutyronitrile is 1:4; The remaining preparation conditions were the same as in Example 1.

[0075] Example 8 This embodiment is basically the same as embodiment 1, except that: The azobisisobutyronitrile content is 0.50 parts; The mass ratio of n-octyl mercaptan to azobisisobutyronitrile is 3:10.

[0076] The remaining preparation conditions were the same as in Example 1.

[0077] Example 9 This embodiment is basically the same as embodiment 1, except that: The content of azobisisobutyronitrile is 0.80 parts; The mass ratio of n-octyl mercaptan to azobisisobutyronitrile is 3:16.

[0078] The remaining preparation conditions were the same as in Example 1.

[0079] Example 10 This embodiment is basically the same as embodiment 1, except that: The amount of dimethyl sulfoxide was 320 parts.

[0080] The remaining preparation conditions were the same as in Example 1.

[0081] Example 11 This embodiment is basically the same as embodiment 1, except that: The amount of dimethyl sulfoxide was 340 parts.

[0082] The remaining preparation conditions were the same as in Example 1.

[0083] Example 12 This embodiment is basically the same as embodiment 1, except that: The comonomer is acrylic acid; The chain transfer agent is n-butanethiol; The initiator is azobisisoheptanenitrile; The organic solvent is dimethylformamide.

[0084] The remaining preparation conditions were the same as in Example 1.

[0085] Example 13 This embodiment is basically the same as embodiment 1, except that: The chain transfer agent includes n-octyl mercaptan and n-butyritin; The mixture contains 0.05 parts of n-octyl mercaptan and 0.10 parts of n-butyl mercaptan, with the mass ratio of n-octyl mercaptan to n-butyl mercaptan being 1:2. The total mass fraction of n-octyl mercaptan and n-butyric acid is 0.15 parts; The remaining preparation conditions were the same as in Example 1.

[0086] Example 14 This embodiment is basically the same as embodiment 1, except that: The chain transfer agent includes n-octyl mercaptan and dodecyl mercaptan; The mixture contains 0.10 parts of n-octyl mercaptan and 0.05 parts of dodecyl mercaptan, with the mass ratio of n-octyl mercaptan to dodecyl mercaptan being 2:1. The total mass fraction of n-octyl mercaptan and dodecyl mercaptan is 0.15 parts; The remaining preparation conditions were the same as in Example 1.

[0087] Comparative Example 1 This comparative example is basically the same as Example 1, except that: No n-octyl mercaptan is added to the polymerization system; The remaining preparation conditions were the same as in Example 1.

[0088] Comparative Example 2 This comparative example is basically the same as Example 1, except that: The amount of n-octylthiol is 0.02 parts.

[0089] The mass ratio of n-octylthiol to azobisisobutyronitrile is: 1:32.5.

[0090] The remaining preparation conditions were the same as in Example 1.

[0091] Comparative Example 3 This comparative example is basically the same as Example 1, except that: 0.50 parts of n-octyl mercaptan; The mass ratio of n-octylthiol to azobisisobutyronitrile is: 10:13; The remaining preparation conditions were the same as in Example 1.

[0092] Comparative Example 4 This comparative example is basically the same as Example 1, except that: Itaconic acid was 0.3 parts; The mass ratio of itaconic acid to acrylonitrile is: 3:1000; The remaining preparation conditions were the same as in Example 1.

[0093] Comparative Example 5 This comparative example is basically the same as Example 1, except that: Itaconic acid content is 2.0 parts; The mass ratio of itaconic acid to acrylonitrile is: 1:50; The remaining preparation conditions were the same as in Example 1.

[0094] Comparative Example 6 This comparative example is basically the same as Example 1, except that: The amount of azobisisobutyronitrile is 1.2 parts; The mass ratio of n-octylthiol to azobisisobutyronitrile is: 1:8; The remaining preparation conditions were the same as in Example 1.

[0095] 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 of the polymerization solution, and monomer conversion rate of the polyacrylonitrile polymer.

[0096] Specifically, the test items include: (1) Weight-average molecular weight (Mw) and number-average molecular weight (Mn) test Gel permeation chromatography (GPC) was used to test the polyacrylonitrile polymerization solutions prepared in each example and comparative example to obtain the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of polyacrylonitrile, and the molecular weight distribution index (PDI) was calculated. =Mw / Mn.

[0097] (2) Viscosity test of polyacrylonitrile polymerization solution Polyacrylonitrile at 25°C was determined using a rotational viscometer. The viscosity was measured to evaluate the flow properties of polyacrylonitrile.

[0098] (3) Solid content test The solid content of the polyacrylonitrile polymer liquids prepared in each example and comparative example was tested using the weighing and drying method.

[0099] Test method: Weigh a certain mass of the polymerization liquid, dry it under constant temperature conditions, and after the mass becomes constant, weigh the remaining solid mass. Calculate the solid content using the following formula:

[0100] The content of effective polyacrylonitrile components in the polymerization solution is evaluated by solid content.

[0101] (4) Polymerization solution stability test The polyacrylonitrile polymerization solutions prepared in each example and comparative example were allowed to stand at room temperature. The viscosity of the polyacrylonitrile polymerization solution was measured after standing for 24 hours, and the viscosity change rate was calculated. The formula for calculating the viscosity change rate is as follows:

[0102] in, The initial viscosity, The viscosity is denoted as t, which is the settling time, t = 24h.

[0103] (5) Polyacrylonitrile-based carbon fiber spinning performance test The polyacrylonitrile polymer solutions prepared in each embodiment and comparative example were used as spinning solutions to prepare polyacrylonitrile-based carbon fibers through a dry-jet wet spinning process.

[0104] The tensile strength, elastic modulus, and elongation at break of the obtained polyacrylonitrile-based carbon fibers were tested.

[0105] The performance test results of polyacrylonitrile polymerization solution are shown in Table 1 below, and the performance test results of polyacrylonitrile-based carbon fiber spinning are shown in Table 2 below. Table 1

[0106] As shown in Table 1: The polyacrylonitrile polymerization solutions prepared in Examples 1-14 all exhibited high weight-average molecular weights and low molecular weight distribution indices, with Example 1 achieving a weight-average molecular weight (Mw) of 62.5. With a molecular weight distribution index (PDI) of 2.63, the polymer exhibits superior molecular weight and distribution properties. Furthermore, in Example 13, a combination of n-octyl mercaptan and n-butane mercaptan was used as a chain transfer agent, increasing the weight-average molecular weight (Mw) of the resulting polyacrylonitrile polymerization solution to 66.8 g / mol. g / mol, the molecular weight distribution index (PDI) decreased to 2.58; in Example 14, a combination of n-octyl mercaptan and dodecyl mercaptan was used as a chain transfer agent, and the weight-average molecular weight (Mw) of the resulting polyacrylonitrile polymerization solution increased to 65.1 g / mol. The molecular weight distribution index (PDI) was reduced to 2.59, which was better than that of Example 1. Among them, Example 13 showed better molecular weight and distribution performance.

[0107] In contrast, Comparative Example 1, which did not include a chain transfer agent, resulted in uneven molecular chain growth due to the lack of regulation of free radical chain growth during polymerization, leading to a decrease in Mw to 38.6. g / mol, while PDI increased to 3.54; Comparative Examples 2 to 6 had chain transfer rate and free radical generation rate imbalance due to the chain transfer agent to initiator ratio deviating from the reasonable range, resulting in a decrease in molecular weight and molecular weight distribution performance.

[0108] This demonstrates that by controlling the ratio of chain transfer agent to initiator and using chain transfer agents with different chain transfer activities in combination, a dynamic balance can be achieved between chain transfer and free radical polymerization, which is beneficial for obtaining high molecular weight and uniformly distributed polyacrylonitrile polymerization solutions.

[0109] Table 2

[0110] As shown in Table 2: The carbon fibers prepared using the polyacrylonitrile polymerization solution of this invention exhibit high tensile strength, elastic modulus, and suitable elongation at break. Specifically, the carbon fiber obtained in Example 1 has a tensile strength of 6200 MPa, an elastic modulus of 255 GPa, and an elongation at break of 2.3%, demonstrating superior overall performance. Furthermore, the mechanical properties of the carbon fibers obtained in Examples 13 and 14 are further improved after using a compound chain transfer agent. The tensile strength of Example 13 reaches 6450 MPa, the elastic modulus reaches 285 GPa, and the elongation at break reaches 2.4%, with overall performance superior to Examples 1 and 14. This indicates that optimizing the chain transfer agent composition can further improve the polyacrylonitrile molecular chain structure and enhance the mechanical properties of the carbon fibers.

[0111] Compared to the embodiments, the comparative example of the present invention lacks chain transfer regulation or disrupts the ratio between comonomers, initiators and chain transfer agents, resulting in a decrease in polymer molecular weight and a wider molecular weight distribution. This leads to a decrease in the molecular chain orientation and regular arrangement ability during spinning, ultimately resulting in a decrease in fiber mechanical properties.

[0112] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover 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 features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A polyacrylonitrile polymerization solution, characterized in that, The polyacrylonitrile polymerization solution is mainly prepared by polymerization reaction of a polymerization system containing acrylonitrile, comonomer, chain transfer agent, initiator and organic solvent; In the polymerization system, the mass fraction of acrylonitrile is 100 parts. The comonomer is in the form of 0.8 to 1.2 parts by mass. The chain transfer agent is present in a mass fraction of 0.05 to 0.3 parts; The initiator is present in a mass fraction of 0.5 to 0.8 parts; The organic solvent is in the form of 320-340 parts by mass. The mass ratio of the chain transfer agent to the initiator is (1:10) to (1:2).

2. The polyacrylonitrile polymerization solution according to claim 1, characterized in that, The mass ratio of the chain transfer agent to the initiator in the polymerization system is (1:8) to (1:3).

3. The polyacrylonitrile polymerization solution according to claim 2, characterized in that, The mass ratio of the chain transfer agent to the initiator in the polymerization system is 3:

13.

4. The polyacrylonitrile polymerization solution according to claim 1, characterized in that, The mass ratio of the comonomer to the acrylonitrile in the polymerization system is (1:125) to (1:83).

5. The polyacrylonitrile polymerization solution according to claim 1, characterized in that, The mass ratio of the comonomer to the acrylonitrile in the polymerization system is 1:

100.

6. The polyacrylonitrile polymerization solution 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.

7. The polyacrylonitrile polymerization solution according to claim 6, characterized in that, The chain transfer agent includes n-octyl mercaptan and n-butyritin, and the mass ratio of n-octyl mercaptan to n-butyritin is (1:3) to (1:1).

8. The polyacrylonitrile polymerization solution according to claim 7, characterized in that, The chain transfer agent includes n-octyl mercaptan and dodecyl mercaptan, wherein the mass ratio of n-octyl mercaptan to dodecyl mercaptan is (2:2) to (2:1).

9. A method for preparing a polyacrylonitrile polymerization solution as described in any one of claims 1 to 8, characterized in that, include: Acrylonitrile, comonomer, chain transfer agent and organic solvent are mixed according to the preset mass ratio to form a polymerization system; The initiator is added to the polymerization system at a mass ratio of (1:10) to (1:2) of the chain transfer agent to the initiator; Under preset polymerization conditions, the acrylonitrile and the comonomer undergo a polymerization reaction to obtain the polyacrylonitrile polymer solution.

10. Use of the polyacrylonitrile polymerization liquid according to any one of claims 1 to 8, characterized in that, include: The polyacrylonitrile polymerization solution was used as the spinning solution to prepare polyacrylonitrile-based carbon fibers through a dry-jet wet spinning process.

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