High-stereoregularity polyacrylonitrile copolymer, preparation method and high-graphitization carbon fiber

Abstract

According to the high-steric-regularity polyacrylonitrile copolymer, the preparation method and the high-graphitization carbon fiber, Lewis acid or Lewis acid salt serves as a template, acrylonitrile is induced to achieve ordered polymerization in the polymerization process, meanwhile, a novel protonic acid comonomer is introduced, and the high-steric-regularity polyacrylonitrile copolymer is prepared through the synergistic effect of the Lewis acid or the Lewis acid salt and the novel protonic acid comonomer. The preparation method has the advantages of simple production process, no need of special equipment, low cost, short time consumption and the like, can improve the cyclization degree of the PAN in the pre-oxidation process, endows the PAN with a wide-temperature-zone heat release characteristic and a low heat release rate (effectively reduces the heat release rate of cyclization reaction), effectively avoids the problem of concentrated heat release, and is suitable for industrial production. The formation of carbon fibers with higher graphitization degree in the subsequent carbonization process is promoted, a high-quality precursor is provided for the preparation of the high-performance PAN-based carbon fibers, and a feasible technical scheme is provided for the industrial production of the high-performance PAN-based carbon fibers.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and in particular relates to a high stereoregularity polyacrylonitrile copolymer, its preparation method, and highly graphitized carbon fiber. Background Technology

[0002] Carbon fiber, as a high-performance fiber material, is widely used and highly favored in high-end fields such as aerospace, vehicle engineering, and national defense due to its excellent mechanical properties, lightweight characteristics, and chemical stability. Among many carbon fiber precursors, polyacrylonitrile (PAN) occupies more than 90% of the global high-performance carbon fiber market and has become the core precursor material for the preparation of high-performance carbon fibers due to its significant advantages such as high theoretical carbon yield, stable "trapezoidal skeleton" after pre-oxidation, strong controllability of chemical structure, and great graphitization potential.

[0003] The preparation of high-performance PAN-based carbon fibers involves a series of processes, including polymerization, spinning, thermal oxidative stabilization (TOS), carbonization, and graphitization, among which the thermal stabilization process is crucial. This process mainly involves the free radical cyclization reaction of cyano groups (-CN) at 200℃-300℃, which is often accompanied by uncontrollable and intense exothermic phenomena. This concentrated exothermic phenomenon easily leads to the breakage of carbon fiber macromolecular chains, significantly damaging the integrity of the carbon fiber's microstructure and ultimately adversely affecting its mechanical properties. Therefore, the control of the thermal stabilization process largely determines the final quality level of the carbon fibers.

[0004] The structure of the PAN molecular chain significantly influences the polymer cyclization reaction process, with different molecular structures triggering different cyclization reaction pathways. The stereoregularity of PAN has a significant impact on its cyclization process; industrially polymerized PAN backbones are typically predominantly atactic, resulting in a low probability of effective collisions. Furthermore, the radical reaction is highly exothermic once triggered, leading to premature crosslinking of the outer layer before the core cyclizes, becoming a molecular-level bottleneck that must be overcome to achieve high-strength, high-modulus carbon fibers. In atactic polyacrylonitrile homopolymers, the cyano groups in the molecular chain are randomly and disordered (distributed on both sides of the molecular chain). During thermal stabilization, the cyano groups struggle to achieve effective collisions to form a stable ladder structure, typically terminating the reaction after forming 4-5 cyclization units, resulting in a low degree of cyclization in the final product. Simultaneously, homopolymers are prone to concentrated exothermic phenomena during thermal stabilization. This uneven exothermic process leads to numerous internal defects and increased defect size in the carbon fiber during subsequent carbonization, ultimately causing a significant decrease in carbon fiber strength and modulus, failing to meet the application requirements of high-performance carbon fibers. High stereoregularity polyacrylonitrile (i-PAN) exhibits a highly ordered arrangement of cyano groups in its molecular chain, which reduces steric hindrance to effective cyano group collisions, significantly increasing the probability of such collisions. This promotes the growth of continuous trapezoidal units, thereby significantly enhancing the cyclization degree of PAN and, to some extent, lowering the cyclization reaction temperature. However, i-PAN still faces challenges such as concentrated exothermic reactions during thermal stabilization.

[0005] Currently, various methods for preparing highly stereoregular PANs have been reported in studies. For example, Zou et al. (doi.org / 10.1021 / ma3026089) uniformly mixed urea and acrylonitrile, then froze the mixture at low temperature to form a urea-acrylonitrile complex. Subsequently, they used gamma-ray radiation to initiate a polymerization reaction, ultimately preparing isotactically regular PANs (with an isotactic triunit content greater than 98%). Ignacio Rintoul et al. (doi:10.1016 / j.polymer.2007.02.002) used a high-intensity magnetic field to induce acrylonitrile to undergo free radical polymerization under isothermal conditions to prepare highly stereoregular polyacrylonitrile. Although the above two methods can achieve the ordered arrangement of cyano groups in the molecular chain and prepare highly regular PAN, they both have obvious drawbacks: on the one hand, the reaction process requires complex equipment (such as gamma-ray radiation devices and high-intensity magnetic field generators), and the polymerization conditions are harsh (low temperature, strong magnetic field), resulting in high preparation costs and difficult operation; on the other hand, the highly regular PAN prepared by the above methods are all homopolymers, and the negative impact of concentrated exothermic reaction during the pre-oxidation process of PAN homopolymer on the subsequent mechanical properties of carbon fibers is not considered, which to some extent restricts the feasibility of large-scale industrial application of PAN-based carbon fibers.

[0006] To address the problem of concentrated exothermic reactions in PAN homopolymers, existing research typically introduces acidic copolymers containing carbonyl functional groups, such as itaconic acid (IA), acrylic acid (AA), crotonic acid (CA), and 2-hexylacrylic acid (EHA), into the PAN macromolecular chain, utilizing ionic cyclization mechanisms to improve the thermal stabilization process. However, current research is mainly limited to comonomers containing carbonyl functional groups, with limited exploration of other types of comonomers. Furthermore, for PANs with high stereoregularity, the ordered arrangement of cyano groups increases effective collisions while accelerating the formation of continuous structures, leading to a further increase in the exothermic rate. Introducing comonomers containing carbonyl functional groups does not effectively mitigate the exothermic rate of regular PANs, making it difficult to effectively solve the problem of concentrated exothermic reactions. Summary of the Invention

[0007] The first objective of this invention is to provide a method for preparing a polyacrylonitrile copolymer with high stereoregularity.

[0008] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution: A method for preparing a polyacrylonitrile copolymer with high stereoregularity includes the following steps: S1. Acrylonitrile complexation with template: Acrylonitrile and template are mixed evenly in a certain proportion, and then frozen at a constant low temperature for a certain period of time. The template is a Lewis acid or Lewis salt, and the molar ratio between acrylonitrile and the template is (1:3) to (1:0.5). S2, Free radical polymerization: Add a certain amount of initiator and protic acid comonomer to the above mixture, purge with nitrogen for a certain time, heat to a certain temperature, and stir continuously for a certain time under nitrogen atmosphere; The molar ratio between the initiator and acrylonitrile is (1:10) to (1:300), and the molar ratio between acrylonitrile and protic acid comonomer is (92:8) to (99:1). S3. Post-treatment: Pour the mixture after the above reaction into a low-temperature alcohol reagent to precipitate, filter, wash repeatedly with deionized water, filter again, and dry under vacuum.

[0009] Highly stereoregular polyacrylonitrile copolymers were prepared by inducing ordered polymerization of acrylonitrile using Lewis acids or Lewis salts as templates. In the highly stereoregular polyacrylonitrile (i-PAN) molecular chain, most cyano groups are arranged on the same side, which facilitates the transformation of the cyano groups from a linear structure to a stable aromatic ladder structure during the TOS process. After the cyclization reaction begins, the ordered cyano groups rapidly form a stable six-membered ring structure, and the probability of termination of the ladder sequence formed by cyano groups on the same side is significantly reduced, thus allowing for the formation of a longer ladder skeleton.

[0010] The cyclization reaction occurs gradually at 200℃-300℃, initially involving dehydrogenation. The cyclization mechanism in this invention differs from free radical cyclization. After dehydrogenation, the protic acid undergoes cyclization via hydrogen exchange catalysis. The hydrogen-bonded association structure cyclizes before the C=C and C=N bonds. The comonomer plays a catalytic role in hydrogen transfer, slowing the cyclization rate and increasing the degree of cyclization.

[0011] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions: As a preferred technical solution of the present invention: in step S1, the Lewis acid or Lewis salt is at least one of MgCl2, CoCl2, AlCl3, FeCl3, CuCl2, BF3, BCl3, BeCl2, SnCl2, TiCl4, ZnCl2, Fe2(SO4)3, CuSO4, MgSO4, Ce(NO3)3, Zn(Ac)2, tetrachloroaluminate, tetrachloroferrate, and tetrafluoroborate.

[0012] As a preferred technical solution of the present invention: in step S1, the freezing temperature is -20℃ to -5℃, and the freezing time is 1-5 h.

[0013] As a preferred technical solution of the present invention: in step S2, the initiator is at least one of azobisisobutyronitrile, benzoyl peroxide, azobiscyanopentanoic acid, NaHSO3, K2S2O8, and B(C6F5)3.

[0014] As a preferred technical solution of the present invention: in step S2, the protic acid comonomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid, p-styrenesulfonic acid, vinylsulfonic acid, methylallylsulfonic acid, sodium styrenesulfonate, 2-hydroxyethyl methacrylate phosphate, vinyl phosphoric acid, hydroxypropyl methacrylate phosphate, and hydroxyethyl acrylate phosphate.

[0015] As a preferred technical solution of the present invention: in step S2, nitrogen gas is introduced for 0.5 h to 2 h.

[0016] As a preferred technical solution of the present invention: in step S2, the reaction temperature is 30℃~80℃, the reaction time is 6 h~24 h, and the stirring rate is 100 rpm~500 rpm.

[0017] As a preferred technical solution of the present invention: in step S3, the alcohol reagent is at least one of methanol, ethanol, isopropanol, n-butanol, ethylene glycol, and glycerol.

[0018] As a preferred technical solution of the present invention: in step S3, the temperature of the alcohol reagent is 0℃~10℃, the temperature of the deionized water is 50℃~80℃, the drying temperature is 40℃~80℃, and the drying time is not less than 24 h.

[0019] The second objective of this invention is to provide a polyacrylonitrile copolymer with high stereoregularity prepared by the preparation method described above, having an isotacticity of 40% to 80%.

[0020] Another objective of this invention is to provide highly graphitized carbon fibers prepared by pre-oxidation and carbonization of high stereoregularity polyacrylonitrile copolymers as described above.

[0021] The high isotactic PAN copolymer has completed more than 85% of the -CN to C=N conversion at 200℃-300℃, forming a stable and heat-resistant six-membered ring ladder structure. No additional dehydrogenation is required during carbonization or further graphitization. In addition, the content of C atoms in the sp2 conjugated state in the highly cyclic molecular chain backbone increases, thereby improving the degree of PAN graphitization.

[0022] The high stereoregularity PAN copolymer exhibits increased -C=N content during the TOS process, and the G and D peaks of i-PAN are relatively sharp after carbonization. D / I G The value decreases, sp 2 Increased carbon content leads to improved conductivity of the carbon film.

[0023] Simultaneously introducing high isotacticity and protic acid copolymer monomers can achieve a high degree of cyclization while avoiding concentrated "explosive" heat release, inhibiting chain breakage, reducing fiber defects, and ensuring the high modulus and high tensile strength of PAN-based carbon fibers.

[0024] This invention provides a high stereoregularity polyacrylonitrile copolymer, its preparation method, and highly graphitized carbon fibers. By using Lewis acid or Lewis acid salts as templates to induce ordered polymerization of acrylonitrile during the polymerization process, and simultaneously introducing novel protic acid comonomers, a high stereoregularity polyacrylonitrile copolymer is prepared through the synergistic effect of both. This preparation method has advantages such as simple production process, no need for special equipment, low cost, and short time consumption. It can improve the degree of cyclization of PAN during the pre-oxidation process while endowing PAN with wide-temperature-range exothermic characteristics and a low exothermic rate (effectively reducing the exothermic rate of the cyclization reaction), effectively avoiding concentrated exothermic problems, and promoting the formation of carbon fibers with a higher degree of graphitization in the subsequent carbonization process. This provides a high-quality precursor for the preparation of high-performance PAN-based carbon fibers and a practical technical solution for the industrial production of high-performance PAN-based carbon fibers.

[0025] This invention achieves precise control over the cyclization process and exothermic behavior of PAN ("high cyclization degree - stable exothermic reaction") through the synergistic effect of a highly stereoregular structure and a protic acid comonomer. On the one hand, the ordered cyano groups can rapidly undergo cyclization reactions to form long-chain, continuous, and stable ladder-like units, significantly increasing the cyclization degree of PAN. On the other hand, during the thermal stabilization process, the protic acid comonomer plays a role through a self-catalytic cyclization mechanism. The associated structure formed by the interaction of heat-treated hydrogen bonds and protic acid bonds such as S=O bonds in the system changes preferentially, and then gradually forms a stable cyclization structure composed of C=C and C=N bonds, effectively widening the exothermic range and effectively avoiding the "explosive" exothermic phenomenon in the traditional PAN cyclization process. Compared with freezing urea-acrylonitrile complexes at low temperatures, using gamma-ray radiation to initiate polymerization, and using high-intensity magnetic fields to induce free radical polymerization of acrylonitrile under isothermal conditions to obtain highly stereoregular polyacrylonitrile, this invention has the advantages of low cost, simple operation, and suitability for large-scale production. Attached Figure Description

[0026] Figure 1 The high isotactic copolymer iP(AN-co-AMPS) prepared in Example 1 13 C10 NMR spectrum.

[0027] Figure 2 The DSC curves are shown for the highly isotactic copolymer iP (AN-co-AMPS) and the highly stereoregular polyacrylonitrile homopolymer (i-PAN) prepared in Example 1.

[0028] Figure 3 The high isotactic copolymer iP(AN-co-AMPS) prepared in Example 2 13 C10 NMR spectrum.

[0029] Figure 4 The Fourier transform infrared spectra of the high isotactic copolymer iP(AN-co-AMPS) prepared in Example 2 after being kept at 220°C for different times are shown.

[0030] Figure 5 This is a comparison chart showing the cyclization progress of the high isotactic copolymer iP (AN-co-AMPS) prepared in Example 2 and the low stereoregularity polyacrylonitrile copolymer aP (AN-co-AMPS).

[0031] Figure 6 The iP(AN-co-AMPS) with different monomer contents prepared in Examples 3-6 13 C10 NMR spectrum.

[0032] Figure 7The DSC curves are for iP (AN-co-AMPS) with different monomer contents and high stereoregularity polyacrylonitrile homopolymer (i-PAN) prepared in Examples 3-6.

[0033] Figure 8 This is a comparison chart showing the cyclization progress of iP(AN-co-AMPS) with different monomer contents and low stereoregularity polyacrylonitrile copolymer aP(AN-co-AMPS) prepared in Examples 3-6.

[0034] Figure 9 The DSC curves are shown for the highly isotactic copolymer iP (AN-co-PSS) and the highly stereoregular polyacrylonitrile homopolymer (i-PAN) prepared in Example 7.

[0035] Figure 10 The DSC curves are for iP (AN-co-PSS) with different monomer contents and high stereoregularity polyacrylonitrile homopolymer (i-PAN) prepared in Examples 8-10. Detailed Implementation

[0036] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0037] Example 1 S1. Acrylonitrile complexation with template: Add acrylonitrile (12 g) and magnesium chloride (21.56 g) in a molar ratio of 1:1 to a reaction flask and stir until homogeneous. Freeze at -5°C for 2 hours.

[0038] S2, Free radical polymerization: Add 0.24 g of initiator AIBN (molar ratio of acrylonitrile monomer to acrylonitrile monomer is 1:155) and 0.96 g of 2-acrylamido-2-methylpropanesulfonic acid (molar ratio of acrylonitrile to 2-acrylamido-2-methylpropanesulfonic acid is 98:2) to the above mixture, purge with nitrogen for 30 minutes, heat to 60°C, and maintain the reaction under nitrogen atmosphere with continuous stirring for 24 hours at a stirring speed of 200 rpm.

[0039] S3. Post-treatment: Pour the mixture after the above reaction into methanol at 5°C. After the polymer precipitates, filter it. Wash and filter it repeatedly with a large amount of deionized water at 80°C. Then dry it under vacuum at 60°C for 24 hours.

[0040] The polymerization yield in this embodiment was 36.3%, and the weight-average molecular weight of the polymer was 1.2 × 10⁻⁶. 5 The molecular weight distribution is 2.46. (The sentence appears to be incomplete and requires further context.) 13 C NMR characterized the stereoregularity of the obtained polyacrylonitrile copolymer, such as Figure 1 As shown, the stereoregularity of the obtained copolymer is 55%. Figure 2 As shown Figure 2 Figure 2 is the DSC curve of highly stereoregular polyacrylonitrile homopolymer (i-PAN) and the highly isotactic copolymer i-P(AN-co-AMPS) synthesized in Example 1. It can be seen that the exothermic peak of i-PAN is sharp and narrow, and the heat release is concentrated, while the exothermic peak of i-P(AN-co-AMPS) becomes significantly wider and the heat release rate is slow, effectively reducing the heat release rate.

[0041] The above-mentioned highly stereoregular polyacrylonitrile homopolymer (i-PAN) is prepared by the following method: Acrylonitrile and magnesium chloride (43.12 g) with a complexation molar ratio of acrylonitrile to template of 1:2 (12 g of acrylonitrile) are frozen at -5°C for 2 hours, heated to 60°C after introducing nitrogen for 30 minutes, and continuously stirred and reacted for 24 hours under a nitrogen atmosphere. Then the polymer is poured into cold methanol to precipitate, washed repeatedly with hot deionized water, and dried in an oven at 60°C.

[0042] Example 2 S1. Complexation of acrylonitrile with template: Acrylonitrile (12 g) and magnesium chloride (43.12 g) with a molar ratio of 1:2 are added to a reaction flask, stirred and mixed evenly, and frozen at -5°C for 2 hours.

[0043] S2. Radical polymerization: 0.24 g of initiator AIBN (molar ratio to acrylonitrile monomer is 1:155) and 0.96 g of 2-acrylamido-2-methylpropane sulfonic acid (acrylonitrile:2-acrylamido-2-methylpropane sulfonic acid molar ratio is 98:2) are added to the above mixture. After introducing nitrogen for 60 minutes, it is heated to 60°C and continuously stirred and reacted for 24 hours under a nitrogen atmosphere, and the stirring rate is 300 rpm.

[0044] S3. Post-treatment: The above reaction mixture is poured into methanol at 5°C. After the polymer precipitates, it is filtered by suction, washed repeatedly with a large amount of deionized water at 80°C and filtered by suction, and then dried under vacuum at 60°C for 24 hours.

[0045] The polymerization reaction yield is 30.0%, the weight-average molecular weight is 1.3×10 5 , and the molecular weight distribution is 2.54. The stereoregularity of the obtained polyacrylonitrile copolymer is characterized by 13 13C NMR. As Figure 3 shown, the stereoregularity of the obtained copolymer is 60%. Figure 4 Figure 4 is the Fourier transform infrared spectrum (FTIR) of i-P(AN-co-AMPS) obtained in this example after being kept at 220°C for different times. It can be observed from the figure that the cyclization reaction continues with the prolongation of the holding time. Figure 5The graph shows a comparison of the cyclization progress of the low stereoregularity acrylonitrile copolymer aP(AN-co-AMPS) and the iP(AN-co-AMPS) obtained in this example. The results show that under the same heat treatment time, the cyclization degree of iP(AN-co-AMPS) is significantly higher than that of aP(AN-co-AMPS), proving that high stereoregularity can effectively promote the cyclization reaction, and the synergistic effect with AMPS can further improve the thermal stabilization process of PAN.

[0046] The aforementioned low stereoregularity acrylonitrile copolymer aP (AN-co-AMPS) was prepared by the following method: 53g AN, 0.053g AIBN, 4.23g AMPS, and 192g DMSO were stirred and reacted at 60℃ under a nitrogen atmosphere for 24 h. After the reaction was completed, the solution was poured into deionized water to precipitate aP(AN-co-AMPS). After washing with a large amount of deionized water, the solution was dried in a vacuum oven at 60℃.

[0047] Examples 3-6 S1. Acrylonitrile complexation with template: Add acrylonitrile (12 g) and magnesium chloride (21.56 g) in a molar ratio of 1:1 to a reaction flask and stir until homogeneous. Freeze at -5°C for 2 hours.

[0048] S2. Free radical polymerization: Add 0.24 g of initiator AIBN (molar ratio of acrylonitrile monomer to acrylonitrile monomer of 1:155) and 0.96 g (Example 3), 1.45 g (Example 4), 1.95 g (Example 5), and 2.47 g (Example 6) of 2-acrylamido-2-methylpropanesulfonic acid (molar ratio of acrylonitrile to 2-acrylamido-2-methylpropanesulfonic acid of 98:2 (Example 3), 97:3 (Example 4), 96:4 (Example 5), and 95:5 (Example 6) to the above mixture. After purging with nitrogen for 60 minutes, heat to 60°C and maintain the reaction under nitrogen atmosphere with continuous stirring for 24 hours at a stirring rate of 400 rpm.

[0049] S3. Post-treatment: Pour the mixture after the above reaction into methanol at 8°C. After the polymer precipitates, filter it. Wash and filter it repeatedly with a large amount of deionized water at 70°C. Then dry it under vacuum at 60°C for 24 hours.

[0050] The stereoregularity of iP(AN-co-AMPS) with different monomer contents obtained in the examples was 60% (Example 3), 64% (Example 4), 70% (Example 5), and 75% (Example 6), respectively. The NMR spectra are shown below. Figure 6 As shown. Figure 7 As shown, Figure 7The figures show the DSC curves of iP (AN-co-AMPS) with different monomer contents and high stereoregularity polyacrylonitrile homopolymers (i-PAN) prepared in Examples 3-6. The results show that regardless of the AMPS content, the introduction of monomers significantly achieves a slow-release effect, and the exothermic range slightly widens with increasing AMPS content, demonstrating that AMPS has a clear advantage in widening the exothermic range of PAN and reducing the cyclization rate. Figure 8 As shown, Figure 8 The graphs show a comparison of the cyclization progress of iP(AN-co-AMPS) with different monomer contents and low stereoregularity polyacrylonitrile copolymer aP(AN-co-AMPS) prepared in Examples 3-6. The results indicate that as the AMPS content increases, the cyclization degree of iP(AN-co-AMPS) slightly decreases, suggesting that AMPS content has a dual effect on the cyclization degree: appropriate amounts of AMPS can promote cyclization through autocatalysis, while excessive AMPS may inhibit effective cyano group collisions due to steric hindrance. The highest cyclization degree, exceeding 90%, is achieved when the molar ratio of acrylonitrile to AMPS is 98:2. In conclusion, AMPS not only effectively solves the problem of rapid concentrated exothermic reactions in highly stereoregular PANs but also further promotes PAN cyclization by optimizing the cyclization process through dosage control.

[0051] Example 7 S1. Acrylonitrile complexation with template: Add acrylonitrile (12 g) and magnesium chloride (21.56 g) in a molar ratio of 1:1 to a reaction flask and stir until homogeneous. Freeze at -5°C for 3 hours.

[0052] S2, Free radical polymerization: Add 0.28 g of initiator AIBN (molar ratio of acrylonitrile monomer to acrylonitrile monomer is 1:133) and 0.85 g of p-styrene sulfonic acid (molar ratio of acrylonitrile to p-styrene sulfonic acid is 98:2) to the above mixture, purge with nitrogen for one hour, heat to 60°C, and maintain the reaction under nitrogen atmosphere with continuous stirring for 24 hours at a stirring rate of 300 rpm.

[0053] S3. Post-treatment: Pour the mixture after the above reaction into methanol at 5°C. After the polymer precipitates, filter it. Wash and filter it repeatedly with a large amount of deionized water at 80°C. Then dry it under vacuum at 60°C for 24 hours.

[0054] like Figure 9 As shown, Figure 9The DSC curves of the highly isotactic copolymer iP (AN-co-PSS) and the highly stereoregular polyacrylonitrile homopolymer (i-PAN) prepared in Example 7 show that the exothermic peak of iP (AN-co-PSS) is broadened, the peak intensity decreases, and the exothermic rate is slow. The PSS monomer can effectively distribute the heat released by the polymer over a wider range. These results indicate that, in addition to AMPS, other protic acid monomers such as styrene sulfonic acid (PSS) can also synergistically interact with highly stereoregular PAN, improving its thermal stabilization process and avoiding adverse consequences such as macromolecular chain breakage and fiber defects caused by concentrated exothermic reactions.

[0055] Examples 8-10 S1. Acrylonitrile complexation with template: Add acrylonitrile (12 g) and magnesium chloride (21.56 g) in a molar ratio of 1:1 to a reaction flask and stir until homogeneous. Freeze at -5°C for 2 hours.

[0056] S2, Free radical polymerization: Add 0.24 g of initiator azodicyanovalerate (molar ratio of azodicyanovalerate to acrylonitrile monomer is 1:264 and 1.29 g (Example 8), 1.73 g (Example 9), 2.19 g (Example 10) of p-styrenesulfonic acid (molar ratio of acrylonitrile to p-styrenesulfonic acid is 97:3 (Example 8), 96:4 (Example 9), 95:5 (Example 10)) to the above mixture, heat to 60°C after purging with nitrogen for 30 minutes, and continuously stir the reaction under nitrogen atmosphere for 24 hours at a stirring rate of 200 rpm.

[0057] S3. Post-treatment: Pour the mixture after the above reaction into methanol at 5°C. After the polymer precipitates, filter it. Wash and filter it repeatedly with a large amount of deionized water at 70°C. Then dry it under vacuum at 60°C for 24 hours.

[0058] Figure 10 The DSC curves for the high stereoregularity polyacrylonitrile homopolymer (i-PAN) and the resulting iP (AN-co-PSS) are shown below. Figure 10 As shown, the exothermic peaks of all iP(AN-co-PSS) samples exhibit broadening characteristics, with a significant decrease in peak intensity and a slow exothermic rate, effectively dispersing the heat of the cyclization reaction. Furthermore, the exothermic range slightly increases with the increase of PSS content, indicating that PSS also has the effect of broadening the exothermic range of PAN and reducing the exothermic heat, further verifying that the regulatory effect of sulfonic acid monomers on the thermal stabilization process of highly stereoregular PAN is universal.

[0059] Examples 11-16 S1. Acrylonitrile complexation with template: Add acrylonitrile (12 g) and aluminum chloride (15.1 g) in a molar ratio of 1:2 to a reaction flask and stir until homogeneous. Freeze at -10°C for 3 hours.

[0060] S2, Free radical polymerization: Add 0.28 g of initiator AIBN (molar ratio of acrylonitrile monomer to acrylonitrile monomer of 1:133) and 0.36 g (Example 11), 0.73 g (Example 12), 1.11 g (Example 13), 1.49 g (Example 14), 1.88 g (Example 15), and 2.28 g (Example 16) sodium methyl allyl sulfonate (molar ratio of acrylonitrile to sodium methyl allyl sulfonate of 99:1 (Example 11), 98:2 (Example 12), 97:3 (Example 13), 96:4 (Example 14), 95:5 (Example 15), and 94:6 (Example 16) to the above mixture. After purging with nitrogen for 60 minutes, heat to 70°C and maintain the reaction under nitrogen atmosphere with continuous stirring for 24 hours at a stirring rate of 400 rpm.

[0061] S3. Post-treatment: Pour the mixture after the above reaction into methanol at 10°C. After the polymer precipitates, filter it. Wash and filter it repeatedly with a large amount of deionized water at 70°C. Then dry it under vacuum at 60°C for 24 hours.

[0062] The obtained iP(AN-co-MAS) with different monomer contents have high cyclization degree (85%~90%) and effectively widen the cyclization temperature range to 30-35℃. The effect of MAS content on reducing the exothermic rate varies. The exothermic rates of the copolymer iP(AN-co-MAS) obtained after introducing MAS are 26.65 (J / g) / ℃ (Example 11), 20.85 (J / g) / ℃ (Example 12), 13.05 (J / g) / ℃ (Example 13), 12.28 (J / g) / ℃ (Example 14), 11.56 (J / g) / ℃ (Example 15), and 10.33 (J / g) / ℃ (Example 16), respectively. They show a decreasing trend with increasing MAS content, indicating that increasing the amount of MAS can further reduce the exothermic rate, providing a flexible parameter selection space for different exothermic control requirements. After carbonization at 1600°C, the graphitization degree of the resulting high isotactic stereopolymer iP(AN-co-MAS) was significantly improved, and its I D / I G The values ​​were 0.903 (Example 11), 0.916 (Example 12), 0.945 (Example 13), 0.951 (Example 14), 0.965 (Example 15), and 1.008 (Example 16), respectively. It is noteworthy that when the degree of cyclization was higher than 88%, the carbonized iP(AN-co-MAS) exhibited a significant 2D peak, and I...2D / I G The values ​​were 0.426 (Example 14), 0.183 (Example 15), and 0.084 (Example 16). In contrast, at the same monomer ratio, the I... D / I G The values ​​were relatively high, at 1.369, 1.158, 1.175, 1.182, 1.197, and 1.212 respectively.

[0063] The above results indicate that the synergistic effect of high stereoregularity and protic acid helps to improve the degree of cyclization, thereby promoting a higher degree of graphitization in carbon fibers during carbonization. Therefore, carbon fibers prepared from high stereoregularity copolymers through pre-oxidation and carbonization provide a more unimpeded migration path for free electrons due to their highly graphitized structure, resulting in a higher conductivity of iP(AN-co-MAS) (7.0*10⁻⁶). 3 (Example 11), 6.82*10 3 (Example 12), 6.50*10 3 (Example 13), 6.21*10 3 (Example 14), 5.80*10 3 (Example 15), 5.35*10 3 S / m (Example 16) was significantly higher than aP (AN-co-MAS) (4.0*10). 3 3.90*10 3 3.75*10 3 3.56*10 3 3.49*10 3 3.36*10 3 S / m).

[0064] Examples 17-22 S1. Acrylonitrile complexation with template: Add acrylonitrile (12 g) and cobalt chloride (58.7 g) in a molar ratio of 1:2 to a reaction flask and stir until homogeneous. Freeze at -10°C for 3 hours.

[0065] S2, Free radical polymerization: Add 0.20 g of initiator AIBN (molar ratio of acrylonitrile monomer to acrylonitrile monomer of 1:186) and 0.25 g (Example 17), 0.51 g (Example 18), 0.77 g (Example 19), 1.04 g (Example 20), 1.31 g (Example 21), 1.59 g (Example 22) ethanesulfonic acid (molar ratio of acrylonitrile to ethanesulfonic acid of 99:1 (Example 17), 98:2 (Example 18), 97:3 (Example 19), 96:4 (Example 20), 95:5 (Example 21), 94:6 (Example 22) to the above mixture, then heat to 50°C after purging with nitrogen for 60 minutes, and continuously stir the reaction under nitrogen atmosphere for 24 hours at a stirring rate of 20 rpm.

[0066] S3. Post-treatment: Pour the mixture after the above reaction into methanol at 10°C. After the polymer precipitates, filter it. Wash and filter it repeatedly with a large amount of deionized water at 80°C. Then dry it under vacuum at 60°C for 24 hours.

[0067] The obtained iP(AN-co-ESA) undergoes autocatalytic cyclization. The isotacticity of the iP(AN-co-ESA) samples obtained in this embodiment is higher than 55%, and they exhibit a wide exothermic range (20-40℃). The degree of cyclization is 80-92%, significantly higher than that of traditional PAN homopolymers (which typically have a cyclization degree below 60%, referencing the paper "Study on the Reactivity of Cyclization Reaction of Highly Isotactic Polyacrylonitrile by XRD" published in the Journal of Beijing University of Chemical Technology). These results demonstrate that using CoCl2 instead of MgCl2 as a template can effectively induce ordered polymerization of acrylonitrile, preparing highly stereoregular PAN. Furthermore, ethanesulfonic acid (ESA), as another protic acid monomer, can synergistically work with highly stereoregular PAN to achieve the performance target of "high cyclization degree - wide temperature range exothermic reaction." This further proves that the technical solution proposed in this invention has broad applicability, is not overly limited by the types of Lewis acids / salts or protic acid monomers, and provides flexibility for raw material selection in industrial production. The synergistic effect of ESA monomers and high stereoisotacticity is key to improving the performance of iP(AN-co-ESA). This synergistic effect promotes higher cyclization, resulting in a carbon structure with higher graphitization and significantly improved carbon layer order (Lc, La) during subsequent carbonization. D / I G The value was optimized from 1.002 to 0.913. In contrast, the I of the random stereotyped aP(AN-co-ESA)... D / I GThe lowest value is only 1.369, indicating poor graphitization order. The advantage of this ordered graphite structure in iP(AN-co-ESA) directly translates into excellent electrical conductivity; the conductivity range of iP(AN-co-ESA) is (7.56*10). 3 ~ 6.16*10 3 S / m) was significantly higher than aP(AN-co-ESA) (4.22*10). 3 ~ 3.19*10 3 The S / m ratio indicates that the high stereoregularity and the introduction of protic acid comonomers are beneficial to improving the electrical conductivity of carbon materials.

[0068] The above-mentioned atactic aP(AN-co-ESA) was prepared by the following method: 53g AN, 0.053g AIBN, 2.25g EAS, and 185g DMSO were stirred and reacted at 60℃ under a nitrogen atmosphere for 24h. After the reaction was completed, the solution was poured into a deionizer to precipitate aP(AN-co-ESA). After washing with a large amount of deionized water, the solution was dried in a vacuum oven at 60℃.

[0069] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyacrylonitrile copolymer with high stereoregularity, characterized in that: Includes the following steps: S1. Acrylonitrile complexation with template: Acrylonitrile and template are mixed evenly in a certain proportion, and then frozen at a constant low temperature for a certain period of time. The template is a Lewis acid or Lewis salt, and the molar ratio between acrylonitrile and the template is (1:3) to (1:0.5). S2, Free radical polymerization: Add a certain amount of initiator and protic acid comonomer to the above mixture, purge with nitrogen for a certain time, heat to a certain temperature, and stir continuously for a certain time under nitrogen atmosphere; The molar ratio between the initiator and acrylonitrile is (1:10) to (1:300), and the molar ratio between acrylonitrile and protic acid comonomer is (92:8) to (99:1). S3. Post-treatment: Pour the mixture after the above reaction into a low-temperature alcohol reagent to precipitate, filter, wash repeatedly with deionized water, filter again, and dry under vacuum.

2. The preparation method according to claim 1, characterized in that: In step S1, the Lewis acid or Lewis salt is at least one of MgCl2, CoCl2, AlCl3, FeCl3, CuCl2, BF3, BCl3, BeCl2, SnCl2, TiCl4, ZnCl2, Fe2(SO4)3, CuSO4, MgSO4, Ce(NO3)3, Zn(Ac)2, tetrachloroaluminate, tetrachloroferrate, and tetrafluoroborate.

3. The preparation method according to claim 1, characterized in that: In step S1, the freezing temperature is -20℃ to -5℃, and the freezing time is 1-5 hours.

4. The preparation method according to claim 1, characterized in that: In step S2, the initiator is at least one of azobisisobutyronitrile, benzoyl peroxide, azobiscyanopentanoic acid, NaHSO3, K2S2O8, and B(C6F5)3.

5. The preparation method according to claim 1, characterized in that: In step S2, the protic acid comonomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid, p-styrenesulfonic acid, vinylsulfonic acid, methylallylsulfonic acid, sodium styrenesulfonate, 2-hydroxyethyl methacrylate phosphate, vinyl phosphoric acid, hydroxypropyl methacrylate phosphate, and hydroxyethyl acrylate phosphate.

6. The preparation method according to claim 1, characterized in that: In step S2, the reaction temperature is 30℃~80℃, the reaction time is 6 h~24 h, and the stirring rate is 100 rpm~500 rpm.

7. The preparation method according to claim 1, characterized in that: In step S3, the alcohol reagent is at least one of methanol, ethanol, isopropanol, n-butanol, ethylene glycol, and glycerol.

8. The preparation method according to claim 1, characterized in that: In step S3, the temperature of the alcohol reagent is 0℃~10℃, the temperature of the deionized water is 50℃~80℃, the drying temperature is 40℃~80℃, and the drying time is not less than 24 h.

9. The high stereoregularity polyacrylonitrile copolymer prepared by the preparation method according to any one of claims 1-8 has an isotacticity of 40% to 80%.

10. Highly graphitized carbon fibers prepared by pre-oxidation and carbonization of the high stereoregularity polyacrylonitrile copolymer according to claim 9.

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