Polyacrylonitrile spinning solution as well as preparation method and application thereof

Abstract

The invention provides a polyacrylonitrile spinning solution as well as a preparation method and application thereof, and belongs to the technical field of preparation of textile chemicals and high-performance polyacrylonitrile fibers. The preparation method comprises the following steps: mixing an acrylonitrile monomer, a comonomer, a chain transfer agent and a photocatalyst in a sodium thiocyanate aqueous solution to form a mixed solution; then carrying out polymerization reaction on the mixed solution under a light source to obtain a polyacrylonitrile spinning stock solution; wherein the chain transfer agent is one or more of bis (carboxymethyl) trithiocarbonate, 2-(n-butyl trithiocarbonate) propionic acid, 2-(dodecyl trithiocarbonate)-2-methyl propionic acid and 2-sulfydryl-S-thiobenzoylacetic acid. The preparation method comprises the following steps: adding the chain transfer agent into a reaction kettle; according to the preparation method, the polyacrylonitrile spinning solution with high stability, high solid content and proper viscosity can be synthesized, and the requirement for producing high-performance acrylic fibers is met.

Description

Technical Field

[0001] The invention belongs to the technical field of textile chemicals and high-performance polyacrylonitrile fiber preparation, and specifically relates to a polyacrylonitrile spinning solution and a preparation method and application thereof. Background Art

[0002] Synthetic fibers are widely used in the world today. As one of the three major synthetic fiber varieties, acrylic fiber has good physical and chemical stability, weather resistance, and light resistance. On the one hand, its textiles can be directly used in clothing, decoration and other fields; on the other hand, as a raw material for the production of carbon fiber, it can be made into high-grade carbon fiber through further processing.

[0003] The production process of acrylic fiber mainly includes two categories: one-step method and two-step method. The one-step method usually involves initiating acrylonitrile and comonomers with azo initiators, directly forming polyacrylonitrile spinning solution through homogeneous solution polymerization, and then directly spinning to obtain polyacrylonitrile fiber after stripping and degassing. The two-step method usually uses aqueous precipitation polymerization, and the obtained polyacrylonitrile powder is washed with water, dried, and then dissolved in a solvent to prepare polyacrylonitrile spinning solution, and then the polyacrylonitrile spinning solution is degassed and spun to obtain polyacrylonitrile fiber.

[0004] However, due to the residual azo initiators or insufficient dissolution of polyacrylonitrile powder, as well as the sensitivity of polyacrylonitrile spinning solution prepared with organic solvents such as DMSO and DMAc to moisture in the air, bubbles or microgels will be formed in the polyacrylonitrile spinning solution, resulting in reduced stability of the polyacrylonitrile spinning solution, which will cause trouble for the spinning process, leading to unstable spinning state, poor production stability, and easy occurrence of hairy and broken yarns.

[0005] In addition, traditional free radical polymerization technology cannot effectively control the molecular weight and distribution of the polymer. The molecular weight of the obtained polyacrylonitrile is small and the molecular weight distribution is wide. The solubility of polyacrylonitrile in the spinning solution is poor, resulting in a low solid content and low viscosity of the spinning solution, which is difficult to meet the needs of producing high-performance acrylic fibers. Summary of the invention

[0006] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, an embodiment of the present invention provides a polyacrylonitrile spinning solution and a preparation method and application thereof. The preparation method can synthesize a polyacrylonitrile spinning solution with high stability, high solid content and suitable viscosity to meet the needs of producing high-performance acrylic fibers.

[0007] In a first aspect, an embodiment of the present invention provides a method for preparing a polyacrylonitrile spinning solution, comprising the following steps: mixing acrylonitrile monomer, comonomer, chain transfer agent and photocatalyst in a sodium thiocyanate aqueous solution to form a mixed solution; and then subjecting the mixed solution to a polymerization reaction under a light source to obtain a polyacrylonitrile spinning solution; Wherein, the chain transfer agent is one or more of bis(carboxymethyl)trithiocarbonate, 2-(n-butyltrithiocarbonate)propionic acid, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid and 2-mercapto-S-thiobenzoylacetic acid.

[0008] The advantages and technical effects brought by the method for preparing polyacrylonitrile spinning solution according to the embodiment of the present invention are as follows: (1) The method for preparing the polyacrylonitrile spinning solution of the embodiment of the present invention uses an inorganic sodium thiocyanate aqueous solution as a solvent, which can reduce the sensitivity of the polyacrylonitrile spinning solution to air, moisture, etc., and ensure that the polyacrylonitrile spinning solution maintains good stability for a long time.

[0009] (2) The method for preparing polyacrylonitrile spinning solution in the embodiment of the present invention utilizes light to initiate and control the polymerization reaction process, the reaction conditions are mild, and the system product is pure.

[0010] (3) The photo-controlled polymerization reaction system of the embodiment of the present invention can synthesize polyacrylonitrile spinning solution with a preset molecular weight and a narrow molecular weight distribution (PDI≤1.5). Polyacrylonitrile has a high solubility in sodium thiocyanate aqueous solution. The obtained spinning solution has high stability, high solid content and suitable viscosity. After simple debonding and degassing, it can be directly used for spinning.

[0011] (4) In the photo-controlled polymerization reaction system of the embodiment of the present invention, the molecular weight and molecular weight distribution (PDI ≤ 1.5) of the free radical polymer product can be effectively controlled by using the chain transfer agent of the specified type, and the controllability is relatively strong.

[0012] In some embodiments, the molar ratio of the acrylonitrile monomer to the chain transfer agent is (100-20000):1.

[0013] In some embodiments, based on the total mass of the mixed solution being 100 wt %, the mass fraction of the acrylonitrile monomer is 5-40 wt %.

[0014] In some embodiments, based on the total mass of the acrylonitrile monomer and the comonomer as 100 wt %, the mass fraction of the comonomer is 0.5-20 wt %.

[0015] In some embodiments, the molar ratio of the photocatalyst to the chain transfer agent is 1:(5-500).

[0016] In some embodiments, based on the total mass of the mixed solution being 100 wt %, the mass fraction of the sodium thiocyanate is 35-50 wt %.

[0017] In some embodiments, the light source is one or more of ultraviolet light, blue light and white light; and / or the light intensity of the light source is 0.2-20 mW·cm -2 .

[0018] In some embodiments, the photocatalyst is one or more of phenyl (2,4,6-trimethylbenzoyl) lithium phosphate, eosin Y and rose bengal; and / or, the comonomer is one or more of vinyl acetate, butyl acrylate, itaconic acid, acrylic acid, methyl methacrylate, methyl acrylate, methacrylic acid, n-butyl methacrylate, isobutyl methacrylate, sodium itaconate, sodium propylene sulfonate, sodium methpropylene sulfonate, acrylamido-2-methylpropane sulfonic acid sodium salt solution, 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate and acrylamide.

[0019] In a second aspect, an embodiment of the present invention provides a polyacrylonitrile spinning solution obtained by the preparation method of the first aspect.

[0020] The advantages and technical effects brought by the polyacrylonitrile spinning solution of the embodiment of the present invention are as follows: Since the preparation method of the polyacrylonitrile spinning solution of the first aspect is adopted, the polyacrylonitrile spinning solution of the embodiment of the present invention has high stability, high solid content and suitable viscosity, and can be directly used for spinning after simple stripping and degassing.

[0021] In a third aspect, use of the polyacrylonitrile spinning solution according to the second aspect in the preparation of polyacrylonitrile fiber or carbon fiber. The advantages and technical effects brought by the application of the embodiments of the present invention are as follows: In the embodiment of the present invention, after the polymerization reaction is completed, the polyacrylonitrile spinning stock solution can be directly used for "one-step" spinning to prepare acrylic fiber or carbon fiber precursor after de-sing and degassing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the GPC spectrum of polyacrylonitrile obtained by the light-controlled synthesis method of polyacrylonitrile spinning solution in Example 3.

[0023] Figure 2 This is the GPC spectrum of polyacrylonitrile obtained by the light-controlled synthesis method of the polyacrylonitrile spinning solution in Comparative Example 1. DETAILED DESCRIPTION

[0024] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0025] In comparison, the use of inorganic sodium thiocyanate aqueous solution as a solvent can reduce the sensitivity of polyacrylonitrile spinning solution to air, moisture, etc., and ensure that the polyacrylonitrile spinning solution maintains good stability for a long time. Based on the advantages of sodium thiocyanate aqueous solution as a solvent in terms of non-toxicity and storage stability, it can be used as a solvent for acrylic fiber production. However, polyacrylonitrile has a low solubility in sodium thiocyanate aqueous solution, and microgels are easily generated during the two-step dissolution process, which are important factors restricting the preparation of high-performance polyacrylonitrile fibers.

[0026] Compared with traditional free radical polymerization technology, controlled active free radical polymerization technology can effectively control the molecular weight and distribution of polymers, improve the solubility of polymers in solution, and is conducive to obtaining polyacrylonitrile spinning solution with high solid content and suitable viscosity, showing great application potential in the field of high-quality acrylic fiber and carbon fiber preparation. At the same time, the light-controlled free radical polymerization technology developed in recent years, while retaining the advantages of traditional controlled free radical polymerization such as designable molecular weight and narrow molecular weight distribution, can achieve two-dimensional spatiotemporal control of the polymerization system through its unique light switching effect. At the same time, the reaction conditions are milder, the energy consumption is lower, and the operation is more convenient. The above characteristics are of great value for stabilizing the polyacrylonitrile spinning solution after the polymerization reaction.

[0027] In a first aspect, an embodiment of the present invention provides a method for preparing a polyacrylonitrile spinning solution, comprising the following steps: mixing acrylonitrile monomer, comonomer, chain transfer agent and photocatalyst in a sodium thiocyanate aqueous solution to form a mixed solution; and then subjecting the mixed solution to a polymerization reaction under a light source to obtain a polyacrylonitrile spinning solution; Wherein, the chain transfer agent is one or more of bis(carboxymethyl)trithiocarbonate, 2-(n-butyltrithiocarbonate)propionic acid, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid and 2-mercapto-S-thiobenzoylacetic acid.

[0028] The method for preparing the polyacrylonitrile spinning solution of the embodiment of the present invention uses an inorganic sodium thiocyanate aqueous solution as a solvent, which can reduce the sensitivity of the polyacrylonitrile spinning solution to air, moisture, etc., and ensure that the polyacrylonitrile spinning solution maintains good stability for a long time. In addition, the method for preparing the polyacrylonitrile spinning solution of the embodiment of the present invention uses light to initiate and control the polymerization reaction process, the reaction conditions are mild, and the system product is pure. The light-controlled polymerization reaction system of the embodiment of the present invention can synthesize a polyacrylonitrile spinning solution with a preset molecular weight and a narrow molecular weight distribution (PDI≤1.5). Polyacrylonitrile has a high solubility in a sodium thiocyanate aqueous solution. The obtained spinning solution has high stability, high solid content and suitable viscosity. After simple de-singling and degassing, it can be directly used for spinning. In the light-controlled polymerization reaction system of the embodiment of the present invention, the use of a chain transfer agent of a specified type can effectively control the molecular weight and molecular weight distribution (PDI≤1.5) of the free radical polymer product, and the controllability is strong.

[0029] In some embodiments, the molar ratio of the acrylonitrile monomer to the chain transfer agent is (100-20000):1, such as 100:1, 1000:1, 2000:1, 5000:1, 10000:1, 15000:1, 20000:1, etc. When the molar ratio is too low, the molecular weight of the obtained polymer is too low, which is not conducive to spinning; when the molar ratio is too high, the molecular weight of the obtained polymer is too high, which is not conducive to improving the spinning efficiency.

[0030] In some embodiments, the mass fraction of the acrylonitrile monomer is 5-40 wt%, such as 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, etc., based on the total mass of the mixed solution as 100 wt%. Preferably, the mass fraction of the acrylonitrile monomer is 10-25 wt%. When the mass fraction of the acrylonitrile monomer in the mixed solution is too low, it is not conducive to increasing the solid content of the polyacrylonitrile spinning solution. When the mass fraction of the acrylonitrile monomer in the mixed solution is too high, the solid content of the polyacrylonitrile spinning solution is too high, the viscosity is too large, and it is not conducive to spinning.

[0031] In some embodiments, the mass fraction of the comonomer is 0.5-20 wt%, such as 0.5 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, etc., based on the total mass of the acrylonitrile monomer and the comonomer as 100 wt%. Preferably, the mass fraction of the comonomer is 2-5 wt%. When the mass fraction of the comonomer is too high or too low, it will have an adverse effect on the physical properties and processing properties of the polyacrylonitrile fiber.

[0032] In some embodiments, the comonomer is one or more of vinyl acetate, butyl acrylate, itaconic acid, acrylic acid, methyl methacrylate, methyl acrylate, methacrylic acid, n-butyl methacrylate, isobutyl methacrylate, sodium itaconate, sodium propylene sulfonate, sodium methpropylene sulfonate, acrylamido-2-methylpropanesulfonic acid sodium salt solution, 2-acrylamido-2-methylpropanesulfonic acid, sodium styrene sulfonate and acrylamide. The above types of comonomers are beneficial to improving the physical properties, dyeing properties, processing properties and functionality of polyacrylonitrile fibers, thereby meeting the needs of different application fields.

[0033] In some embodiments, the molar ratio of the photocatalyst to the chain transfer agent is 1:(5-500), such as 1:5, 1:10, 1:100, 1:200, 1:300, 1:400, 1:500, etc. When the molar ratio is too low, the rate of the polymerization reaction is too slow, which is not conducive to the control of the polymerization reaction process, and thus is not conducive to improving the reaction efficiency. When the molar ratio is too high, the rate of the polymerization reaction is too fast, which is also not conducive to the control of the polymerization reaction process, and thus is not conducive to improving the quality of the polymerization reaction product.

[0034] In some embodiments, the photocatalyst is one or more of phenyl (2,4,6-trimethylbenzoyl) lithium phosphate, eosin Y and red bengal. The above photocatalysts can effectively increase the rate of photopolymerization reaction.

[0035] In some embodiments, based on the total mass of the mixed solution being 100 wt%, the mass fraction of the sodium thiocyanate is 35-50 wt%, such as 35 wt%, 36 wt%, 38 wt%, 40 wt%, 42 wt%, 45 wt%, 48 wt%, 50 wt%, etc. Preferably, the mass fraction of the sodium thiocyanate is 40-45 wt%. When the mass fraction of sodium thiocyanate in the mixed solution is too low, it is not conducive to the dissolution of the polymer.

[0036] In some embodiments, the light source is one or more of ultraviolet light, blue light and white light; preferably, the wavelength of the light source is 420-460 nm; and / or the light intensity of the light source is 0.2-20 mW cm -2 The reaction system of the embodiment of the present invention does not need to be heated, and the reaction can be initiated using light of relatively low energy density, and the initiation conditions are mild, which greatly saves energy consumption.

[0037] In the embodiment of the present invention, since the polymerization reaction is photo-initiated, there is no special restriction on the reaction temperature. Preferably, the polymerization reaction temperature is 0-80°C, such as 0°C, 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc. More preferably, the polymerization reaction temperature is 15-35°C.

[0038] In some embodiments, the polymerization reaction time is 0.5 to 48 h, for example, 0.5 h, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, 48 h, etc. Preferably, the polymerization reaction time is 3 to 24 h.

[0039] In the reaction system of the embodiment of the present invention, the molecular weight and molecular weight distribution of the free radical polymer product can be controlled by adjusting one or more factors including illumination time, monomer concentration and chain transfer agent dosage, and the controllability is relatively strong.

[0040] In a second aspect, an embodiment of the present invention provides a polyacrylonitrile spinning solution obtained by the method for preparing the polyacrylonitrile spinning solution of the first aspect.

[0041] Since the preparation method of the polyacrylonitrile spinning solution of the first aspect is adopted, the polyacrylonitrile spinning solution of the embodiment of the present invention has high stability, high solid content and suitable viscosity, and can be directly used for spinning after simple stripping and degassing.

[0042] In a third aspect, use of the polyacrylonitrile spinning solution according to the second aspect in the preparation of polyacrylonitrile fiber or carbon fiber.

[0043] In the embodiment of the present invention, after the polymerization reaction is completed, the polyacrylonitrile spinning stock solution can be directly used for "one-step" spinning to prepare acrylic fiber or carbon fiber precursor after de-sing and degassing.

[0044] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0045] Example 1 This embodiment provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled free radical polymerization method, and specifically comprises the following steps: Acrylonitrile monomer and methyl methacrylate were filtered with alumina powder, 1.2 g acrylonitrile monomer, 0.1 g methyl methacrylate, 5 mg 2-(n-butyl trithiocarbonate) propionic acid (i.e., chain transfer agent), 0.2 mg phenyl (2,4,6-trimethylbenzoyl) lithium phosphate (i.e., photocatalyst) and 3.0 mL 50 wt% sodium thiocyanate aqueous solution were weighed, and the above substances were mixed to obtain a mixed solution. Among them, the molar ratio of acrylonitrile monomer to chain transfer agent was 1080:1, and the molar ratio of photocatalyst to chain transfer agent was 1:31; based on the total mass of the mixed solution as 100 wt%, the mass fraction of acrylonitrile monomer was 23 wt%, and the mass fraction of sodium thiocyanate was 37.5 wt%; based on the total mass of acrylonitrile monomer and comonomer as 100 wt%, the mass fraction of comonomer was 7 wt%.

[0046] The mixed solution was added to a 10 mL quartz reaction tube, which was sealed with a rubber stopper and purged with nitrogen for 10 min to remove excess oxygen in the system. -2 The reaction was carried out under the irradiation of blue light at 25°C for 16 hours to obtain polyacrylonitrile spinning solution.

[0047] The polyacrylonitrile spinning solution was precipitated with a mixed solution of methanol and water as a precipitant, filtered, washed, dried, and the final solid product was collected. The obtained solid product was dissolved with N, N-dimethylformamide, and the molecular weight and molecular weight distribution parameters were tested by gel permeation chromatography analyzer. The results are shown in Table 1.

[0048] Example 2 This embodiment provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled free radical polymerization method, and specifically comprises the following steps: Acrylonitrile monomer and methyl acrylate were filtered with alumina powder, and 1.3 g acrylonitrile monomer, 0.1 g methyl acrylate, 0.05 g itaconic acid, 6 mg 2-mercapto-S-thiobenzoylacetic acid (chain transfer agent), 0.2 mg phenyl (2,4,6-trimethylbenzoyl) lithium phosphate (photocatalyst) and 4.5 mL 50 wt% sodium thiocyanate aqueous solution were weighed and mixed to obtain a mixed solution. The mixed solution was added to a 10 mL quartz reaction tube, sealed with a rubber stopper, and nitrogen was passed for 10 min to remove excess oxygen in the system. The reaction mixture was stirred at 5 mW cm -2 The reaction was carried out under white light irradiation at 25°C for 12 hours to obtain polyacrylonitrile spinning solution.

[0049] The polyacrylonitrile spinning solution was precipitated with a mixed solution of ethanol and water as a precipitant, and the final solid product was collected by filtration, washing, and drying. The obtained solid product was dissolved in N, N-dimethylformamide, and the molecular weight and molecular weight distribution parameters were tested by gel permeation chromatography. The results are shown in Table 1.

[0050] Example 3 This embodiment provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled free radical polymerization method, and specifically comprises the following steps: Acrylonitrile monomer and butyl acrylate were filtered with alumina powder, and 1.5 g acrylonitrile monomer, 0.1 g butyl acrylate, 8 mg bis(carboxymethyl) trithiocarbonate (chain transfer agent), 0.1 mg eosin Y (photocatalyst) and 5.0 mL 54 wt% sodium thiocyanate aqueous solution were weighed and mixed to obtain a mixed solution. The mixed solution was added to a 10 mL quartz reaction tube, sealed with a rubber stopper, and nitrogen was passed for 10 min to remove excess oxygen in the system. The reaction mixture was stirred at 3 mW cm -2Under blue light irradiation, the reaction was carried out at 25°C for 8 hours to obtain polyacrylonitrile spinning solution.

[0051] The polyacrylonitrile spinning stock solution was precipitated with a mixed solution of ethanol and water as a precipitant, and the final solid product was collected after filtration, washing, and drying. The obtained solid product was dissolved in N, N-dimethylformamide, and the molecular weight and molecular weight distribution parameters were tested by gel permeation chromatography. The results are shown in Table 1, and the GPC spectrum is shown in Figure 1 .

[0052] Example 4 This embodiment provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled free radical polymerization method, and specifically comprises the following steps: Filter the acrylonitrile monomer and acrylamide with alumina powder, weigh 1.3 g acrylonitrile monomer, 0.05 g acrylamide, 0.1 g itaconic acid, 10 mg 2-mercapto-S-thiobenzoylacetic acid (chain transfer agent), 0.2 mg Bengal rose and 4.0 mL 56 wt% sodium thiocyanate aqueous solution, and mix the above substances to obtain a mixed solution. Add the mixed solution into a 10 mL quartz reaction tube, seal it with a rubber stopper, and pass nitrogen for 10 min to remove excess oxygen in the system. -2 The reaction was carried out under blue light irradiation at 25°C for 10 hours to obtain polyacrylonitrile spinning solution.

[0053] The polyacrylonitrile spinning solution was precipitated with a mixed solution of methanol and water as a precipitant, and the final solid product was collected after filtering, washing, and drying. The obtained solid product was dissolved in N, N-dimethylformamide, and the molecular weight and molecular weight distribution parameters were tested by gel permeation chromatography analyzer. The results are shown in Table 1.

[0054] Example 5 This embodiment provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled free radical polymerization method, and specifically comprises the following steps: Acrylonitrile monomer and vinyl acetate were filtered with alumina powder, and 0.9 g acrylonitrile monomer, 0.1 g vinyl acetate, 0.05 g itaconic acid, 4 mg 2-(n-butyl trithiocarbonate) propionic acid (i.e., chain transfer agent), 0.1 mg phenyl (2,4,6-trimethylbenzoyl) lithium phosphate (i.e., photocatalyst) and 3.0 mL 52 wt% sodium thiocyanate aqueous solution were weighed and mixed to obtain a mixed solution. The mixed solution was added to a 10 mL quartz reaction tube, sealed with a rubber stopper, and nitrogen was passed through for 10 min to remove excess oxygen in the system. The reaction mixture was stirred at 3 mW cm -2 The reaction was carried out under the irradiation of blue light at 25°C for 12 hours to obtain polyacrylonitrile spinning solution.

[0055] The polyacrylonitrile spinning stock solution was precipitated with a mixed solution of ethanol and water as a precipitant, and the final solid product was collected after filtering, washing, and drying. The obtained solid product was dissolved in N, N-dimethylformamide, and the molecular weight and molecular weight distribution parameters were tested by gel permeation chromatography analyzer. The results are shown in Table 1.

[0056] Comparative Example 1 This comparative example provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled reversible addition-fragmentation chain transfer polymerization method. The preparation method is the same as that of Example 1, except that dimethyl sulfoxide is used instead of sodium thiocyanate aqueous solution as the solvent.

[0057] The polyacrylonitrile spinning stock solution was precipitated with a mixed solution of ethanol and water as a precipitant, and the final solid product was collected after being filtered, washed, and dried. The obtained solid product was dissolved in N, N-dimethylformamide, and the molecular weight and molecular weight distribution parameters were tested by gel permeation chromatography. The results are shown in Table 1, and the GPC spectrum is shown in Figure 2 .

[0058] Comparative Example 2 This comparative example provides a method for preparing polyacrylonitrile spinning solution, which is a light-controlled reversible addition-fragmentation chain transfer polymerization method. Its preparation method is the same as that of Example 1, except that N,N-dimethylacetamide is used as a solvent instead of sodium thiocyanate aqueous solution.

[0059] Table 1 Results of photocatalytic acrylonitrile free radical polymerization

[0060] The experimental results of Example 1 prove that the photocatalytic reaction effect of the reaction system is good, the molecular weight of the obtained product is controllable, the molecular weight distribution is narrow, and it can be used for polymer liquid spinning.

[0061] The photocatalytic reaction effects in the remaining embodiments are good, the molecular weight of the obtained products is controllable, and the molecular weight distribution is narrow. The effects are equivalent to those in Example 1, and they are not listed one by one here.

[0062] The experimental results of Comparative Example 1 show that when dimethyl sulfoxide is used as the solvent, the reaction efficiency is very low and the polymer molecular weight is very low, only 5,160 (see Figure 2 ), cannot be used for polymer liquid spinning.

[0063] The experimental results of Comparative Example 2 show that when N,N-dimethylacetamide is used as the solvent, the polymer product precipitates due to the easy occurrence of chain transfer in the N,N-dimethylacetamide solvent, and cannot be directly used for spinning.

[0064] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0065] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing polyacrylonitrile spinning solution, characterized in that: The following steps are involved: Mixing acrylonitrile monomer, comonomer, chain transfer agent and photocatalyst in a sodium thiocyanate aqueous solution to form a mixed solution; then subjecting the mixed solution to a polymerization reaction under a light source to obtain a polyacrylonitrile spinning stock solution; Wherein, the chain transfer agent is one or more of bis(carboxymethyl)trithiocarbonate, 2-(n-butyltrithiocarbonate)propionic acid, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid and 2-mercapto-S-thiobenzoylacetic acid.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the acrylonitrile monomer to the chain transfer agent is (100-20000):

1.

3. The preparation method according to claim 1 or 2, characterized in that: Based on the total mass of the mixed solution being 100 wt %, the mass fraction of the acrylonitrile monomer is 5-40 wt %.

4. The preparation method according to claim 1 or 2, characterized in that: Based on the total mass of the acrylonitrile monomer and the comonomer as 100 wt %, the mass fraction of the comonomer is 0.5-20 wt %.

5. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the photocatalyst to the chain transfer agent is 1:(5-500).

6. The preparation method according to claim 1 or 2, characterized in that: Based on the total mass of the mixed solution being 100 wt %, the mass fraction of the sodium thiocyanate is 35-50 wt %.

7. The preparation method according to claim 1, characterized in that: The light source is one or more of ultraviolet light, blue light and white light; and / or the light intensity of the light source is 0.2-20 mW·cm -2 .

8. The preparation method according to claim 1, characterized in that: The photocatalyst is one or more of phenyl (2,4,6-trimethylbenzoyl) lithium phosphate, eosin Y and rose bengal; and / or the comonomer is one or more of vinyl acetate, butyl acrylate, itaconic acid, acrylic acid, methyl methacrylate, methyl acrylate, methacrylic acid, n-butyl methacrylate, isobutyl methacrylate, sodium itaconate, sodium propylene sulfonate, sodium methpropylene sulfonate, acrylamide-2-methylpropane sulfonic acid sodium salt solution, 2-acrylamido-2-methylpropane sulfonic acid, sodium styrene sulfonate and acrylamide.

9. A polyacrylonitrile spinning solution, characterized in that: Obtained by the method for preparing the polyacrylonitrile spinning solution according to any one of claims 1 to 8.

10. Use of the polyacrylonitrile spinning solution according to claim 9 in the preparation of polyacrylonitrile fibers or carbon fibers.

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