A process for the preparation of high molecular weight polyacrylonitrile

Abstract

The present application relates to the technical field of high polymer synthesis and processing, and provides a preparation method of high molecular weight polyacrylonitrile.The present application controls the proportion of monomer, initiator and acidified water, so that the polymerization reaction is carried out at low monomer concentration, monomer droplet polymerization can be avoided, the generation of solid particles is effectively avoided, and the difficulty of dissolving high molecular weight polyacrylonitrile in solution when preparing spinning solution is greatly reduced.At the same time, the present application uses acidified water as the polymerization medium, which is conducive to reducing the viscosity of the polymerization system, realizing equal consumption of copolymerization composition, and also can well solve the phenomenon of scabbing of the polymerization reactor, and finally obtain high molecular weight polyacrylonitrile particles with uniform particle size distribution and loose particle surface.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis and processing technology, and in particular to a method for preparing high molecular weight polyacrylonitrile. Background Technology

[0002] With the development of aerospace, wind turbine blades, electric vehicles, pressure vessels, and other fields, the demand for lightweight, high-strength composite materials is becoming increasingly urgent. Carbon fiber is often combined with matrices such as plastics, metals, and ceramics to form fiber-reinforced composite materials for the preparation of high-strength structural materials, thus making carbon fiber one of the engineering materials for high-end applications. The raw materials used for spinning carbon fiber, i.e., the "precursors," mainly include polyacrylonitrile (PAN), viscose fiber, and pitch. Among them, polyacrylonitrile-based carbon fiber has become the mainstream of carbon fiber production due to its excellent finished product quality, simple process, and excellent mechanical properties.

[0003] Studies have shown that the quality of polyacrylonitrile precursor fibers determines the performance of carbon fibers, and the production of high-performance carbon fibers is inseparable from high-quality polyacrylonitrile precursors. Currently, most industrial production of polyacrylonitrile uses homogeneous solution polymerization, which involves dissolving monomers and initiators in an organic solvent to carry out the polymerization reaction. This method has a simple process flow and produces a relatively high-quality spinning solution, but its disadvantages include a low monomer conversion rate, and the solvents used in this method generally have a large chain transfer constant, making it difficult to obtain polyacrylonitrile with a high average molecular weight, and the resulting polymer also has a wide molecular weight distribution.

[0004] Aqueous precipitation polymerization involves dispersing acrylonitrile monomers and initiators in an aqueous phase for polymerization. Since polyacrylonitrile is insoluble in water, the polymer precipitates continuously from the aqueous phase as the polymerization reaction proceeds. Compared to homogeneous solution polymerization, heterogeneous aqueous precipitation polymerization has a more complex process flow, but it can yield polymers with higher molecular weights. Currently, industrial aqueous precipitation polymerization easily produces large, solid particles, severely affecting the molecular weight distribution and solubility of the polymer product, thus impacting the spinnability of the spinning solution and the operability of subsequent pre-oxidation and carbonization, which is detrimental to improving the mechanical properties of polyacrylonitrile and carbon fibers. Another technical challenge of aqueous precipitation polymerization is the tendency of the polymer product to adhere to the polymerization reactor wall, a phenomenon known as "scaling." Because the polymerization environment at the scalded area differs from that inside the reactor, the molecular weight and copolymer composition of the product at the scalded area differ significantly from the normal product inside the reactor, resulting in a wider molecular weight distribution of polyacrylonitrile. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing high molecular weight polyacrylonitrile. The preparation method provided by the present invention can obtain high molecular weight polyacrylonitrile particles with uniform particle size, narrow particle size distribution, and loose particle surface.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A method for preparing high molecular weight polyacrylonitrile, comprising the following raw materials in parts by mass through a polymerization reaction: 5-14 parts acrylonitrile monomer, 0-10 parts first auxiliary monomer, 0-10 parts second auxiliary monomer, 86-95 parts acidified water, and 0.01-4 parts initiator.

[0008] The first auxiliary monomer includes one or more of vinyl ester monomers, vinylimidazole, 4-acryloylmorpholine, and styrene;

[0009] The second auxiliary monomer includes one or more of vinyl acid monomers, vinyl amine monomers, vinyl amide monomers, and ammonium salts of vinyl acids;

[0010] The high molecular weight polyacrylonitrile has a viscosity-average molecular weight of 300,000 to 1,200,000 and a molecular weight distribution of less than 2.

[0011] Preferably, the vinyl ester monomers include one or more of methyl acrylate, methyl methacrylate, vinyl acetate, propylene acetate, ethyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, cyclohexyl methacrylate, isobutyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, dimethyl maleate, dimethyl itaconic acid, monomethyl itaconic acid, monoethyl itaconic acid, monopropyl itaconic acid, monoisopropyl itaconic acid, monobutyl itaconic acid, monoisobutyl itaconic acid, ethyl 2-(dimethylamino)acrylate, propyl 3-(dimethylamino)acrylate, and ethyl acrylate.

[0012] Preferably, the vinyl acid monomers include one or more of acrylic acid, methacrylic acid, itaconic acid, methyl fumaric acid, 2-butenoic acid, maleic acid, methyl maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, and methacryloylsulfonic acid;

[0013] The vinylamine monomers include one or more of N,N-dimethylallylamine, methpropylene sulfonate amine, and styrene sulfonate amine;

[0014] The vinylamide monomers include one or more of acrylamide, methacrylamide, N-hydroxymethylacrylamide, and N,N-dimethylacrylamide;

[0015] The ammonium salt of the vinyl acid includes ammonium itaconic acid.

[0016] Preferably, the initiator includes one or more of water-soluble azo initiators, peroxide initiators, persulfate initiators, and water-soluble redox complex initiation systems.

[0017] Preferably, the water-soluble azo initiator includes one or more of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azodimethyl N-2-hydroxybutylpropionamide;

[0018] The peroxide initiator includes one or more of hydrogen peroxide and benzoyl peroxide;

[0019] The persulfate initiator includes one or more of persulfates and hydrogen persulfates;

[0020] The water-soluble redox complex initiation system includes one or more of the following: persulfate-sulfite system, benzoyl peroxide-amine system, hydrogen peroxide-iron salt system, dodecyl peroxide-cycloalkanoate system, and persulfate-sulfate system.

[0021] Preferably, the amounts of the water-soluble azo initiator, peroxide initiator, and persulfate initiator are independently 0.1% to 1% of the weight of acrylonitrile monomer; the amount of oxidant in the water-soluble redox composite initiator system is 0.1% to 1% of the weight of acrylonitrile monomer; and the molar ratio of oxidant to reductant in the water-soluble redox composite initiator system is 1:0.5 to 1.5.

[0022] Preferably, the acidified water is prepared by mixing acid and water, wherein the acid includes one or more of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; and the pH value of the acidified water is 1 to 6.

[0023] Preferably, acidified water, acrylonitrile monomer, first auxiliary monomer, second auxiliary monomer and initiator are mixed to obtain a polymerization system, and the polymerization system is subjected to a polymerization reaction; when the mass fraction of the first auxiliary monomer and / or the second auxiliary monomer is 0, the addition of the first auxiliary monomer and / or the second auxiliary monomer is omitted.

[0024] Preferably, the total concentration of acrylonitrile monomer, the first auxiliary monomer, and the second auxiliary monomer in the polymerization system is 5-10 wt%.

[0025] Preferably, the polymerization reaction is carried out at a temperature of 40–100°C.

[0026] This invention provides a method for preparing high molecular weight polyacrylonitrile, which is obtained by polymerization reaction from raw materials comprising the following parts by mass: 5-14 parts acrylonitrile monomer, 0-10 parts first auxiliary monomer, 0-10 parts second auxiliary monomer, 86-95 parts acidified water, and 0.01-4 parts initiator; the first auxiliary monomer includes one or more of vinyl ester monomers, vinylimidazole, 4-acryloylmorpholine, and styrene; the second auxiliary monomer includes one or more of vinyl acid monomers, vinyl amine monomers, vinyl amide monomers, and ammonium salts of vinyl acid; the high molecular weight polyacrylonitrile has a viscosity-average molecular weight of 300,000 to 1,200,000 and a molecular weight distribution of less than 2. This invention has discovered that monomer droplet polymerization under high monomer concentration conditions easily produces large solid particles, which adversely affect subsequent dissolution and the rheological stability of the solution. This invention controls the ratio of monomer, initiator, and acidified water to allow the polymerization reaction to proceed at a low monomer concentration, thereby avoiding monomer droplet polymerization and effectively preventing the formation of solid particles. This results in high molecular weight polyacrylonitrile particles with loose particle surfaces and good solubility, greatly reducing the difficulty of dissolving high molecular weight polyacrylonitrile in solution when preparing spinning solutions.

[0027] Furthermore, this invention uses acidified water as the polymerization medium, ensuring that all raw materials are soluble in it. This facilitates the equal consumption of copolymer components, resulting in polyacrylonitrile particles with uniform size and narrow molecular weight distribution. Simultaneously, acidified water cannot dissolve polyacrylonitrile, leaving the granular particles dispersed in the water. Compared to solution polymerization, the polymerization system of this invention has a very low viscosity. Additionally, the low monomer concentration and low viscosity of the system promote mass and heat transfer, resulting in strong heat dissipation. The polymerization product is less likely to adhere to the polymerization reactor wall, effectively solving the problem of scaling in the polymerization reactor. Ultimately, this yields high molecular weight polyacrylonitrile particles with uniform and narrow particle size distribution. Moreover, the polymerization medium used in this invention has low heat of vaporization, enabling rapid drying, reducing production costs, and improving production efficiency.

[0028] In summary, the preparation method provided by this invention is convenient to operate, environmentally friendly, and produces almost no scaling. It can prepare polyacrylonitrile polymers with high molecular weight, narrow molecular weight distribution, loose surface, and easy solubility, providing a basic raw material for the preparation of high-performance carbon fibers. Attached Figure Description

[0029] Figure 1 SEM image of a commercial polyacrylonitrile sample, scale bar is 10 μm;

[0030] Figure 2 SEM image of a commercial polyacrylonitrile sample, scale bar is 100 μm;

[0031] Figure 3SEM image of the high molecular weight polyacrylonitrile prepared in Example 5, scale bar is 10 μm;

[0032] Figure 4 The image shows a SEM image of the high molecular weight polyacrylonitrile prepared in Example 5, with a scale bar of 100 μm.

[0033] Figure 5 This is a photograph of the polymerization reaction process in Example 5. Detailed Implementation

[0034] This invention provides a method for preparing high molecular weight polyacrylonitrile, which is obtained by polymerization reaction from raw materials comprising the following parts by mass: 5-14 parts of acrylonitrile monomer, 0-10 parts of first auxiliary monomer, 0-10 parts of second auxiliary monomer, 86-95 parts of acidified water, and 0.01-4 parts of initiator.

[0035] The first auxiliary monomer includes one or more of vinyl ester monomers, vinylimidazole, 4-acryloylmorpholine, and styrene;

[0036] The second auxiliary monomer includes one or more of vinyl acid monomers, vinyl amine monomers, vinyl amide monomers, and ammonium salts of vinyl acids;

[0037] The high molecular weight polyacrylonitrile has a viscosity-average molecular weight of 300,000 to 1,200,000 and a molecular weight distribution of less than 2.

[0038] Unless otherwise specified, all raw materials / components used in this invention are commercially available.

[0039] Based on mass parts, the raw materials used in the preparation of high molecular weight polyacrylonitrile in this invention include 5 to 14 parts of acrylonitrile monomer, specifically 5, 6, 7, 8, 9, or 10 parts.

[0040] Based on the mass fraction of the acrylonitrile monomer, the raw materials used in the preparation of high molecular weight polyacrylonitrile in this invention include 0 to 10 parts of the first auxiliary monomer, specifically 0 parts (i.e. no first auxiliary monomer added), 0.05 parts, 0.15 parts, 0.5 parts, 1 part, 1.5 parts, 5 parts, or 10 parts.

[0041] In this invention, the first auxiliary monomer comprises one or more of vinyl ester monomers, vinylimidazole, 4-acryloylmorpholine, and styrene; the vinyl ester monomer preferably comprises one or more of methyl acrylate, methyl methacrylate, vinyl acetate, propylene acetate, ethyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, cyclohexyl methacrylate, isobutyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, dimethyl maleate, dimethyl itaconic acid, monomethyl itaconic acid, monoethyl itaconic acid, monopropyl itaconic acid, monoisopropyl itaconic acid, monobutyl itaconic acid, monoisobutyl itaconic acid, ethyl 2-(dimethylamino)acrylate, propyl 3-(dimethylamino)acrylate, and ethyl acrylate.

[0042] Based on the mass fraction of the acrylonitrile monomer, the raw materials used in the preparation of high molecular weight polyacrylonitrile in this invention include 0 to 10 parts of the second auxiliary monomer, specifically 0 parts (i.e. no second auxiliary monomer added), 0.1 parts, 0.2 parts, 0.5 parts, 0.8 parts, 1 part, 2 parts, 4 parts, 5 parts, 8 parts, or 10 parts.

[0043] In this invention, the second auxiliary monomer comprises one or more of vinyl acid monomers, vinyl amine monomers, vinyl amide monomers, and ammonium salts of vinyl acids; the vinyl acid monomers preferably comprise one or more of acrylic acid, methacrylic acid, itaconic acid, methyl fumaric acid, 2-butenoic acid, maleic acid, methyl maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, and methpropylene sulfonic acid; the vinyl amine monomers preferably comprise one or more of N,N-dimethylallylamine, methpropylene sulfonic acid amine, and styrene sulfonic acid amine; the vinyl amide monomers preferably comprise one or more of acrylamide, methacrylamide, N-hydroxymethylacrylamide, and N,N-dimethylacrylamide; and the ammonium salt of the vinyl acid preferably comprises ammonium itaconic acid.

[0044] Based on the mass fraction of the acrylonitrile monomer, the raw materials used in this invention to prepare high molecular weight polyacrylonitrile include 86-95 parts of acidified water, specifically 86, 87, 88, 90, 91, 93, 94, or 95 parts. The acidified water is preferably prepared by mixing acid and water, and the acid preferably includes one or more of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. The pH value of the acidified water is preferably 1-6, specifically 1, 2, 3, 4, 5, or 6. This invention uses acidified water as the polymerization medium, ensuring that all raw materials can dissolve in the acidified water. This facilitates the equal consumption of copolymer components, thereby improving the particle size uniformity of the resulting polyacrylonitrile and obtaining polyacrylonitrile with uniform particle size and narrow molecular weight distribution.

[0045] Based on the mass fraction of the acrylonitrile monomer, the raw materials used in the preparation of high molecular weight polyacrylonitrile according to this invention include 0.01 to 4 parts of initiator, specifically 0.01, 0.05, 0.1, 1, 2, 3, or 4 parts. In this invention, the decomposition rate of the initiator is affected by the pH of the reaction system. By controlling the amount of initiator within the above-mentioned range, this invention can ensure the formation of high molecular weight polymers and effectively control the molecular weight distribution of the polymers.

[0046] In this invention, the initiator preferably includes one or more of water-soluble azo initiators, peroxide initiators, persulfate initiators, and water-soluble redox complex initiation systems; the water-soluble azo initiator preferably includes one or more of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azodimethyl N-2-hydroxybutylpropionamide; the peroxide initiator preferably includes one or more of hydrogen peroxide and benzoyl peroxide; the benzoyl peroxide preferably includes one or more of potassium benzoate and sodium benzoate. One or two types; the persulfate initiator includes one or more of persulfate and peroxymonosulfate; the persulfate preferably includes one or more of potassium persulfate, ammonium persulfate, and sodium persulfate; the peroxymonosulfate preferably includes one or more of ammonium peroxymonosulfate, sodium peroxymonosulfate, and potassium peroxymonosulfate; the water-soluble redox complex initiation system preferably includes one or more of the following: persulfate-sulfite system, benzoyl peroxide-amine system, hydrogen peroxide-iron salt system, dodecyl peroxide-cycloalkanoate system, and persulfate-sulfate system.

[0047] In this invention, the oxidant in the persulfate-sulfite system is persulfate or persulfate, wherein the persulfate includes one or more of ammonium persulfate and potassium persulfate; the reducing agent in the persulfate-sulfite system is one or more of sulfite and bisulfite, wherein the sulfite includes sodium sulfite and the bisulfite includes sodium bisulfite.

[0048] In this invention, the oxidant in the hydrogen peroxide-sulfite system is hydrogen peroxide, and the reducing agent is one or more of sulfite and bisulfite. The sulfite preferably includes sodium sulfite, and the bisulfite includes sodium bisulfite.

[0049] In this invention, the oxidant in the benzoyl peroxide-amine system is benzoyl peroxide, and the reducing agent is an amine compound, preferably including N,N-dimethylaniline.

[0050] In this invention, the oxidant in the hydrogen peroxide-iron salt system is hydrogen peroxide, and the reducing agent is an iron salt, preferably including ferrous sulfate.

[0051] In this invention, the oxidant in the peroxydodecyl-cycloalkanoate system is peroxydodecyl, and the reducing agent is a cycloalkanoate. The cycloalkanoate preferably includes one or more of cobalt cycloalkanoate, manganese cycloalkanoate, vanadium cycloalkanoate, and iron cycloalkanoate.

[0052] In this invention, the oxidant in the persulfate-sulfate system is a persulfate, which preferably includes one or more of ammonium persulfate and potassium persulfate, and the reducing agent in the persulfate-sulfate system preferably includes one or two of sodium bisulfite and ferrous sulfate.

[0053] In this invention, the molar ratio of oxidant to reductant in the water-soluble redox composite initiator system is preferably 1:0.5 to 1.5, specifically 1:0.5, 1:0.6, 1:0.8, 1:1, 1:1.2 or 1:1.5.

[0054] In this invention, the amounts of the water-soluble azo initiator, peroxide initiator, and persulfate initiator are preferably 0.1% to 1% of the weight of acrylonitrile monomer, specifically 0.1%, 0.3%, 0.5%, 0.6%, 0.8%, or 1%; the amount of oxidant in the water-soluble redox composite initiator system is preferably 0.1% to 1% of the weight of acrylonitrile monomer, specifically 0.1%, 0.3%, 0.5%, 0.6%, 0.8%, or 1%.

[0055] In this invention, the polymerization reaction preferably includes: mixing acidified water, acrylonitrile monomer, a first auxiliary monomer, a second auxiliary monomer, and an initiator to obtain a polymerization system; subjecting the polymerization system to a polymerization reaction; omitting the addition of the first auxiliary monomer and / or the second auxiliary monomer when the mass fraction of the first auxiliary monomer and / or the second auxiliary monomer is 0; the total concentration of acrylonitrile monomer, the first auxiliary monomer, and the second auxiliary monomer in the polymerization system is preferably 5-10 wt%, specifically 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%. This invention controls the total monomer concentration within the above range, which avoids the formation of solid particles and ensures that the product has a high conversion rate and molecular weight. In this invention, the initiator is preferably added in the form of an initiator solution, and the solvent used in the initiator solution is acidified water. Preferably, this invention first mixes a portion of the acidified water, acrylonitrile monomer, the first auxiliary monomer, and the second auxiliary monomer to obtain a primary mixed raw material; then prepares an initiator solution using the remaining portion of the acidified water and the initiator, and mixes the initiator solution with the primary mixed raw material to obtain the polymerization system.

[0056] In this invention, the polymerization reaction temperature is preferably 40–100°C, specifically 50°C, 55°C, 60°C, 65°C, or 70°C; the polymerization reaction is preferably carried out under nitrogen protection. In specific embodiments of this invention, the reaction temperature varies depending on the amount of monomer in the reaction system, ensuring that the monomer can be completely dissolved in the acidified water.

[0057] In this invention, the polymerization reaction is preferably carried out in a continuous polymerization reactor. Specifically, the present invention preferably first adds a portion of acidified water, acrylonitrile monomer, a first auxiliary monomer, and a second auxiliary monomer to the continuous polymerization reactor to obtain a primary mixed raw material. Then, an initiator and an initiator solution prepared with the remaining portion of acidified water are added. The resulting polymerization system (denoted as the initial polymerization system) is reacted at a constant temperature for 30 minutes. Then, the reaction liquid is continuously pumped into the continuous polymerization reactor. The residence time of the reaction liquid in the continuous polymerization reactor is preferably 60 minutes. The ratio of acidified water, acrylonitrile monomer, the first auxiliary monomer, the second auxiliary monomer, and the initiator in the reaction liquid is the same as the ratio in the initial polymerization system.

[0058] After the polymerization reaction is completed, the present invention preferably separates the solid and liquid of the obtained reaction liquid to obtain polymer material, washes the polymer material with water and dries it to obtain the high molecular weight polyacrylonitrile.

[0059] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0060] In the following examples, all parts by weight are parts by weight, where 1 part by weight is 200g.

[0061] Example 1

[0062] Nine parts acrylonitrile and 87 parts acidified water (pH 3, prepared from water and sulfuric acid) were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.018 parts ammonium persulfate and 5 parts acidified water (pH 3) were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain a polymer. The polymer was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The high molecular weight polyacrylonitrile prepared in this example had a viscosity-average molecular weight of 114.4 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 8.5 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.98.

[0063] Example 2

[0064] 5.742 parts acrylonitrile, 0.06 parts itaconic acid, 0.18 parts methyl acrylate, and 89 parts acidified water (prepared from water and sulfuric acid) with a pH of 3 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.018 parts ammonium persulfate and 5 parts acidified water with a pH of 3 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 50.2 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 4.58 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.86.

[0065] Example 3

[0066] 6.699 parts acrylonitrile, 0.07 parts itaconic acid, 0.21 parts methyl acrylate, and 88 parts acidified water (prepared from water and sulfuric acid) with a pH of 3 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.021 parts ammonium persulfate and 5 parts acidified water with a pH of 3 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 53.1 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 4.78 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.83.

[0067] Example 4

[0068] 7.653 parts acrylonitrile, 0.08 parts itaconic acid, 0.24 parts methyl acrylate, and 87 parts acidified water (prepared from water and sulfuric acid) with a pH of 3 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.024 parts ammonium persulfate and 5 parts acidified water with a pH of 3 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain a polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 56.8 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 5.03 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.95.

[0069] Example 5

[0070] 8.613 parts acrylonitrile, 0.09 parts itaconic acid, 0.27 parts methyl acrylate, and 86 parts acidified water (prepared from water and sulfuric acid) with a pH of 3 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.027 parts ammonium persulfate and 5 parts acidified water with a pH of 3 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was measured to be 61.72 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 5.35 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.80.

[0071] Example 6

[0072] 9.570 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 3 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts ammonium persulfate and 5 parts acidified water with a pH of 3 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 72.4 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.03 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.95.

[0073] Example 7

[0074] 5.992 parts acrylonitrile, 0.06 parts itaconic acid, and 89 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.018 parts azobisisobutyramidine hydrochloride and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 120 min. The reaction was stopped after 10 residence times, and the reaction mixture was subjected to solid-liquid separation during the reaction to obtain a polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 51.0 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 4.63 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.79.

[0075] Example 8

[0076] 9.570 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts ammonium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 73.8 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.12 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.97.

[0077] Example 9

[0078] 9.570 parts acrylonitrile, 0.10 parts acrylamide, 0.30 parts methacrylic acid, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts ammonium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial mixed raw material was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was subjected to solid-liquid separation during the reaction to obtain a polymer. The polymer was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 78.5 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.41 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.94.

[0079] Example 10

[0080] 9.570 parts acrylonitrile, 0.20 parts itaconic acid, 0.20 parts methyl methacrylate, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts ammonium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 75.3 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.21 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.95.

[0081] Example 11

[0082] 9.570 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts sodium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated into solid and liquid phases during the reaction to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high molecular weight polyacrylonitrile was tested to be 74.8 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.18 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.97.

[0083] Example 12

[0084] 9.570 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts potassium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial mixed raw material was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was subjected to solid-liquid separation during the reaction to obtain a polymer. The polymer was washed with water and dried at 65°C to obtain high-molecular-weight polyacrylonitrile. The viscosity-average molecular weight of the obtained high-molecular-weight polyacrylonitrile was measured to be 73.7 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.11 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.93.

[0085] Example 13

[0086] 9.555 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, 0.015 parts ammonium sulfite, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.018 parts ammonium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was added to the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated from the reaction liquid in a timely manner during this period to obtain a polymer. The polymer was washed with water and dried at 65°C to obtain high-content polyacrylonitrile. The obtained high-content polyacrylonitrile had a viscosity-average molecular weight of 88.6 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 7.02 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.92.

[0087] Example 14

[0088] 9.555 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, 0.015 parts sodium sulfite, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.018 parts ammonium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated from the reaction liquid in a timely manner during this period to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The obtained high molecular weight polyacrylonitrile had a viscosity-average molecular weight of 87.6 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 6.96 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.94.

[0089] Example 15

[0090] 9.555 parts acrylonitrile, 0.10 parts itaconic acid, 0.30 parts methyl acrylate, 0.015 parts ammonium bisulfite, and 85 parts acidified water (prepared from water and sulfuric acid) with a pH of 2.5 were added to a continuous polymerization reactor and stirred at 200 rpm for 15 min to obtain a primary mixed raw material. 0.030 parts ammonium persulfate and 5 parts acidified water with a pH of 2.5 were mixed to obtain an initiator solution. Under nitrogen protection, when the reactor temperature reached 65°C, the initiator solution was added to obtain the initial polymerization system. The initial polymerization system was reacted at a constant temperature of 65°C for 30 min. A reaction solution with the same monomer and initiator ratio as the initial polymerization system was pumped into the reactor, and the residence time was controlled at 60 min. The reaction was stopped after 10 residence times, and the reaction mixture was separated from the reaction liquid in a timely manner during this period to obtain the polymer material. The polymer material was washed with water and dried at 65°C to obtain high molecular weight polyacrylonitrile. The obtained high molecular weight polyacrylonitrile had a viscosity-average molecular weight of 56.2 × 10⁻⁶. 4 g / mol, intrinsic viscosity of 4.99 dL / g (25℃, dimethylacetamide), and molecular weight distribution of 1.96.

[0091] Performance testing

[0092] SEM observations were performed on the commercial polyacrylonitrile sample and the high molecular weight polyacrylonitrile particles prepared in this example, and the results are as follows: Figures 1-4 As shown, where Figure 1 and Figure 2 The sample is polyacrylonitrile. Figure 3 and Figure 4 The polyacrylonitrile sample used in Example 5 was prepared by aqueous precipitation polymerization at high monomer concentrations.

[0093] according to Figures 1-4 It can be seen that the polyacrylonitrile prepared by the present invention has uniform particle size and loose surface; while the commercial polyacrylonitrile sample has uneven particle size and denser surface.

[0094] The polyacrylonitrile particles prepared in the other examples were observed, and the results showed that the obtained polyacrylonitrile particles all had the characteristics of uniform particle size and loose surface.

[0095] Solubility test: Under a water bath at 70°C, the commercial material and the polyacrylonitrile powder prepared in Example 2 of this invention were dissolved in dimethylacetamide, and the time required to form a homogeneous solution was tested. The results showed that the commercial material required more than 4 hours to form a homogeneous solution, while the polyacrylonitrile powder of this invention achieved the same effect in only 3 hours. The viscosity-average molecular weight of the commercial material used for dissolution was 420,000, and the viscosity-average molecular weight of the powder of this invention used for dissolution was 502,000.

[0096] Dissolution time tests were conducted on the polyacrylonitrile powders prepared in the other examples, and the results showed that they could all dissolve relatively quickly.

[0097] Furthermore, observations of the polymerization process in Examples 1-15 revealed that almost no polymerization products adhered to the reactor wall, and almost no "scalding" occurred during the reaction. Figure 5 This is a photograph of the polymerization reaction process in Example 5 of the present invention.

[0098] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high molecular weight polyacrylonitrile, characterized in that, From the following parts by weight of raw materials The polymerization reaction yields: 5-14 parts of acrylonitrile monomer, 0.18-10 parts of the first auxiliary monomer, 0.06-10 parts of the second auxiliary monomer, 86-95 parts of acidified water, and 0.01-4 parts of initiator; The first auxiliary monomer includes one or more of vinyl ester monomers, vinylimidazole, 4-acryloylmorpholine, and styrene; The second auxiliary monomer includes one or more of vinyl acid monomers, vinyl amine monomers, vinyl amide monomers, and ammonium salts of vinyl acids; The high molecular weight polyacrylonitrile has a viscosity-average molecular weight of 300,000 to 1,200,000 and a molecular weight distribution of less than 2. The polymerization reaction includes: mixing acidified water, acrylonitrile monomer, a first auxiliary monomer, a second auxiliary monomer and an initiator to obtain a polymerization system, and carrying out a polymerization reaction on the polymerization system; the total concentration of acrylonitrile monomer, the first auxiliary monomer and the second auxiliary monomer in the polymerization system is 5~10wt%.

2. The preparation method according to claim 1, characterized in that, The vinyl ester monomers include one or more of the following: methyl acrylate, methyl methacrylate, vinyl acetate, propylene acetate, ethyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, cyclohexyl methacrylate, isobutyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, dimethyl maleate, dimethyl itaconic acid, monomethyl itaconic acid, monoethyl itaconic acid, monopropyl itaconic acid, monoisopropyl itaconic acid, monobutyl itaconic acid, monoisobutyl itaconic acid, ethyl 2-(dimethylamino)acrylate, propyl 3-(dimethylamino)acrylate, and ethyl acrylate.

3. The preparation method according to claim 1, characterized in that, The vinyl acid monomers include one or more of acrylic acid, methacrylic acid, itaconic acid, methyl fumaric acid, 2-butenoic acid, maleic acid, methyl maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, and methacryloylsulfonic acid. The vinylamine monomers include one or more of N,N-dimethylallylamine, methpropylene sulfonate amine, and styrene sulfonate amine; The vinylamide monomers include one or more of acrylamide, methacrylamide, N-hydroxymethylacrylamide, and N,N-dimethylacrylamide; The ammonium salt of the vinyl acid includes ammonium itaconic acid.

4. The preparation method according to claim 1, characterized in that, The initiator includes one or more of the following: water-soluble azo initiators, peroxide initiators, persulfate initiators, and water-soluble redox complex initiation systems.

5. The preparation method according to claim 4, characterized in that, The water-soluble azo initiators include one or more of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azodimethyl N-2-hydroxybutylpropionamide; The peroxide initiator includes one or more of hydrogen peroxide and benzoyl peroxide; The persulfate initiator includes one or more of persulfates and hydrogen persulfates; The water-soluble redox complex initiation system includes one or more of the following: persulfate-sulfite system, benzoyl peroxide-amine system, hydrogen peroxide-iron salt system, dodecyl peroxide-cycloalkanoate system, and persulfate-sulfate system.

6. The preparation method according to claim 4 or 5, characterized in that, The amounts of the water-soluble azo initiator, peroxide initiator, and persulfate initiator are independently 0.1-1% of the weight of acrylonitrile monomer; the amount of oxidant in the water-soluble redox composite initiation system is 0.1-1% of the weight of acrylonitrile monomer; and the molar ratio of oxidant to reductant in the water-soluble redox composite initiation system is 1:0.5-1.

5.

7. The preparation method according to claim 1, characterized in that, The acidified water is prepared by mixing acid and water, wherein the acid includes one or more of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid; and the pH value of the acidified water is 1 to 6.

8. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 40~100℃.

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