阅读说明：本技术 窄分布聚丙烯腈基碳纤维纺丝原液的制备方法 (Preparation method of narrow-distribution polyacrylonitrile-based carbon fiber spinning solution ) 是由 沈志刚 王贺团 李磊 缪金根 于 2018-07-06 设计创作，主要内容包括：本发明涉及一种窄分布聚丙烯腈基碳纤维纺丝原液的制备方法,主要解决现有技术中聚丙烯腈分子量分布宽、残留单体含量高和聚合反应时间长的问题,通过采用窄分布聚丙烯腈基碳纤维纺丝原液的制备方法,包括以下步骤：1)将聚合原料丙烯腈、共聚单体1和/或者共聚单体2、溶剂、引发剂加入反应器,在与反应物质呈惰性的气体保护下开始恒温反应,控制反应温度为60～65℃；2)当转化率超过T<Sub>1</Sub>以后,温度升高5～10℃；3)当转化率超过T<Sub>2</Sub>以后,温度升高5～10℃；4)当转化率达到T<Sub>3</Sub>时,结束反应,完成纺丝原液制备的技术方案,较好地解决了该问题,可用于的聚丙烯腈基碳纤维纺丝原液的工业生产中。(The invention relates to a preparation method of narrow-distribution polyacrylonitrile-based carbon fiber spinning solution, which mainly solves the problems of wide molecular weight distribution, high residual monomer content and long polymerization reaction time of polyacrylonitrile in the prior art, and adopts the preparation method of the narrow-distribution polyacrylonitrile-based carbon fiber spinning solution, and comprises the following steps: 1) copolymerizing acrylonitrile as raw materialAdding a monomer 1 and/or a comonomer 2, a solvent and an initiator into a reactor, starting constant-temperature reaction under the protection of gas inert to reaction substances, and controlling the reaction temperature to be 60-65 ℃; 2) when the conversion rate exceeds T 1 Then, raising the temperature by 5-10 ℃; 3) when the conversion rate exceeds T 2 Then, raising the temperature by 5-10 ℃; 4) when the conversion rate reaches T 3 The technical scheme of finishing the reaction and finishing the preparation of the spinning solution well solves the problem and can be used in the industrial production of the polyacrylonitrile-based carbon fiber spinning solution.)

1. A preparation method of narrow-distribution polyacrylonitrile-based carbon fiber spinning solution comprises the following steps:

(1) adding polymerization raw materials acrylonitrile, a comonomer 1 and/or a comonomer 2, a solvent and an initiator into a reactor, starting constant-temperature reaction under the protection of gas inert to reaction substances, and controlling the reaction temperature to be 60-65 ℃;

(2) when the conversion rate exceeds T₁Then, raising the temperature by 5-10 ℃, and continuing to react;

(3) when the conversion rate exceeds T₂Then, raising the temperature by 5-10 ℃, and continuing to react;

(4) when the conversion rate reaches T₃Then, finishing the reaction to obtain the spinning solution;

wherein, the conversion rate T₁60-70%; said conversion rate T₂80-90%; said conversion rate T₃Is greater than 90%.

2. The method of claim 1, wherein the comonomer 1 is at least one of itaconic acid, acrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl acrylic acid, β -butyl itaconate, acrylamide, acrylamidooxime, hydroxyethylacrylonitrile, α -chloroacrylonitrile, or diacetone acrylamide.

3. The method of claim 1, wherein the comonomer 2 is at least one of itaconic acid, acrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl acrylic acid, β -butyl itaconate, acrylamide, acrylamidooxime, hydroxyethylacrylonitrile, α -chloroacrylonitrile, or diacetone acrylamide.

4. The preparation method of the narrow-distribution polyacrylonitrile-based carbon fiber spinning solution according to claim 1, wherein the molecular weight of the spinning solution is 6-12 ten thousand.

5. The preparation method of the narrow-distribution polyacrylonitrile-based carbon fiber spinning solution according to claim 1, wherein the molecular weight distribution of the spinning solution is 2-4.

6. The preparation method of the narrow-distribution polyacrylonitrile-based carbon fiber spinning solution according to claim 1, wherein the viscosity of the spinning solution at 60 ℃ is 20-100 Pa-s.

7. The preparation method of the spinning solution of the narrow-distribution polyacrylonitrile-based carbon fiber according to claim 1, wherein the residual monomer content of the spinning solution is 500-1700 ppm.

8. The preparation method of the narrow-distribution polyacrylonitrile-based carbon fiber spinning solution according to claim 1, wherein the polymerization raw materials comprise, by weight, 10-35 parts of acrylonitrile, 1-10 parts of comonomer, 0.1-10 parts of comonomer, 45-86 parts of solvent, and the amount of the initiator is 0.2-1% of the total weight of the polymerization monomers.

9. The method of claim 1, wherein the gas inert to the reactive substance is selected from at least one of nitrogen, argon, and helium.

10. The method for preparing spinning dope of narrow distribution polyacrylonitrile-based carbon fiber according to claim 1, characterized in that the viscosity of the dope is measured by using a rotational rheometer and with a shear rate of 0.1s^-1～10s^-1By 8s^-1The viscosity of the dope was taken as the final viscosity of the dope, and the test conditions included both pre-shearing and non-pre-shearing.

Technical Field

The invention belongs to a preparation method of narrow-distribution polyacrylonitrile-based carbon fiber spinning solution.

Background

Polyacrylonitrile (PAN) based carbon fibers are a novel material which is rapidly developed in the 1960 s, and have excellent properties of light weight, high specific strength, high specific modulus, high temperature resistance, corrosion resistance, wear resistance, fatigue resistance, electric conduction, heat conduction and the like, so that the Polyacrylonitrile (PAN) based carbon fibers are widely applied to military industries such as satellites, carrier rockets, tactical missiles, spacecrafts and the like, and become an indispensable material in the aerospace industry. The excellent carbon fiber protofilament has the characteristics of high heat resistance, less pore structure, less surface defects, compact structure, good stretchability and the like.

The precondition for producing the high-performance carbon fiber is to use high-quality polyacrylonitrile precursor, and the precondition for preparing the high-performance spinning solution is high-quality polyacrylonitrile precursor. As a high-performance spinning solution, the polyacrylonitrile fiber spinning solution is required to have the characteristics of moderate molecular weight and viscosity, narrow molecular weight distribution, regular polyacrylonitrile molecular chain structure, no branching and crosslinking, uniform distribution of a comonomer on a main chain and the like.

On the premise of ensuring spinnability, the spinning solution has high solid content. The polyacrylonitrile protofilament spun by the high-solid-content spinning solution has compact structure, low unevenness and high strength, can improve the spinning speed in the spinning process, saves energy, reduces consumption and simultaneously can greatly reduce the manufacturing cost of carbon fiber; meanwhile, the spinning protofilament with high solid content is pre-oxidized and carbonized to easily form a large-area graphite sheet structure. Therefore, the grid defects in the disordered-layer graphite structure can be reduced, the structure of the carbon fiber tends to be perfect, and the strength of the carbon fiber is finally improved. However, the spinning solution with high solid content is easy to generate gel structure, and has too high viscosity, which is not beneficial to polymerization and continuous spinning. Therefore, the polyacrylonitrile spinning solution with high solid content, moderate molecular weight and molecular weight distribution and moderate viscosity opens up a new way for preparing the high-strength carbon fiber.

At present, in the process of preparing a high-performance polyacrylonitrile spinning solution, an azo compound is mostly used as an initiator, Azobisisobutyronitrile (ABIN) is used as an initiator, the polyacrylonitrile spinning solution (Carbon, 2003, 41, 2805-2812) is prepared by a DMSO (dimethyl sulfoxide) one-step method, the weight average molecular weight is about 20 ten thousand, the molecular weight distribution is 3-3.5, the viscosity of the spinning solution is high, the reaction process is difficult to control, a small amount of side reactions such as oxidation and the like, and poor structures such as branching, crosslinking and the like are easily generated, and the product can be yellowed and even generate microgel, which is unfavorable for subsequent spinning.

The conventional means for industrially adjusting the molecular weight include controlling the temperature, adjusting the content of an initiator, adding a molecular weight regulator and the like, but if the molecular weight is reduced by increasing the temperature, the molecular weight distribution is widened while the molecular weight is adjusted, and the polymerization process is difficult to control; when the molecular weight is reduced by increasing the initiator content, the molecular weight distribution is widened, and at the same time, the initiator content is too much, so that bubbles which are difficult to remove are formed in the spinning solution, which is not beneficial to industrial operation; the use of mercaptans such as dodecyl mercaptan or isopropyl alcohol as a chain transfer agent for radical polymerization can effectively adjust the molecular weight of acrylonitrile, but has a disadvantage of lowering the conversion rate of monomers. In the conventional spinning dope production, mercaptans mainly composed of dodecyl mercaptan or isopropanol are used as a chain transfer agent for radical polymerization, and the molecular weight of acrylonitrile can be effectively adjusted, but the conversion rate of monomers is lowered. In addition, mercaptans have a strong pungent odor and strong toxicity, while isopropanol has no pungent odor, but is not sufficiently modulating. The use of conventional chain transfer agents causes a decrease in molecular weight and a broadening of molecular weight distribution while adjusting the molecular weight of the copolymer, and these transfer agents are not easily removed from the dope (patent application No. 200710056083.6).

Disclosure of Invention

The invention aims to solve the technical problems of wide polyacrylonitrile molecular weight distribution, high residual monomer content and long reaction time in the prior art, and provides a preparation method of a spinning solution for narrow-distribution polyacrylonitrile-based carbon fibers.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a preparation method of a spinning solution for narrow-distribution polyacrylonitrile-based carbon fibers comprises the following steps:

(1) adding polymerization raw materials acrylonitrile, a comonomer 1 and (or) a comonomer 2, a solvent and an initiator into a reactor, starting constant-temperature reaction under the protection of gas inert to reaction substances, and controlling the reaction temperature to be 60-65 ℃;

(2) when the conversion rate exceeds T₁Then, raising the temperature by 5-10 ℃, and continuing to react;

(3) when the conversion rate exceeds T₂Then, raising the temperature by 5-10 ℃, and continuing to react;

(4) when the conversion rate reaches T₃Then, finishing the reaction to obtain the spinning solution;

wherein, the conversion rate T₁60-70%, the conversion rate T₂80-90%; said conversion rate T₃Not less than 90%.

In the above technical solution, preferably, the preparation process of the spinning solution is completed by demonomerization and deaeration after the step (4).

In the above technical solution, the comonomer 1 is preferably at least one of itaconic acid, acrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl acrylic acid, β -butyl itaconate, acrylamide oxime, hydroxyethylacrylonitrile, α -chloroacrylonitrile, or diacetone acrylamide.

In the above technical solution, the comonomer 2 is preferably at least one of itaconic acid, acrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl acrylic acid, β -butyl itaconate, acrylamide oxime, hydroxyethylacrylonitrile, α -chloroacrylonitrile, or diacetone acrylamide.

In the above technical solution, the solvent is preferably dimethyl sulfoxide.

In the above technical solution, the initiator is preferably an azo compound, and more preferably azobisisobutyronitrile.

In the technical scheme, the molecular weight of the spinning solution is preferably 6-12 ten thousand.

In the technical scheme, the molecular weight distribution of the spinning solution is preferably 2-4.

In the above technical solution, the viscosity () of the spinning solution at 60 ℃ is preferably 20 to 100Pa · s.

In the technical scheme, the content of the residual monomers in the spinning solution is preferably 500-1700 ppm.

In the technical scheme, the polymerization raw material ratio is preferably 10-35 parts by weight of acrylonitrile, 1-10 parts by weight of comonomer 1, 0.1-10 parts by weight of comonomer 2, 45-86 parts by weight of solvent and 0.2-1% by weight of the total weight of the copolymerization components.

In the above technical solution, the gas inert to the reaction substance is preferably at least one selected from nitrogen, argon, and helium.

In the above technical solution, the method for measuring the viscosity of the stock solution preferably uses a rotational rheometer, and the shear rate is preferably 0.1s^-1～10s^-1By 8s^-1The viscosity of the dope was taken as the final viscosity of the dope, and the test conditions included both pre-shearing and non-pre-shearing.

In the above technical solution, a further preferred solution is: t is₁Preferably 65 to 70%, T₂Preferably 85-90%, T₃Preferably 95%. The polymerization raw material ratio is calculated according to the weight portion, acrylonitrile is preferably 20-30 portions, comonomer 1 is preferably 1-4 portions, comonomer 2 is preferably 0.1-2 portions, solvent is preferably 64-79 portions, and the dosage of the initiator is preferably 0.2-1% of the total weight of the copolymerization components.

The method of the invention adjusts the reaction temperature in a gradient way according to the change of the conversion rate in the polymerization reaction process, improves the mass transfer and heat transfer efficiency of reactants, reduces the half-life period of the initiator, reduces the residue of the initiator in the spinning solution, shortens the polymerization reaction time, and has narrow molecular weight distribution of polyacrylonitrile and less residual monomer content of the spinning solution.

By adopting the scheme of the invention, the obtained spinning solution has the molecular weight of 6-12 ten thousand, the molecular weight distribution is 2-4, the viscosity (60 ℃) of the solution can be controlled to be 20-100 Pa.s, the residual monomer content is 500-1700 ppm, and a better technical effect is achieved.

The following is a specific embodiment of the present invention and is described in detail with reference to comparative examples.

Detailed Description

[ example 1 ]

990g of distilled Acrylonitrile (AN), 5g of Itaconic Acid (IA), 2.5g of sodium methallylsulfonate, 5g of Azobisisobutyronitrile (AIBN) and 3900g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under nitrogen protection and micro-positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, raising the temperature to 5-65 ℃, and continuing the reaction; when the conversion rate reaches 90%, raising the temperature to 5-70 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 22 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 70 ℃ and the pressure to be 200 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 150 Pa.

Spinning dope molecular weight 7 ten thousand, molecular weight distribution 3.3, dope viscosity (@8 s)^-1@60 ℃ C., 70 pas, and a residual monoacrylonitrile content of 1000 ppm.

[ example 2 ]

1210g of distilled Acrylonitrile (AN), 27.5g of methyl methacrylate, 2g of sodium propylene sulfonate, 7.5g of Azobisisobutyronitrile (AIBN) and 3760g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under helium protection micro-positive pressure, and the reaction temperature is controlled to be 65 ℃. When the conversion rate reaches 65%, raising the temperature to 5-70 ℃, and continuing the reaction; when the conversion rate reaches 85 percent, raising the temperature to 10-80 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 90% and the total polymerization time was 20 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 75 ℃ and the pressure to be 300 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 200 Pa.

Spinning dope molecular weight 6 ten thousand, molecular weight distribution 2.6, dope viscosity (@8 s)^-1@60 ℃ C.) 80 pas and a residual monoacrylonitrile content of 1200 ppm.

[ example 3 ]

1460g of distilled Acrylonitrile (AN), 30g of acrylamide, 15g of sodium methallylsulfonate, 9g of Azobisisobutyronitrile (AIBN) and 3500g of dimethyl sulfoxide (DMSO) are added into a reactor, the mixture is uniformly stirred, the reactor is closed, a constant-temperature reaction is started under the protection of argon and under a slight positive pressure, and the reaction temperature is controlled at 62 ℃. When the conversion rate reaches 60 percent, raising the temperature to 10-72 ℃, and continuing the reaction; when the conversion rate reaches 80%, raising the temperature to 5-77 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 22 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 70 ℃ and the pressure to be 100 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 100 Pa.

Spinning dope molecular weight 8 ten thousand, molecular weight distribution 3.7, dope viscosity (@8 s)^-1@60 ℃ C.) 90 pas and a residual monoacrylonitrile content of 1700 ppm.

[ example 4 ]

1460g of distilled Acrylonitrile (AN), 20g of acrylamide oxime, 2g of sodium methallylsulfonate, 9g of Azobisisobutyronitrile (AIBN) and 3500g of dimethyl sulfoxide (DMSO) are added into a reactor, the mixture is uniformly stirred, the reactor is closed, a constant-temperature reaction is started under the protection of nitrogen and under a slight positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, raising the temperature to 5-65 ℃, and continuing the reaction; when the conversion rate reaches 90%, raising the temperature to 5-70 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 20 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 70 ℃ and the pressure to be 50 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 200 Pa.

Molecular weight of spinning dope 9 ten thousand, molecular weight distribution 4.0, dope viscosity (@8 s)^-1@60 ℃ C.) 100 pas and a residual monoacrylonitrile content of 800 ppm.

[ example 5 ]

1200g of distilled Acrylonitrile (AN), 10g of itaconic acid, 5g of sodium methallylsulfonate, 5g of Azobisisobutyronitrile (AIBN) and 3750g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under the protection of helium and micro-positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, raising the temperature to 5-65 ℃, and continuing the reaction; when the conversion rate reaches 90%, raising the temperature to 5-70 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 22 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 75 ℃ and the pressure to be 300 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 200 Pa.

Spinning dope molecular weight 8 ten thousand, molecular weight distribution 2.9, dope viscosity (@8 s)^-1@60 ℃ C., 70 pas, and a residual monoacrylonitrile content of 1200 ppm.

[ example 6 ]

1200g of distilled Acrylonitrile (AN), 35g of hydroxyethyl acrylonitrile, 15g of sodium methallyl sulfonate, 5g of Azobisisobutyronitrile (AIBN) and 3750g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under the protection of argon and under a slight positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, raising the temperature to 5-65 ℃, and continuing the reaction; when the conversion rate reaches 80%, raising the temperature to 5-70 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 22 hours. The demould is started for 6 hours, the temperature is controlled to be 72 ℃, and the pressure is controlled to be 300 Pa; standing for defoaming for 10 hours, controlling the temperature at 74 ℃ and the pressure at 100 Pa.

Spinning dope molecular weight 6.5 ten thousand, molecular weight distribution 3.6, dope viscosity (@8 s)^-1@60 ℃ C.) 68 pas and a residual acrylonitrile content of 1500 ppm.

[ example 7 ]

1130g of distilled Acrylonitrile (AN), 2g of itaconic acid, 3g of sodium propylene sulfonate, 5g of Azobisisobutyronitrile (AIBN) and 3850g of dimethyl sulfoxide (DMSO) are added into a reactor, the mixture is uniformly stirred, the reactor is sealed, a constant-temperature reaction is started under the protection of nitrogen and under a slight positive pressure, and the reaction temperature is controlled at 63 ℃. When the conversion rate reaches 70%, raising the temperature to 5-68 ℃, and continuing the reaction; when the conversion rate reaches 90%, raising the temperature to 5-73 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 20 hours. The demould is started for 6 hours, the temperature is controlled to be 73 ℃, and the pressure is controlled to be 300 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 200 Pa.

Spinning dope molecular weight 8 ten thousand, molecular weight distribution 3.5, dope viscosity (@8 s)^-1@60 ℃ C., 65 pas, residual monoacrylonitrile content 600 ppm.

[ example 8 ]

1130g of distilled Acrylonitrile (AN), 3g of itaconic acid, 1g of sodium methallylsulfonate, 8g of Azobisisobutyronitrile (AIBN) and 3850g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under the protection of helium and micro-positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, raising the temperature to 5-65 ℃, and continuing the reaction; when the conversion rate reaches 90%, raising the temperature to 5-70 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 22 hours. Removing the seed sheet for 8 hours, controlling the temperature at 70 ℃ and the pressure at 300 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 200 Pa.

Spinning dope molecular weight 8 ten thousand, molecular weight distribution 3.5, dope viscosity (@8 s)^-1@60 ℃ C.) 70 pas and a residual monoacrylonitrile content of 1700 ppm.

[ example 9 ]

1130g of distilled Acrylonitrile (AN), 13g of itaconic acid, 8g of sodium methallylsulfonate, 9.2g of Azobisisobutyronitrile (AIBN) and 3850g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under the protection of argon and under a slight positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, raising the temperature to 5-65 ℃, and continuing the reaction; when the conversion rate reaches 90%, raising the temperature to 5-70 ℃, and continuing the reaction; the polymerization was stopped when the conversion reached 95% and the total polymerization time was 20 hours. Removing the seed sheet for 8 hours, controlling the temperature at 70 ℃ and the pressure at 300 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 200 Pa.

Spinning dope molecular weight 6.5 ten thousand, molecular weight distribution 3.2, dope viscosity (@8 s)^-1@60 ℃ C.) 75 pas and a residual monoacrylonitrile content of 1600 ppm.

[ COMPARATIVE EXAMPLE 1 ]

990g of distilled Acrylonitrile (AN), 5g of Itaconic Acid (IA), 2.5g of sodium methallylsulfonate, 5g of Azobisisobutyronitrile (AIBN) and 3900g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under nitrogen protection and micro-positive pressure, and the reaction temperature is controlled at 60 ℃. The total polymerization time was 28 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 70 ℃ and the pressure to be 200 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 150 Pa.

Spinning dope molecular weight 5.6 ten thousand, molecular weight distribution 6.6, dope viscosity (@8 s)^-1@60 ℃ C.) 85 pas and a residual monoacrylonitrile content of 8000 ppm.

[ COMPARATIVE EXAMPLE 2 ]

990g of distilled Acrylonitrile (AN), 5g of Itaconic Acid (IA), 2.5g of sodium methallylsulfonate, 5g of Azobisisobutyronitrile (AIBN) and 3900g of dimethyl sulfoxide (DMSO) are added into a reactor, stirred uniformly, the reactor is sealed, a constant temperature reaction is started under nitrogen protection and micro-positive pressure, and the reaction temperature is controlled at 60 ℃. When the conversion rate reaches 70%, the temperature is raised to 5 ℃ to 65 ℃, the reaction is continued, and when the conversion rate reaches 95%, the polymerization is stopped, and the total polymerization time is 26 hours. Removing the seed sheet for 8 hours, controlling the temperature to be 70 ℃ and the pressure to be 200 Pa; standing and defoaming for 12 hours, controlling the temperature at 75 ℃ and the pressure at 150 Pa.

Spinning dope molecular weight 6.2 ten thousand, molecular weight distribution 6.1, dope viscosity (@8 s)^-1@60 ℃ C.) 78 pas and a residual monoacrylonitrile content of 6800 ppm.

It can be seen from comparative examples 1, 2 and 1 that the polymerization process with gradient temperature rise can effectively shorten the polymerization reaction time, reduce the molecular weight distribution of the spinning solution, and significantly reduce the residual monomer content of the spinning solution by more than 75% under the comparable single removal condition.