Low molecular weight anionic polyacrylamide and preparation method thereof

Abstract

The invention discloses low-molecular-weight anionic polyacrylamide and a preparation method of the low-molecular-weight anionic polyacrylamide, and the preparation method comprises the following specific steps: adding an acrylamide monomer, a maleic acid monomer, isopropanol, sodium hydroxide, urea, sodium formate and a water solvent into a reactor, and removing air in a nitrogen purging and vacuumizing treatment manner; continuously carrying out nitrogen purging and controlling the reaction system to be maintained at a low-temperature condition; the method comprises the following steps: respectively dissolving an oxidant and an azo initiator in deionized water, carrying out nitrogen purging to remove air, adding the system, carrying out an initial reaction under a low-temperature condition, raising the temperature after the initial reaction, continuing the polymerization reaction for a certain time, and drying and crushing the product to obtain the low-molecular-weight anionic polyacrylamide. The polyacrylamide product with low molecular weight, high anion degree and high dissolution speed is successfully prepared by a simple polymerization method, and the method has the advantages of simple production process, short period, low cost and the like.

Description

Technical Field

[0001] The invention belongs to the field of high molecular weight polymers, and in particular relates to low molecular weight anionic polyacrylamide. The invention also relates to a preparation method of the low molecular weight anionic polyacrylamide. Background Art

[0002] Polyacrylamide (PAM), as a linear water-soluble polymer, is widely used in water treatment, papermaking, oil extraction, textiles, medicine and other fields. Traditional polyacrylamide products usually have a high molecular weight, which can provide good performance in some applications, but is also accompanied by problems such as high production costs and slow dissolution.

[0003] In the prior art, the preparation method of high molecular weight polyacrylamide is relatively mature, but the research on low molecular weight (weight average molecular weight not exceeding 1 million) polyacrylamide is relatively small. Low molecular weight polyacrylamide has its unique advantages in specific applications, such as polymer emulsifiers, adhesives, paper strengthening agents, etc., such as rapid dissolution and low production cost. However, due to the high reactivity and large heat effect of acrylamide monomer, conventional aqueous solution polymerization reaction is prone to cause large-scale cross-linking, resulting in molecular weight that is difficult to control, making the preparation of low molecular weight polyacrylamide face challenges. Summary of the invention

[0004] The purpose of the present invention is to provide a low molecular weight anionic polyacrylamide, which has the characteristics of excellent solubility, high stability, wide applicability, convenience for subsequent processing and saving production costs.

[0005] Another object of the present invention is to provide a method for preparing low molecular weight anionic polyacrylamide.

[0006] The technical solution adopted by the present invention is that the low molecular weight anionic polyacrylamide has the following structural formula:

[0007] Wherein, m represents the number of acrylamide monomers, and n represents the number of maleic acid monomers.

[0008] The present invention is also characterized in that: The molecular weight of low molecular weight anionic polyacrylamide is 500,000 to 1,000,000.

[0009] Another technical solution adopted by the present invention is a method for preparing low molecular weight anionic polyacrylamide, which specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio and add them into a reactor, and then add a chain transfer agent and a stabilizer, and then add deionized water and stir until the components are dissolved to obtain a precursor solution; Step 2: controlling the temperature of the precursor solution within the range of 0 to 5°C, and introducing nitrogen into the precursor solution for deoxygenation; Step 3: Weigh a certain amount of oxidant, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azo initiator, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution; Step 4: adding the oxidant solution and the azo initiator solution in step 3 to the deoxygenated precursor solution obtained in step 2 in sequence, and maintaining the solution temperature within the range of 0 to 5° C. to carry out a primary polymerization reaction; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction, dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0010] Another technical solution of the present invention is also characterized in that: In step 1, the chain transfer agent is urea and the stabilizer is sodium formate.

[0011] The specific mass ratio of the components in step 1 is: 11% to 12% acrylamide, 3% to 13% maleic acid, 0.05% to 0.2% isopropanol, 0.25% to 1% sodium hydroxide, 4.5% urea, 0.03% sodium formate, and the rest is water.

[0012] In step 3, the oxidant is potassium persulfate, and the mass of the oxidant weighed accounts for 0.4% of the mass of the precursor solution.

[0013] In step 3, the azo initiator is azobisisobutylimidazoline hydrochloride, and the mass of the azo initiator weighed accounts for 0.5% to 1.5% of the mass of the precursor solution.

[0014] The initial polymerization reaction time in step 4 is 0.1 to 1 h.

[0015] The polymerization reaction time in step 5 is 0.5 to 24 h.

[0016] The invention has the beneficial effects that: the low molecular weight anionic polyacrylamide preparation method provided by the invention has an adjustable anionicity, acrylamide is used as the main monomer, and carboxylic acid groups are introduced by copolymerization with the participation of maleic acid to give the polymer anionic properties, and maleic acid, as a dicarboxylic acid, has a molecular structure similar to acrylic acid. The copolymerization of acrylamide and maleic acid is achieved by an oxidoreductant and an initiator, and the anionicity can be regulated by changing the amount of maleic acid. Compared with the existing technology, the carboxyl groups on the equimolar monomers are more, and the anionic charges exhibited are also more. At the same time, more carboxyl groups can improve the hydrophilicity of the product, so that it exhibits higher water solubility, and the synthesized product dissolves faster, has a high degree of solubility, and has the advantages of low synthesis cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an infrared spectrum of the low molecular weight anionic polyacrylamide prepared in Example 1 of the present invention; Figure 2 The gel permeation chromatogram of the low molecular weight anionic polyacrylamide prepared in Example 1 of the present invention; Figure 3 This is a gel permeation chromatogram of the low molecular weight anionic polyacrylamide prepared in Example 2 of the present invention; Figure 4 This is the gel permeation chromatogram of the low molecular weight anionic polyacrylamide prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0018] The present invention is described in detail below in conjunction with specific implementation modes.

[0019] The low molecular weight anionic polyacrylamide provided by the present invention has a structural formula as follows:

[0020] Wherein, m represents the number of acrylamide monomers, and n represents the number of maleic acid monomers. Specifically, the amount of acrylamide and maleic acid can be changed to adjust the molecular weight within the range of 500,000 to 1,000,000. The molecular weight in the present invention is the weight average molecular weight, which is measured by gel permeation chromatography.

[0021] The present invention also provides a method for preparing low molecular weight anionic polyacrylamide, which specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio and add them into a reactor, and then add a chain transfer agent and a stabilizer, and then add deionized water and stir until the components are dissolved to obtain a precursor solution; Wherein, in step 1, the chain transfer agent may be urea, which can improve the solubility of the polymer. During the polymerization reaction, the presence of urea can make the structure of the polymer chain more regular and reduce the entanglement between the molecular chains. The stabilizer may be sodium formate, which has a certain reducing property and can prevent some components in the polymerization reaction system from being oxidized. It can react with free radicals to form relatively stable intermediates, slowing down the rate of polymerization initiated by free radicals.

[0022] The specific mass ratio of the components in step 1 is: 11% to 12% acrylamide, 3% to 13% maleic acid, 0.05% to 0.2% isopropanol, 0.25% to 1% sodium hydroxide, 4.5% urea, 0.03% sodium formate, and the rest is water.

[0023] Step 2: controlling the temperature of the precursor solution within the range of 0 to 5°C, and introducing nitrogen into the precursor solution for deoxygenation; Step 3: Weigh a certain amount of oxidant, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azo initiator, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution; In step 3, the oxidant is potassium persulfate, and the mass of the weighed oxidant accounts for 0.4% of the mass of the precursor solution. Potassium persulfate can effectively control the initiation of the polymerization reaction, and by adjusting the dosage of potassium persulfate and the reaction temperature, the polymerization reaction rate and the molecular weight of the polymer can be controlled to a certain extent.

[0024] In step 3, the azo initiator is azobisisobutylimidazoline hydrochloride, and the mass of the azo initiator weighed accounts for 0.5% to 1.5% of the mass of the precursor solution. Compared with other initiators, the decomposition reaction of azobisisobutylimidazoline hydrochloride is relatively smooth and stable, and the rate and progress of the polymerization reaction can be better controlled, which is conducive to the synthesis of polymers with specific molecular weight and structure.

[0025] Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2, and the solution temperature is kept within the range of 0 to 5°C to carry out a primary polymerization reaction; the initial polymerization reaction time in step 4 is generally 0.1 to 1 h.

[0026] Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is generally 0.5 to 24 hours. Dry and crush the product after the reaction to obtain a low molecular weight anionic polyacrylamide.

[0027] The preparation method of low molecular weight anionic polyacrylamide provided by the present invention has a synthesis mechanism based on free radical polymerization reaction. The effective copolymerization of acrylamide and maleic acid is achieved by controlling the reaction conditions. In the starting stage of the polymerization reaction, potassium persulfate and urea in the redox initiation system are activated in an oxygen-free environment purged with nitrogen to generate necessary free radicals. These free radicals react with acrylamide and maleic acid monomers to form a growth chain. Since the polymerization activity of acrylamide is usually higher than that of maleic acid, the molecular weight and anionicity of the polymer can be adjusted by accurately controlling the molar ratio of the two. On the other hand, the molecular weight and molecular weight distribution of the polymer can be adjusted by controlling the reaction temperature and time. The initial polymerization reaction is carried out at a low temperature (0-5°C) to slow down the chain growth rate and prevent side reactions. Subsequently, the temperature is gradually increased to 30°C to promote further growth of the polymer chain while maintaining the stability of the reaction system. The addition of isopropanol helps to stabilize the free radicals and control the chain transfer reaction, thereby obtaining a polymer with a lower molecular weight. The synergistic effect of sodium hydroxide, urea and sodium formate not only adjusts the pH value of the reaction system and optimizes the polymerization conditions, but also helps to improve the water solubility and stability of the polymer. Urea and sodium formate act as chain transfer agents and stabilizers to effectively control the length of the polymer chain and prevent excessive molecular weight caused by excessive chain growth.

[0028] Example 1 The preparation method of the low molecular weight anionic polyacrylamide provided in this embodiment 1 specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio, add them into a reactor, add urea and sodium formate, and then add deionized water and stir until the components are dissolved to obtain a precursor solution, wherein acrylamide 11%, maleic acid 3%, isopropanol 0.2%, sodium hydroxide 1%, urea 4.5%, sodium formate 0.03%, and the rest is water; Step 2: Control the temperature of the precursor solution within the range of 0-5 °C, and introduce nitrogen into the precursor solution for deoxygenation. The precursor solution can be placed in a tetrafluoroethylene reaction bottle, a magnetic rod is added, the tube mouth is sealed, and the reaction bottle is placed in a 5 °C water bath. Vacuum it, blow nitrogen to deoxygenate, and repeat the cycle 3 times; Step 3: Weigh a certain amount of potassium sulfate, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azobisisobutylimidazoline hydrochloride, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution, wherein the mass of the oxidant accounts for 0.4% of the mass of the precursor solution; the mass of the azo initiator accounts for 0.5% of the mass of the precursor solution; Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2. The oxidant solution and the azo initiator solution can be added to the reaction bottle using a syringe, and the solution temperature is kept within the range of 0 to 5°C to perform an initial polymerization reaction; the initial polymerization reaction time in step 4 is 1 h; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is 8 hours. Dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0029] The low molecular weight anionic polyacrylamide prepared in Example 1 was tested by infrared spectroscopy. The results are as follows: Figure 1 As shown, it can be seen that the obtained product has carboxyl groups. The weight average molecular weight is 635022 as tested by gel permeation chromatography. Figure 2 shown.

[0030] Example 2 The preparation method of low molecular weight anionic polyacrylamide provided in this embodiment 2 specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio, add them into a reactor, add urea and sodium formate, and then add deionized water and stir until the components are dissolved to obtain a precursor solution, wherein acrylamide 12%, maleic acid 8%, isopropanol 0.05%, sodium hydroxide 0.5%, urea 4.5%, sodium formate 0.03%, and the rest is water; Step 2: Control the temperature of the precursor solution within the range of 0-5 °C, and introduce nitrogen into the precursor solution for deoxygenation. The precursor solution can be placed in a tetrafluoroethylene reaction bottle, a magnetic rod is added, the tube mouth is sealed, and the reaction bottle is placed in a 5 °C water bath. Vacuum it, blow nitrogen to deoxygenate, and repeat the cycle 3 times; Step 3: Weigh a certain amount of potassium sulfate, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azobisisobutylimidazoline hydrochloride, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution, wherein the mass of the oxidant accounts for 0.4% of the mass of the precursor solution; the mass of the azo initiator accounts for 1.5% of the mass of the precursor solution; Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2. The oxidant solution and the azo initiator solution can be added to the reaction bottle using a syringe, and the solution temperature is kept within the range of 0 to 5°C to perform an initial polymerization reaction; the initial polymerization reaction time in step 4 is 0.1 h; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is 24 hours. Dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0031] The low molecular weight anionic polyacrylamide prepared in Example 2 was tested by gel permeation chromatography and its weight average molecular weight was 764781. Figure 3 shown.

[0032] Example 3 The preparation method of low molecular weight anionic polyacrylamide provided in this embodiment 3 specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio, add them into a reactor, add urea and sodium formate, and then add deionized water and stir until the components are dissolved to obtain a precursor solution, wherein acrylamide 11.5%, maleic acid 13%, isopropanol 0.1%, sodium hydroxide 0.25%, urea 4.5%, sodium formate 0.03%, and the rest is water; Step 2: Control the temperature of the precursor solution within the range of 0-5 °C, and introduce nitrogen into the precursor solution for deoxygenation. The precursor solution can be placed in a tetrafluoroethylene reaction bottle, a magnetic rod is added, the tube mouth is sealed, and the reaction bottle is placed in a 5 °C water bath. Vacuum it, blow nitrogen to deoxygenate, and repeat the cycle 3 times; Step 3: Weigh a certain amount of potassium sulfate and dissolve it in deionized water, and introduce nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azobisisobutylimidazoline hydrochloride and dissolve it in deionized water, and introduce nitrogen to deoxygenate to obtain an azo initiator solution, wherein the mass of the oxidant accounts for 0.4% of the mass of the precursor solution; the mass of the azo initiator accounts for 1% of the mass of the precursor solution; Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2. The oxidant solution and the azo initiator solution can be added to the reaction bottle using a syringe, and the solution temperature is kept within the range of 0 to 5°C to perform an initial polymerization reaction; the initial polymerization reaction time in step 4 is 0.5 h; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is 0.5h. Dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0033] The low molecular weight anionic polyacrylamide prepared in Example 3 was tested by gel permeation chromatography and its weight average molecular weight was 717998. Figure 4 shown.

[0034] Example 4 The preparation method of low molecular weight anionic polyacrylamide provided in this embodiment 4 specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio, add them into a reactor, add urea and sodium formate, and then add deionized water and stir until the components are dissolved to obtain a precursor solution, wherein acrylamide 12%, maleic acid 5%, isopropanol 0.15%, sodium hydroxide 0.3%, urea 4.5%, sodium formate 0.03%, and the rest is water; Step 2: Control the temperature of the precursor solution within the range of 0-5 °C, and introduce nitrogen into the precursor solution for deoxygenation. The precursor solution can be placed in a tetrafluoroethylene reaction bottle, a magnetic rod is added, the tube mouth is sealed, and the reaction bottle is placed in a 5 °C water bath. Vacuum it, blow nitrogen to deoxygenate, and repeat the cycle 3 times; Step 3: Weigh a certain amount of potassium sulfate, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azobisisobutylimidazoline hydrochloride, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution, wherein the mass of the oxidant accounts for 0.4% of the mass of the precursor solution; the mass of the azo initiator accounts for 1.5% of the mass of the precursor solution; Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2. The oxidant solution and the azo initiator solution can be added to the reaction bottle using a syringe, and the solution temperature is kept within the range of 0 to 5°C to perform an initial polymerization reaction; the initial polymerization reaction time in step 4 is 0.5 h; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is 24 hours. Dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0035] The weight average molecular weight of the low molecular weight anionic polyacrylamide prepared in Example 4 was tested by gel permeation chromatography and was found to be 790817.

[0036] Example 5 The preparation method of low molecular weight anionic polyacrylamide provided in this embodiment 5 specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio, add them into a reactor, add urea and sodium formate, and then add deionized water and stir until the components are dissolved to obtain a precursor solution, wherein acrylamide 11%, maleic acid 9%, isopropanol 0.2%, sodium hydroxide 0.5%, urea 4.5%, sodium formate 0.03%, and the rest is water; Step 2: Control the temperature of the precursor solution within the range of 0-5 °C, and introduce nitrogen into the precursor solution for deoxygenation. The precursor solution can be placed in a tetrafluoroethylene reaction bottle, a magnetic rod is added, the tube mouth is sealed, and the reaction bottle is placed in a 5 °C water bath. Vacuum it, blow nitrogen to deoxygenate, and repeat the cycle 3 times; Step 3: Weigh a certain amount of potassium sulfate and dissolve it in deionized water, and introduce nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azobisisobutylimidazoline hydrochloride and dissolve it in deionized water, and introduce nitrogen to deoxygenate to obtain an azo initiator solution, wherein the mass of the oxidant accounts for 0.4% of the mass of the precursor solution; the mass of the azo initiator accounts for 1% of the mass of the precursor solution; Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2. The oxidant solution and the azo initiator solution can be added to the reaction bottle using a syringe, and the solution temperature is kept within the range of 0 to 5°C to perform a primary polymerization reaction; the primary polymerization reaction time in step 4 is 0.2 h; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is 24 hours. Dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0037] The weight average molecular weight of the low molecular weight anionic polyacrylamide prepared in Example 5 was tested by gel permeation chromatography and was found to be 810946.

[0038] Example 6 The preparation method of low molecular weight anionic polyacrylamide provided in this embodiment 6 specifically comprises the following steps: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio, add them into a reactor, add urea and sodium formate, and then add deionized water and stir until the components are dissolved to obtain a precursor solution, wherein acrylamide 11%, maleic acid 10%, isopropanol 0.05%, sodium hydroxide 1%, urea 4.5%, sodium formate 0.03%, and the rest is water; Step 2: Control the temperature of the precursor solution within the range of 0-5 °C, and introduce nitrogen into the precursor solution for deoxygenation. The precursor solution can be placed in a tetrafluoroethylene reaction bottle, a magnetic rod is added, the tube mouth is sealed, and the reaction bottle is placed in a 5 °C water bath. Vacuum it, blow nitrogen to deoxygenate, and repeat the cycle 3 times; Step 3: Weigh a certain amount of potassium sulfate, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azobisisobutylimidazoline hydrochloride, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution, wherein the mass of the oxidant accounts for 0.4% of the mass of the precursor solution; the mass of the azo initiator accounts for 0.5% of the mass of the precursor solution; Step 4: The oxidant solution and the azo initiator solution in step 3 are sequentially added to the deoxygenated precursor solution obtained in step 2. The oxidant solution and the azo initiator solution can be added to the reaction bottle using a syringe, and the solution temperature is kept within the range of 0 to 5°C to perform an initial polymerization reaction; the initial polymerization reaction time in step 4 is 1 h; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction. The polymerization reaction time in step 5 is 24 hours. Dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

[0039] The weight average molecular weight of the low molecular weight anionic polyacrylamide prepared in Example 6 was tested by gel permeation chromatography and was found to be 706434.

Claims

1. Low molecular weight anionic polyacrylamide, characterized in that: The low molecular weight anionic polyacrylamide structural formula is as follows: Wherein, m represents the number of acrylamide monomers, and n represents the number of maleic acid monomers.

2. The low molecular weight anionic polyacrylamide according to claim 1, characterized in that: The molecular weight of the low molecular weight anionic polyacrylamide is 500,000 to 1,000,000.

3. A method for preparing low molecular weight anionic polyacrylamide, characterized in that: The specific steps include: Step 1: Weigh a certain amount of acrylamide, maleic acid, isopropanol, and sodium hydroxide according to the mass ratio and add them into a reactor, and then add a chain transfer agent and a stabilizer, and then add deionized water and stir until the components are dissolved to obtain a precursor solution; Step 2: controlling the temperature of the precursor solution within a range of 0 to 5° C., and introducing nitrogen into the precursor solution for deoxygenation; Step 3: Weigh a certain amount of oxidant, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an oxidant solution; weigh a certain amount of azo initiator, dissolve it in deionized water, and pass nitrogen to deoxygenate to obtain an azo initiator solution; Step 4: adding the oxidant solution and the azo initiator solution in step 3 to the deoxygenated precursor solution obtained in step 2 in sequence, and maintaining the solution temperature within the range of 0 to 5° C. to carry out a primary polymerization reaction; Step 5: Adjust the temperature of the solution after the initial polymerization reaction to 30°C to continue the polymerization reaction, dry and crush the product after the reaction to obtain low molecular weight anionic polyacrylamide.

4. The method for preparing low molecular weight anionic polyacrylamide according to claim 3, characterized in that: In step 1, the chain transfer agent is urea, and the stabilizer is sodium formate.

5. The method for preparing low molecular weight anionic polyacrylamide according to claim 4, characterized in that: The specific mass ratio of the components in step 1 is: 11% to 12% acrylamide, 3% to 13% maleic acid, 0.05% to 0.2% isopropanol, 0.25% to 1% sodium hydroxide, 4.5% urea, 0.03% sodium formate, and the rest is water.

6. The method for preparing low molecular weight anionic polyacrylamide according to claim 5, characterized in that: In step 3, the oxidant is potassium persulfate, and the mass of the weighed oxidant accounts for 0.4% of the mass of the precursor solution.

7. The method for preparing low molecular weight anionic polyacrylamide according to claim 6, characterized in that: The azo initiator in step 3 is azobisisobutylimidazoline hydrochloride, and the mass of the weighed azo initiator accounts for 0.5% to 1.5% of the mass of the precursor solution.

8. The method for preparing low molecular weight anionic polyacrylamide according to claim 7, characterized in that: The initial polymerization reaction time in step 4 is 0.1 to 1 h.

9. The method for preparing low molecular weight anionic polyacrylamide according to claim 8, characterized in that: The polymerization reaction time in step 5 is 0.5 to 24 h.

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