A method for preparing polyacrylamide with a molecular weight of 26-30 million

Abstract

The present invention relates to the technical field of polyacrylamide, and discloses a preparation method of a 2600-3000 million molecular weight polyacrylamide. The present invention obtains a 2600-3000 million molecular weight polyacrylamide by polymerizing acrylamide, quaternary phosphonium salt modified benzoxazine, and alkenyl quaternary ammonium salt modified phenolic resin. The positive charge of the quaternary phosphonium salt helps to resist the interference of external salts, thereby improving the salt resistance of polyacrylamide; the six-membered ring structure of benzoxazine is not easily deformed or decomposed at high temperatures, thereby improving the high temperature resistance of polyacrylamide; the quaternary ammonium salt has both hydrophilicity and hydrophobicity, and when salt is present in the solution, the hydrophobic groups of the quaternary ammonium salt will gather together to form micelles or vesicles, thereby reducing the contact area with water molecules and reducing the influence of salt; the benzene ring and three-dimensional network structure in the phenolic resin improve the high temperature resistance of polyacrylamide; the hyperbranched structure in the polyacrylamide weakens the shielding effect of small molecule electrolytes on the charges carried by the polymer, thereby improving the salt resistance of polyacrylamide.

Description

Technical Field

[0001] The invention relates to the technical field of polyacrylamide, in particular to a method for preparing polyacrylamide with a molecular weight of 26-30 million. Background Art

[0002] Polyacrylamide is a high molecular polymer generated by the polymerization of acrylamide monomers. Ultra-high molecular weight polyacrylamide is widely used as an oil displacement agent in oil production. It can reduce the water-oil mobility ratio, reduce water fingering, and adjust the rheology of water to improve the sweep index of the oil displacement agent, thereby improving the recovery rate of the oil layer. However, there are still many problems when polyacrylamide commonly used in oil production is used for oil displacement, such as severe hydrolysis of polyacrylamide at high temperature and poor salt resistance. Therefore, how to avoid this phenomenon is the key to solving the problem. For example, patent CN105778878B discloses a degradable polyacrylamide oil displacement agent and a preparation method thereof, which solves the problem of environmental pollution caused by the discharge of oil produced water, has the characteristics of environmental protection and cost reduction, but its high temperature resistance and salt resistance need to be improved. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] In view of the deficiencies of the prior art, the present invention provides a method for preparing polyacrylamide with a molecular weight of 26-30 million, which has good high temperature resistance and salt resistance.

[0005] (II) Technical solution

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing polyacrylamide with a molecular weight of 26 million to 30 million, the method for preparing polyacrylamide with a molecular weight of 26 million to 30 million comprising the following steps:

[0007] (1) adding 4-7 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stirring to dissolve, heating to 115-120° C., dissolving 6-8 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, and then dropwise adding to 3-chlorophenol, reflux and react at a constant temperature for 10-14 hours, cooling after the reaction, and distilling under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt;

[0008] (2) adding 3-6 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 4-8 parts by weight of acrylamide, and 7-12 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating and reacting for 4-6 hours, cooling after the reaction, washing and drying to obtain a quaternary phosphonium salt modified benzoxazine;

[0009] (3) Add deionized water to deionized water, stir at 8-15°C for 45-50 minutes to fully dissolve the deionized water, dropwise add 2-chloro-3,4-epoxy-1-butene to the deionized water, heat to 20-25°C to react for 2-3 hours, then heat to 30-35°C to continue reacting for 1.5-2.5 hours. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1;

[0010] (4) Add 7-9 parts by weight of phenolic resin to n-butanol solvent, heat to 58-62° C., stir to dissolve, add 0.3-0.6 parts by weight of catalyst, stir at 78-80° C. for 40-60 min, cool to 35-40° C., dropwise add 2-4 parts by weight of intermediate 1, heat to 80-85° C. and react for 4-6 h after the reaction, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin;

[0011] (5) 5-8 parts by weight of acrylamide, 10-14 parts by weight of quaternary phosphonium salt-modified benzoxazine, 9-12 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.3-0.5 parts by weight of azo initiator are added to deionized water, stirred and dissolved at 25-30° C., nitrogen is introduced to drive out oxygen for 8-10 minutes, 0.2-0.5 parts by weight of oxidant is added, nitrogen is continued to be introduced for 5-8 minutes, 0.4-0.6 parts by weight of reducing agent is added, nitrogen is stopped after 3-5 minutes, and the polymerization reaction is carried out in a closed manner for 4-5 hours. After the reaction is completed, polyacrylamide with a molecular weight of 26-30 million is obtained.

[0012] Preferably, the dripping speed of triphenylphosphine in (1) is 12-15 drops / min.

[0013] Preferably, the reaction temperature in (2) is 82-90°C.

[0014] Preferably, the mass ratio of dodecyltrimethylammonium chloride to 2-chloro-3,4-epoxy-1-butene in (3) is 1:1.04-1.08.

[0015] Preferably, the catalyst in (4) is potassium hydroxide.

[0016] Preferably, in (5), the azo initiator is azoisobutylcyanamide, the oxidant is ammonium persulfate, and the reducing agent is sodium bisulfite.

[0017] 3. Beneficial technical effects

[0018] The invention obtains polyacrylamide with a molecular weight of 26-30 million by mixing acrylamide, quaternary phosphonium salt modified benzoxazine and alkenyl quaternary ammonium salt modified phenolic resin, and polymerizing them under the action of an azo initiator, an oxidant and a reducing agent.

[0019] 3-Chlorophenol and triphenylphosphine undergo quaternization reaction to obtain phenolic hydroxyl quaternary phosphonium salt, phenolic hydroxyl quaternary phosphonium salt undergoes condensation reaction with acrylamide and polyformaldehyde to obtain quaternary phosphonium salt modified benzoxazine and introduce alkenyl group, quaternary ammonium salt group in decanyltrimethylammonium chloride attacks epoxy group in 2-chloro-3,4-epoxy-1-butene to undergo ring-opening reaction to obtain intermediate 1 and introduce chlorine and alkenyl group, chlorine in intermediate 1 undergoes substitution reaction with hydroxyl group in phenolic resin to obtain alkenyl quaternary ammonium salt modified phenolic resin, acrylamide, quaternary phosphonium salt modified benzoxazine and alkenyl quaternary ammonium salt modified phenolic resin undergo polymerization reaction to obtain 26-30 million molecular weight polyacrylamide.

[0020] The positive charge of quaternary phosphonium salt forms a positively charged ion atmosphere in water, which helps to resist the interference of external salt. Since charges of the same kind repel each other, the interaction between quaternary phosphonium salt ions is enhanced, so that it can still maintain a stable state in a high-salinity environment, improving the salt resistance of polyacrylamide. The bond energy between the phosphorus atom and the carbon atom is relatively high, which makes the quaternary phosphonium salt difficult to decompose at high temperatures; the oxazine ring in the benzoxazine molecule increases the rigidity of the molecule through its six-membered ring structure. This rigid structure is not easy to deform or decompose at high temperatures, thereby improving the high temperature resistance of polyacrylamide; the nitrogen atom in the quaternary ammonium salt molecule carries a positive charge, and the alkyl group connected to the nitrogen provides hydrophobicity. This structure makes the quaternary ammonium salt both hydrophilic and hydrophilic in aqueous solution. The hydrophobicity and hydrophobicity of quaternary ammonium salts are good. When there is a large amount of salt in the solution, the hydrophobic groups of quaternary ammonium salts tend to gather together to form structures such as micelles or vesicles, reducing the contact area with water molecules and reducing the impact of salt on polyacrylamide. The large number of benzene rings and highly cross-linked three-dimensional network structure in phenolic resin further improve the high temperature resistance of polyacrylamide. The 26-30 million molecular weight polyacrylamide synthesized from acrylamide, quaternary phosphonium salt-modified benzoxazine, and alkenyl quaternary ammonium salt-modified phenolic resin has a hyperbranched structure. The network structure it forms in the solution weakens the shielding effect of small molecule electrolytes on the charge carried by the polymer molecular chain to a certain extent, reduces the curling degree of the molecular chain, and thus improves the salt resistance of polyacrylamide. DETAILED DESCRIPTION Example 1

[0021] (1) Add 4 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stir to dissolve, heat to 115°C, dissolve 6 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, then add dropwise to 3-chlorophenol at a rate of 12 drops / min, reflux and react at constant temperature for 10 hours. After the reaction is completed, cool and distill under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt;

[0022] (2) adding 3 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 4 parts by weight of acrylamide, and 7 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating to 82° C. to react for 4 hours, and after the reaction is completed, cooling, washing, and drying to obtain a quaternary phosphonium salt-modified benzoxazine;

[0023] (3) Add deionized water with trimethyl ammonium chloride, stir at 8°C for 45 min to fully dissolve the trimethyl ammonium chloride, add 2-chloro-3,4-epoxy-1-butene dropwise into the trimethyl ammonium chloride, wherein the mass ratio of trimethyl ammonium chloride to 2-chloro-3,4-epoxy-1-butene is 1:1.04, heat to 20°C and react for 2 h, then heat to 30°C and continue to react for 1.5 h. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1;

[0024] (4) Add 7 parts by weight of phenolic resin to n-butanol solvent, heat to 58° C., stir to dissolve, add 0.3 parts by weight of potassium hydroxide catalyst, stir at 78° C. for 40 min, cool to 35° C., dropwise add 2 parts by weight of intermediate 1, heat to 80° C. and react for 4 h, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin;

[0025] (5) 5 parts by weight of acrylamide, 10 parts by weight of quaternary phosphonium salt-modified benzoxazine, 9 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.3 parts by weight of azoisobutylcyanamide are added to deionized water, stirred and dissolved at 25° C., nitrogen is introduced to drive out oxygen for 8 minutes, 0.2 parts by weight of ammonium persulfate is added, nitrogen is continued to be introduced for 5-8 minutes, 0.4 parts by weight of sodium bisulfite is added, nitrogen is stopped after 3 minutes, and the polymerization reaction is carried out in a closed manner for 4 hours. After the reaction is completed, polyacrylamide with a molecular weight of 26-30 million is obtained. Example 2

[0026] (1) adding 7 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stirring to dissolve, heating to 120°C, dissolving 8 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, and then adding dropwise to 3-chlorophenol at a rate of 15 drops / min, reflux and react at a constant temperature for 14 hours, cooling after the reaction, and distilling under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt;

[0027] (2) adding 6 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 8 parts by weight of acrylamide, and 12 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating to 90° C. to react for 6 hours, and after the reaction is completed, cooling, washing and drying to obtain a quaternary phosphonium salt-modified benzoxazine;

[0028] (3) Add deionized water with trimethyl ammonium chloride, stir at 15°C for 50 min to fully dissolve the trimethyl ammonium chloride, add 2-chloro-3,4-epoxy-1-butene dropwise into the trimethyl ammonium chloride, wherein the mass ratio of trimethyl ammonium chloride to 2-chloro-3,4-epoxy-1-butene is 1:1.08, heat to 25°C and react for 3 h, then heat to 35°C and continue to react for 2.5 h. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1;

[0029] (4) Add 9 parts by weight of phenolic resin to n-butanol solvent, heat to 62° C., stir to dissolve, add 0.6 parts by weight of potassium hydroxide catalyst, stir at 80° C. for 60 min, cool to 40° C., dropwise add 4 parts by weight of intermediate 1, heat to 85° C. and react for 6 h. After the reaction, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin;

[0030] (5) 8 parts by weight of acrylamide, 14 parts by weight of quaternary phosphonium salt-modified benzoxazine, 12 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.5 parts by weight of azoisobutylcyanamide are added to deionized water, stirred and dissolved at 30° C., nitrogen is introduced to drive out oxygen for 10 minutes, 0.5 parts by weight of ammonium persulfate is added, nitrogen is continued to be introduced for 8 minutes, 0.6 parts by weight of sodium bisulfite is added, nitrogen is stopped after 5 minutes, and the polymerization reaction is carried out in a closed manner for 5 hours. After the reaction is completed, polyacrylamide with a molecular weight of 26-30 million is obtained. Example 3

[0031] (1) Add 5 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stir and dissolve, heat to 118°C, dissolve 7 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, then add dropwise to 3-chlorophenol at a rate of 13 drops / min, reflux and react at constant temperature for 12 hours, cool after the reaction, and distill under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt;

[0032] (2) adding 4 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 6 parts by weight of acrylamide, and 9 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating to 86° C. to react for 5 hours, and after the reaction is completed, cooling, washing, and drying to obtain a quaternary phosphonium salt-modified benzoxazine;

[0033] (3) Add deionized water with trimethyl ammonium chloride, stir at 12°C for 48 minutes to fully dissolve the trimethyl ammonium chloride, add 2-chloro-3,4-epoxy-1-butene dropwise to the trimethyl ammonium chloride, wherein the mass ratio of trimethyl ammonium chloride to 2-chloro-3,4-epoxy-1-butene is 1:1.06, heat to 23°C and react for 2.5 hours, then heat to 32°C and continue to react for 2 hours. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1;

[0034] (4) Add 8 parts by weight of phenolic resin to n-butanol solvent, heat to 60° C., stir to dissolve, add 0.4 parts by weight of potassium hydroxide catalyst, stir at 79° C. for 50 min, cool to 38° C., dropwise add 3 parts by weight of intermediate 1, heat to 82° C. and react for 5 h. After the reaction, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin;

[0035] (5) 6 parts by weight of acrylamide, 12 parts by weight of quaternary phosphonium salt-modified benzoxazine, 11 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.4 parts by weight of azoisobutylcyanamide were added to deionized water, stirred and dissolved at 28°C, and nitrogen was introduced to drive out oxygen for 9 minutes. Then, 0.3 parts by weight of ammonium persulfate was added, and nitrogen was continued to be introduced for 6 minutes. Then, 0.5 parts by weight of sodium bisulfite was added, and nitrogen was stopped after 4 minutes. The closed polymerization reaction was carried out for 4.5 hours. After the reaction was completed, polyacrylamide with a molecular weight of 26-30 million was obtained. Example 4

[0036] (1) Add 4 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stir to dissolve, heat to 115°C, dissolve 6 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, then add dropwise to 3-chlorophenol at a rate of 12 drops / min, reflux and react at constant temperature for 10 hours. After the reaction is completed, cool and distill under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt;

[0037] (2) adding 3 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 4 parts by weight of acrylamide, and 7 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating to 82° C. to react for 4 hours, and after the reaction is completed, cooling, washing, and drying to obtain a quaternary phosphonium salt-modified benzoxazine;

[0038] (3) Add deionized water with trimethyl ammonium chloride, stir at 15°C for 50 min to fully dissolve the trimethyl ammonium chloride, add 2-chloro-3,4-epoxy-1-butene dropwise into the trimethyl ammonium chloride, wherein the mass ratio of trimethyl ammonium chloride to 2-chloro-3,4-epoxy-1-butene is 1:1.08, heat to 25°C and react for 3 h, then heat to 35°C and continue to react for 2.5 h. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1;

[0039] (4) Add 9 parts by weight of phenolic resin to n-butanol solvent, heat to 62° C., stir to dissolve, add 0.6 parts by weight of potassium hydroxide catalyst, stir at 80° C. for 60 min, cool to 40° C., dropwise add 4 parts by weight of intermediate 1, heat to 85° C. and react for 6 h. After the reaction, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin;

[0040] (5) 6 parts by weight of acrylamide, 12 parts by weight of quaternary phosphonium salt-modified benzoxazine, 11 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.4 parts by weight of azoisobutylcyanamide were added to deionized water, stirred and dissolved at 28°C, and nitrogen was introduced to drive out oxygen for 9 minutes. Then, 0.3 parts by weight of ammonium persulfate was added, and nitrogen was continued to be introduced for 6 minutes. Then, 0.5 parts by weight of sodium bisulfite was added, and nitrogen was stopped after 4 minutes. The closed polymerization reaction was carried out for 4.5 hours. After the reaction was completed, polyacrylamide with a molecular weight of 26-30 million was obtained. Example 5

[0041] (1) Add 5 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stir and dissolve, heat to 118°C, dissolve 7 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, then add dropwise to 3-chlorophenol at a rate of 13 drops / min, reflux and react at constant temperature for 12 hours, cool after the reaction, and distill under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt;

[0042] (2) adding 4 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 6 parts by weight of acrylamide, and 9 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating to 86° C. to react for 5 hours, and after the reaction is completed, cooling, washing, and drying to obtain a quaternary phosphonium salt-modified benzoxazine;

[0043] (3) Add deionized water with trimethyl ammonium chloride, stir at 8°C for 45 min to fully dissolve the trimethyl ammonium chloride, add 2-chloro-3,4-epoxy-1-butene dropwise into the trimethyl ammonium chloride, wherein the mass ratio of trimethyl ammonium chloride to 2-chloro-3,4-epoxy-1-butene is 1:1.04, heat to 20°C and react for 2 h, then heat to 30°C and continue to react for 1.5 h. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1;

[0044] (4) Add 7 parts by weight of phenolic resin to n-butanol solvent, heat to 58° C., stir to dissolve, add 0.3 parts by weight of potassium hydroxide catalyst, stir at 78° C. for 40 min, cool to 35° C., dropwise add 2 parts by weight of intermediate 1, heat to 80° C. and react for 4 h, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin;

[0045] (5) 8 parts by weight of acrylamide, 14 parts by weight of quaternary phosphonium salt-modified benzoxazine, 12 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.5 parts by weight of azoisobutylcyanamide are added to deionized water, stirred and dissolved at 30° C., nitrogen is introduced to drive out oxygen for 10 minutes, 0.5 parts by weight of ammonium persulfate is added, nitrogen is continued to be introduced for 8 minutes, 0.6 parts by weight of sodium bisulfite is added, nitrogen is stopped after 5 minutes, and the polymerization reaction is carried out in a closed manner for 5 hours. After the reaction is completed, polyacrylamide with a molecular weight of 26-30 million is obtained.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 5 is that no quaternary phosphonium salt-modified benzoxazine is added.

[0048] Comparative Example 2

[0049] The difference between this comparative example and Example 5 is that no alkenyl quaternary ammonium salt-modified phenolic resin is added.

[0050] Sodium chloride, calcium chloride, magnesium chloride and deionized water were mixed to prepare brine with a mineralization degree of 5000 mg / L. Polyacrylamide with a molecular weight of 26-30 million was dissolved in the brine to prepare a polymer solution with a concentration of 1800 mg / L. The apparent viscosity was tested at different temperatures. The results are shown in Table 1.

[0051] Table 1: Apparent viscosity test.

[0052]

[0053] It can be seen from Table 1 that, compared with Comparative Examples 1-2, Examples 1-5 of the present invention still have higher apparent viscosity at high temperatures and have better high temperature resistance.

[0054] Sodium chloride, calcium chloride, magnesium chloride and deionized water were mixed to prepare brine with different mineralization degrees. Polyacrylamide with a molecular weight of 26-30 million was dissolved in the brine to prepare a polymer solution with a concentration of 1800 mg / L. The apparent viscosity was tested at 70°C. The results are shown in Table 2.

[0055] Table 2: Apparent viscosity test.

[0056]

[0057] As can be seen from Table 2, compared with Comparative Examples 1-2, Examples 1-5 of the present invention still have higher apparent viscosity at high mineralization and have better salt resistance effect.

[0058] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing polyacrylamide with a molecular weight of 26-30 million, characterized in that: The preparation method of the 26-30 million molecular weight polyacrylamide comprises the following steps: (1) adding 4-7 parts by weight of 3-chlorophenol to N,N-dimethylformamide solvent, stirring to dissolve, heating to 115-120° C., dissolving 6-8 parts by weight of triphenylphosphine in N,N-dimethylformamide solvent, and then dropwise adding to 3-chlorophenol, reflux and react at a constant temperature for 10-14 hours, cooling after the reaction, and distilling under reduced pressure to obtain phenolic hydroxyl quaternary phosphonium salt; (2) adding 3-6 parts by weight of phenolic hydroxyl quaternary phosphonium salt, 4-8 parts by weight of acrylamide, and 7-12 parts by weight of polyformaldehyde to a toluene solvent, stirring and mixing, heating and reacting for 4-6 hours, cooling after the reaction, washing and drying to obtain a quaternary phosphonium salt modified benzoxazine; (3) Add deionized water to deionized water, stir at 8-15°C for 45-50 minutes to fully dissolve the deionized water, dropwise add 2-chloro-3,4-epoxy-1-butene to the deionized water, heat to 20-25°C to react for 2-3 hours, then heat to 30-35°C to continue reacting for 1.5-2.5 hours. After the reaction is completed, cool and distill at atmospheric pressure to obtain intermediate 1; (4) Add 7-9 parts by weight of phenolic resin to n-butanol solvent, heat to 58-62° C., stir to dissolve, add 0.3-0.6 parts by weight of catalyst, stir at 78-80° C. for 40-60 min, cool to 35-40° C., dropwise add 2-4 parts by weight of intermediate 1, heat to 80-85° C. and react for 4-6 h after the reaction, cool, filter and rotary evaporate to obtain alkenyl quaternary ammonium salt modified phenolic resin; (5) 5-8 parts by weight of acrylamide, 10-14 parts by weight of quaternary phosphonium salt-modified benzoxazine, 9-12 parts by weight of alkenyl quaternary ammonium salt-modified phenolic resin, and 0.3-0.5 parts by weight of azo initiator are added to deionized water, stirred and dissolved at 25-30° C., nitrogen is introduced to drive out oxygen for 8-10 minutes, 0.2-0.5 parts by weight of oxidant is added, nitrogen is continued to be introduced for 5-8 minutes, 0.4-0.6 parts by weight of reducing agent is added, nitrogen is stopped after 3-5 minutes, and the polymerization reaction is carried out in a closed manner for 4-5 hours. After the reaction is completed, polyacrylamide with a molecular weight of 26-30 million is obtained.

2. The method for preparing the 26-30 million molecular weight polyacrylamide according to claim 1, characterized in that: The dripping speed of triphenylphosphine in (1) is 12-15 drops / min.

3. The method for preparing the 26-30 million molecular weight polyacrylamide according to claim 1, characterized in that: The reaction temperature in (2) is 82-90°C.

4. The method for preparing the 26-30 million molecular weight polyacrylamide according to claim 1, characterized in that: The mass ratio of dodecyltrimethylammonium chloride to 2-chloro-3,4-epoxy-1-butene in (3) is 1:1.04-1.

08.

5. The method for preparing the 26-30 million molecular weight polyacrylamide according to claim 1, characterized in that: The catalyst in (4) is potassium hydroxide.

6. The method for preparing the 26-30 million molecular weight polyacrylamide according to claim 1, characterized in that: In the above (5), the azo initiator is azoisobutylcyanamide, the oxidant is ammonium persulfate, and the reducing agent is sodium bisulfite.

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