A polyacrylamide, its preparation method and use

Abstract

This invention relates to the field of oilfield chemical technology, specifically disclosing a polyacrylamide, its preparation method, and its application. The method involves mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, modified monomer b, additives, and a solvent in a mixture reaction. This polyacrylamide, through linear inclusion self-assembly, forms a cross-linked structure after dissolving in brine, effectively improving its viscosity in brine, its viscosity after high-temperature shearing, and its sand-carrying capacity.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical technology, specifically to a polyacrylamide, its preparation method, and its application. Background Technology

[0002] Hydraulic fracturing is a core technology for enhancing the production of low-permeability, tight oil and gas reservoirs. It involves pumping high-pressure fracturing fluid into the formation to create artificial fractures that carry proppant, thereby increasing formation permeability and ensuring oil and gas production. Anionic polyacrylamide (APAM) has become a widely used thickener in fracturing fluids due to its excellent thickening, drag-reducing, and proppant-carrying properties, as well as its low cost and ease of preparation.

[0003] As oil and gas development extends to complex reservoirs, the technical challenges arising from the need for high-salinity formations and the reuse of fracturing flowback fluids are becoming increasingly prominent. Traditional anionic polyacrylamide has poor salt resistance, particularly in formation water and flowback fluids containing sodium. + Ca 2+ Mg 2+ Under the action of plasma, the double electric layer of molecular chains is compressed, making them prone to curling and entanglement, which leads to a sharp reduction in thickening ability. The solution viscosity retention rate can drop to below 50%, affecting the sand carrying effect.

[0004] In view of this, there is an urgent need to provide a polyacrylamide that can maintain high performance in highly saline solutions. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low viscosity of polyacrylamide in high-salinity brine, poor resistance to high-temperature shear, and poor sand-carrying capacity in the prior art. This invention provides a polyacrylamide, its preparation method, and its application. This polyacrylamide has high viscosity in high-salinity brine, high viscosity after high-temperature shear, and good sand-carrying capacity.

[0006] The first aspect of this invention provides a polyacrylamide, wherein the raw materials for preparing the polyacrylamide contain: acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a shown in Formula I, and modified monomer b shown in Formula II. Formula I, Formula II, Where R is a C2-C6 alkyl group, m is an integer between 3 and 7, and n is an integer between 6 and 8.

[0007] Further, the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a and modified monomer b is 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048.

[0008] Furthermore, the molar ratio of the modified monomer a to the modified monomer b is 1:0.38-0.52.

[0009] The second aspect of the present invention provides a method for preparing polyacrylamide, the method comprising: mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a shown in Formula I, modified monomer b shown in Formula II, alkali I, surfactant, catalyst and solvent to carry out a polymerization reaction; Formula I, Formula II, Where R is a C2-C6 alkyl group, m is an integer between 3 and 7, and n is an integer between 6 and 8.

[0010] Furthermore, the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, and modified monomer b is 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048.

[0011] Furthermore, the molar ratio of the modified monomer a to the modified monomer b is 1:0.38-0.52.

[0012] Furthermore, the preparation steps of the modified monomer a include: a1) A glycol compound is reacted with base II and toluenesulfonyl chloride in a contact reaction I to obtain reaction product I, wherein the glycol compound is selected from at least one of hexaethylene glycol, heptaethylene glycol, octaethylene glycol, nonaethylene glycol and decaethylene glycol; a2) The reaction product I, 3,4-dihydroxy-2-methylbenzoate, and alkali metal carbonate are heated under reflux I to obtain reaction product II; a3) The reaction product II and the reducing agent I are subjected to contact reaction II to obtain reaction product III; a4) The reaction product III is reacted with triethylamine and acryloyl chloride in a contact reaction III.

[0013] Furthermore, the alkali II is sodium hydroxide and / or potassium hydroxide, the alkali metal carbonate is potassium carbonate, the reducing agent I is lithium aluminum hydride, and the conditions for the contact reaction III include: a temperature of 2-6°C and a time of 8-12 h.

[0014] Furthermore, the preparation steps of the modified monomer b include: b1) The diol and HBr are heated under reflux II to obtain reaction product A, wherein the diol is a C6-C10 straight-chain diol; b2) The reaction product A is reacted with 4-hydroxybenzaldehyde and an alkali metal salt of carbonate in a contact reaction IV to obtain reaction product B; b3) The reaction product B and the alkylamine are heated and then reacted with reducing agent II in a contact reaction V to obtain reaction product C, wherein the alkylamine is a C8-C10 alkylamine; b4) The reaction product C and NH4PF6 are subjected to a contact reaction VI to obtain reaction product D; b5) The reaction product D is reacted with triethylamine and acryloyl chloride in a contact reaction VII.

[0015] Furthermore, the alkali metal carbonate is potassium carbonate, the reducing agent II is NaBH4, the conditions for contact reaction IV include: a temperature of 85-95℃ and a time of 4-6h; the conditions for the heating reaction include: a temperature of 65-75℃ and a time of 10-14h; and the conditions for contact reaction VII include: a temperature of 2-6℃ and a time of 8-12h.

[0016] Furthermore, the base I is sodium hydroxide, the surfactant is a nonionic surfactant, and the catalyst contains an initiator, an oxidant, a reducing agent, a chain transfer agent, and a complexing agent.

[0017] Furthermore, the nonionic surfactant is nonylphenol polyoxyethylene ether.

[0018] Furthermore, the initiator is 2,2'-azobisisobutyramidine dihydrochloride, the reducing agent is ferrous ammonium sulfate, and the oxidizing agent is tert-butyl hydroperoxide.

[0019] Furthermore, the chain transfer agent is sodium hypophosphite, and the complexing agent is diethyltriaminepentaacetic acid pentasodium.

[0020] Further, based on the theoretical yield of the polyacrylamide, the amount of alkali I added is 7-10.5 wt%, the amount of surfactant added is 20-30 ppm, the amount of initiator added is 90-1100 ppm, the amount of reducing agent added is 4-13 ppm, the amount of oxidizing agent added is 4-13 ppm, the amount of chain transfer agent added is 8-130 ppm, and the amount of complexing agent added is 40-85 ppm.

[0021] Further, the mixing step includes: first mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, modified monomer b, base I, surfactant and solvent to obtain mixture I, and then mixing mixture I with catalyst in an inert gas atmosphere.

[0022] A third aspect of the present invention provides a polyacrylamide prepared by the above-described preparation method.

[0023] A fourth aspect of the present invention provides the application of the above-mentioned polyacrylamide in oilfield thickeners.

[0024] Compared with the prior art, the present invention has the following advantages: The polyacrylamide provided by this invention forms a cross-linking-like effect through the linear inclusion self-assembly of modified monomer a and modified monomer b, which significantly improves the viscosity, high-temperature shear viscosity and sand-carrying capacity of the polyacrylamide in high-mineralization brine. Attached Figure Description

[0025] Figure 1 This is a diagram illustrating the reaction mechanism of the present invention. Figure 2 The viscosity of the examples and comparative examples in brine; Figure 3 The viscosity after high-temperature shearing is shown in the examples and comparative examples; Figure 4 The sand-carrying performance is shown in the examples and comparative examples. Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this document.

[0027] As previously stated, the first aspect of this invention provides a polyacrylamide, wherein the raw materials for preparing the polyacrylamide contain: acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a shown in Formula I, and modified monomer b shown in Formula II. Formula I, Formula II, Where R is a C2-C6 alkyl group, m is an integer between 3 and 7, and n is an integer between 6 and 8.

[0028] The inventor discovered during the research process that, see Figure 1By adding structural units formed by modified monomer a as shown in Formula I and modified monomer b as shown in Formula II to anionic polyacrylamide containing acrylic acid structure and 2-acrylamido-2-methylpropanesulfonic acid structure, the cross-linking-like effect generated by the linear inclusion self-assembly between the two structural units can significantly improve the viscosity, high-temperature shear viscosity and sand carrying capacity of the polyacrylamide in high-salinity brine.

[0029] According to the present invention, R can be ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, 2,2-dimethylpropyl, n-hexyl, or isohexyl. m can be 3, 4, 5, 6, or 7, and n can be 6, 7, or 8. Preferably, R is a C3-C5 alkyl group, m is an integer between 5 and 6, and n is 6 or 8.

[0030] Preferably, the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, and modified monomer b is 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048. Controlling the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, and modified monomer b to 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048 can further enhance the interaction between the structural units formed by modified monomer a and modified monomer b in polyacrylamide, thereby further improving the viscosity, high-temperature shear viscosity, and sand-carrying capacity of polyacrylamide in high-salinity brine. Considering the need to further enhance the interaction between the structural units formed by modified monomer a and modified monomer b in polyacrylamide, and thus further improve the viscosity, high-temperature shear viscosity, and sand-carrying capacity of polyacrylamide in high-mineralization brine, it is further preferred that the molar ratio of modified monomer a to modified monomer b is 1:0.38-0.52.

[0031] Furthermore, a second aspect of the present invention provides a method for preparing polyacrylamide, the method comprising: mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a shown in Formula I, modified monomer b shown in Formula II, alkali I, surfactant, catalyst and solvent to carry out a polymerization reaction; Formula I, Formula II, Where R is a C2-C6 alkyl group, m is an integer between 3 and 7, and n is an integer between 6 and 8.

[0032] Studies have found that when acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a (Formula I), modified monomer b (Formula II), alkali I, surfactant, catalyst, and solvent are mixed and polymerized, structural units formed by modified monomer a and modified monomer b are added to anionic polyacrylamide containing acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid structures. A crosslinking-like effect is generated through the linear inclusion self-assembly between the two structural units (see...). Figure 1 This can significantly improve the viscosity of the anionic polyacrylamide in high-salinity brine, its viscosity after high-temperature shearing, and its sand-carrying capacity.

[0033] Preferably, the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, and modified monomer b is 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048. Controlling the molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, and modified monomer b to 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048 can further enhance the interaction between the structural units formed by modified monomer a and modified monomer b in polyacrylamide, thereby further improving the viscosity, high-temperature shear viscosity, and sand-carrying capacity of polyacrylamide in high-salinity brine. Considering the need to further enhance the interaction between the structural units formed by modified monomer a and modified monomer b in polyacrylamide, and thus further improve the viscosity, high-temperature shear viscosity, and sand-carrying capacity of polyacrylamide in high-mineralization brine, it is further preferred that the molar ratio of modified monomer a to modified monomer b is 1:0.38-0.52.

[0034] Preferably, the preparation steps of the modified monomer a include: a1) A glycol compound is reacted with base II and toluenesulfonyl chloride in a contact reaction I to obtain reaction product I, wherein base II can be sodium hydroxide and / or potassium hydroxide, and the glycol compound is selected from at least one of hexaethylene glycol (CAS No.: 2615-15-8), heptaethylene glycol (CAS No.: 5617-32-3), octaethylene glycol (CAS No.: 5117-19-1), nonaethylene glycol (CAS No.: 3386-18-3) and decaethylene glycol (CAS No.: 5579-66-8), preferably heptaethylene glycol and / or octaethylene glycol; a2) The reaction product I, 3,4-dihydroxy-2-methylbenzoate, and alkali metal carbonate are heated under reflux I to obtain reaction product II; the alkali metal carbonate may be potassium carbonate. a3) The reaction product II and the reducing agent I are subjected to contact reaction II to obtain reaction product III; a4) The reaction product III is reacted with triethylamine and acryloyl chloride in a contact reaction III. The modified monomer a prepared by the above method has high purity and yield.

[0035] According to the present invention, the reaction that occurs in step a1) is: HO-(CH2CH2O) (m+2) -CH2CH2OH + 2 TsCl + 2 NaOH → TsO-(CH2CH2O) (m+2) -CH2CH2OTs + 2 NaCl + 2 H2O‌; (Where, Ts = p-toluenesulfonyl, i.e., p-CH3C6H4SO2—).

[0036] To further improve the reaction effect of glycol compounds with base II and toluenesulfonyl chloride, preferably, in step a1), the contact reaction I of glycol compounds with base II and toluenesulfonyl chloride includes: adding a solution containing toluenesulfonyl chloride dropwise to a mixed solution containing glycol compounds and base II under stirring conditions, followed by continued stirring. More preferably, the continued stirring time is 44-52 hours, and the temperature is 15-30°C.

[0037] Preferably, the solvent for the solution containing toluenesulfonyl chloride can be tetrahydrofuran (THF), and the preparation method of the mixed solution containing glycol compounds and base II includes: dissolving the glycol compound in an organic solvent, then stirring at 0°C to obtain a solution containing glycol organic compounds; dissolving base II in water, cooling to 20-25°C, and then mixing it with the solution containing glycol organic compounds. More preferably, the organic solvent can be tetrahydrofuran.

[0038] Preferably, the mass ratio of the glycol compound, base II, and toluenesulfonyl chloride is 45-55:22-26:58.

[0039] Preferably, step a1) further includes: adding water to the mixture obtained from contact reaction I, evaporating the mixture to remove most of the organic solvent (such as THF), then adding dichloromethane to the mixture for extraction, and purifying the extracted organic phase. More preferably, the method for evaporating the mixture is rotary evaporation.

[0040] Preferably, the purification process includes washing and purifying the organic phase to remove impurities and organic solvents. More preferably, the washing agent used is water and a saturated sodium chloride solution.

[0041] Preferably, in step a2), the step of heating the reaction product I, 3,4-dihydroxy-2-methylbenzoate, and potassium carbonate under reflux I comprises: heating the reaction product I, 3,4-dihydroxy-2-methylbenzoate, potassium carbonate, and acetonitrile under reflux I in an inert gas atmosphere and with stirring. Preferably, the conditions for heating under reflux I include: a temperature of 85-90°C and a time of 56-78 hours.

[0042] Preferably, step a2) further includes: cooling the distillate obtained by heating and reflux I, filtering it, then evaporating to remove acetonitrile, adding chloroform for extraction, and washing and purifying the extracted organic phase. Preferably, the washing agent used is a saturated sodium chloride solution. Preferably, step a2) further includes: drying the washed organic phase.

[0043] Preferably, the mass ratio of reaction product I, 3,4-dihydroxy-2-methylbenzoate, and potassium carbonate is 36:10-11:25-26.

[0044] Preferably, the step of contacting the reaction product II and the reducing agent I in reaction II includes: adding the reducing agent I in batches to the solution containing the reaction product II and then continuing to stir. Preferably, the stirring time is 10-14 hours. Preferably, the solvent in the solution containing the reaction product II is THF. Preferably, the reducing agent I is added to the solution containing the reaction product II in 3-5 portions.

[0045] Preferably, step a3) further includes: after the contact reaction II is completed, adding water and sodium hydroxide aqueous solution to the mixed system to quench the reaction.

[0046] Preferably, the mass ratio of reaction product II to reducing agent I is 15:1.2-1.5.

[0047] Preferably, the step of contacting reaction product III with triethylamine and acryloyl chloride in reaction III comprises: adding a solution containing acryloyl chloride dropwise to a mixed solution containing reaction product III and triethylamine under a nitrogen atmosphere and stirring conditions, and continuing the reaction at a temperature of 2-6°C for 8-12 hours. Preferably, the solvent used in the solution containing acryloyl chloride and the mixed solution containing reaction product III and triethylamine can be toluene.

[0048] Preferably, the mass ratio of the reaction product III, triethylamine, and acryloyl chloride is 9-10:3.2-3.8:0.2.

[0049] Preferably, step a4) further includes: after the reaction is complete, immersing and washing the product in acetone, separating the solid and liquid, and then drying it.

[0050] Preferably, the preparation steps of the modified monomer b include: b1) The diol and HBr are heated under reflux II to obtain reaction product A, wherein the diol is a C6-C10 straight-chain diol; b2) The reaction product A is reacted with 4-hydroxybenzaldehyde and an alkali metal carbonate in a contact reaction IV to obtain reaction product B; the alkali metal carbonate may be potassium carbonate. b3) The reaction product B and the alkylamine are heated and then reacted with reducing agent II in a contact reaction V to obtain reaction product C, wherein the alkylamine is a C8-C10 alkylamine; b4) The reaction product C and NH4PF6 are subjected to a contact reaction VI to obtain reaction product D; b5) The reaction product D is reacted with triethylamine and acryloyl chloride in a contact reaction VII. The modified monomer b prepared by the above method has high purity and yield.

[0051] Preferably, in step b1), the step of heating the diol and HBr under reflux II includes: heating the diol, HBr, and toluene under reflux II. Preferably, the conditions for heating under reflux II include: a temperature of 110-115°C and a time of 70-80 hours.

[0052] Preferably, the mass ratio of the diol to hydrogen bromide is 30-36:19.5.

[0053] Preferably, step b1) further includes: extracting, washing, drying, and purifying the distillate obtained by heating and reflux II. Preferably, the extractant used for extraction is diethyl ether. More preferably, the washing agent used is an aqueous solution of sodium hydroxide and water.

[0054] Preferably, in step b2), the step of contacting the reaction product A with 4-hydroxybenzaldehyde and potassium carbonate in reaction IV includes: adding the reaction product A dropwise to a mixed solution containing 4-hydroxybenzaldehyde and potassium carbonate under stirring and heating conditions, while continuing to stir. More preferably, the solvent of the mixed solution containing 4-hydroxybenzaldehyde and potassium carbonate can be N,N-dimethylformamide (DMF).

[0055] Preferably, the mass ratio of the reaction product A, 4-hydroxybenzaldehyde, and potassium carbonate is 16-19:10:12-16.

[0056] Preferably, the heating temperature is 85-95℃, the dripping time is 40-50 minutes, and the stirring time is 4-6 hours.

[0057] Preferably, step b2) further includes: extracting, washing, drying, and purifying the mixture obtained from contact reaction IV. Preferably, the extractant used for extraction is diethyl ether, and the washing agent used is potassium hydroxide solution and water.

[0058] Preferably, the step of heating the reaction product B and the alkylamine includes: mixing the reaction product B, the alkylamine, and the solvent, and then heating the mixture. Preferably, the conditions for the heating reaction include: a temperature of 65-75°C and a time of 10-14 hours.

[0059] Preferably, step b3) further includes: cooling the mixture obtained from the heated reaction and then contacting it with reducing agent II in a contact reaction V. Preferably, the reducing agent II is sodium borohydride. More preferably, the contact reaction V is carried out under stirring conditions for 10-18 hours. The contact reaction V is terminated by adding water dropwise to the reaction system.

[0060] Preferably, step b3) further includes: removing the organic solvent from the mixture obtained from contact reaction V, followed by extraction; drying the extracted organic phase and then separating the solid and liquid phases; the resulting solid is the reaction product C. Preferably, the extractant used in the extraction is dichloromethane (DCM).

[0061] Preferably, in step b4), the step of contacting the reaction product C and NH4PF6 in reaction VI includes: dissolving the reaction product C in acetone, adding hydrochloric acid solution, and adding NH4PF6 solution under stirring conditions. Preferably, the stirring time is 10-18 hours.

[0062] Preferably, step b4) further includes: extracting the product obtained from contact reaction VI with DCM and drying it to remove the solvent.

[0063] Preferably, in step b5), the step of contacting the reaction product D with triethylamine and acryloyl chloride in reaction VII includes: adding a solution containing acryloyl chloride dropwise to a solution containing reaction product D and triethylamine under a nitrogen atmosphere and with stirring, and continuing the reaction at a temperature of 2-6°C for 8-12 hours. Preferably, the solvent used in the solution containing acryloyl chloride and the mixed solution containing reaction product D and triethylamine can be toluene.

[0064] Preferably, the mass ratio of the reaction product D, triethylamine, and acryloyl chloride is 10-11.5:3.2-3.8:0.2.

[0065] Preferably, step b5) further includes: after the reaction is complete, immersing and washing the product in acetone, separating the solid and liquid, and then drying it.

[0066] Preferably, the alkali I is sodium hydroxide, the surfactant is a nonionic surfactant, and the catalyst contains an initiator, an oxidant, a reducing agent, a chain transfer agent, and a complexing agent.

[0067] To further improve the reaction effect, the nonionic surfactant is preferably nonylphenol polyoxyethylene ether.

[0068] Preferably, the initiator is 2,2'-azobisisobutyramidine dihydrochloride, the oxidant is tert-butyl hydroperoxide, and the reducing agent is ferrous ammonium sulfate. This can further improve the reaction effect.

[0069] Preferably, the chain transfer agent is sodium hypophosphite, and the complexing agent is pentasodium diethylenetriaminepentaacetate. Using the above-mentioned chain transfer agent and complexing agent can further improve the purity and yield of the product.

[0070] Preferably, based on the theoretical yield of the polyacrylamide, the addition amount of alkali I is 7-10.5 wt%, the addition amount of surfactant is 20-30 ppm, the addition amount of initiator is 90-1100 ppm, the addition amount of reducing agent is 4-13 ppm, the addition amount of oxidizing agent is 4-13 ppm, the addition amount of chain transfer agent is 8-130 ppm, and the addition amount of complexing agent is 40-85 ppm. Controlling the dosage of each additive within the above ranges can reduce reaction costs while ensuring the reaction effect.

[0071] Further, the mixing step includes: first mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, modified monomer b, base I, surfactant and solvent to obtain mixture I, and then mixing mixture I with catalyst in an inert gas atmosphere.

[0072] Preferably, the mixing step further includes freezing the mixture I to -2°C to -4°C before mixing the mixture I with the alkali I and the surfactant.

[0073] Preferably, the step of mixing the mixture I and the catalyst includes: firstly mixing the mixture I with the initiator, complexing agent, and chain transfer agent to obtain mixture II; secondly mixing the mixture II with the oxidant to obtain mixture III; and thirdly mixing the mixture III with the reducing agent. More preferably, the mixing time in the first step is 25-40 min, and the mixing time in the second step is 0.5-1.5 min.

[0074] To further improve the viscosity of the product in highly salinized water, the preparation method preferably further includes: aging the product of the polymerization reaction. More preferably, the aging time is 1.5-2.5 hours.

[0075] A third aspect of this invention provides a polyacrylamide prepared by the above-described preparation method. This polyacrylamide possesses all the advantages of the above-described preparation method, which will not be elaborated here.

[0076] A fourth aspect of this invention provides the application of the aforementioned polyacrylamide in oilfield thickeners. The polyacrylamide provided by this invention exhibits high viscosity, high high-temperature shear viscosity, and good sand-carrying capacity in high-salinity brine.

[0077] In a relatively preferred embodiment of the present invention, a method for preparing polyacrylamide is provided, comprising the following steps: 1. Synthesis of modified monomer a: (1) Dissolve 45-55 parts of glycol compound (selected from at least one of hexaethylene glycol, heptaethylene glycol, octaethylene glycol, nonaethylene glycol, and decaethylene glycol) in 120 parts of THF and stir at 0°C. Dissolve 22-26 parts of sodium hydroxide in 80 parts of water, cool at room temperature, and add to the glycol compound solution. Dissolve 58 parts of toluenesulfonyl chloride in 120 parts of THF and add dropwise to the mixture of glycol compound and sodium hydroxide. After stirring at room temperature for 44-52 hours, add 500 parts of H2O to the mixture to dissolve the precipitated sodium chloride and remove most of the THF by rotary evaporator. Then extract the residual liquid with 400 parts of dichloromethane, wash the combined organic phases with water and brine, and purify to obtain compound 1.

[0078] (2) A mixture of 10-11 parts of 3,4-dihydroxy-2-methylbenzoate, 25-26 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 66-78 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0079] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.2-1.5 parts of lithium aluminum hydride in batches. Stir the mixture at room temperature for 10-14 h, and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0080] (4) Dissolve 9-10 parts of compound 3 and 3.2-3.8 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it dropwise slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a, with the following structural formula: m is an integer between 3 and 7.

[0081] 2. Synthesis of modified monomer b: By mass fraction, (1) 30-35.73 parts of C6-C10 straight-chain diol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 110-115℃ for 70-80 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2×100 parts), then with water (3×100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0082] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 16.47-18.98 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0083] (3) Transfer 11.5-12.79 parts of the product from step (2) and 3.36 parts of n-butylamine to 500 parts of methanol and heat to 70°C for 12 hours. After cooling the reaction mixture to room temperature, add 1.67 parts of NaBH4 and stir the mixture overnight at room temperature. Stop the reaction by adding water dropwise. Evaporate the organic solvent under vacuum and extract the aqueous layer twice with DCM. Dry the combined organic layers with Na2SO4, filter and purify. Dissolve the obtained solid in acetone and then add 6 mol / L HCl solution. After stirring for 5 minutes, add saturated NH4PF6 solution and stir overnight. Extract the product three times with DCM, dry the combined organic layers with Na2SO4 and filter. Evaporate the solution to obtain the product.

[0084] (4) Dissolve 10.42-11.07 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer b, with the following structural formula: R is a C2-C6 alkyl group, and n is an integer between 6 and 8.

[0085] 3. Mix 250-275 parts of pure water, 70-75 parts of acrylamide, 12.5-20 parts of acrylic acid, 4-6 parts of 2-acrylamido-2-methylpropanesulfonic acid, 7.25-12.25 parts of sodium hydroxide, 0.002-0.003 parts of nonylphenol polyoxyethylene ether, 4-5 parts of modified monomer a, and 2.06-2.49 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add... Add 0.05-0.125 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.005-0.01 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.0025-0.015 parts of sodium hypophosphite; after 30 minutes, add 0.0005-0.0015 parts of tert-butyl hydroperoxide; after 0.5 minutes, add 0.0005-0.0015 parts of ferrous ammonium sulfate; after the polymerization reaction begins, remove the nitrogen gas tube and stop the nitrogen flow; after the reaction stops and the temperature rises, mature for 2 hours, then granulate, dry, and grind to obtain polyacrylamide.

[0086] The polyacrylamide prepared by the above method has high viscosity, high viscosity after high temperature shear and good sand carrying capacity in high-mineralized brine.

[0087] The present invention will be further illustrated by the following examples.

[0088] Example 1: 1. Synthesis of modified monomer a: (1) 47.3 parts heptaethylene glycol were dissolved in 120 parts THF and stirred at 0°C. 24 parts sodium hydroxide were dissolved in 80 parts water, cooled at room temperature, and added to the glycol solution. 58 parts toluenesulfonyl chloride were dissolved in 120 parts THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by rotary evaporator. The residual liquid was then extracted with 400 parts dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0089] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0090] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0091] (4) Dissolve 9 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0092] Characterization revealed that the modified monomer a is: .

[0093] 2. Synthesis of modified monomer b: By mass fraction, (1) 30 parts of 1,8-octanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0094] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and a thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 16.47 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0095] (3) Transfer 11.5 parts of the product from step (2) and 3.36 parts of n-butylamine to 500 parts of methanol and heat to 70°C for 12 hours. After cooling the reaction mixture to room temperature, add 1.67 parts of NaBH4 and stir the mixture overnight at room temperature. Stop the reaction by adding water dropwise. Evaporate the organic solvent under vacuum and extract the aqueous layer twice with DCM. Dry the combined organic layers with Na2SO4, filter and purify. Dissolve the obtained solid in acetone and then add 6 mol / L HCl solution. After stirring for 5 minutes, add saturated NH4PF6 solution and stir overnight. Extract the product three times with DCM, dry the combined organic layers with Na2SO4 and filter. Evaporate the solution to obtain the product.

[0096] (4) Dissolve 10.42 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0097] Characterization revealed that the modified monomer b is: n=6.

[0098] 3. Solution preparation: Mix 258 parts of pure water, 73 parts of acrylamide, 15 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 8.5 parts of sodium hydroxide, 0.003 parts of nonylphenol polyoxyethylene ether, 4 parts of modified monomer a, and 2.06 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.005 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.008 parts of sodium hypophosphite. After 30 minutes, add 0.0005 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0005 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0099] Example 2: 1. Synthesis of modified monomer a: (1) 52.7 parts of octaethylene glycol were dissolved in 120 parts of THF and stirred at 0°C. 24 parts of sodium hydroxide were dissolved in 80 parts of water, cooled at room temperature, and added to the glycol solution. 58 parts of toluenesulfonyl chloride were dissolved in 120 parts of THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts of H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by a rotary evaporator. The residual liquid was then extracted with 400 parts of dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0100] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0101] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0102] (4) Dissolve 10 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0103] Characterization revealed that the modified monomer a is: .

[0104] 2. Synthesis of modified monomer b: By mass fraction, (1) 30 parts of 1,8-octanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0105] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and a thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 16.47 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0106] (3) Transfer 11.5 parts of the product from step (2) and 3.36 parts of n-butylamine to 500 parts of methanol and heat to 70°C for 12 hours. After cooling the reaction mixture to room temperature, add 1.67 parts of NaBH4 and stir the mixture overnight at room temperature. Stop the reaction by adding water dropwise. Evaporate the organic solvent under vacuum and extract the aqueous layer twice with DCM. Dry the combined organic layers with Na2SO4, filter and purify. Dissolve the obtained solid in acetone and then add 6 mol / L HCl solution. After stirring for 5 minutes, add saturated NH4PF6 solution and stir overnight. Extract the product three times with DCM, dry the combined organic layers with Na2SO4 and filter. Evaporate the solution to obtain the product.

[0107] (4) Dissolve 10.42 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0108] Modified monomer b is: n=6.

[0109] 3. Solution preparation: Mix 260 parts of pure water, 73 parts of acrylamide, 16 parts of acrylic acid, 6 parts of 2-acrylamido-2-methylpropanesulfonic acid, 9.2 parts of sodium hydroxide, 0.0027 parts of nonylphenol polyoxyethylene ether, 5 parts of modified monomer a, and 2.06 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.11 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.008 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.007 parts of sodium hypophosphite. After 30 minutes, add 0.0006 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0006 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0110] Example 3: 1. Synthesis of modified monomer a: (1) 47.3 parts heptaethylene glycol were dissolved in 120 parts THF and stirred at 0°C. 24 parts sodium hydroxide were dissolved in 80 parts water, cooled at room temperature, and added to the glycol solution. 58 parts toluenesulfonyl chloride were dissolved in 120 parts THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by rotary evaporator. The residual liquid was then extracted with 400 parts dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0111] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0112] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0113] (4) Dissolve 9 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0114] Modified monomer a is: .

[0115] 2. Synthesis of modified monomer b: By mass fraction, (1) 35.73 parts of 1,10-decanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0116] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 18.98 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0117] (3) 12.79 parts of the product from step (2) and 3.36 parts of n-butylamine were transferred to 500 parts of methanol and heated to 70°C for 12 hours. After cooling the reaction mixture to room temperature, 1.67 parts of NaBH4 were added, and the mixture was stirred overnight at room temperature. The reaction was stopped by adding water dropwise. The organic solvent was evaporated under vacuum, and the aqueous layer was extracted twice with DCM. The combined organic layers were dried with Na2SO4, filtered, and purified. The obtained solid was dissolved in acetone, and then 6 mol / L HCl solution was added. After stirring for 5 minutes, saturated NH4PF6 solution was added and stirred overnight. The product was extracted three times with DCM, and the combined organic layers were dried with Na2SO4 and filtered. The solution was evaporated to obtain the product.

[0118] (4) Dissolve 11.07 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry it in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0119] Characterization revealed that the modified monomer b is: n=8.

[0120] 3. Solution preparation: Mix 268 parts of pure water, 74 parts of acrylamide, 18 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of sodium hydroxide, 0.0027 parts of nonylphenol polyoxyethylene ether, 4 parts of modified monomer a, and 2.49 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.006 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.005 parts of sodium hypophosphite. After 30 minutes, add 0.0008 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0008 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0121] Example 4: 1. Synthesis of modified monomer a: (1) 52.7 parts of octaethylene glycol were dissolved in 120 parts of THF and stirred at 0°C. 24 parts of sodium hydroxide were dissolved in 80 parts of water, cooled at room temperature, and added to the glycol solution. 58 parts of toluenesulfonyl chloride were dissolved in 120 parts of THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts of H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by a rotary evaporator. The residual liquid was then extracted with 400 parts of dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0122] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0123] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0124] (4) Dissolve 10 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0125] Modified monomer a is: .

[0126] 2. Synthesis of modified monomer b: By mass fraction, (1) 35.73 parts of 1,10-decanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0127] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 18.98 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0128] (3) 12.79 parts of the product from step (2) and 3.36 parts of n-butylamine were transferred to 500 parts of methanol and heated to 70°C for 12 hours. After cooling the reaction mixture to room temperature, 1.67 parts of NaBH4 were added, and the mixture was stirred overnight at room temperature. The reaction was stopped by adding water dropwise. The organic solvent was evaporated under vacuum, and the aqueous layer was extracted twice with DCM. The combined organic layers were dried with Na2SO4, filtered, and purified. The obtained solid was dissolved in acetone, and then 6 mol / L HCl solution was added. After stirring for 5 minutes, saturated NH4PF6 solution was added and stirred overnight. The product was extracted three times with DCM, and the combined organic layers were dried with Na2SO4 and filtered. The solution was evaporated to obtain the product.

[0129] (4) Dissolve 11.07 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry it in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0130] Modified monomer b is: n=8.

[0131] 3. Solution preparation: Mix 271 parts of pure water, 75 parts of acrylamide, 16 parts of acrylic acid, 6 parts of 2-acrylamido-2-methylpropanesulfonic acid, 9.2 parts of sodium hydroxide, 0.003 parts of nonylphenol polyoxyethylene ether, 5 parts of modified monomer a, and 2.49 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.011 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.008 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.0011 parts of sodium hypophosphite. After 30 minutes, add 0.0005 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0005 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0132] Example 5: 1. Synthesis of modified monomer a: (1) 52.7 parts of octaethylene glycol were dissolved in 120 parts of THF and stirred at 0°C. 24 parts of sodium hydroxide were dissolved in 80 parts of water, cooled at room temperature, and added to the glycol solution. 58 parts of toluenesulfonyl chloride were dissolved in 120 parts of THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts of H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by a rotary evaporator. The residual liquid was then extracted with 400 parts of dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0133] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0134] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0135] (4) Dissolve 10 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0136] Modified monomer a is: .

[0137] 2. Synthesis of modified monomer b: By mass fraction, (1) 30 parts of 1,8-octanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0138] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and a thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 16.47 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0139] (3) Transfer 11.5 parts of the product from step (2) and 3.36 parts of n-butylamine to 500 parts of methanol and heat to 70°C for 12 hours. After cooling the reaction mixture to room temperature, add 1.67 parts of NaBH4 and stir the mixture overnight at room temperature. Stop the reaction by adding water dropwise. Evaporate the organic solvent under vacuum and extract the aqueous layer twice with DCM. Dry the combined organic layers with Na2SO4, filter and purify. Dissolve the obtained solid in acetone and then add 6 mol / L HCl solution. After stirring for 5 minutes, add saturated NH4PF6 solution and stir overnight. Extract the product three times with DCM, dry the combined organic layers with Na2SO4 and filter. Evaporate the solution to obtain the product.

[0140] (4) Dissolve 10.42 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0141] Modified monomer b is: n=6.

[0142] 3. Solution preparation: Mix 260 parts of pure water, 73 parts of acrylamide, 16 parts of acrylic acid, 6 parts of 2-acrylamido-2-methylpropanesulfonic acid, 9.2 parts of sodium hydroxide, 0.0027 parts of nonylphenol polyoxyethylene ether, 5 parts of modified monomer a, and 1.9 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.11 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.008 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.007 parts of sodium hypophosphite. After 30 minutes, add 0.0006 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0006 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0143] Example 6: 1. Synthesis of modified monomer a: (1) 47.3 parts heptaethylene glycol were dissolved in 120 parts THF and stirred at 0°C. 24 parts sodium hydroxide were dissolved in 80 parts water, cooled at room temperature, and added to the glycol solution. 58 parts toluenesulfonyl chloride were dissolved in 120 parts THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by rotary evaporator. The residual liquid was then extracted with 400 parts dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0144] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0145] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0146] (4) Dissolve 9 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0147] Modified monomer a is: .

[0148] 2. Synthesis of modified monomer b: By mass fraction, (1) 35.73 parts of 1,10-decanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0149] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 18.98 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0150] (3) 12.79 parts of the product from step (2) and 3.36 parts of n-butylamine were transferred to 500 parts of methanol and heated to 70°C for 12 hours. After cooling the reaction mixture to room temperature, 1.67 parts of NaBH4 were added, and the mixture was stirred overnight at room temperature. The reaction was stopped by adding water dropwise. The organic solvent was evaporated under vacuum, and the aqueous layer was extracted twice with DCM. The combined organic layers were dried with Na2SO4, filtered, and purified. The obtained solid was dissolved in acetone, and then 6 mol / L HCl solution was added. After stirring for 5 minutes, saturated NH4PF6 solution was added and stirred overnight. The product was extracted three times with DCM, and the combined organic layers were dried with Na2SO4 and filtered. The solution was evaporated to obtain the product.

[0151] (4) Dissolve 11.07 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry it in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0152] Modified monomer b is: n=8.

[0153] 3. Solution preparation: Mix 268 parts of pure water, 74 parts of acrylamide, 18 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of sodium hydroxide, 0.0027 parts of nonylphenol polyoxyethylene ether, 4 parts of modified monomer a, and 3.6 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.006 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.005 parts of sodium hypophosphite. After 30 minutes, add 0.0008 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0008 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0154] Comparative Example 1: 1. Synthesis of modified monomer b: By mass fraction, (1) 30 parts of 1,8-octanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0155] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and a thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 16.47 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0156] (3) Transfer 11.5 parts of the product from step (2) and 3.36 parts of n-butylamine to 500 parts of methanol and heat to 70°C for 12 hours. After cooling the reaction mixture to room temperature, add 1.67 parts of NaBH4 and stir the mixture overnight at room temperature. Stop the reaction by adding water dropwise. Evaporate the organic solvent under vacuum and extract the aqueous layer twice with DCM. Dry the combined organic layers with Na2SO4, filter and purify. Dissolve the obtained solid in acetone and then add 6 mol / L HCl solution. After stirring for 5 minutes, add saturated NH4PF6 solution and stir overnight. Extract the product three times with DCM, dry the combined organic layers with Na2SO4 and filter. Evaporate the solution to obtain the product.

[0157] (4) Dissolve 10.42 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0158] Modified monomer b is: n=6.

[0159] 2. Solution preparation: Mix 258 parts of pure water, 73 parts of acrylamide, 15 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 8.5 parts of sodium hydroxide, 0.003 parts of nonylphenol polyoxyethylene ether, and 2.06 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.005 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.008 parts of sodium hypophosphite. After 30 minutes, add 0.0005 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0005 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0160] Comparative Example 2: 1. Synthesis of modified monomer a: (1) 47.3 parts heptaethylene glycol were dissolved in 120 parts THF and stirred at 0°C. 24 parts sodium hydroxide were dissolved in 80 parts water, cooled at room temperature, and added to the glycol solution. 58 parts toluenesulfonyl chloride were dissolved in 120 parts THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by rotary evaporator. The residual liquid was then extracted with 400 parts dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0161] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0162] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0163] (4) Dissolve 9 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0164] Modified monomer a is: .

[0165] 2. Solution preparation: Mix 258 parts of pure water, 73 parts of acrylamide, 15 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 8.5 parts of sodium hydroxide, 0.003 parts of nonylphenol polyoxyethylene ether, and 4 parts of modified monomer a until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.005 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.008 parts of sodium hypophosphite. After 30 minutes, add 0.0005 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0005 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0166] Comparative Example 3: 1. Synthesis of modified monomer C: 59.5 parts by mass of pentaethylene glycol, 100 parts by mass of benzene and 50 parts by mass of pyridine were added sequentially to a 500 mL three-necked flask. The mixture was stirred and refluxed at 80 °C for 1 h. Subsequently, 45 parts by mass of SOCl2 were added to the flask, and the mixture was stirred and refluxed at 80 °C for another 15 h. The reaction mixture was then cooled to room temperature, acidified with 35 mL of 3 mol / L HCl solution, and finally purified to obtain the product.

[0167] Characterization revealed that the modified monomer c is: .

[0168] 2. Synthesis of modified monomer b: By mass fraction, (1) 30 parts of 1,8-octanediol and 19.44 parts of HBr were placed in a single-necked round-bottom flask equipped with a double-walled reflux condenser, and 500 parts of toluene were added to the flask. The reaction mixture was refluxed at 113°C for 75 hours. Then the reaction mixture was cooled to room temperature, transferred to a separatory funnel, and extracted with 500 parts of diethyl ether. The collected organic layers were washed first with 1 mol / L NaOH solution (2 × 100 parts), then with water (3 × 100 parts), and dried with anhydrous Na2SO4 to obtain the product after purification.

[0169] (2) Place 10 parts of 4-hydroxybenzaldehyde into a three-necked round-bottom flask equipped with a stirrer and a thermometer. Add 350 parts of DMF and 14 parts of potassium carbonate. Stir the resulting mixture while maintaining the temperature at 90°C. Add 16.47 parts of the product from step (1) dropwise through a constant-pressure dropping funnel over 45 minutes, continue stirring for 5 hours, and then cool the reaction mixture to room temperature and pour it into a beaker. Dilute the contents with 500 parts of water and then transfer it to a separatory funnel for extraction with diethyl ether. Wash the collected ether layer with 10 wt% potassium hydroxide solution (2 × 100 parts) and distilled water (3 × 100 parts). Then dry the organic layer with anhydrous sodium sulfate to obtain the product after purification.

[0170] (3) Transfer 11.5 parts of the product from step (2) and 3.36 parts of n-butylamine to 500 parts of methanol and heat to 70°C for 12 hours. After cooling the reaction mixture to room temperature, add 1.67 parts of NaBH4 and stir the mixture overnight at room temperature. Stop the reaction by adding water dropwise. Evaporate the organic solvent under vacuum and extract the aqueous layer twice with DCM. Dry the combined organic layers with Na2SO4, filter and purify. Dissolve the obtained solid in acetone and then add 6 mol / L HCl solution. After stirring for 5 minutes, add saturated NH4PF6 solution and stir overnight. Extract the product three times with DCM, dry the combined organic layers with Na2SO4 and filter. Evaporate the solution to obtain the product.

[0171] (4) Dissolve 10.42 parts of the product from step (3) and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the three-necked flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the solution at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer b.

[0172] Modified monomer b is: n=6.

[0173] 3. Solution preparation: Mix 258 parts of pure water, 73 parts of acrylamide, 15 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 8.5 parts of sodium hydroxide, 0.003 parts of nonylphenol polyoxyethylene ether, 4 parts of modified monomer c, and 2.06 parts of modified monomer b until homogeneous. Then freeze to 0°C and transfer to an insulated reactor. Purge the solution in the reactor with nitrogen to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.005 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.008 parts of sodium hypophosphite. After 30 minutes, add 0.0005 parts of tert-butyl hydroperoxide. After 0.5 minutes, add 0.0005 parts of ferrous ammonium sulfate. After the polymerization reaction begins, remove the nitrogen pipe and stop the nitrogen flow. After the reaction stops and the temperature rises, allow it to mature for 2 hours. Then granulate, dry, and grind to obtain polyacrylamide.

[0174] Comparative Example 4: 1. Synthesis of modified monomer a: (1) 47.3 parts heptaethylene glycol were dissolved in 120 parts THF and stirred at 0°C. 24 parts sodium hydroxide were dissolved in 80 parts water, cooled at room temperature, and added to the glycol solution. 58 parts toluenesulfonyl chloride were dissolved in 120 parts THF and added dropwise to the mixture of glycol and sodium hydroxide. After stirring at room temperature for 48 hours, 500 parts H2O were added to the mixture to dissolve the precipitated sodium chloride, and most of the THF was removed by rotary evaporator. The residual liquid was then extracted with 400 parts dichloromethane, and the combined organic phases were washed with water and brine. After purification, compound 1 was obtained.

[0175] (2) A mixture of 10.26 parts of methyl 3,4-dihydroxy-2-methylbenzoate, 25.4 parts of K2CO3, and 36 parts of compound 1 in 600 parts of CH3CN was stirred and refluxed under nitrogen for 72 h. After cooling, the mixture was filtered, CH3CN was removed by rotary evaporator, and then chloroform was added. After washing eight times with brine, the organic phase was dried with Na2SO4, and compound 2 was obtained after purification.

[0176] (3) Dissolve 15 parts of compound 2 in 300 parts of dry THF and stir. Add 1.365 parts of lithium aluminum hydride in portions. Stir the mixture at room temperature for 12 h and then quench it with 3 parts of water and 3 parts of 15 wt% sodium hydroxide aqueous solution. Dry the mixture with MgSO4 and filter to obtain compound 3 after purification.

[0177] (4) Dissolve 9 parts of compound 3 and 3.5 parts of triethylamine in 15 parts of toluene, then transfer the solution to a three-necked flask and purge with nitrogen. Place the flask in an ice-water bath and turn on the stirrer. Dissolve 0.207 parts of acryloyl chloride in 5 parts of toluene, transfer the solution to a constant pressure dropping funnel, and add it slowly. After the addition is complete, react the product at 4 °C for 10 h. After the reaction is complete, soak and wash the product in 50 parts of acetone, filter under reduced pressure, and dry in a vacuum oven at 50 °C for 10 h to obtain modified monomer a.

[0178] Modified monomer a is: .

[0179] 2. Solution preparation: Mix 258 parts of pure water, 73 parts of acrylamide, 15 parts of acrylic acid, 5 parts of 2-acrylamido-2-methylpropanesulfonic acid, 8.5 parts of sodium hydroxide, 0.003 parts of nonylphenol polyoxyethylene ether, 4 parts of modified monomer a, and 2.06 parts of 1-vinyl-3-butylimidazolium hexafluorophosphate until homogeneous, then freeze to 0°C and transfer to an insulated reactor; introduce nitrogen gas into the solution in the reactor to remove oxygen and add 0.1 parts of 2,2'-azobisisobutyramidine dihydrochloride, 0.005 parts of diethylenetriaminepentaacetic acid pentasodium salt, and 0.008 parts of sodium hypophosphite; after 30 minutes, add 0.0005 parts of tert-butyl hydroperoxide; after 0.5 minutes, add 0.0005 parts of ferrous ammonium sulfate; after the polymerization reaction begins, remove the nitrogen gas pipe and stop the nitrogen flow; after the reaction stops and the temperature rises, allow it to mature for 2 hours, then granulate, dry, and grind to obtain polyacrylamide.

[0180] Test example: Performance evaluation was performed on the examples and comparative examples: (1) Thickening properties: Prepare the saline solution: Accurately weigh 3.4 g of calcium chloride, 2.3 g of magnesium chloride, and 30.1 g of sodium chloride, then dissolve and dilute with pure water to 2 L.

[0181] The samples from the examples and comparative examples were prepared into 0.4% (w / w) solutions using the aforementioned saline solution. The solutions were dissolved using magnetic stirring at 500 rpm for 5 minutes, and the viscosities were measured. Specific results are shown in [link to results]. Figure 2As shown, the samples in the examples, after dissolving in salt water, formed a cross-linked structure through linear inclusion self-assembly, increasing the viscosity of the system. Comparative Examples 1-2, lacking monomers a or b, had lower viscosity. In Comparative Example 3, the absence of a benzene ring on the crown ether group resulted in a lack of rigid modification and electronic effects, reducing the host-guest recognition performance and structural stability of the crown ether, thus hindering self-assembly and resulting in lower viscosity. In Comparative Example 4, the quaternary ammonium salt group on the five-membered ring caused rigid steric hindrance, directly blocking the N⁺ coordination site and significantly increasing steric hindrance, thus almost eliminating self-assembly and resulting in lower polymer viscosity. Compared to Examples 1-4, Example 5, with reduced monomer b, showed decreased self-assembly and lower viscosity. In Example 6, excessive monomer b led to decreased polyacrylamide solubility and lower viscosity.

[0182] (2) Viscosity after high-temperature shearing Different polyacrylamides dissolved in salt water (0.4 wt%) were tested at 90 °C for 100 s. -1 The viscosity after shearing at a certain speed for 60 minutes is as follows: Figure 3 As shown. The examples exhibited higher viscosity after high-temperature shearing, especially the polyacrylamide provided in Examples 1-4, with a viscosity > 37.5 mPa·s. This is because the linear inclusion effect has a certain temperature resistance. Examples 5-6 had significantly lower viscosity after high-temperature shearing due to poor linear inclusion effect or low sample solubility. In contrast, Comparative Examples 1-4 did not show significant self-assembly, resulting in significantly lower viscosity after high-temperature shearing compared to Examples 1-6.

[0183] (3) Sand carrying capacity Weigh 0.8 g of each sample from the examples and comparative examples and dissolve them in 199.2 g of brine. After dissolving for 5 min, take 100 mL of the solution and place it in a 250 mL beaker. Then take 30 mL of fine sand (20-40 mesh), stir well, transfer it to a graduated cylinder, and observe and record the settling velocity of the fine sand. See the results below. Figure 4 The samples in Examples 1-6 generated a cross-linked structure through linear inclusion self-assembly, which significantly improved the viscosity and sand-carrying capacity. In contrast, the samples in Comparative Examples 1-4 had lower viscosity and therefore poor sand-carrying effect.

Claims

1. A polyacrylamide, characterized in that, The raw materials for preparing the polyacrylamide include: acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a shown in Formula I, and modified monomer b shown in Formula II. Formula I: , Formula II: , Where R is a C2-C6 alkyl group, m is an integer between 3 and 7, and n is an integer between 6 and 8.

2. The polyacrylamide according to claim 1, characterized in that, The molar ratio of acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, and modified monomer b is 1:0.2-0.25:0.025-0.035:0.008-0.01:0.0035-0.0048; Preferably, the molar ratio of the modified monomer a to the modified monomer b is 1:0.38-0.

52.

3. A method for preparing polyacrylamide according to claim 1 or 2, characterized in that, The preparation method includes: mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, modified monomer b, alkali I, surfactant, catalyst and solvent to carry out a polymerization reaction.

4. The method for preparing polyacrylamide according to claim 3, characterized in that, The preparation steps of the modified monomer a include: a1) A glycol compound is reacted with base II and toluenesulfonyl chloride in a contact reaction I to obtain reaction product I, wherein the glycol compound is selected from at least one of hexaethylene glycol, heptaethylene glycol, octaethylene glycol, nonaethylene glycol and decaethylene glycol; a2) The reaction product I, 3,4-dihydroxy-2-methylbenzoate, and alkali metal carbonate are heated under reflux I to obtain reaction product II; a3) The reaction product II and the reducing agent I are subjected to contact reaction II to obtain reaction product III; a4) The reaction product III is reacted with triethylamine and acryloyl chloride in a contact reaction III; Preferably, the alkali II is sodium hydroxide and / or potassium hydroxide, the alkali metal carbonate is potassium carbonate, the reducing agent I is lithium aluminum hydride, and the conditions for the contact reaction III include: a temperature of 2-6°C and a time of 8-12 hours.

5. The method for preparing polyacrylamide according to claim 3, characterized in that, The preparation steps of the modified monomer b include: b1) The diol and HBr are heated under reflux II to obtain reaction product A, wherein the diol is a C6-C10 straight-chain diol; b2) The reaction product A is reacted with 4-hydroxybenzaldehyde and an alkali metal salt of carbonate in a contact reaction IV to obtain reaction product B; b3) The reaction product B and the alkylamine are heated and then reacted with reducing agent II in a contact reaction V to obtain reaction product C, wherein the alkylamine is a C8-C10 alkylamine; b4) The reaction product C and NH4PF6 are subjected to a contact reaction VI to obtain reaction product D; b5) The reaction product D is reacted with triethylamine and acryloyl chloride in reaction VII; Preferably, the alkali metal carbonate is potassium carbonate, the reducing agent II is NaBH4, and the conditions for the contact reaction IV include: a temperature of 85-95℃ and a time of 4-6h; the conditions for the heating reaction include: a temperature of 65-75℃ and a time of 10-14h; and the conditions for the contact reaction VII include: a temperature of 2-6℃ and a time of 8-12h.

6. The method for preparing polyacrylamide according to any one of claims 3 to 5, characterized in that, The base I is sodium hydroxide, the surfactant is a nonionic surfactant, preferably nonylphenol polyoxyethylene ether; the catalyst contains an initiator, an oxidant, a reducing agent, a chain transfer agent, and a complexing agent; Preferably, the initiator is 2,2'-azobisisobutyramidine dihydrochloride, the reducing agent is ferrous ammonium sulfate, and the oxidizing agent is tert-butyl hydroperoxide; The chain transfer agent is sodium hypophosphite, and the complexing agent is diethyltriaminepentaacetic acid pentasodium.

7. The method for preparing polyacrylamide according to claim 6, characterized in that, Based on the theoretical yield of the polyacrylamide, the amount of alkali I added is 7-10.5 wt%, the amount of surfactant added is 20-30 ppm, the amount of initiator added is 90-1100 ppm, the amount of reducing agent added is 4-13 ppm, the amount of oxidizing agent added is 4-13 ppm, the amount of chain transfer agent added is 8-130 ppm, and the amount of complexing agent added is 40-85 ppm.

8. The method for preparing polyacrylamide according to any one of claims 3 to 5, characterized in that, The mixing step includes: first mixing acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, modified monomer a, modified monomer b, base I, surfactant and solvent to obtain mixture I, and then mixing mixture I with catalyst in an inert gas atmosphere.

9. The polyacrylamide prepared by the method of any one of claims 3 to 8.

10. The use of the polyacrylamide according to any one of claims 1, 2 or 9 in oilfield thickeners.

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