Preparation of high reaction temperature DPAM with improved standard viscosity and water solubility

Abstract

The present invention generally relates to compositions and methods for preparing high reaction temperature dry polyacrylamide (DPAM) polymers. In particular, the present disclosure provides methods for increasing the reaction temperature to above 100 DEG C (Tmaxgt; the invention relates to a method for the adiabatic redox-initiated free-radical polymerization of a reaction mixture comprising at least an acrylamide monomer, optionally a free-radical scavenger-based stabilizer, an azo initiator and a redox initiator, at a pH of at least 100 DEG C and at an initial temperature. The gel polymerization under these conditions yields an anionic DPAM polymer that is useful in a variety of industrial applications, with improved standard viscosity and high water solubility.

Description

Technical Field

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 511,978, filed July 5, 2023, and Finnish Application No. 20236044, filed September 21, 2023, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0002] This invention generally relates to compositions and methods for preparing high-reaction-temperature dry polyacrylamide (DPAM) polymers. Specifically, this disclosure provides a method for adiabatic redox-initiated free radical polymerization of a reaction mixture under pH and initial temperature conditions that allow the heat of polymerization to raise the reaction temperature to above 100°C (Tmax > 100°C), said reaction mixture comprising at least an acrylamide monomer, optionally a free radical scavenger stabilizer, an azo initiator, and a redox initiator. Gel polymerization under these conditions yields anionic DPAM polymers for various industrial applications, exhibiting improved standard viscosity and high water solubility. Background Technology

[0003] Polyacrylamide homopolymers and copolymers with high molecular weight, high water solubility and high standard viscosity in solution are used in many industrial fields, such as as thickeners, flocculants, paper reinforcing agents, for enhancing oil recovery, for tailings treatment, wastewater treatment, drinking water treatment and for mining applications.

[0004] These polymers, especially high molecular weight polyacrylamide, are crucial for enhanced oil recovery (EOR). EOR technologies, such as polymer flooding, in which large volumes of polymer solutions are injected into underground reservoirs, can be used to increase the amount of unrefined petroleum (e.g., crude oil) that can be extracted from a reservoir (e.g., an oil field). For example, EOR can typically extract approximately 40-60% of the original petroleum from a reservoir, compared to only 20-40% extracted using conventional primary and secondary recovery technologies (e.g., via water injection or natural gas injection).

[0005] One of the most common uses of polyacrylamide is to flocculate solids in liquids for dewatering and filtration. Many industrial processes use dewatering and filtration steps, where the water content of bulk solids or slurries is reduced by filtration or other methods. Dewatering processes are necessary, for example, in the treatment of sludge (e.g., sludge in sludge ponds or municipal wastewater treatment processes), slurry and paper-based pulp, and other paper processing processes. Dewatering methods are also used in mining, for example, for the dewatering of tailings and metallic ores. Specifically, the mining, processing, and purification of naturally occurring minerals typically involves one or more processing or treatment operations in which fine-mesh-sized particles of the mineral of interest are suspended or dispersed in a continuous medium (e.g., a continuous aqueous medium), and then the mineral particles are separated from the medium.

[0006] Flocculants containing high molecular weight polyacrylamide homopolymers and copolymers are commonly used in the chemical treatment of oil sands tailings, sludge, and other wastewater. Polyacrylamide flocculants are widely used in drinking water purification, wastewater treatment, stormwater treatment, and industrial wastewater stream treatment, and they also aid in the settling of slurries containing mined minerals and ores.

[0007] Polyacrylamide and its copolymers are also widely used in pulping and papermaking applications. Polyacrylamide homopolymers and copolymers are used as retention aids (if molecular weight > 2 million g / mol), dry strength resins, asphalt control agents, and micropolymer filter aids.

[0008] The preparation of acrylamide homopolymers and copolymers with high molecular weight, high water solubility, and high standard viscosity in solution is crucial for the aforementioned industrial applications. These polymers are typically prepared as dry polyacrylamide (DPAM) using gel polymerization methods such as adiabatic redox-initiated free radical gel polymerization.

[0009] Significant efforts have been made to develop gel polymerization methods for preparing high-reaction-temperature DPAM (i.e., produced at high temperatures (Tmax) exceeding 100°C) with high molecular weight, good solubility (low residual insoluble gel), and high viscosity (SV 6–7.5 mPas). Using high monomer concentrations is beneficial for achieving optimal molecular weight and high viscosity. However, such efforts have not been successful due to undesirable side reactions at Tmax above 100°C, and the potential formation of ultra-high molecular weight polymer chains during polymerization at high monomer concentrations. These phenomena result in an undesirable amount of insoluble matter in the final DPAM, leading to insoluble and therefore unusable DPAM.

[0010] Therefore, the object of the present invention is to provide a method for preparing polyacrylamide by gel polymerization, wherein the polymerization can be carried out at a maximum temperature above 100°C to provide industrially available DPAM with high molecular weight and good solubility. Summary of the Invention

[0011] This invention generally relates to compositions and methods for preparing high-reaction-temperature dry polyacrylamide (DPAM) polymers. Specifically, this disclosure provides a method for adiabatic redox-initiated free radical polymerization of a reaction mixture comprising at least an acrylamide monomer, optionally a free radical scavenger stabilizer, an azo initiator, and a redox initiator, under initial pH and redox initiation temperature conditions that allow the heat of polymerization to raise the reaction temperature to above 100°C (Tmax > 100°C). Gel polymerization under these conditions yields anionic DPAM polymers suitable for various industrial applications, exhibiting improved standard viscosity, high water solubility, and virtually no residual insoluble matter.

[0012] On one hand, the present invention provides a method for preparing high-reaction-temperature dry polyacrylamide (DPAM) via redox-initiated free radical polymerization, the method comprising:

[0013] (a) Providing or producing an aqueous solution of an olefinically unsaturated monomer, said aqueous solution comprising water and (i) acrylamide or (ii) acrylamide and one or more other monomers capable of copolymerizing with acrylamide;

[0014] (b) Optionally add one or more stabilizers;

[0015] (c) Optionally add one or more additives, including but not limited to one or more chelating agents, and optionally one or more liquid-leaching agents, one or more chain transfer agents, or any combination thereof;

[0016] (d) Add one or more azo initiators;

[0017] (e) Adjust the pH to a range of 7-9, 7-8, 7.1-7.8, or 7.25-7.75;

[0018] (f) Cooling to below 25°C the redox initiation temperature;

[0019] (g) Add one or more redox initiators to produce a redox-initiated reaction mixture;

[0020] (h) Allowing gel polymerization to occur under substantially adiabatic conditions, wherein the redox-initiated reaction mixture is heated to a maximum reaction temperature (Tmax) above 100°C by the exothermic polymerization; and

[0021] (i) The Tmax is maintained for a curing time, thereby providing a high reaction temperature polyacrylamide gel.

[0022] In some exemplary embodiments, the method further includes drying and grinding the high reaction temperature polyacrylamide gel after step (i) to form the high reaction temperature DPAM as a homopolymer, copolymer, or terpolymer.

[0023] In some exemplary embodiments of the method, the gel polymerization:

[0024] (a) Occurs in an atmosphere containing nitrogen, argon, helium, or a combination thereof;

[0025] (b) It occurs at a high pressure above atmospheric pressure and is optionally maintained by exothermic heating of the polymerization or by pressurization with an inert gas, including but not limited to nitrogen, argon, helium or any combination thereof, and further wherein the high pressure is sufficient to prevent the aqueous reaction mixture from boiling when subjected to temperatures above 100°C.

[0026] In some exemplary implementations of the method:

[0027] (a) The redox initiation temperature range is -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to 3°C;

[0028] (b) The final reaction temperature range is 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, 100°C to 110°C or 100°C to 105°C;

[0029] (c) After the addition of one or more of the aforementioned redox initiators, the final reaction temperature is reached within a time range of 5-120 minutes, 10-90 minutes, 20-90 minutes, or 20-60 minutes; and

[0030] (d) The curing time range is 10-240 minutes, 30-180 minutes or 60-120 minutes.

[0031] In some exemplary embodiments of the method, the one or more additional monomers comprise:

[0032] (a) One or more olefinically unsaturated, preferably water-soluble, nonionic monomers, including but not limited to (meth)acrylamide; N-alkylacrylamides, including but not limited to N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, and N-butylacrylamide; N,N-dialkylacrylamides, including but not limited to N,N-dimethylacrylamide and N,N-diethylacrylamide; N-alkylmethylacrylamide; alkyl acrylates; hydroxyalkyl acrylates and hydroxyalkyl methacrylates, including but not limited to methyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxyacrylate... 2-Hydroxybutyl methacrylate, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; dialkyl acrylates and dialkyl methacrylates, including but not limited to 2,3-dihydroxypropyl acrylate, 3,4-dihydroxybutyl acrylate, 2,3-dihydroxypropyl methacrylate (DHPMA), and 3,4-dihydroxybutyl methacrylate; alkyl acrylates, including but not limited to methyl methacrylate; acrylonitrile; N-vinylmethylacetamide, N-vinylmethylformamide; N-vinyl acetate, acetoxylated acrylamide, and vinylpyrrolidone; and

[0033] (b) One or more olefinically unsaturated anionic monomers, including but not limited to acrylic acid, methacrylic acid; sulfonic acid, phosphonic acid, maleic acid, itaconic acid, vinyl sulfonic acid, acrylamidotert-butyl sulfonic acid (ATBS), acrylamidomethanesulfonic acid, acrylamidoethanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, and their alkali metal salts, alkaline earth metal salts, and ammonium salts; and

[0034] (c) Any combination of the foregoing terms.

[0035] In some exemplary embodiments of the method, the aqueous solution of the olefinically unsaturated monomer comprises:

[0036] (a) Acrylamide,

[0037] (b) Acrylamide and acrylic acid, or

[0038] (c) Acrylamide, acrylic acid and ATBS.

[0039] In some exemplary implementations of the method:

[0040] (a) The one or more optional stabilizers comprise one or more free radical scavengers, including but not limited to thiourea, N,N'-dimethylthiourea, N,N'-diethylthiourea, N,N'-diphenylthiourea, thiocyanate, tetramethylthiuram disulfide, 2-mercaptobenzothiazole (MBT) and its salts, 2-mercaptobenzimidazole and its salts, sodium dimethyl dithiocarbamate, sodium diethyl dithiocarbamate, 2,2'-dithiobis(benzothiazole), 4,4'-thiobis(6-tert-butyl-m-cresol), and bis(benzothiazole). Cyanamide, cyanamide, p-methoxyphenol, 2,6-di-tert-butyl-4-methylphenol, butylated hydroxyanisole, 8-hydroxyquinoline, 2,5-di(tert-amyl)hydroquinone, 5-hydroxy-1,4-naphthoquinone, dimethyl ketone, propyl-3,4,5-trihydroxybenzoate, N-nitrosophenylhydroxylamine, 4-hydroxy-2,2,6,6-tetramethyloxypiperidine, (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 1,2,2,6,6-pentamethyl-4-piperidinol or any combination thereof;

[0041] (b) The one or more additives comprise: (i) the one or more chelating agents, including but not limited to diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid (EDTA) and its salts, 2,2',2",2"'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA), phosphoric acid and its alkali metal salts, alkaline earth metal salts and ammonium salts; (ii) the one or more dissociating agents, including but not limited to urea, thiourea, alcohols, glycerol, guanidine and guanidine cation halide salts; (iii) the one or more chain transfer agents, including but not limited to hypophosphite and its salts, sodium hypophosphite, sodium formate, pentamethyldisilane (PMDS), isopropanol, n-butanethiol, chloroform, carbon tetrachloride, carbon tetrabromide, chloroform, 4-methylbenzenethiol and 4,4'-thiobisbenzenethiol; or (iv) any combination of the foregoing;

[0042] (c) The one or more azo initiators are selected from the group consisting of: azobisisobutyronitrile (AIBN), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride; 2,2-azobis(2-methylpropanediamine) dihydrochloride; 2,2'-azobis(N-(2-carboxyethyl)-2-methylpropanediamine hydrate; 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propene} dihydrochloride; and 2,2'-azobis(1-imino-1-pyrrolidine-2-ethylpropane) dihydrochloride; and

[0043] (d) The one or more redox initiators are selected from the group consisting of redox initiator systems composed of: ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS); tert-butyl hydroperoxide and sodium sulfite (tBHP / SS); Fe(II) / Fe(III)-hydroperoxide system, Fe(II) / Fe(III)-alkyl hydroperoxide system, alkyl hydroperoxide-sulfite system, peroxide-thiosulfate system, alkyl hydroperoxide-sulfinate system; alkyl hydroperoxide-hydroxymethane sulfinate system and tert-butyl hydroperoxide-hydroxymethane sulfinate system.

[0044] In some exemplary implementations of the method:

[0045] (a) The one or more optional stabilizers comprise sodium 2-mercaptobenzothiazole (Na-2-MBT);

[0046] (b) The one or more azo initiators comprise AIBN; and

[0047] (c) The one or more redox initiators comprise ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS) or tert-butyl hydroperoxide and sodium sulfite (tBHP / SS).

[0048] In some exemplary embodiments of the method, the one or more additives comprise:

[0049] (a) Diethylenetriaminepentaacetic acid;

[0050] (b) Diethylenetriaminepentaacetic acid and urea;

[0051] (c) Diethylenetriaminepentaacetic acid and sodium hypophosphite; or

[0052] (d) Diethylenetriaminepentaacetic acid, sodium hypophosphite and urea.

[0053] In some exemplary embodiments of the method, the redox-initiated reaction mixture comprises:

[0054] (a) Based on all components therein, a total monomer concentration ranging from 30-60 wt%, 32-55 wt%, 32-50 wt%, or 36-42 wt%, wherein the total monomer concentration is sufficient to heat the redox-initiated reaction mixture from the redox initiation temperature to the Tmax above 100 °C, wherein the redox-initiated reaction mixture is heated by the exothermic polymerization.

[0055] (b) Acrylamide in the total monomer concentration ranges from 1-100%, 35-95%, or 65-85% in molar percentage;

[0056] (c) The molar percentage of one or more additional monomers in the total monomer concentration ranges from 0-99%, 5-65%, or 15-35%;

[0057] (d) Optionally, a stabilizer concentration ranging from 0.01-2 wt%, 0.02-1.5 wt%, or 0.05-1.0 wt% based on the total weight of the monomers therein; and

[0058] (e) The range is 50-6000 [(µmol / kg)] 2 ]、100-5000 [(µmol / kg) 2 ]、200-5000 [(µmol / kg) 2 500-5000 [(µmol / kg)] 2 1000-5000 [(µmol / kg)] 2 ] or 1000-3000 [(µmol / kg)] 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant).

[0059] In some exemplary implementations of the method:

[0060] (a) The pH range is 7.2-7.8, and the equilibrium redox initiator product concentration range of tBHP / SS is 750-5000 [(µmol / kg)]. 2 The redox initiation temperature ranges from -4°C to 6°C, -4°C to 2°C, or -4°C to -2°C, and the total monomer concentration ranges from 36-42 wt%; or

[0061] (b) The pH range is 7.2-7.8, and the equilibrium redox initiator product concentration range of APS / FAS is 50-400 [(µmol / kg)]. 2 Furthermore, the redox initiation temperature ranges from -4°C to 6°C, -4°C to 2°C, or -4°C to -2°C, and the total monomer concentration ranges from 36 to 42 wt%.

[0062] In some exemplary embodiments of the method, the high reaction temperature DPAM:

[0063] (a) Standard viscosity (SV) with a range of 6.0-7.5 mPas, 6.5-7.4 mPas or 7.0-7.2 mPas, determined using a Brookfield DV1MLV viscometer with a UL adapter and ULA-DIN-Y spindle at 25°C ± 0.2°C and 60 rpm;

[0064] (b) Having high water solubility as determined by the content of residual insoluble gel in the range of 0-0.5wt%, 0-0.2wt%, 0-0.1wt% or 0-<0.1wt%, determined by dissolving 1g of the high reaction temperature DPAM in 1L of water at 25°C and then filtering through 300µm pores;

[0065] (c) Compared to DPAM polymers prepared using the same monomers and the same high-temperature (Tmax > 100°C) method, it exhibits higher standard viscosity (SV) and higher water solubility, the difference being a lower pH; or

[0066] (d) Any combination of the foregoing items.

[0067] On the other hand, the present invention provides a method for preparing high-reaction-temperature dry polyacrylamide (DPAM) via redox-initiated free radical polymerization, the method comprising:

[0068] (a) Provide an aqueous solution of an olefinic unsaturated monomer, the aqueous solution comprising water and (i) acrylamide or (ii) acrylamide and one or more additional monomers selected from the group consisting of: acrylic acid and its salt, acrylamide tert-butyl sulfonic acid (ATBS) and its salt, or a combination of acrylic acid and sodium ATBS.

[0069] (b) Add 2-mercaptobenzothiazole (MBT) or a salt thereof;

[0070] (c) Add diethylenetriaminepentaacetic acid;

[0071] (d) Add azobisisobutyronitrile (AIBN);

[0072] (e) Adjust the pH to a range of 7-8, 7.1-7.8, or 7.25-7.75;

[0073] (f) Cool to a redox initiation temperature in the range of below 25°C, -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to 3°C;

[0074] (g) Add one or more redox initiators selected from the group consisting of the following redox initiator systems: ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS) system; tert-butyl hydroperoxide and sodium sulfite (tBHP / SS) system, thereby producing a redox-initiated reaction mixture;

[0075] (h) Allowing gel polymerization to occur under substantially adiabatic conditions and in a high-pressure inert gas atmosphere, wherein the high pressure is sufficient to prevent boiling, wherein the redox-initiated reaction mixture is heated by the exothermic reaction to a maximum reaction temperature (Tmax) in the range of above 100°C, 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, or 100°C to 110°C, wherein the gel polymerization occurs;

[0076] (i) The Tmax is maintained for a curing time ranging from 10 to 240 minutes, 30 to 180 minutes, or 60 to 120 minutes, thereby providing a high reaction temperature polyacrylamide gel;

[0077] (j) Optionally, the high reaction temperature polyacrylamide gel is dried and ground to form the high reaction temperature DPAM;

[0078] The high-reaction-temperature DPAM is a homopolymer, copolymer, or terpolymer.

[0079] In some exemplary embodiments of the method, the redox-initiated reaction mixture comprises:

[0080] (a) Based on the total monomer concentration of all components, ranging from 32-50 wt% or 36-42 wt%;

[0081] (b) Acrylamide in the total monomer concentration ranges from 1-100%, 35-95%, or 65-85% in molar percentage;

[0082] (c) The molar percentage of one or more additional monomers in the total monomer concentration ranges from 0-99%, 5-65%, or 15-35%;

[0083] (d) Optionally, based on the total weight of the monomers therein, the stabilizer concentration ranges from 0.01-2 wt%, 0.02-1.5 wt%, or 0.05-1.0 wt%.

[0084] (e) The range of tBHP / SS is 750-5000 [(µmol / kg)] 2 1000-5000 [(µmol / kg)] 2 ] or 1000-3000 [(µmol / kg)] 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant) or APS / FAS ranges from 50 to 1000 [µmol / kg]. 2 50-600 [(µmol / kg)] 2 ] or 50-400 [(µmol / kg) 2The equilibrium redox initiator product concentration (e.g., oxidant × reductant); or

[0085] (f) Any combination of the foregoing terms.

[0086] On the other hand, the present invention provides a composition comprising high-reaction-temperature dry polyacrylamide (DPAM) that can be obtained by the method according to any one of the foregoing claims. Attached Figure Description

[0087] The present invention will now be described in more detail with reference to the accompanying drawings.

[0088] Figure 1 Exemplary graphs are provided showing the relationship between the SV (UL viscosity) of high reaction temperature DPAMs prepared according to Examples 1-6 and Comparative Examples 1-3 and the pH of the reaction.

[0089] Figure 2 Exemplary graphs of SV (UL viscosity) versus maximum reaction temperature (Tmax) for high reaction temperature DPAMs prepared at different pH, redox levels, and monomer concentrations are provided, including Examples 1-10 and Comparative Examples 1-6. Detailed Implementation

[0090] Before describing the present invention, the following definitions are provided. Unless otherwise stated, all terms should be interpreted in accordance with the understanding of those skilled in the art.

[0091] definition

[0092] As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” include plural indicators.

[0093] As used herein, the term "enhanced oil recovery" or "EOR" (sometimes also referred to as improved oil recovery ("IOR") or tertiary mineral oil production) generally refers to a technique used to increase the amount of unrefined petroleum (e.g., crude oil) that can be extracted from reservoirs such as oilfields. Examples of EOR techniques include, for example, miscible gas injection (e.g., carbon dioxide flooding), chemical injection (sometimes referred to as chemical enhanced oil recovery ("CEOR")), and include, for example, polymer flooding, alkaline flooding, surfactant flooding, micellar polymer flooding, consistency control operations, and combinations thereof, such as alkaline-polymer flooding or alkaline-surfactant-polymer flooding), microbial injection, and thermal recovery (e.g., circulating steam, steam flooding, or fire flooding). In some embodiments, EOR operations may include polymer ("P") flooding operations, alkaline-polymer ("AP") flooding operations, surfactant-polymer ("SP") flooding operations, alkaline-surfactant-polymer ("ASP") flooding operations, consistency control operations, or any combination thereof.

[0094] As used herein, the terms “polymer flood” or “polymer flooding” generally refer to a chemically enhanced oil recovery (EOR) technique that typically involves injecting an aqueous fluid thickened with one or more water-soluble polymers into an oil reservoir via an injection borehole to facilitate the movement of oil left behind after primary and / or secondary recovery. As a general result of injecting one or more polymers, oil may be forced toward the production borehole, and oil may be generated through the production borehole. Detailed information on exemplary polymer flooding and polymers suitable for this purpose is disclosed, for example, in “Petroleum, Enhanced Oil Recovery, Kirk - Othmer, Encyclopedia of Chemical Technology, online version, John Wiley & Sons, 2010,” which is incorporated herein by reference in its entirety.

[0095] As used herein, the term "polyacrylamide" or "PAM" generally refers to polymers and copolymers containing an acrylamide moiety, and the term covers any polymer or copolymer (including terpolymers) containing an acrylamide moiety, such as one or more acrylamide polymers (copolymers) and additional monomers capable of copolymerizing with acrylamide. Furthermore, PAM may include any of the polymers or copolymers discussed herein.

[0096] As used herein, the term "high reaction temperature DPAM" refers to DPAM produced by a method in which the highest reaction temperature (Tmax) reached during polymerization is above 100°C. High reaction temperature DPAM produced by exemplary embodiments of the methods of the present invention can be used for friction reduction, paper retention, as a paper strengthening agent, as a thickener and / or flocculant, water treatment, tailings treatment, wastewater treatment, drinking water treatment, mineral mining applications, and oil and gas extraction applications, such as any EOR technology, including but not limited to polymer flooding.

[0097] As used herein, the term "monomer" generally refers to nonionic monomers, anionic monomers, cationic monomers, zwitterionic monomers, betaine monomers, and zwitterionic-pair monomers.

[0098] As used herein, the terms “polymer” or “polymer additive” and similar terms are used in their ordinary meaning as understood by those skilled in the art, and are therefore used herein to refer to or describe macromolecules (or groups of such molecules) that may contain repeating units. Polymers can be formed in a variety of ways, including by polymerizing monomers and / or by chemically modifying one or more repeating units of a precursor polymer. Unless otherwise stated, polymers may comprise “homopolymers” that may contain substantially the same repeating units, which can be formed, for example, by polymerizing a particular monomer. Unless otherwise stated, polymers may also comprise “copolymers” that may contain two or more different repeating units, which can be formed, for example, by copolymerizing two or more different monomers and / or by chemically modifying one or more repeating units of a precursor polymer. Unless otherwise stated, polymers or copolymers may also comprise “terpolymers” or “quaternary copolymers,” which generally refer to polymers containing three, four, or more different repeating monomer units. As used herein, the term “polymer” is intended to include both the acidic form of the polymer and its various salts. Polymers can be inherently amphoteric, that is, containing both anionic and cationic substituents, but not necessarily in equal proportions.

[0099] As used herein, the term "nonionic monomer" generally refers to a monomer having a neutral charge. Exemplary nonionic monomers may comprise, but are not limited to, monomers comprising the group consisting of: acrylamide ("AMD"), methacrylamide, vinyl, allyl, ethyl, etc., all of which may be substituted with side chains selected from, for example, alkyl, aralkyl, dialkyl, ethoxy, and / or hydrophobic groups. In one exemplary embodiment, the nonionic monomer may comprise AMD. In some embodiments, the nonionic monomer may comprise, but is not limited to, vinylamides (e.g., acrylamide, methacrylamide, N-methacrylamide, N,N-dimethylacrylamide), 4-acryloylmorpholine, maleic anhydride, N-vinylpyrrolidone, vinyl acetate, N-vinylformamide, and their derivatives, such as hydroxyethyl(meth(acrylate)CH2=CR-COO-CH2CH2OH (I) and CH2=CR-CO-N(Z1)(Z2) (2) N-substituted (meth)acrylamide (II), R = H or Me; Z1 = 5-15C alkyl; 1-3C alkyl substituted with 1-3 phenyl, phenyl, or 6-12C cycloalkyl (both optionally substituted), and Z2 = H; or Z1 and Z2 are each 3-10C alkyl; (II) is N-tert-hexyl, tert-octyl, methylundecyl, cyclohexyl, benzyl, diphenylmethyl, or triphenylacrylamide. Nonionic monomers include N-isopropylacrylamide, N-vinylformamide, methacrylamide; N-alkylacrylamide, including but not limited to N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, and N-butylacrylamide; N,N-dialkylacrylamide, including but not limited to N,N-dimethylacrylamide and N,N-diethylacrylamide; N-alkylmethylacrylamide; alkyl acrylates; hydroxyalkyl acrylates and hydroxyalkyl methacrylates, including but not limited to methyl acrylate, 2-hydroxy acrylate... Ethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; dialkyl acrylates and dialkyl methacrylates, including but not limited to 2,3-dihydroxypropyl acrylate, 3,4-dihydroxybutyl acrylate, 2,3-dihydroxypropyl methacrylate (DHPMA), and 3,4-dihydroxybutyl methacrylate; alkyl acrylates, including but not limited to methyl methacrylate; acrylonitrile; N-vinylmethylacetamide, N-vinylmethylformamide; N-vinyl acetate, glyoxylated acrylamide, and vinylpyrrolidone. For example, nonionic monomers can be combined with acrylamide to form copolymers.

[0100] As used herein, the term "anionic monomer" can refer to an anionic monomer that is substantially all or part (in equilibrium) anionic in a pH range of about 1.0 to about 10.0. Depending on the pKa value of the acidic protons contained therein, anionic monomers may be neutral at low pH levels (e.g., about 0-1, 0-2, or 0-3). Some anionic monomers are obtained in anionic form, such as alkali metal salts, alkaline earth metal salts, and ammonium salts, such as acrylic acid and sodium acrylamide tert-butyl sulfonate (ATBS).

[0101] Examples of anionic monomers that may be used herein include, but are not limited to, anionic monomers comprising acrylic acid, methacrylic acid, maleic acid monomers, acrylic acid, calcium diacrylate, and / or any monomer substituted with a carboxylic acid group or a salt thereof. In some embodiments, the anionic monomer may be substituted with a carboxylic acid group and includes, for example, acrylic acid and methacrylic acid. In some embodiments, the anionic monomer that may be used herein may be a (meth)acrylamide monomer, wherein the amide group has been hydrolyzed to a carboxyl group. According to other embodiments, the monomer may be a derivative or salt of a monomer. Further examples of anionic monomers include, but are not limited to, anionic monomers comprising a sulfonic acid or a sulfonic acid group or both. In some embodiments, anionic monomers that may be used herein may comprise a sulfonic acid functional group, which may comprise, for example, 2-acrylamido-2-methylpropanesulfonic acid (acrylamido-tert-butylsulfonic acid or "ATBS"). In some embodiments, the anionic monomer may comprise an organic acid. In some embodiments, the anionic monomer may comprise acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamidomethylpropanesulfonic acid, vinylphosphonic acid, styrene sulfonic acid, and salts thereof, such as sodium, ammonium, and potassium. In other embodiments, the anionic monomer may comprise acrylic acid, methacrylic acid; sulfonic acid, phosphonic acid, maleic acid, itaconic acid, vinyl sulfonic acid, acrylamido-tert-butyl sulfonic acid (ATBS), acrylamido-methanesulfonic acid, acrylamido-ethanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, and their alkali metal salts, alkaline earth metal salts, and ammonium salts. The anionic monomers may be combined, for example, to form a terpolymer of acrylamide, acrylic acid, and acrylamido-tert-butyl sulfonic acid (ATBS). In an exemplary embodiment, one or more acrylamide polymers (polymers) may comprise at least one monoolefinically unsaturated monomer containing an acid group, such as a monomer containing at least one group selected from -COOH, SO3H, or -PO3H2. Examples of such monomers may include, but are not limited to, acrylic acid, methacrylic acid, vinyl sulfonic acid, allyl sulfonic acid, or 2-acrylamido-2-methylpropanesulfonic acid, particularly preferably acrylic acid and / or 2-acrylamido-2-methylpropanesulfonic acid, and most preferably acrylic acid or a salt thereof. In one exemplary embodiment, one or more acrylamide polymers (copolymers), or each of one or more acrylamide polymers (copolymers), may contain acrylic acid and / or 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof.

[0102] The term "water-soluble polymer" generally refers to any polymer that can be dissolved and / or dispersed in water. The polymer can alter the physical properties of aqueous systems undergoing gelation, thickening, viscousening, or emulsification / stabilization. The polymer can perform a variety of functions, including but not limited to use as a dispersant and suspending agent, stabilizer, thickener, viscous agent, gelling agent, flocculant and coagulant accelerator, film-forming agent, humectant, adhesive, and lubricant.

[0103] As used herein, the terms "aqueous solution" or "solution" generally refer to a mixture of water and one or more water-soluble solutes, which are completely dissolved with little or no residual undissolved polymer gel. The solution may be homogeneous. When mixed with excess water, the polymer article preferably dissolves completely, and the resulting polymer solution preferably does not contain discrete polymer particles or residual gel.

[0104] The term "gel polymerization" refers to a polymerization reaction carried out without stirring, resulting in a solid polymer gel. The preparation of high molecular weight polyacrylamide can be particularly advantageously carried out via adiabatic gel polymerization. In this case, a solution of acrylamide and optionally a water-soluble copolymer is first prepared in water. The monomer concentration can be from 20% to 70% by weight or from 30% to 60% by weight. The solution is polymerized without stirring, and the reactor is typically neither heated nor cooled. This produces a solid polymer gel, which is dried and ground to obtain granules or powder.

[0105] The term "redox-initiated radical polymerization" refers to radical polymerization initiated by a radical formed by a redox reaction involving a single electron transfer between an oxidizing agent and a reducing agent. Radical polymerization is a polymerization method in which polymer units are formed by the continuous addition of radicals. It is a chain-growing polymerization, where polymers are formed by the continuous addition of radical building blocks (repeating units). Radicals can be formed through a variety of different mechanisms, typically involving a single initiator molecule. After its formation, the initiating radical adds a (non-radical) monomer unit, thereby causing the polymer chain to grow. Chain elongation ends with a termination step, in which two radicals react to form a stable covalent bond. Almost all radical chain reactions require a separate initiation step, in which radical species are generated in the reaction mixture. The mechanism involves initiation, chain growth, and then chain termination in sequence. Initiation can be achieved by directly adding stable radicals to the reactants, which show little or no tendency to self-bind, but still involves a separate initiation step because these stable radicals are typically inorganic ions or metals. A very efficient method for generating radicals under mild conditions is through single electron transfer reactions, among which redox initiation is the most efficient. This method has been widely used in initiating polymerization reactions and is of industrial importance (e.g., in low-temperature emulsion polymerization). Besides the very short induction period (almost negligible), the low activation energy (40-80 kJ / mol) allows redox polymerization to proceed under milder conditions than thermal polymerization. This reduces the likelihood of side-chain reactions producing high molecular weight polymers in high yields.

[0106] The term "redox initiator" or "redox initiator system" refers to a chemical substance (e.g., an oxidizing agent and a reducing agent) that reacts in the form of a redox reaction to form free radicals, which can then initiate a free radical polymerization reaction. Unlike thermal initiators (e.g., azo initiators) that require high temperatures, redox initiators provide a reliable source of free radicals under mild conditions (e.g., temperatures below 25°C, below 0°C, or below -2°C). Redox initiators for free radical polymerization are known in principle to those skilled in the art. Suitable examples of “redox initiator systems” include ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS); tert-butyl hydroperoxide and sodium sulfite (tBHP / SS); Fe(II) / Fe(III)-hydroperoxide systems, Fe(II) / Fe(III)-alkyl hydroperoxide systems, alkyl hydroperoxide-sulfite systems, peroxide-thiosulfate systems, alkyl hydroperoxide-sulfinate systems; alkyl hydroperoxide-hydroxymethane sulfinate systems, and tert-butyl hydroperoxide-hydroxymethane sulfinate systems. Preferably, the tBHP / SS system or the APS / FAS system is used. The oxidant and reductant can be added individually or together (i.e., premixed) as separate compounds or as solutions. The redox initiator system can be added before, simultaneously with, or shortly after the addition of monomers, azo initiators, additives, and optional stabilizers. Redox initiator systems are non-renewable and may be consumed; therefore, the time between the addition of the redox initiator and the addition of the monomer must be minimized. Preferably, the redox initiator is added simultaneously with or after the monomer is added to the reactor. In some embodiments, the redox initiator is added after adjusting the pH to a range of 7-9, 7-8, 7.1-7.8, or 7.25-7.75, and after cooling to a redox initiation temperature below 25°C. The redox initiator can be added before or after placing the reaction under an inert gas such as N2, Ar, or He (i.e., inertization). Preferably, the reaction environment is inertized under an inert gas before adding the redox initiator. A reducing agent can also be added to reduce molecular oxygen in the solution.

[0107] Typically, redox initiators are added until prior to polymerization. A solution of the redox initiator, such as an aqueous solution, is preferred. For example, they can be metered in during or after the charging of the polymerization reactor. Advantageously, the redox initiator can be metered into the monomer feed of the polymerization reactor during the charging process. To ensure rapid mixing of the redox initiator, the monomer feed can advantageously be equipped with a static mixer. Under adiabatic conditions, the heat generated by redox-initiated polymerization causes an increase in reaction temperature, thereby providing sufficient heat to cause the homolytic dissociation of bonds in the azo initiator, which may be present in solution. Preferably, a maximum temperature (Tmax) above 100°C is reached, more preferably 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, 100°C to 110°C, or 100°C to 105°C. Therefore, after using a redox initiator, the polymerization begins to release heat, causing the azo initiator to eventually decompose and form free radicals as the temperature rises, essentially causing thermally initiated polymerization to occur.

[0108] The term "redox initiation temperature" refers to the reaction temperature at which a redox initiator is added. Suitable redox initiation temperature ranges are -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to 3°C.

[0109] In the kinetic rate expression for each redox reaction, the terms "equilibrium redox initiator product" and "oxidant × reductant" can be calculated using the initial concentration of the present redox initiator (e.g., ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS); tert-butyl hydroperoxide and sodium sulfite (tBHP / SS)). The equilibrium redox initiator product has [(µmol / kg)] 2 The unit is ].

[0110] The term "stabilizer" refers to a compound typically added to a polymerization reaction to prevent the polymer from being degraded by molecular oxygen. Common practice involves adding a stabilizer or combination of stabilizers to the polymer solution to prevent further degradation of the polymer by molecular oxygen or molecular oxygen free radicals. Such stabilizers may be free radical scavengers. Free radical scavengers react with free radicals (e.g., oxygen free radicals, or other undesirable free radicals formed by UV light or other redox processes), rendering them unable to attack and chemically degrade the polymer. Examples of such stabilizers include sulfur compounds (e.g., 2-mercaptobenzothiazole) or sterically hindered amines. WO 2010 / 133258 A1 and the literature cited therein outline the use of various stabilizers in polymer solutions to prevent molecular oxygen from degrading the polymer by free radicals produced from tertiary mineral oils. Their reactivity to free radicals arising during free radical polymerization cannot be too high (so that they significantly affect the polymerization). Therefore, suitable stabilizers are either only low in reactivity under polymerization conditions or inert to free radicals arising during polymerization. Examples of stabilizers include one or more free radical scavengers, including but not limited to thiourea, N,N'-dimethylthiourea, N,N'-diethylthiourea, N,N'-diphenylthiourea, thiocyanate, tetramethylthiuram disulfide, 2-mercaptobenzothiazole (MBT) and its salts (e.g., sodium MBT (Na)). 2-MBT), 2-mercaptobenzimidazole and its salts, sodium dimethyl dithiocarbamate, sodium diethyl dithiocarbamate, 2,2'-dithiobis(benzothiazole), 4,4'-thiobis(6-tert-butyl-m-cresol), dicyandiamide, cyanamide, p-methoxyphenol, 2,6-di-tert-butyl-4-methylphenol, butylated hydroxyanisole, 8-hydroxyquinoline, 2,5-di(tert-pentyl)hydroquinone, 5-hydroxy-1,4-naphthoquinone, dimethyl ketone, propyl-3,4,5-trihydroxybenzoate, N-nitrosophenylhydroxylamine, 4-hydroxy-2,2,6,6-tetramethyloxypiperidine, (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 1,2,2 6,6-Pentamethyl-4-piperidinol or any combination thereof. The stabilizer may optionally be added at any point during the polymerization process (e.g., before, during, or after polymerization). In this embodiment, the stabilizer may optionally be added directly to the aqueous monomer solution at any time before, during, or after monomer addition. A single or multiple stabilizers may be added. The stabilizer may also be added before or after cooling, before or after pH adjustment, and before or after redox initiation. More than one stabilizer may be added together or in single or multiple doses consecutively. In a preferred embodiment, the stabilizer (e.g., MBT or Na2-MBT) is added directly to the aqueous solution of the olefinic unsaturated monomer before pH adjustment, before cooling, and before redox initiation.

[0111] The term "azo initiator" refers to a compound typically added to a polymerization reaction to form free radicals through homolytic bond splitting (thermal or photoinitiation), thereby forming initiating free radicals that participate in polymerization. According to the invention, the aqueous solution further comprises at least one azo initiator having a 10-hour half-life in water having a temperature of 40°C to 90°C, preferably 50°C to 75°C. The 10-hour half-life temperature of the azo initiator is a parameter known to those skilled in the art describing the behavior of the initiator. This value describes the temperature at which half of the initially present amount of initiator decomposes after 10 hours in each case. For example, the corresponding value can be obtained from a datasheet of azo initiators. Based on a 10-hour half-life of 40°C to 75°C, the initiator will not decompose at room temperature, or at least will not decompose at a significant rate. This value is based on a solution in water.

[0112] To obtain high molecular weight polymers with high viscosity, it is desirable to initiate polymerization at the lowest possible temperature. An exemplary initiation temperature range is -10°C to room temperature (e.g., about 25°C). Preferably, lower temperatures, such as -10°C to 10°C or -6°C to +3°C, are used for initiation. Following redox initiation, the heat released by polymerization heats the mixture. Upon reaching a sufficient temperature, the azo initiator begins to decompose to form free radicals, which also initiate polymerization.

[0113] Examples of suitable azo initiators include azobisisobutyronitrile (AIBN), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride; 2,2-azobis(2-methylpropanediamine) dihydrochloride; 2,2'-azobis(N-(2-carboxyethyl)-2-methylpropanediamine hydrate; 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propene} dihydrochloride; and 2,2'-azobis(1-imino-1-pyrrolidine-2-ethylpropane) dihydrochloride. Azo initiators are preferably completely water-soluble, but it is sufficient if they are dissolved in the monomer solution in the desired amount. For example, AIBN ( Azobis(isobutyronitrile) is practically insoluble in water but soluble in aqueous solutions optionally containing 25% to 45% by weight of the monomer. The azo initiator can be added before or after cooling, before or after pH adjustment, and before, simultaneously with, or after redox initiation, preferably simultaneously with or before redox initiation. A single or multiple azo initiators can be added. More than one azo initiator can be added together or in single or multiple doses consecutively. In a preferred embodiment, the azo initiator (e.g., AIBN) is added directly to the aqueous solution of the olefinically unsaturated monomer before pH adjustment, cooling, and redox initiation.

[0114] The term "chelator" refers to a chelating agent that bonds with a multivalent metal in solution through chelation, thereby preventing the metal from participating in harmful reactions. Chelation is the bonding of an ion or molecule to a metal ion. It involves the formation or presence of two or more individual coordinate bonds between a multi-coordinate (multi-bonded) ligand and a single central metal atom. Suitable chelating agents include diethylenetriaminepentaacetic acid (pentetic acid), ethylenediaminetetraacetic acid (EDTA) and its salts, 2,2',2",2"'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA), phosphoric acid, and their alkali metal salts, alkaline earth metal salts, and ammonium salts. These can be added before or after cooling, before or after pH adjustment, and before, simultaneously with, or after redox initiation, preferably simultaneously with or before redox initiation. Single or multiple chelating agents can be added. Multiple chelating agents can be added together or in single or multiple doses consecutively. In a preferred embodiment, the chelating agent (e.g., penteacin) is added directly to the aqueous solution of the olefinic unsaturated monomer before pH adjustment, cooling, and redox initiation.

[0115] The term "liquidation agent" refers to a molecule in an aqueous solution that can disrupt the hydrogen bonding network between water molecules (i.e., exhibit liquidation activity). This affects the stability of the native state of other molecules (primarily macromolecules, such as polymers) in the solution by weakening hydrophobic effects and preventing the formation of higher-order polymer structures and aggregation. A liquidation agent is a structure-disrupting additive, and general examples can include surfactants, low-molecular-weight polymers, urea, some salts, etc. A liquidation agent can also be considered an additive that induces or increases "chaos" or entropy in a system. Suitable examples of liquidation agents for preventing aggregation during gel polymerization include urea, thiourea, alcohols, glycerol, guanidine, and guanidine cation halide salts, which can be added before or after cooling, before or after pH adjustment, and before, simultaneously with, or after redox initiation, preferably simultaneously with or before redox initiation. A single or multiple liquidation agents can be added. Multiple liquidation agents can be added together or in single or multiple doses consecutively. In a preferred embodiment, the ionizing agent (e.g., urea) is added directly to the aqueous solution of the olefinic unsaturated monomer before pH adjustment, cooling, and redox initiation.

[0116] The term "chain transfer agent" refers to a molecule that participates in the chain termination reaction during polymerization, and this molecule affects the final molecular weight of the polymer and may also cause branching. In conventional free radical polymerization, controlling the polymer chain length is difficult. A classic method for controlling molecular weight is to add a chain transfer agent to the polymerization medium to reduce the molecular weight of the polymer chain and prevent the formation of abnormally long polymer chains. Such abnormally long chains can lead to inappropriate solubility of the final polymer. Suitable chain transfer agents include hypophosphite and its salts, sodium hypophosphite, sodium formate, pentamethyldisilane (PMDS), isopropanol, n-butanethiol, chloroform, carbon tetrachloride, carbon tetrabromide, chloroform, 4-methylbenzenethiol, and 4,4'-thiobisphenylthiol. These chain transfer agents can be added before or after cooling, before or after pH adjustment, and before, simultaneously with, or after redox initiation, preferably simultaneously with or before redox initiation. Single or multiple chain transfer agents can be added. Multiple chain transfer agents can be added together or in single or multiple doses consecutively. In a preferred embodiment, the chain transfer agent (e.g., sodium hypophosphite) is added directly to the aqueous solution of the olefinic unsaturated monomer before pH adjustment, cooling, and redox initiation.

[0117] The term "adiabatic conditions" or "basically adiabatic conditions" refers to conditions under which heat is almost impossible to escape from the polymerization reaction. "Adiabatic" as understood by those skilled in the art means the absence of heat exchange with the environment. This ideal is naturally difficult to achieve in practical chemical engineering. Therefore, in the context of this invention, "adiabatic" should be understood to mean "basically adiabatic," meaning that the reactor is not supplied with any heat from the outside during polymerization, i.e., it is not heated, and the reactor is not cooled during polymerization. The adiabatic reactor is properly insulated to allow minimal heat to flow into or out of the reactor. Those skilled in the art will understand that, depending on the internal temperature of the reactor and the ambient temperature, a certain amount of heat can be released or absorbed through the reactor walls due to the temperature gradient, but this effect naturally diminishes as the reactor size increases. Exothermic gel polymerization reactions carried out under basically adiabatic conditions will generate heat, and the reaction temperature will increase because the heat cannot escape. The solution polymerizes without stirring, and the reactor is typically neither heated nor cooled. This produces a solid polymer gel, which is dried and ground to obtain granules or powder.

[0118] The terms “inert atmosphere” or “inert gas atmosphere” are commonly known phrases in the art, referring to an atmosphere containing a sufficiently high concentration of an inert gas (e.g., N2, argon, helium, etc.) and a sufficiently low concentration of a reactive gas (e.g., less than 300 ppb, 200 ppb, or 100 ppb of O2) to allow redox-initiated polymerization reactions to occur.

[0119] As used herein, the phrase “wt.%” means 100% of the dry weight of additives in a formulation, solution or slurry per dry weight of solids.

[0120] Detailed description of the invention

[0121] This invention generally relates to compositions and methods for preparing high-reaction-temperature dry polyacrylamide (DPAM) polymers. Specifically, this disclosure provides a method for adiabatic redox-initiated free radical polymerization of a reaction mixture under pH and initial temperature conditions that allow the heat of polymerization to raise the reaction temperature to above 100°C (Tmax > 100°C), said reaction mixture comprising at least an acrylamide monomer, optionally a free radical scavenger stabilizer, an azo initiator, and a redox initiator. Gel polymerization under these conditions yields DPAM with improved standard viscosity and water solubility.

[0122] Significant efforts have been made to develop adiabatic free radical gel polymerization methods for preparing high-reaction-temperature DPAM (i.e., produced at high temperatures (Tmax) exceeding 100°C) with high molecular weight, good solubility (low residual insoluble gel and high viscosity (SV 6-7.5 mPas)). However, these efforts have not been successful due to undesirable side reactions at Tmax above 100°C and the potential formation of ultra-high molecular weight polymer chains during polymerization at high monomer concentrations. These phenomena result in an undesirable amount of insoluble matter in the final DPAM.

[0123] Those skilled in the art generally know that polymer solubility gradually decreases as the maximum polymerization temperature (Tmax) increases. Some patent disclosures (e.g., US 5633329, US 5296577, US 10233272 B2) indicate that polymers with good solubility and high SV cannot be produced at reaction temperatures exceeding 100°C.

[0124] Therefore, the object of the present invention is to provide a method for preparing polyacrylamide by gel polymerization, wherein the polymerization can be carried out at temperatures up to and above 100°C, which provides for the industrial-scale production of dry polyacrylamide-type polymers with high standard viscosity (SV 6-7.5 mPas) and good solubility (i.e., less than 0.5 wt% insoluble matter).

[0125] Previous in-house development has further demonstrated that, within a Tmax range of approximately 100°C to 130°C, SV decreases significantly with increasing total mass percentage (M solids, wt%) of monomer solids in the polymerization reaction mixture. High M solids (i.e., sufficient energy to be generated by the exothermic polymerization to heat the redox-initiated reaction mixture from a redox initiation temperature below 25°C to a maximum reaction temperature (Tmax) above 100°C) is highly beneficial for achieving high molecular weight polymers and is therefore a preferred reaction condition.

[0126] Therefore, another object of the present invention is to provide a method for preparing polyacrylamide by gel polymerization, the method using a high M solid with sufficient heat to generate enough heat to achieve a Tmax above 100°C, to provide industrial-scale production of dry polyacrylamide-type polymers with high standard viscosity (SV 6-7.5 mPas) and good solubility (i.e., less than 0.5 wt% insoluble matter).

[0127] The method of the present invention for preparing acrylamide polymers comprises, in the presence of an azo series initiator, in an aqueous medium having a pH of 7 or higher, polymerizing acrylamide monomer alone or a mixture of acrylamide monomers and monomers capable of copolymerizing with the acrylamide monomer at a reaction temperature range increased to above 100°C, followed by drying the resulting material. This is achieved by carefully balancing the combination of M solids, reaction mixture pH, initiation temperature, redox initiator chemistry and concentration, additives, and thermal initiator chemistry in the polymerization formulation.

[0128] By preparing the polymer according to the invention under increased M solids, sufficient heat was generated to achieve a Tmax above 100°C. Surprisingly, the early SV-M solids dependence was overcome, and a polymer with SV > 6 mPas and good solubility was produced. The improvement is significant and meets the quality requirements for SV and insoluble matter percentage, such as EOR, friction reduction, etc. The method of the present invention for preparing high reaction temperature dry polyacrylamide (DPAM) via redox-initiated free radical polymerization also provides a means to improve manufacturing capabilities.

[0129] According to the present invention, gel polymerization is affected by higher monomer solids and higher reaction temperatures (Tmax > 100 °C) than usual, and surprisingly, DPAM with SV > 6 mPas and good solubility is produced under equilibrium reaction conditions.

[0130] This invention generally relates to compositions and methods for preparing high-reaction-temperature dry polyacrylamide (DPAM) polymers. Specifically, this disclosure provides a method for adiabatic redox-initiated free radical polymerization of a reaction mixture comprising at least an acrylamide monomer, optionally a free radical scavenger stabilizer, an azo initiator, and a redox initiator, under initial pH and redox initiation temperature conditions that allow the heat of polymerization to raise the reaction temperature to above 100°C (Tmax > 100°C). Gel polymerization under these conditions yields DPAM with improved standard viscosity, improved water solubility, and little to no residual insoluble matter.

[0131] On one hand, the present invention provides a method for preparing high-reaction-temperature dry polyacrylamide (DPAM) via redox-initiated free radical polymerization, the method comprising:

[0132] (a) Providing or producing an aqueous solution of an olefinically unsaturated monomer, said aqueous solution comprising water and (i) acrylamide or (ii) acrylamide and one or more other monomers capable of copolymerizing with acrylamide;

[0133] (b) Optionally add one or more stabilizers;

[0134] (c) Optionally add one or more additives, including but not limited to one or more chelating agents, and optionally one or more liquid-leaching agents, one or more chain transfer agents, or any combination thereof;

[0135] (d) Add one or more azo initiators;

[0136] (e) Adjust the pH to a range of 7-9, 7-8, 7.1-7.8, or 7.25-7.75;

[0137] (f) Cooling to below 25°C the redox initiation temperature;

[0138] (g) Add one or more redox initiators to produce a redox-initiated reaction mixture;

[0139] (h) Allowing gel polymerization to occur under substantially adiabatic conditions, wherein the redox-initiated reaction mixture is heated to a maximum reaction temperature (Tmax) above 100°C by the exothermic polymerization; and

[0140] (i) The Tmax is maintained for a curing time, thereby providing a high reaction temperature polyacrylamide gel.

[0141] In some preferred embodiments, the total monomer content (M solids) is greater than 36 wt%, the pH range is 7.25-7.5, and the redox initiator system comprises tert-butyl hydroperoxide and sodium sulfite (tBHP / SS), added at a sufficiently high redox dosage level to initiate polymerization. Further improvements in solubility can be achieved by adding hypophosphite or urea.

[0142] In some exemplary embodiments, the method further includes drying and grinding the high reaction temperature polyacrylamide gel after step (i) to form the high reaction temperature DPAM as a homopolymer, copolymer, or terpolymer.

[0143] Adiabatic redox-initiated free radical gel polymerization can be carried out without stirring in any suitable adiabatic polymerization reactor system that can be pressurized to prevent the reaction mixture from boiling at temperatures exceeding 100°C.

[0144] In some exemplary embodiments of the method, the gel polymerization:

[0145] (a) Occurs in an atmosphere containing nitrogen, argon, helium, or a combination thereof; and / or

[0146] (b) It occurs at a high pressure above atmospheric pressure and is optionally maintained by exothermic heating of the polymerization or by pressurization with an inert gas, including but not limited to nitrogen, argon, helium or any combination thereof, and further wherein the high pressure is sufficient to prevent the aqueous reaction mixture from boiling when subjected to temperatures above 100°C.

[0147] Before adding the redox initiator system, the reaction mixture can be cooled to a redox initiation temperature suitable for preventing thermal initiation by the azo initiator.

[0148] In some exemplary embodiments, the method includes one or more of the following:

[0149] (a) The redox initiation temperature range is -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to 3°C;

[0150] (b) The final reaction temperature range is 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, 100°C to 110°C or 100°C to 105°C;

[0151] (c) After the addition of one or more of the aforementioned redox initiators, the final reaction temperature is reached within a time range of 5-120 minutes, 10-90 minutes, 20-90 minutes, or 20-60 minutes; and

[0152] (d) The curing time range is 10-240 minutes, 30-180 minutes or 60-120 minutes.

[0153] In some exemplary embodiments of the method, the one or more additional monomers comprise:

[0154] (a) One or more olefins, preferably water-soluble unsaturated nonionic monomers, including but not limited to methacrylamide; N-alkylacrylamides, including but not limited to N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide and N-butylacrylamide; N,N-dialkylacrylamides, including but not limited to N,N-dimethylacrylamide and N,N-diethylacrylamide; N-alkylmethylacrylamide; alkyl acrylates; hydroxyalkyl acrylates and hydroxyalkyl methacrylates, including but not limited to methyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxyethyl acrylate, etc. Hydroxybutyl ester, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; dialkyl acrylates and dialkyl methacrylates, including but not limited to 2,3-dihydroxypropyl acrylate, 3,4-dihydroxybutyl acrylate, 2,3-dihydroxypropyl methacrylate (DHPMA), and 3,4-dihydroxybutyl methacrylate; alkyl acrylates, including but not limited to methyl methacrylate; acrylonitrile; N-vinylmethylacetamide, N-vinylmethylformamide; N-vinyl acetate, acetoxylated acrylamide, and vinylpyrrolidone; and

[0155] (b) One or more olefinically unsaturated anionic monomers, including but not limited to acrylic acid, methacrylic acid; sulfonic acid, phosphonic acid, maleic acid, itaconic acid, vinyl sulfonic acid, acrylamidotert-butyl sulfonic acid (ATBS), acrylamidomethanesulfonic acid, acrylamidoethanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, and their alkali metal salts, alkaline earth metal salts, and ammonium salts; and

[0156] (c) Any combination of the foregoing terms.

[0157] In some exemplary embodiments of the method, the aqueous solution of the olefinically unsaturated monomer comprises:

[0158] (a) Acrylamide,

[0159] (b) Acrylamide and acrylic acid, or

[0160] (c) Acrylamide, acrylic acid and ATBS.

[0161] In some exemplary embodiments, the method comprises one, two, three, or all four of the following:

[0162] (a) The one or more optional stabilizers comprise one or more free radical scavengers, including but not limited to thiourea, N,N'-dimethylthiourea, N,N'-diethylthiourea, N,N'-diphenylthiourea, thiocyanate, tetramethylthiuram disulfide, 2-mercaptobenzothiazole (MBT) and its salts, 2-mercaptobenzimidazole and its salts, sodium dimethyl dithiocarbamate, sodium diethyl dithiocarbamate, 2,2'-dithiobis(benzothiazole), 4,4'-thiobis(6-tert-butyl-m-cresol), and bis(benzothiazole). Cyanamide, cyanamide, p-methoxyphenol, 2,6-di-tert-butyl-4-methylphenol, butylated hydroxyanisole, 8-hydroxyquinoline, 2,5-di(tert-amyl)hydroquinone, 5-hydroxy-1,4-naphthoquinone, dimethyl ketone, propyl-3,4,5-trihydroxybenzoate, N-nitrosophenylhydroxylamine, 4-hydroxy-2,2,6,6-tetramethyloxypiperidine, (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 1,2,2,6,6-pentamethyl-4-piperidinol or any combination thereof;

[0163] (b) The one or more additives comprise: (i) the one or more chelating agents, including but not limited to diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid (EDTA) and its salts, 2,2',2",2"'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA), phosphoric acid and its alkali metal salts, alkaline earth metal salts and ammonium salts; (ii) the one or more dissociating agents, including but not limited to urea, thiourea, alcohols, glycerol, guanidine and guanidine cation halide salts; (iii) the one or more chain transfer agents, including but not limited to hypophosphite and its salts, sodium hypophosphite, sodium formate, pentamethyldisilane (PMDS), isopropanol, n-butanethiol, chloroform, carbon tetrachloride, carbon tetrabromide, chloroform, 4-methylbenzenethiol and 4,4'-thiobisbenzenethiol; or (iv) any combination of the foregoing;

[0164] (c) The one or more azo initiators are selected from the group consisting of: azobisisobutyronitrile (AIBN), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride; 2,2-azobis(2-methylpropanediamine) dihydrochloride; 2,2'-azobis(N-(2-carboxyethyl)-2-methylpropanediamine hydrate; 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propene} dihydrochloride; and 2,2'-azobis(1-imino-1-pyrrolidine-2-ethylpropane) dihydrochloride; or

[0165] (d) The one or more redox initiators are selected from the group consisting of redox initiator systems composed of: ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS); tert-butyl hydroperoxide and sodium sulfite (tBHP / SS); Fe(II) / Fe(III)-hydroperoxide system, Fe(II) / Fe(III)-alkyl hydroperoxide system, alkyl hydroperoxide-sulfite system, peroxide-thiosulfate system, alkyl hydroperoxide-sulfinate system; alkyl hydroperoxide-hydroxymethane sulfinate system and tert-butyl hydroperoxide-hydroxymethane sulfinate system.

[0166] In some exemplary implementations of the method:

[0167] (a) The one or more optional stabilizers comprise sodium 2-mercaptobenzothiazole (Na-2-MBT);

[0168] (b) The one or more azo initiators comprise AIBN; and

[0169] (c) The one or more redox initiators comprise ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS) or tert-butyl hydroperoxide and sodium sulfite (tBHP / SS).

[0170] In some exemplary embodiments of the method, the one or more additives comprise:

[0171] (a) Diethylenetriaminepentaacetic acid;

[0172] (b) Diethylenetriaminepentaacetic acid and urea;

[0173] (c) Diethylenetriaminepentaacetic acid and sodium hypophosphite; or

[0174] (d) Diethylenetriaminepentaacetic acid, sodium hypophosphite and urea.

[0175] In some exemplary embodiments of the method, the redox-initiated reaction mixture comprises one or more of the following:

[0176] (a) Based on all components therein, a total monomer concentration ranging from 30-60 wt%, 32-55 wt%, 32-50 wt%, or 36-42 wt%, wherein the total monomer concentration is sufficient to heat the redox-initiated reaction mixture from the redox initiation temperature to the Tmax above 100 °C, wherein the redox-initiated reaction mixture is heated by the exothermic polymerization.

[0177] (b) Acrylamide in the total monomer concentration ranges from 1-100%, 35-95%, or 65-85% in molar percentage;

[0178] (c) The molar percentage of one or more additional monomers in the total monomer concentration ranges from 0-99%, 5-65%, or 15-35%;

[0179] (d) Optionally, a stabilizer concentration ranging from 0.01-2 wt%, 0.02-1.5 wt%, or 0.05-1.0 wt% based on the total weight of the monomers therein; and

[0180] (e) The range is 50-6000 [(µmol / kg)] 2 ]、100-5000 [(µmol / kg) 2 ]、200-5000 [(µmol / kg) 2 500-5000 [(µmol / kg)] 2 1000-5000 [(µmol / kg)] 2 1000-3000 [(µmol / kg)] 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant).

[0181] In some exemplary implementations of the method:

[0182] (a) The pH range is 7.2-7.8, and the equilibrium redox initiator product concentration range of tBHP / SS is 750-5000 [(µmol / kg)]. 2 The redox initiation temperature ranges from -4°C to 6°C, -4°C to 2°C, or -4°C to -2°C, and the total monomer concentration ranges from 36-42 wt%; or

[0183] (b) The pH range is 7.2-7.8, and the equilibrium redox initiator product concentration range of APS / FAS is 50-400 [(µmol / kg)]. 2 Furthermore, the redox initiation temperature ranges from -4°C to 6°C, -4°C to 2°C, or -4°C to -2°C, and the total monomer concentration ranges from 36 to 42 wt%.

[0184] In some exemplary embodiments of the method, the high reaction temperature DPAM includes one or more of the following:

[0185] (a) Standard viscosity (SV) in the range of 6.0–7.5 mPas, 6.5–7.4 mPas, or 7.0–7.2 mPas, determined using a Brookfield DV1MLV viscometer with a UL adapter and ULA-DIN-Y spindle at 25 °C ± 0.2 °C and 60 rpm;

[0186] (b) High water solubility, as determined by the residual insoluble gel content in the range of 0-0.5wt%, 0-0.2wt%, 0-0.1wt%, or 0-<0.1wt%, is determined by dissolving 1g of the high reaction temperature DPAM in 1L of water at 25°C and then filtering through 300µm pores.

[0187] (c) Higher standard viscosity (SV) and higher water solubility compared to DPAM polymers prepared using the same monomers and the same high-temperature (Tmax > 100°C) method, differing only in lower monomer concentration and lower pH; or

[0188] (d) Any combination of the foregoing items.

[0189] On the other hand, the present invention provides a method for preparing high-reaction-temperature dry polyacrylamide (DPAM) via redox-initiated free radical polymerization, the method comprising:

[0190] (a) Provide an aqueous solution of an olefinic unsaturated monomer, the aqueous solution comprising water and (i) acrylamide or (ii) acrylamide and one or more additional monomers selected from the group consisting of: acrylic acid and its salt, acrylamide tert-butyl sulfonic acid (ATBS) and its salt, or a combination of acrylic acid and sodium ATBS.

[0191] (b) Add 2-mercaptobenzothiazole (MBT) or a salt thereof;

[0192] (c) Add diethylenetriaminepentaacetic acid;

[0193] (d) Add azobisisobutyronitrile (AIBN);

[0194] (e) Adjust the pH to a range of 7-8, 7.1-7.8, or 7.25-7.75;

[0195] (f) Cool to a redox initiation temperature in the range of below 25°C, -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to +3°C;

[0196] (g) Add one or more redox initiators selected from the group consisting of the following redox initiator systems: ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS) system; tert-butyl hydroperoxide and sodium sulfite (tBHP / SS) system, thereby producing a redox-initiated reaction mixture;

[0197] (h) Allowing gel polymerization to occur under substantially adiabatic conditions and in a high-pressure inert gas atmosphere, wherein the high pressure is sufficient to prevent boiling, wherein the redox-initiated reaction mixture is heated by the exothermic reaction to a maximum reaction temperature (Tmax) in the range of above 100°C, 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, or 100°C to 110°C, wherein the gel polymerization occurs;

[0198] (i) Maintaining the Tmax for a curing time ranging from 10-240 minutes, 30-180 minutes, or 60-120 minutes, thereby providing a high-reaction-temperature polyacrylamide gel; and

[0199] (j) Optionally, the high reaction temperature polyacrylamide gel is dried and ground to form the high reaction temperature DPAM;

[0200] The high-reaction-temperature DPAM is a homopolymer, copolymer, or terpolymer.

[0201] In some exemplary embodiments of the method, the redox-initiated reaction mixture comprises one or more of the following:

[0202] (a) Based on the total monomer concentration of all components, ranging from 32-50 wt% or 36-42 wt%;

[0203] (b) Acrylamide in the total monomer concentration ranges from 1-100%, 35-95%, or 65-85% in molar percentage;

[0204] (c) The molar percentage of one or more additional monomers in the total monomer concentration ranges from 0-99%, 5-65%, or 15-35%;

[0205] (d) Optionally, based on the total weight of the monomers therein, the stabilizer concentration ranges from 0.01-2 wt%, 0.02-1.5 wt%, or 0.05-1.0 wt%.

[0206] (e) The range of tBHP / SS is 750-5000 [(µmol / kg)] 2 1000-5000 [(µmol / kg)] 2 ] or 1000-3000 [(µmol / kg)] 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant) or APS / FAS ranges from 50 to 1000 [µmol / kg]. 2 50-600 [(µmol / kg)] 2 ] or 50-400 [(µmol / kg)2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant); or

[0207] (f) Any combination of the foregoing terms.

[0208] On the other hand, the present invention provides a composition comprising high-reaction-temperature dry polyacrylamide (DPAM) that can be obtained or acquired by the method according to any one of the foregoing claims.

[0209] The methods and compositions illustratively disclosed herein may be practiced in the absence of any elements not specifically disclosed herein and / or any elements specifically disclosed herein. Exemplary embodiments of the invention and their advantages will be further disclosed in the following examples.

[0210] Example

[0211] The embodiments provided herein are for illustrative purposes only, in order to provide a more complete understanding of the invention. These embodiments should not be construed as limiting the invention in any way.

[0212] General methods

[0213] Laboratory reactor setup and gel polymerization

[0214] Adiabatic redox-initiated free radical gel polymerization was carried out in a low-temperature flask placed in a pressure chamber to prevent the reaction mixture from boiling at temperatures exceeding 100°C. The pressure chamber was converted from the interior of a pressure vessel used for painting (10-liter paint pressure vessel, without stirrer, manufacturer Protima, and distributed by Pressurepots.co.uk). Additional safety features were modified, and temperature measurements were obtained within the vessel.

[0215] Add polymerization reagents (e.g., monomers, azo initiators, additives, including but not limited to chelating agents, stabilizers, and / or chain transfer agents) to a low-temperature flask. Adjust the pH and cool the mixture, purging it with N2 gas. Add a redox initiator and visually inspect the polymerization to verify initiation by observing gel chains and / or temperature rise.

[0216] The pressure chamber was then closed and pressurized with N2 gas to prevent boiling when the reaction temperature rose above 100°C. The heat generated by the polymerization reaction caused the reaction temperature to rise to a maximum temperature (Tmax) above 100°C. After reaching Tmax, the reaction continued at Tmax for the required ripening time (i.e., reaction time), and then the chamber pressure was reduced to atmospheric pressure. The resulting polymer gel was cooled, pulverized, dried, and ground according to standard processing and drying procedures. The gel content and standard viscosity (SV) of the resulting polymer were evaluated.

[0217] Determination of gel content

[0218] The obtained polymer (1 g) was dissolved in 1 L of tap water at 25 °C (concentration: 1000 ppm). The solution was filtered through a stainless steel sieve with a mesh size of 300 µm, dried, and the amount of polymer gel remaining on the sieve was weighed. The weight percentage of the insoluble polymer residue was calculated.

[0219] Determination of standard viscosity (UL viscosity):

[0220] Standard viscosity was determined in each case. The resulting polymer was dispersed in deionized water and stirred until dissolved. NaCl solution was then added to achieve a polymer concentration of 0.1% and a NaCl concentration of 1.0 M. The UL viscosity (standard viscosity, SV) was determined at 25 ± 0.2 °C using a Brookfield DV1MLV viscometer with a UL adapter and a ULA-DIN-Y spindle at 60 rpm.

[0221] Example 1: Preparation of high-reaction-temperature DPAM copolymers

[0222] pH 7.25

[0223] Triggering temperature: -3℃.

[0224] Monomer concentration: 36.5% by weight

[0225] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0226] Adiabatic redox-initiated free radical gel polymerization was carried out according to general methods. 82.1 g of distilled water was added to a glass beaker equipped with a magnetic stirrer, followed by the sequential addition of 267.4 g of acrylamide (49.9% aqueous solution), 170.0 g of 35% sodium acrylate (SODAC) aqueous solution, 15.9 mg of the chelating agent diethylenetriaminepentaacetic acid pentaacetic acid pentasodium salt (sodium pentate, as a 40% aqueous solution), 0.38 g of the free radical oxygen scavenging stabilizer 2-mercaptobenzothiazole sodium (Na-2-MBT, as a 50% aqueous solution), and 185.0 mg of the azo initiator 2,2'-azobis(2-methylpropionitrile) (AIBN) dispersed in a small amount of monomer solution. AIBN was then subjected to oxidation in toluene at 67 °C. 1 / 2 It lasts for 10 hours.

[0227] The monomer solution was adjusted to pH 7.25 using a 50% sulfuric acid solution and then cooled to -5°C.

[0228] The cooled monomer solution was transferred to a low-temperature flask equipped with a temperature sensor, and the solution was purged by bubbling with N2 gas for 20 minutes. The initiation temperature after purging was -3°C. Subsequently, redox initiation (tBHP / SS) was achieved by adding 4 mL of an aqueous solution of 0.043% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0229] After mixing, the low-temperature flask was placed in a pressure chamber. After visualization of proper polymerization initiation (gel chain / temperature increase), the N2 purge was removed. The chamber was closed and then pressurized with N2 gas. The temperature was increased from -3°C to Tmax of 104°C over 50 minutes. After observing Tmax, the gel was cured at Tmax for another 2 hours, and then the N2 pressurization was removed.

[0230] After cooling, the obtained solid polymer gel block was pulverized using a meat grinder (LM-10 / P, Koneteollisuus Oy, Finland), and the resulting gel particles were dried in a fluidized bed dryer at 95°C (FBD95) for 30 minutes. A white, hard granular material was obtained, which was then converted into coarse powder with a particle size of <1000µm by centrifugal milling.

[0231] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0232] Example 2: Second preparation of high-reaction-temperature DPAM copolymers

[0233] pH 7.25

[0234] Triggering temperature: -3℃.

[0235] Monomer concentration: 36.5% by weight

[0236] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0237] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a smaller amount of redox initiator.

[0238] Redox initiation (tBHP / SS) was achieved by adding 2.4 mL of an aqueous solution of 0.051% tert-butyl hydroperoxide (tBHP) and 3.2 mL of an aqueous solution of sodium sulfite (SS).

[0239] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0240]

[0241] Example 3: Third preparation of high-reaction-temperature DPAM copolymers

[0242] pH 7.25

[0243] Triggering temperature: -3℃.

[0244] Monomer concentration: 36.5% by weight

[0245] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0246] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using different redox initiators. Redox initiation (APS / FAS) was achieved by adding 2.4 mL of an aqueous solution of 0.074% ammonium persulfate (APS) and 2.4 mL of an aqueous solution of 0.127% ammonium ferric(II) sulfate (FAS).

[0247] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0248] Example 4: Fourth preparation of high-reaction-temperature DPAM copolymers

[0249] pH 7.5

[0250] Triggering temperature: -3℃.

[0251] Monomer concentration: 36.5% by weight

[0252] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0253] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a higher pH and a smaller amount of redox initiator. Redox initiation (tBHP / SS) was achieved by adding 2.4 mL of an aqueous solution of 0.051% tert-butyl hydroperoxide (tBHP) and 2.4 mL of an aqueous solution of sodium sulfite (SS).

[0254] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0255] Example 5: The fifth preparation method of high reaction temperature DPAM copolymer

[0256] pH 7.5

[0257] Triggering temperature: -3℃.

[0258] Monomer concentration: 36.5% by weight

[0259] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0260] According to Example 3, adiabatic redox-initiated free radical polymerization was carried out using a higher pH. Redox initiation (APS / FAS) was achieved by adding 2.4 mL of an aqueous solution of 0.074% ammonium persulfate (APS) and 2.4 mL of an aqueous solution of 0.127% ammonium ferric(II) sulfate (FAS).

[0261] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0262] Example 6: The sixth preparation method of high reaction temperature DPAM copolymer

[0263] pH 7.75

[0264] Triggering temperature: -3℃.

[0265] Monomer concentration: 36.5% by weight

[0266] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0267] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a higher pH and a larger amount of redox initiator. Redox initiation (tBHP / SS) was achieved by adding 4 mL of an aqueous solution of 0.051% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0268] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0269] Example 7: The seventh preparation method of high reaction temperature DPAM copolymer

[0270] pH 7.5

[0271] Triggering temperature: +3℃.

[0272] Monomer concentration: 41.5% by weight

[0273] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0274] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a higher pH, a higher initiation temperature, a higher monomer concentration, and a larger amount of redox initiator.

[0275] Add 23.3 g of distilled water to a glass beaker equipped with a magnetic stirrer, and then sequentially add 303.3 g of acrylamide (49.9% aqueous solution), 192.8 g of 35% sodium acrylate (SODAC) aqueous solution, 15.9 mg of chelating agent diethylenetriaminepentaacetic acid pentasodium salt (sodium pentate, as a 40% aqueous solution), 0.43 g of free radical oxygen scavenging stabilizer 2-mercaptobenzothiazole sodium (Na-2-MBT, as a 50% aqueous solution), and 185.0 mg of azo initiator 2,2'-azobis(2-methylpropionitrile) (AIBN) dispersed in a small amount of monomer solution. AIBN in toluene at 67 °C... 1 / 2 It lasts for 10 hours.

[0276] The monomer solution was adjusted to pH 7.5 with a 50% sulfuric acid solution and then cooled to +1°C.

[0277] The cooled monomer solution was transferred to a low-temperature flask equipped with a temperature sensor and purged by bubbling with N2 gas for 20 minutes. The initiation temperature after purging was +3°C. Subsequently, redox initiation (tBHP / SS) was achieved by adding 2.4 mL of an aqueous solution of 0.068% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0278] After mixing, the low-temperature flask was placed in a pressure chamber. After visualization of proper polymerization initiation (gel chain / temperature increase), the N2 purge was removed. The chamber was closed and then pressurized with N2 gas. The temperature was increased from +3°C to Tmax at 127°C over 20 minutes. After observing Tmax, the gel was cured at Tmax for another 2 hours, and then the N2 pressurization was removed.

[0279] After cooling, the obtained solid polymer gel block was pulverized using a meat grinder (LM-10 / P, Koneteollisuus Oy, Finland), and the resulting gel particles were dried in a fluidized bed dryer at 95°C (FBD95) for 30 minutes. A white, hard granular material was obtained, which was then converted into coarse powder with a particle size of <1000µm by centrifugal milling.

[0280] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0281] Example 8: Eighth preparation method of high reaction temperature DPAM copolymer

[0282] pH 7.25

[0283] Triggering temperature: -3℃.

[0284] Monomer concentration: 36.5% by weight

[0285] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0286] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out by adding a chain transfer agent.

[0287] Add 81.8 g of distilled water to a glass beaker equipped with a magnetic stirrer, and then sequentially add 267.4 g of acrylamide (49.9% aqueous solution), 170.0 g of 35% sodium acrylate (SODAC) aqueous solution, 15.9 mg of chelating agent diethylenetriaminepentaacetic acid pentasodium salt (sodium pentate, as a 40% aqueous solution), 0.38 g of free radical oxygen scavenging stabilizer 2-mercaptobenzothiazole sodium (Na-2-MBT, as a 50% aqueous solution), 0.26 g of chain transfer agent sodium hypophosphite (0.2% aqueous solution), and 185.0 mg of azo initiator 2,2'-azobis(2-methylpropionitrile) (AIBN) dispersed in a small amount of monomer solution. AIBN in toluene at 67 °C... 1 / 2 It lasts for 10 hours.

[0288] The monomer solution was adjusted to pH 7.25 using a 50% sulfuric acid solution and then cooled to -5°C.

[0289] The cooled monomer solution was transferred to a low-temperature flask equipped with a temperature sensor, and the solution was purged by bubbling with N2 gas for 20 minutes. The initiation temperature after purging was -3°C. Subsequently, redox initiation (tBHP / SS) was achieved by adding 4 mL of an aqueous solution of 0.043% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0290] After mixing, the low-temperature flask was placed in a pressure chamber. After visualization of proper polymerization initiation (gel chain / temperature increase), the N2 purge was removed. The chamber was closed and then pressurized with N2 gas. The temperature was increased from -3°C to Tmax of 107°C over 50 minutes. After observing Tmax, the gel was cured at Tmax for another 2 hours, and then the N2 pressure was removed.

[0291] After cooling, the obtained solid polymer gel block was pulverized using a meat grinder (LM-10 / P, Koneteollisuus Oy, Finland), and the resulting gel particles were dried in a fluidized bed dryer at 95°C (FBD95) for 30 minutes. A white, hard granular material was obtained, which was then converted into coarse powder with a particle size of <1000µm by centrifugal milling.

[0292] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0293] Example 9: Ninth preparation of high-reaction-temperature DPAM copolymers

[0294] pH 7.5

[0295] Triggering temperature: -3℃.

[0296] Monomer concentration: 37% by weight

[0297] Monomer ratio: 61% by weight acrylamide and 39% by weight sodium acrylate.

[0298] Adiabatic redox-initiated free radical gel polymerization was carried out according to general methods. 62.9 g of distilled water was added to a glass beaker equipped with a magnetic stirrer, followed by the sequential addition of 240.1 g of acrylamide (49.9% aqueous solution), 216.4 g of 35% sodium acrylate (SODAC) aqueous solution, 15.9 mg of chelating agent diethylenetriaminepentaacetic acid pentasodium salt (sodium pentetrate, as a 40% aqueous solution), 0.39 g of free radical oxygen scavenging stabilizer 2-mercaptobenzothiazole sodium (Na-2-MBT, as a 50% aqueous solution), and 185.0 mg of azo initiator 2,2'-azobis(2-methylpropionitrile) (AIBN) dispersed in a small amount of monomer solution. AIBN was then subjected to oxidation in toluene at 67 °C. 1 / 2 It lasts for 10 hours.

[0299] The monomer solution was adjusted to pH 7.5 with a 50% sulfuric acid solution and then cooled to -5°C.

[0300] The cooled monomer solution was transferred to a low-temperature flask equipped with a temperature sensor and purged by bubbling with N2 gas for 20 minutes. The initiation temperature after purging was -3°C. Subsequently, redox initiation (tBHP / SS) was achieved by adding 3.2 mL of an aqueous solution of 0.051% tert-butyl hydroperoxide (tBHP) and 3.2 mL of an aqueous solution of sodium sulfite (SS).

[0301] After mixing, the low-temperature flask was placed in a pressure chamber. After visualization of proper polymerization initiation (gel chain / temperature increase), the N2 purge was removed. The chamber was closed and then pressurized with N2 gas. The temperature was increased from -3°C to Tmax of 110°C over 60 minutes. After observing Tmax, the gel was cured at Tmax for another 2 hours, and then the N2 pressure was removed.

[0302] After cooling, the obtained solid polymer gel block was pulverized using a meat grinder (LM-10 / P, Koneteollisuus Oy, Finland), and the resulting gel particles were dried in a fluidized bed dryer at 95°C (FBD95) for 30 minutes. A white, hard granular material was obtained, which was then converted into coarse powder with a particle size of <1000µm by centrifugal milling.

[0303] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0304] Example 10: The tenth preparation method of high reaction temperature DPAM copolymer

[0305] pH 7.5

[0306] Triggering temperature: -3℃.

[0307] Monomer concentration: 36.5% by weight

[0308] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0309] According to Example 5, adiabatic redox-initiated free radical polymerization was carried out by adding a chain transfer agent, for example, 0.26 g of sodium hypophosphite (0.2% aqueous solution) and 0.13 g of orthophosphoric acid (75% aqueous solution) were added to the reaction mixture before redox initiation.

[0310] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0311] Comparative Example 1: Preparation of the First Comparative Copolymer

[0312] pH 6.25

[0313] Triggering temperature: -1℃.

[0314] Monomer concentration: 36.5% by weight

[0315] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0316] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a lower pH and a smaller amount of redox initiator. Redox initiation (tBHP / SS) was achieved by adding 4 mL of an aqueous solution of 0.018% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0317] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0318] Comparative Example 2: Preparation of the Second Comparative Copolymer

[0319] pH 6.75

[0320] Triggering temperature: -2℃.

[0321] Monomer concentration: 36.5% by weight

[0322] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0323] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a lower pH and a smaller amount of redox initiator. Redox initiation (tBHP / SS) was achieved by adding 4 mL of an aqueous solution of 0.024% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0324] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0325] Comparative Example 3: Preparation of the Third Comparative Copolymer

[0326] pH 6.95

[0327] Triggering temperature: -2℃.

[0328] Monomer concentration: 36.5% by weight

[0329] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0330] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a lower pH and a smaller amount of redox initiator. Redox initiation (tBHP / SS) was achieved by adding 2.8 mL of an aqueous solution of 0.043% tert-butyl hydroperoxide (tBHP) and 4 mL of an aqueous solution of sodium sulfite (SS).

[0331] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0332] Comparative Example 4: Preparation of the Fourth Comparative Copolymer

[0333] pH 6.85

[0334] Initiation temperature: +5℃.

[0335] Monomer concentration: 41.5% by weight

[0336] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0337] According to Example 1, adiabatic redox-initiated free radical polymerization was carried out using a lower pH, a higher initiation temperature, a higher monomer concentration, and a smaller amount of redox initiator.

[0338] Add 23.3 g of distilled water to a glass beaker equipped with a magnetic stirrer, and then sequentially add 303.3 g of acrylamide (49.9% aqueous solution), 192.8 g of 35% sodium acrylate (SODAC) aqueous solution, 38.9 mg of chelating agent diethylenetriaminepentaacetic acid pentasodium salt (sodium pentate, as a 40% aqueous solution), 0.43 g of free radical oxygen scavenging stabilizer 2-mercaptobenzothiazole sodium (Na-2-MBT, as a 50% aqueous solution), and 312.0 mg of azo initiator 2,2'-azobis(2-methylpropionitrile) (AIBN) dispersed in a small amount of monomer solution. The AIBN in toluene at 67 °C... 1 / 2 It lasts for 10 hours.

[0339] The monomer solution was adjusted to pH 6.85 using a 50% sulfuric acid solution and then cooled to +4°C.

[0340] The cooled monomer solution was transferred to a low-temperature flask equipped with a temperature sensor, and the solution was purged by bubbling with N2 gas for 20 minutes. The initiation temperature after purging was +5°C. Subsequently, redox initiation (tBHP / SS) was achieved by adding 2 mL of an aqueous solution of 0.072% tert-butyl hydroperoxide (tBHP) and 2 mL of an aqueous solution of sodium sulfite (SS).

[0341] After mixing, the low-temperature flask was placed in a pressure chamber. After visualization of proper polymerization initiation (gel chain / temperature increase), the N2 purge was removed. The chamber was closed and then pressurized with N2 gas. The temperature was increased from +5°C to Tmax of 133°C over 15 minutes. After observing Tmax, the gel was cured at Tmax for another 2 hours, and then the N2 pressurization was removed.

[0342] After cooling, the obtained solid polymer gel block was pulverized using a meat grinder (LM-10 / P, Koneteollisuus Oy, Finland), and the resulting gel particles were dried in a fluidized bed dryer at 95°C (FBD95) for 30 minutes. A white, hard granular material was obtained, which was then converted into coarse powder with a particle size of <1000µm by centrifugal milling.

[0343] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0344] Comparative Example 5: Preparation of a fifth comparative copolymer of 69% by weight acrylamide and 31% by weight sodium acrylate.

[0345] pH 7.25

[0346] Triggering temperature: -3℃.

[0347] Monomer concentration: 36.5% by weight

[0348] According to Example 8, adiabatic redox-initiated free radical polymerization was performed without the use of Na-2-MBT.

[0349] The insoluble gel content and standard viscosity (SV) were determined using general methods. The polymerization conditions and results are summarized in Table 1.

[0350] Comparative Example 6: Preparation of the Sixth Comparative Copolymer

[0351] pH 7.75

[0352] Triggering temperature: -3℃.

[0353] Monomer concentration: 36.5% by weight

[0354] Monomer ratio: 69% by weight acrylamide and 31% by weight sodium acrylate.

[0355] According to Example 4, adiabatic redox-initiated free radical polymerization was performed using a higher pH. Polymerization did not initiate, and no gel chain / temperature increase was observed.

[0356] Table 1 summarizes the aggregation conditions.

[0357] Comments on the experiment:

[0358] Figure 1 Exemplary graphs are provided showing the relationship between the SV (UL viscosity) of high reaction temperature DPAMs prepared according to Examples 1-6 and Comparative Examples 1-3 and the pH of the reaction.

[0359] These results indicate that the standard viscosity increases significantly in a stepwise manner as the pH increases from below 7 to 7.25–7.75, with the highest SV achieved through polymerization at pH 7.5. As shown in Table 1, the residual insoluble gel content of all DPAMs is suitable for applications requiring good solubility, such as EOR (i.e., 0.5 wt% or less), where most DPAMs have little or no insoluble content.

[0360] Surprisingly, polymerization using the methods of the present invention in Examples 1-6 yields high-reaction-temperature DPAM with suitable SV values ​​for EOR applications, such as polymer flooding and other industrial applications, including but not limited to its use as a thickener, flocculant, paper reinforcing agent, for enhanced oil recovery, for tailings treatment, wastewater treatment, drinking water treatment, and for mining applications. By preparing the polymer according to the invention with increased M solids (i.e., total monomer content greater than 36 wt%), it was surprisingly found that the early SV-M solids correlation was overcome, and polymers with SV > 7.0 mPas and good solubility were produced. The improvement is significant and meets the quality requirements for SV and insoluble matter percentage. The method of the present invention for preparing high-reaction-temperature dry polyacrylamide (DPAM) via redox-initiated radical polymerization also provides a means to improve manufacturing capabilities.

[0361] Figure 2 Exemplary graphs of SV (UL viscosity) versus maximum reaction temperature (Tmax) for high-reaction-temperature DPAM prepared at different pH, redox levels, and monomer concentrations are provided, including Examples 1-10 and Comparative Examples 1-6. Only data points with good solubility (i.e., insoluble matter content ≤ 0.5 wt%) are shown. Added lines indicate the maximum viscosity achieved. Dashed lines indicate the maximum viscosity obtained when the process product pH < 7. Dotted lines indicate the maximum viscosity obtained when the process product pH > 7. Parameter summary for data points: monomer solids 35.5 - 41.5 wt%; redox initiation temperature -6 °C - +8 °C; Tmax 100-137 °C; pH 5.75-7.75 (triangle pH > 7); M solids 0-7000 ppm Na-2-MBT; fluidized bed drying at 95 °C for 30 min.

[0362] These results indicate that the standard viscosity increases significantly when polymerization is carried out at all the highest reaction temperatures (100-137°C) at pH > 7. As shown in Table 1, the residual insoluble gel content of all DPAMs is suitable for applications requiring good solubility (i.e., 0.5 wt% or less), with most DPAMs having little or no insoluble content. These results are quite surprising given the industry-wide failure to produce highly water-soluble DPAMs with high SV at reaction temperatures above 100°C. Without being bound by theory, it is reasonable to assume that the method of the present invention for producing DPAMs at high reaction temperatures provides optimal conditions to minimize the frequency of undesirable side reactions. Increasing the pH to between 7.2 and 7.8 increases the degree of ionization and thus gives the acrylic units a negative charge. This creates repulsion between the elongated polymer chains, especially at the ends of the elongated chains where additional monomers have been added. The charged anionic monomer units create repulsion at the ends of the grown chains, thereby preventing side reactions that would otherwise increase at higher temperatures.

[0363] This exclusion is intended to minimize undesirable side reactions, thereby minimizing undesirable side reactions between adjacent chains that can lead to molecular weight reduction, branching, and, in the worst case, insolubility. In this way, the method can control the molecular weight distribution (MW) and polymer structure. Therefore, even at high temperatures, the insoluble gel content is minimized.

[0364] The data in Table 1 clearly shows that a correct combination of conditions (redox initiation temperature, redox initiator concentration, and pH) is required to achieve highly soluble DPAM with good SV properties for EOR and other industrial applications, including but not limited to its use as a thickener, flocculant, paper reinforcing agent, for enhanced oil recovery, for tailings treatment, wastewater treatment, drinking water treatment, and for mining applications.

[0365] While the invention and exemplary embodiments have been described, this description is not intended to be limiting. Various modifications to the disclosed embodiments and alternative embodiments of the invention will become apparent to those skilled in the art. Therefore, the following claims are intended to cover any such modifications or embodiments falling within the scope of the invention.

Claims

1. A method for preparing high-reaction-temperature dry polyacrylamide (DPAM) via redox-initiated free radical polymerization, the method comprising: (a) Provide an aqueous solution of an olefinic unsaturated monomer, the aqueous solution comprising water and (i) acrylamide or (ii) acrylamide and one or more other monomers capable of copolymerizing with acrylamide; (b) Optionally add one or more stabilizers; (c) Optionally add one or more additives, including but not limited to one or more chelating agents, and optionally one or more liquid-leaching agents, one or more chain transfer agents, or any combination thereof; (d) Add one or more azo initiators; (e) Adjust the pH to a range of 7-9, 7-8, 7.1-7.8, or 7.25-7.75; (f) Cooling to below 25°C the redox initiation temperature; (g) Add one or more redox initiators to produce a redox-initiated reaction mixture; (h) Allowing gel polymerization to occur under substantially adiabatic conditions, wherein the redox-initiated reaction mixture is heated to a maximum reaction temperature (Tmax) above 100°C by the exothermic polymerization; and (i) The Tmax is maintained for a curing time, thereby providing a high reaction temperature polyacrylamide gel.

2. The method according to claim 1, further comprising drying and grinding the high reaction temperature polyacrylamide gel after step (i) to form the high reaction temperature DPAM as a homopolymer, copolymer or terpolymer.

3. The method according to claim 1 or 2, wherein the gel polymerization: (a) Occurs in an atmosphere containing nitrogen, argon, helium, or a combination thereof; and / or (b) It occurs at a high pressure above atmospheric pressure and is optionally maintained by exothermic heating of the polymerization or by pressurization with an inert gas, including but not limited to nitrogen, argon, helium or any combination thereof, and further wherein the high pressure is sufficient to prevent the aqueous reaction mixture from boiling when subjected to temperatures above 100°C.

4. The method according to any one of claims 1, 2, or 3, wherein one, two, three, or all four of the following conditions are satisfied: (a) The redox initiation temperature range is -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to 3°C; (b) The final reaction temperature range is 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, 100°C to 110°C or 100°C to 105°C; (c) After the addition of one or more of the aforementioned redox initiators, the final reaction temperature is reached within a time range of 5-120 minutes, 10-90 minutes, 20-90 minutes, or 20-60 minutes; and (d) The curing time range is 10-240 minutes, 30-180 minutes or 60-120 minutes.

5. The method according to any one of the preceding claims, wherein the one or more additional monomers comprise: (a) One or more olefinically unsaturated, preferably water-soluble, nonionic monomers, including but not limited to (meth)acrylamide; N-alkylacrylamides, including but not limited to N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide, and N-butylacrylamide; N,N-dialkylacrylamides, including but not limited to N,N-dimethylacrylamide and N,N-diethylacrylamide; N-alkylmethylacrylamide; alkyl acrylates; hydroxyalkyl acrylates and hydroxyalkyl methacrylates, including but not limited to methyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, and acrylic acid. 4-Hydroxybutyl ester, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; dialkyl acrylates and dialkyl methacrylates, including but not limited to 2,3-dihydroxypropyl acrylate, 3,4-dihydroxybutyl acrylate, 2,3-dihydroxypropyl methacrylate (DHPMA), and 3,4-dihydroxybutyl methacrylate; alkyl acrylates, including but not limited to methyl methacrylate; acrylonitrile; N-vinylmethylacetamide, N-vinylmethylformamide; N-vinyl acetate, acetoxylated acrylamide, and vinylpyrrolidone; (b) One or more olefinically unsaturated anionic monomers, including but not limited to acrylic acid, methacrylic acid; sulfonic acid, phosphonic acid, maleic acid, itaconic acid, vinyl sulfonic acid, acrylamidotert-butyl sulfonic acid (ATBS), acrylamidomethanesulfonic acid, acrylamidoethanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, and their alkali metal salts, alkaline earth metal salts, and ammonium salts; or (c) Any combination of the foregoing terms.

6. The method according to any one of the preceding claims, wherein the aqueous solution of the olefinically unsaturated monomer comprises: (a) Acrylamide; (b) Acrylamide and acrylic acid; or (c) Acrylamide, acrylic acid and ATBS.

7. The method according to any one of the preceding claims, wherein: (a) The one or more optional stabilizers comprise one or more free radical scavengers, including but not limited to thiourea, N,N'-dimethylthiourea, N,N'-diethylthiourea, N,N'-diphenylthiourea, thiocyanate, tetramethylthiuram disulfide, 2-mercaptobenzothiazole (MBT) and its salts, 2-mercaptobenzimidazole and its salts, sodium dimethyl dithiocarbamate, sodium diethyl dithiocarbamate, 2,2'-dithiobis(benzothiazole), 4,4'-thiobis(6-tert-butyl-m-cresol), and bis(benzothiazole). Cyanamide, cyanamide, p-methoxyphenol, 2,6-di-tert-butyl-4-methylphenol, butylated hydroxyanisole, 8-hydroxyquinoline, 2,5-di(tert-amyl)hydroquinone, 5-hydroxy-1,4-naphthoquinone, dimethyl ketone, propyl-3,4,5-trihydroxybenzoate, N-nitrosophenylhydroxylamine, 4-hydroxy-2,2,6,6-tetramethyloxypiperidine, (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, 1,2,2,6,6-pentamethyl-4-piperidinol or any combination thereof; (b) The one or more additives comprise: (i) The one or more chelating agents include, but are not limited to, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid (EDTA) and its salts, 2,2',2",2"'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA), phosphoric acid and their alkali metal salts, alkaline earth metal salts and ammonium salts; (ii) The one or more liquid-dissolving agents mentioned above include, but are not limited to, urea, thiourea, alcohol, glycerol, guanidine, and guanidine cation halide salts; (iii) The one or more chain transfer agents mentioned above include, but are not limited to, hypophosphite and its salts, sodium hypophosphite, sodium formate, pentamethyldisilane (PMDS), isopropanol, n-butanethiol, chloroform, carbon tetrachloride, carbon tetrabromide, chloroform, 4-methylbenzenethiol, and 4,4'-thiobisbenzenethiol; or (iv) Any combination of the foregoing items; (c) The one or more azo initiators are selected from the group consisting of: azobisisobutyronitrile (AIBN), 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride; 2,2-azobis(2-methylpropanediamine) dihydrochloride; 2,2'-azobis(N-(2-carboxyethyl)-2-methylpropanediamine hydrate; 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propene} dihydrochloride; and 2,2'-azobis(1-imino-1-pyrrolidine-2-ethylpropane) dihydrochloride; and (d) The one or more redox initiators are selected from the group consisting of redox initiator systems composed of: ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS); tert-butyl hydroperoxide and sodium sulfite (tBHP / SS); Fe(II) / Fe(III)-hydroperoxide system, Fe(II) / Fe(III)-alkyl hydroperoxide system, alkyl hydroperoxide-sulfite system, peroxide-thiosulfate system, alkyl hydroperoxide-sulfinate system; alkyl hydroperoxide-hydroxymethane sulfinate system and tert-butyl hydroperoxide-hydroxymethane sulfinate system; or (e) Any combination of the foregoing terms.

8. The method according to any one of the preceding claims, wherein: (a) The one or more optional stabilizers comprise sodium 2-mercaptobenzothiazole (Na-2-MBT); (b) The one or more azo initiators comprise AIBN; and (c) The one or more redox initiators comprise ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS) or tert-butyl hydroperoxide and sodium sulfite (tBHP / SS).

9. The method according to any one of the preceding claims, wherein the one or more additives comprise: (a) Diethylenetriaminepentaacetic acid; (b) Diethylenetriaminepentaacetic acid and urea; (c) Diethylenetriaminepentaacetic acid and sodium hypophosphite; or (d) Diethylenetriaminepentaacetic acid, sodium hypophosphite and urea.

10. The method according to any one of the preceding claims, wherein the redox-initiated reaction mixture comprises: (a) Based on all components therein, a total monomer concentration ranging from 30-60 wt%, 32-55 wt%, 32-50 wt%, or 36-42 wt%, wherein the total monomer concentration is sufficient to heat the redox-initiated reaction mixture from the redox initiation temperature to the Tmax above 100 °C, wherein the redox-initiated reaction mixture is heated by the exothermic polymerization. (b) Acrylamide in the total monomer concentration ranges from 1-100%, 35-95%, or 65-85% in molar percentage; (c) The molar percentage of one or more additional monomers in the total monomer concentration ranges from 0-99%, 5-65%, or 15-35%; (d) Optionally, a stabilizer concentration ranging from 0.01-2 wt%, 0.02-1.5 wt%, or 0.05-1.0 wt% based on the total weight of the monomers therein; and (e) The range is 50-6000 [(µmol / kg)] 2 ]、100-5000 [(µmol / kg) 2 ]、200-5000 [(µmol / kg) 2 500-5000 [(µmol / kg)] 2 1000-5000 [(µmol / kg)] 2 ] or 1000-3000 [(µmol / kg)] 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant).

11. The method according to any one of the preceding claims, wherein: (a) The pH range is 7.2-7.8, and the equilibrium redox initiator product concentration range of tBHP / SS is 750-5000 [(µmol / kg)]. 2 The redox initiation temperature ranges from -4°C to 6°C, -4°C to 2°C, or -4°C to -2°C, and the total monomer concentration ranges from 36-42 wt%; or (b) The pH range is 7.2-7.8, and the equilibrium redox initiator product concentration range of APS / FAS is 50-400 [(µmol / kg)]. 2 Furthermore, the redox initiation temperature ranges from -4°C to 6°C, -4°C to 2°C, or -4°C to -2°C, and the total monomer concentration ranges from 36 to 42 wt%.

12. The method according to any one of the preceding claims, wherein the high reaction temperature DPAM: (a) Standard viscosity (SV) with a range of 6.0-7.5 mPas, 6.5-7.4 mPas or 7.0-7.2 mPas, determined using a Brookfield DV1MLV viscometer with a UL adapter and ULA-DIN-Y spindle at 25°C ± 0.2°C and 60 rpm; (b) Having high water solubility as determined by the content of residual insoluble gel in the range of 0-0.5wt%, 0-0.2wt%, 0-0.1wt% or 0-<0.1wt%, determined by dissolving 1g of the high reaction temperature DPAM in 1L of water at 25°C and then filtering through 300µm pores; (c) Compared to DPAM polymers prepared using the same monomers and the same high-temperature (Tmax > 100°C) method, it exhibits higher standard viscosity (SV) and higher water solubility, the difference being a lower pH; or (d) Any combination of the foregoing items.

13. A method for preparing high-reaction-temperature dry polyacrylamide (DPAM) by redox-initiated free radical polymerization according to claim 1, the method comprising: (a) Provide an aqueous solution of an olefinic unsaturated monomer, the aqueous solution comprising water and (i) acrylamide or (ii) acrylamide and one or more additional monomers selected from the group consisting of: acrylic acid and its salt, acrylamide tert-butyl sulfonic acid (ATBS) and its salt, or a combination of acrylic acid and sodium ATBS. (b) Add 2-mercaptobenzothiazole (MBT) or a salt thereof; (c) Add diethylenetriaminepentaacetic acid; (d) Add azobisisobutyronitrile (AIBN); (e) Adjust the pH to a range of 7-8, 7.1-7.8, or 7.25-7.75; (f) Cool to a redox initiation temperature in the range of below 25°C, -10°C to 25°C, -10°C to 15°C, -10°C to 10°C, -10°C to 5°C, or -6°C to 3°C; (g) Add one or more redox initiators selected from the group consisting of the following redox initiator systems: ammonium persulfate and ferric(II) ammonium sulfate (APS / FAS) system; tert-butyl hydroperoxide and sodium sulfite (tBHP / SS) system, thereby producing a redox-initiated reaction mixture; (h) Allowing gel polymerization to occur under substantially adiabatic conditions and in a high-pressure inert gas atmosphere, wherein the high pressure is sufficient to prevent boiling, wherein the redox-initiated reaction mixture is heated by the exothermic reaction to a maximum reaction temperature (Tmax) in the range of above 100°C, 100°C to 150°C, 100°C to 140°C, 100°C to 130°C, 100°C to 120°C, or 100°C to 110°C, wherein the gel polymerization occurs; (i) Maintaining the Tmax for a curing time ranging from 10-240 minutes, 30-180 minutes, or 60-120 minutes, thereby providing a high-reaction-temperature polyacrylamide gel; and (j) Optionally, the high reaction temperature polyacrylamide gel is dried and ground to form the high reaction temperature DPAM; The resulting high-reaction-temperature DPAM is a homopolymer, copolymer, or terpolymer.

14. The method of claim 13, wherein the redox-initiated reaction mixture comprises one or more of the following: (a) Based on the total monomer concentration of all components, ranging from 32-50 wt% or 36-42 wt%; (b) Acrylamide in the total monomer concentration ranges from 1-100%, 35-95%, or 65-85% in molar percentage; (c) The molar percentage of one or more additional monomers in the total monomer concentration ranges from 0-99%, 5-65%, or 15-35%; (d) A stabilizer concentration, ranging from 0.01-2 wt%, 0.02-1.5 wt%, or 0.05-1.0 wt%, based on the total weight of the monomers therein; (e) The range of tBHP / SS is 750-5000 [(µmol / kg)] 2 1000-5000 [(µmol / kg)] 2 ] or 1000-3000 [(µmol / kg)] 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant) or APS / FAS ranges from 50 to 1000 [µmol / kg]. 2 50-600 [(µmol / kg)] 2 ] or 50-400 [(µmol / kg) 2 The equilibrium redox initiator product concentration (e.g., oxidant × reductant); or (f) Any combination of the foregoing terms.

15. A composition comprising high-reaction-temperature dry polyacrylamide (DPAM) that can be obtained or produced by the method according to any one of the preceding claims.

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