New polymer and its preparation process

Abstract

The present invention relates to a new water-soluble anionic gradient polymer, its preparation process and its use, particularly in the field of paper.

Description

Title of the invention: New polymer and its preparation process Technical field of the invention

[0001] The present invention relates to a new anionic water-soluble polymer, its preparation process and its use, particularly for applications in the field of paper. Prior state of the art

[0002] The paper industry is constantly seeking to improve its processes for manufacturing paper, cardboard or similar products, particularly with regard to cost reduction, yield, productivity or the quality of the final product.

[0003] This is particularly true for the packaging industry, which is seeking paper, cardboard, or similar materials with improved dry strength performance, notably to meet current environmental challenges and replace plastic packaging. This pursuit of improvement must not come at the expense of productivity.

[0004] The dry strength of paper is, by definition, the strength of the sheet, board, or similar material in its dry state. Mechanical strength values ​​traditionally provide a measure of dry strength. These values ​​include, in particular, resistance to bursting, tensile strength, compression, delamination, etc.

[0005] It is well known to use water-soluble cationic polymers to improve the strength characteristics of paper. By their nature, these polymers can bind directly to anionic cellulose and impart a cationic charge to it, such that, in association with anionic polymers, the latter bind to the cellulosic fibers, thus improving the dry strength of the sheet.

[0006] The most commonly used cationic polymers are cationic starch type compounds, epichlorohydrin polyamide (PAE), epichlorohydrin amine polyamide (PAAE), cationic polyacrylamide possibly glyoxalated, polyvinylamine, polyethyleneimine (PEI), epichlorohydrin (PA) resin polyamines or polymers resulting from Hofmann degradation.

[0007] This combination of cationic and anionic polymers is well known for improving dry strength. It has already been proposed, notably in document FR 2880901 Bl, to combine cationic polymers with an anionic polymer, this combination aiming to provide a high-performance system for the dry strength of the paper sheet.

[0008] The problem with such a combination of two polymers in solution is the loss of the paper's drainage properties. By reducing the drainage properties, the speed of the paper machine is reduced, which causes a significant decrease in productivity.

[0009] The problem is mainly due to anionic polymers that are synthesized via the liquid process and have a low molecular weight. In the liquid process, increasing the molecular weight results in an increase in viscosity. Above a certain molecular weight, it is no longer possible to obtain a liquid.

[0010] To overcome this problem, manufacturers have had to turn to other polymerization techniques, such as gel polymerization, to obtain higher molecular weights. The polymers resulting from these polymerization techniques are in solid form.

[0011] There are many disadvantages to the use of polymers in solid forms, such as: - The manufacturer is required to have a powder dilution system on site; - The increase in the size of the facilities and therefore their footprint; - Increased energy consumption and handling; - Powder stock management; - managing the advance dissolution of powders; - More frequent and more complex maintenance.

[0012] The main problem remains the dilution of a high molecular weight polymer powder.

[0013] Indeed, dissolving such a polymer is not a simple process and requires technical expertise to avoid the risk of improper dissolution, which could lead to the formation of aggregates on the paper sheet, resulting in weakness or, worse, fouling of the machinery that could lead to a complete shutdown and maintenance of the entire production unit. Furthermore, this type of polymer, in powder form and therefore with a high molecular weight, causes over-flocculation and has a detrimental effect on sheet formation, negatively impacting the paper's mechanical properties.

[0014] For a long time, manufacturers have been looking for a solution to obtain a sheet of paper with good dry strength performance, while maintaining good drainage properties and simplifying its installation through the use of polymer in liquid form.

[0015] The Applicant has discovered, surprisingly, that the synthesis of a polymer according to the process of the invention makes it possible to meet the needs of manufacturers without inconvenience to the latter.

[0016] The use of the polymers resulting from the invention is based on a principle The general aim is to improve product performance, and more specifically, dry strength and drainage properties. The improved performance of the polymers according to the invention allows for a reduction in the amount of product required for application, thus implying a reduction in greenhouse gas emissions, such as CO2, associated with the manufacture and use of synthetic polymers. Description of the invention

[0017] The present invention relates to an anionic water-soluble polymer comprising: - at least one anionic monomer A; - at least one non-ionic monomer B; - at least one structuring system comprising: (i) at least one compound I, different from at least one monomer A and selected from: allylsulfonic acid, methallylsulfonic acid, allyl disulfonic acid, methallyl disulfonic acid, their salts and mixtures thereof; (ii) at least one compound II of formula I, different from at least one monomer B:

[0018] [Chem.l] Formula I

[0019] Ri and R2 being, independently of each other, a hydrogen atom, a methyl group, an ethyl group, an isopropyl group or a CH2-OH group; Ri and R2 are not both hydrogen atoms (Ri^H when R2=H; R2^H when Ri=H).

[0020] This anionic water-soluble polymer is obtained according to the following steps: a) formation of a solution (SI) comprising a first fraction (Fl) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; b) polymerization 1 (PI) of the Fl fraction to form a solution of a first gradient polymer (PG1); c) addition, to the solution comprising PG1, of a second fraction (F2) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; d) polymerization 2 (P2) of fraction F2 on PG1 to form a solution of a second gradient polymer (PG2); e) addition, to the solution comprising PG2, of a third fraction (F3) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; f) polymerization 3 (P3) of fraction F3 on PG2 to form a solution comprising an anionic water-soluble polymer.

[0021] This anionic water-soluble polymer is devoid of cationic monomer and zwitterionic monomer.

[0022] The present invention also relates to the process for preparing this anionic water-soluble polymer. This is a sequential polymerization process.

[0023] The present invention also relates to a method for manufacturing paper or cardboard using this anionic water-soluble polymer.

[0024] The present invention also relates to the use of this anionic water-soluble polymer in hydrocarbon recovery (oil and / or gas); in well drilling or cementing; in the stimulation of hydrocarbon (oil and / or gas) wells, for example hydraulic fracturing, conformance, diversion; in open, closed or semi-closed water treatment; in the treatment of fermentation musts; in sludge treatment; in construction; in wood processing; in the treatment of hydraulic compositions (concrete, cement, mortar and aggregates); in the mining industry; in the formulation of cosmetic products; in the formulation of detergents; in textile manufacturing; in geothermal energy; in the manufacture of sanitary diapers; or in agriculture.

[0025] The invention also relates to the use of this anionic water-soluble polymer as a flocculant, coagulant, binding agent, fixing agent, viscosity reducing agent, thickening agent, absorbent agent, friction reducing agent, draining agent, charge retention agent, dehydrating agent, conditioning agent, stabilizing agent, fixing agent, film-forming agent, sizing agent, superplasticizing agent, clay inhibitor or dispersant. Description of the invention

[0026] By "polymer" is meant a copolymer prepared from at least two different monomers, with at least one anionic monomer A and at least one non-ionic monomer B, and a structuring system comprising at least one compound I and at least one compound IL II may optionally comprise at least one hydrophobic monomer and / or a crosslinking agent and / or a transfer agent.

[0027] By water-soluble polymer, we mean a polymer which gives an aqueous solution without insoluble particles when dissolved under stirring at 25°C and with a concentration of 10 gL 1 in deionized water.

[0028] Throughout the description, viscosities are measured with a Brookfield viscometer, at 25°C, with a Brookfield LV3 modulus, in aqueous solution.

[0029] In the present description, it is assumed that a person skilled in the art is able to determine the appropriate module and speed of the Brookfield viscometer for the viscosity range to be measured. This type of measurement is indeed part of general knowledge. of a man of the trade.

[0030] By "X and / or Y", according to the invention, "X", or "Y", or "X and Y".

[0031] Also part of the invention are all possible combinations of the various disclosed embodiments, whether preferred or given by way of example. Furthermore, where ranges of values ​​are indicated, the bounds are part of those ranges. The disclosure also includes all combinations of the bounds of those ranges of values. For example, the ranges of values ​​"1-20, preferably 5-15" imply the disclosure of the ranges "1-5", "1-15", "5-20", and "15-20", and the values ​​1, 5, 15, and 20. Anionic water-soluble polymer

[0032] The anionic water-soluble polymer according to the invention comprises: - at least one anionic monomer A; - at least one non-ionic monomer B; - at least one structuring system comprising: (i) at least one compound I, different from at least one monomer A and selected from: allylsulfonic acid, methallylsulfonic acid, allyl disulfonic acid, methallyl disulfonic acid, their salts and mixtures thereof; (ii) at least one compound II of formula (I), different from the at least monomer B:

[0033] [Chem.l] RÇ R» Formula I

[0034] Ri and R2 being, independently of each other, a hydrogen atom, a methyl group, an ethyl group, an isopropyl group or a CH2-OH group; Ri and R2 are not both hydrogen atoms (Ri^H when R2=H; R2^H when Ri=H).

[0035] This polymer being devoid of cationic monomer and zwitterionic monomer. Monomeric composition

[0036] The anionic water-soluble polymer according to the invention is a synthetic polymer. It may comprise one or more anionic monomers (designated "monomer(s) A"),

[0037] Advantageously, the other anionic monomer(s) A can be chosen from a wide range. These monomers may have a vinyl function, in particular acrylic, maleic, fumaric, malonic, itaconic, or allylic. They may also contain a carboxylate, phosphonate, phosphate, or sulfonate group. or another anionically charged group. Preferred monomers belonging to this class are, for example, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, acrylamido-undecanoic acid, 3-acrylamido-3-methylbutanoic acid, maleic anhydride, 2-acrylamido-2-methylpropane sulfonic acid (ATBS), vinylsulfonic acid, vi-nylphosphonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropyl acrylate, allylphosphonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane disulfonic acid, their salts and mixtures. Preferably, it is acrylic acid or itaconic acid, even more preferably, acrylic acid.

[0038] Thus, in a particular embodiment of the invention, the anionic monomer(s) A can be salified.

[0039] By "salified," it is understood that at least one acid function of the anionic monomer A is replaced by a salt that neutralizes the negative charge of the acid function. In other words, the unsalified form corresponds to the acidic form of the monomer, for example RC(=O)-OH in the case of the carboxylic acid function, while the neutralized form of the monomer corresponds to the form RC(=O)-OH X+, where X+ corresponds to a positively charged salt. The neutralization of the acid functions of the water-soluble polymer may be partial or total.

[0040] The salt form advantageously corresponds to the salts of alkali metals (Li, Na, K...), alkaline earth metals (Ca, Mg...) or ammonium (for example the ammonium ion or a tertiary ammonium). The preferred salts are sodium salts.

[0041] Salification can take place before or after polymerization.

[0042] The anionic water-soluble polymer advantageously comprises between 1 and 99 mol% of anionic monomer(s) A, preferably between 2 and 70 mol%, more preferably between 3 and 50 mol% and even more preferably between 5 and 35 mol%.

[0043] In a particular embodiment of the invention, when the anionic monomer A is 2-acrylamido-2-methylpropane sulfonic acid, it is its hydrated form. The hydrated form of ATBS is a particular form of ATBS that can be obtained by controlled crystallization of the ATBS monomer. US patent 10,759,746 describes this hydrated form of ATBS.

[0044] The anionic water-soluble polymer may comprise one or more non-ionic monomers (designated "monomer(s) B").

[0045] Advantageously, the nonionic monomer(s) B may be selected, in particular, from the group comprising water-soluble vinyl monomers. Preferred monomers belonging to this class are, for example, tacrylamide, methacrylamide, N-vinylformamide (NVF), N-vinyl acetamide, N-vinylpyridine and N-vinylpyrrolidone (NVP), N-vinyl imidazole, N-vinyl suc- cinmide, acryloyl morpholine (ACMO), acryloyl chloride, glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, hydroxyalkyl (meth)acrylate (C1-C3 alkyl), aminoalkyl (meth)acrylate (C1-C3 alkyl), aminoalkyl (meth)acrylamido (C1-C3 alkyl), thioalkyl (meth)acrylate (C1-C3 alkyl) and mixtures thereof. Preferably, it is acrylamide.

[0046] The anionic water-soluble polymer advantageously comprises between 1 and 99 mol% of non-ionic monomers B, preferably between 30 and 98 mol%, more preferably between 50 and 97 mol% and even more preferably between 65 and 95 mol%.

[0047] The anionic water-soluble polymer may optionally include one or more hydrophobic monomers (designated "monomer(s) C").

[0048] Advantageously, the hydrophobic monomer(s) C can be selected from groups consisting of (meth)acrylic acid esters having a C4-C30 alkyl, arylalkyl (C4-C30 alkyl, C4-C30 aryl), propoxylated, ethoxylated, or ethoxylated and propoxylated chain; (meth)acrylamide derivatives having a C1-C3 alkyl, propoxylated (C4-C30 alkyl, C4-C30 aryl), ethoxylated, ethoxylated and propoxylated, or dialkyl (C4-C30 alkyl) chain; alkyl aryl sulfonates (C4-C30 alkyl, C4-C30 aryl), or mono- or di-substituted amides of (meth)acrylamide having a C4-C30 alkyl, arylalkyl (C4-C30 alkyl, C4-C30 aryl), propoxylated, ethoxylated, or ethoxylated and propoxylated chain; (meth)acrylamide derivatives having a C4-C30 alkyl, propoxylated arylalkyl (C4-C30 alkyl, C4-C30 aryl), ethoxylated, ethoxylated and propoxylated, or C4-C30 dialkyl chain;Alkyl aryl sulfonates (C4-C30 alkyl, C4-C30 aryl) and their mixtures.

[0049] The anionic water-soluble polymer advantageously comprises less than 1 mol% of hydrophobic monomers C. It may be devoid of hydrophobic monomer C.

[0050] When the anionic water-soluble polymer according to the invention comprises one or more hydrophobic monomers C, they are present in such quantity that the polymer remains soluble in water.

[0051] The quantities of the different monomers will be adjusted by a person skilled in the art so as not to exceed 100 molar percentage during the preparation of the water-soluble polymer. Preferably, monomers A and B represent 100 molar percentage of the monomers of the anionic water-soluble polymer. Structuring system

[0052] The structuring system of the anionic water-soluble polymer comprises: (i) at least one compound I; (ii) at least one compound II.

[0053] The compound I used in the context of the invention is selected from: allylsulfonic acid, methallylsulfonic acid, allyl disulfonic acid, methallyl disulfonic acid, their salts and mixtures thereof. Preferably, it is meth- lylsulfonic acid, for example sodium methylsulfonate.

[0054] The salt form advantageously corresponds to the salts of alkali metals (Li, Na, K...) of alkaline earth metals (Ca, Mg...) or of ammonium (for example the ammonium ion or a tertiary ammonium). The preferred salts are sodium salts.

[0055] The anionic water-soluble polymer advantageously comprises between 500 and 50,000 ppm of compound I relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 1,000 and 20,000 ppm, more preferably between 2,000 and 10,000 ppm.

[0056] Compound II used in the context of the invention has the general formula:

[0057] [Chem.l] Formula I

[0058] Ri and R2 being, independently of each other, a hydrogen atom, a methyl group, an ethyl group, an isopropyl group or a CH2-OH group; Ri and R2 are not both hydrogen atoms (Ri^H when R2=H; R2^H when Ri=H).

[0059] Compound II used in the context of the invention is advantageously chosen from: N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-isopropylacrylamide, N-methylolacrylamide and mixtures thereof. Preferably, it is N,N-dimethylacrylamide.

[0060] The anionic water-soluble polymer according to the invention advantageously comprises between 500 and 50,000 ppm of compound II relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 1,000 and 20,000 ppm, more preferably between 2,000 and 10,000 ppm.

[0061] In the anionic water-soluble polymer, the mass ratio between compound I and compound II is advantageously between 0.01 and 100, preferably between 0.1 and 10.

[0062] In a preferred mode according to the invention, the quantity of compound I is greater than the quantity of compound IL. Thus, the mass ratio between compound I and compound II is advantageously greater than 1 and less than or equal to 100, preferably greater than 1 and less than or equal to 10. Optional

[0063] The anionic water-soluble polymer may further comprise at least one crosslinking agent. This crosslinking agent may be selected from monomers with Polyethylene monomers (having at least two unsaturated functional groups), such as vinyl groups, particularly allylic groups, acrylic groups, or monomers having at least two epoxy groups. Examples include methylene bisacrylamide (MBA), triallyamine, tetraallylammonium chloride, 1,2-dihydroxyethylene bis-(N-acrylamide), and mixtures thereof. Preferably, this refers to methylene bisacrylamide (MBA).

[0064] The amount of crosslinking agent in the anionic water-soluble polymer is advantageously between 5 and 5,000 ppm, relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, more preferably between 50 and 3,000 ppm.

[0065] In a particular mode according to the invention, the anionic water-soluble polymer does not include a crosslinking agent.

[0066] The anionic water-soluble polymer according to the invention may further comprise at least one transfer agent, for example, selected from methanol, isopropyl alcohol, sodium hypophosphite, 2-mercaptoethanol, and mixtures thereof. Other examples include xanthate, dithiocarbonate, dithiocarbamate, and trithiocarbonate transfer agents and mixtures thereof. Preferably, sodium hypophosphite is used.

[0067] The amount of transfer agent in the anionic water-soluble polymer is advantageously between 10 and 10,000 ppm, relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, more preferably between 50 and 5,000 ppm.

[0068] In a particular mode according to the invention, the anionic water-soluble polymer does not include a transfer agent.

[0069] Physical characteristics of the water-soluble polymer

[0070] The water-soluble polymer has a weight-average molecular weight advantageously between 1,000,000 and 25,000,000 daltons, preferably between 2,000,000 and 15,000,000 daltons, more preferably between 3,000,000 and 10,000,000 daltons. This is the weight-average molecular weight.

[0071] The average molecular weight by weight is preferably measured by gel permeation chromatography (“Gel Permeation Chromatography” in English).

[0072] The anionic water-soluble polymer is obtained and used in liquid form.

[0073] The viscosity of the solution comprising the anionic water-soluble polymer is advantageously between 1,000 and 50,000 cps, preferably between 5,000 and 20,000 cps. Renewable origin

[0074] In a preferred embodiment according to the invention, the anionic water-soluble polymer is prepared from compounds (monomers and / or compounds I and II) at least in part of renewable and non-fossil origin.

[0075] In the context of the invention, the term "of renewable and non-fossil origin" refers to the origin of a chemical compound derived from biomass or syngas, that is, the result of one or more chemical transformations carried out on one or more raw materials of natural, non-fossil origin. The terms "bio-based" or "bio-resourced" may also be used to characterize the renewable and non-fossil origin of a chemical compound. The renewable and non-fossil origin of a compound includes renewable and non-fossil raw materials from the circular economy that have been previously recycled, one or more times, in a biomass-derived material recycling process, such as materials from polymer depolymerization or pyrolysis oil processing.

[0076] According to the invention, "at least partly of renewable and non-fossil origin" means a bio-based carbon content preferably between 5% by weight and 100% by weight relative to the total weight of carbon of said compound, preferably at least 30%, more preferably at least 50%, even more preferably at least 70%, even more preferably at least 90% and even more preferably it is composed of 100% bio-based carbon.

[0077] In the context of the invention, ASTM D6866-21, Method B, is used to characterize the bio-based nature of a chemical compound and to determine the bio-based carbon content of said compound. The value is expressed as a percentage by weight of bio-based carbon relative to the total weight of carbon in said compound. Gradient

[0078] The anionic water-soluble polymer according to the invention is a gradient polymer.

[0079] Polymers with a gradient structure are polymers composed of at least two monomers in which the change in monomer composition is gradual, unlike block polymers, which have an abrupt change in composition, and random polymers, which do not have a continuous change in composition. In the gradient polymer, due to the gradual change in composition along the length of the polymer chain, less intra-chain and inter-chain repulsion is observed.

[0080] The gradient can be formed by a spontaneous or forced gradient. Spontaneous gradient polymerization is due to a difference in the reactivity of the monomers. Forced gradient polymerization involves varying the composition of monomers introduced throughout the polymerization time.

[0081] A forced process comprises (1) the introduction of a first fraction of monomers into a reactor, (2) the addition of at least one further fraction of monomers advantageously different from the first, and (3) the polymerization of the monomers. introduced into the reactor. Polymerization of the monomers is initiated as soon as the first fraction is introduced.

[0082] The addition of the additional monomer fraction can be carried out in parallel with the introduction of the first monomer fraction into the reactor (the introduction of the fractions can therefore start and end simultaneously). The fractions can thus have distinct addition profiles in terms of flow rate, but with the same total addition time. Indeed, the addition rate of a fraction can be continuous or discontinuous, whether or not it is constant throughout the entire addition time. Alternatively, the start of the first monomer feed (first fraction) into the reactor can precede the start of the addition of a second monomer fraction. Alternatively, a first and second fraction can be introduced simultaneously, but the addition time of the second fraction can be longer than the introduction time of the first fraction into the reactor.This embodiment is also applicable to processes using at least 3 monomer fractions.

[0083] According to the process of the invention, the water-soluble anionic polymer obtained is formed by the sequential addition of monomers, in other words, it is preferably a forced gradient process.

[0084] The process according to the invention comprises a first fraction (F1) and at least two additional fractions (F2 and F3). At least one of the fractions F1, F2, and F3 of the process is different from the other fractions. Preferably, the fractions F1, F2, and F3 are different from each other (F1^F2^F3). A different fraction is defined as a fraction having a different monomer composition (ratio and / or nature of the monomers) and / or a different composition of compounds I and II (ratio and / or nature of compounds I and II). Polymerization process

[0085] The sequential preparation process of the anionic water-soluble polymer according to the invention comprises the following steps: a) formation of a solution (SI) comprising at least a first fraction (Fl) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; b) polymerization 1 (PI) of the Fl fraction to form a solution of a first gradient polymer (PG1); c) addition, to the solution comprising PG1, of a second fraction (F2) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; d) polymerization (P2) of fraction F2 on PG1 to form a solution of a second gradient polymer (PG2); e) addition, to the solution comprising PG2, of a third fraction (F3) containing (1) to less one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; f) polymerization (P3) of fraction F3 on PG2 to form a solution comprising an anionic water-soluble polymer.

[0086] This process may include the addition of additional fractions.

[0087] It is possible that the improved performance of the water-soluble anionic polymer according to the invention is due to the fact that the polymerization is carried out sequentially and continuously, i.e. without interruption.

[0088] By "in sequence," it is meant that the polymerization of the monomers of the anionic water-soluble polymer occurs in several fractions without interruption; that is, the addition of fractions is continuous and the polymerization does not stop. The different steps a) to f) are therefore carried out successively. In other words, a first fraction of monomers can be added by pouring and polymerizes to form a first gradient polymer PG1, which continues to polymerize with fraction F2 to form the gradient polymer PG2, which itself continues to polymerize with fraction F3 to obtain, at the end of polymerization, the anionic water-soluble polymer. Preferably, at least one of the fractions F1, F2, and F3 of the process is different from the other fractions. Preferably, the fractions F1, F2, and F3 are different from each other (F1^F2^F3).Adding different fractions during the polymerization process allowed for obtaining a gradient in the composition of the anionic water-soluble polymer.

[0089] In the polymerization process according to the invention, the total sum of the molar percentages of the monomers of the different fractions is equal to the total sum of the molar percentages of the monomers of the anionic water-soluble polymer.

[0090] Step a), formation of an SI solution comprising a first fraction (Fl) SI solution

[0091] The IT solution is advantageously composed of: - of a solvent; - of a priming agent; - of a first fraction FL

[0092] The solvent is advantageously water, or a solvent in which the monomers and the anionic water-soluble polymer are soluble. Preferably, the solvent is water.

[0093] The polymerization initiators used can be any compounds that dissociate into radicals under the polymerization conditions, for example: organic peroxides, hydroperoxides, hydrogen peroxide, persulfates, azo compounds, and redox couples. The use of water-soluble initiators is preferred. In some cases, it is advantageous to use mixtures of various Polymerization initiators, for example mixtures of redox catalysts and azo compounds. Preferably, these are persulfates.

[0094] In a particular mode, the SI solution is formed by mixing the solvent, the initiator and the Fl fraction in a polymerization tank.

[0095] In this particular mode, the Fl fraction can be added all at once, in several stages, or by pouring, that is, gradually (for example, drop by drop) into the solvent / initiator mixture. Preferably, the Fl fraction is added all at once into the polymerization tank.

[0096] In a particular embodiment of the invention, the initiator and the Fl fraction are added by pouring into a polymerization tank containing the solvent. They may be added separately or pre-mixed. Preferably, they are added separately.

[0097] In a preferred embodiment of the invention, the initiator is added continuously throughout the process (steps a) to f)). In this case, the initiator is advantageously added in parallel with the different fractions, during the different polymerization steps and during any aging steps of the different gradient polymers (PG1 and PG2) and the anionic water-soluble polymer.

[0098] In this preferred embodiment of the invention, the duration of the starter flow is between 50 minutes and 560 minutes, preferably between 130 minutes and 430 minutes. First fraction (Fl)

[0099] Advantageously, the Fl fraction comprises between 10 and 40% by weight of monomer (A and / or B, + optionally C) relative to the total weight of monomer (A + B + optionally C) of the anionic water-soluble polymer, preferably between 15 and 30% by weight.

[0100] The Fl fraction advantageously comprises between 0 and 50 mol% of anionic monomers A, preferably between 0 and 35 mol%, relative to the total number of moles of monomers in the Fl fraction.

[0101] The Fl fraction advantageously comprises between 50 and 100 mol% of nonionic monomers B, preferably between 65 and 100 mol%, relative to the total number of moles of monomers in the FL fraction

[0102] The Fl fraction advantageously comprises between 250 and 30,000 ppm of compounds I relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 500 and 10,000 ppm, more preferably between 1,000 and 7,000 ppm.

[0103] The Fl fraction advantageously comprises between 250 and 30,000 ppm of compounds II relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 500 and 10,000 ppm, more preferably between 1,000 and 5,000 ppm.

[0104] The various monomers and compounds composing fraction Fl are advantageously added in the form of solutions. These solutions can be added separately or mixed together in the polymer vat, all at once, in several stages, or by pouring, to form solution SI. Preferably, the addition is made by mixing and all at once.

[0105] When the Fl fraction is added in pouring, the pouring advantageously lasts between 10 minutes and 80 minutes, preferably between 40 minutes and 70 minutes.

[0106] In a preferred mode, the Fl fraction is prepared in the reactor (polymerization tank) before the addition of the initiator.

[0107] In a preferred mode, the Fl fraction contains at least one monomer B, at least one compound I and at least one compound IL

[0108] Step b), polymerization of fraction Fl to form a first gradient polymer (PG1) Polymerization 1 (PI)

[0109] Prior to PI polymerization, the atmosphere of the polymerization tank can be replaced by an inert gas such as nitrogen or argon.

[0110] PI polymerization is advantageously a radical polymerization. Polymerization initiators can be used, in particular initiators that dissociate into radicals under the polymerization conditions.

[0111] PI polymerization is advantageously initiated at a temperature between 70 and 90 °C, preferably between 75 and 85 °C. The polymerization temperature is advantageously controlled by means of cooling so as not to exceed 95 °C.

[0112] The PI polymerization advantageously lasts between 10 minutes and 80 minutes, preferably between 40 minutes and 70 minutes.

[0113] Polymerization advantageously begins when the first monomers, the solvent, and the initiator are in contact. In other words, the polymerization time PI advantageously corresponds to the pouring time of the FL fraction. Gradient Polymer (PG1)

[0114] At the end of the PI polymerization, a PG1 gradient polymer is obtained.

[0115] In a particular mode according to the invention, the gradient polymer PG1 is left to age between 5 minutes and 60 minutes, preferably between 10 minutes and 30 minutes.

[0116] By "left to age" is meant that the temperature of the medium is maintained between 80 and 90°C after the end of polymerization to allow an increase in viscosity through internal branching phenomena of the polymer. This definition of aging applies to all stages of the polymerization process. risation.

[0117] Step c), adding a second fraction (F2) to the solution comprising PG1 Second fraction F2

[0118] Advantageously, the fraction F2 comprises between 30 and 80% by weight of monomer (A and / or B, + optionally C) relative to the total weight of monomer (A + B + optionally C) of the anionic water-soluble polymer, preferably between 40 and 70%.

[0119] The fraction F2 advantageously comprises between 0 and 70 mol% of anionic monomers A, preferably between 0 and 50 mol%, relative to the total number of moles of monomers in the fraction F2.

[0120] The fraction F2 advantageously comprises between 30 and 100 mol% of non-ionic monomers B, preferably between 65 and 100 mol%, relative to the total number of moles of monomers in the fraction F2.

[0121] The fraction F2 advantageously comprises between 250 and 30,000 ppm of compounds I relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 500 and 10,000 ppm, more preferably between 1,000 and 5,000 ppm.

[0122] The fraction F2 advantageously comprises between 250 and 30,000 ppm of compounds II relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 500 and 10,000 ppm, more preferably between 1,000 and 5,000 ppm.

[0123] The various monomers and compounds comprising F2 are advantageously added in the form of solutions. These solutions can be added separately or mixed together in the polymer vat, all at once, in several stages, or by pouring. Preferably, the addition is carried out by mixing and pouring.

[0124] The pouring of fraction F2 advantageously lasts between 10 minutes and 100 minutes, preferably between 30 minutes and 90 minutes.

[0125] In a preferred mode, the fraction F2 contains at least one monomer A and B, at least one compound I and at least one compound II.

[0126] Step d), polymerization of fraction F2 on PG1 to form a second gradient polymer (PG2) Polymerization (P2)

[0127] The P2 polymerization takes place in continuity with the PI polymerization, it takes place under the same temperature conditions (advantageously 70 to 90 °C).

[0128] The PI polymerization advantageously lasts between 10 minutes and 100 minutes, preferably between 30 minutes and 90 minutes.

[0129] The P2 polymerization begins with the addition of the first monomers of the fraction F2.

[0130] Advantageously, the polymerization time P2 corresponds to the pouring time of fraction F2. Gradient polymer (PG2)

[0131] At the end of the P2 polymerization, a PG2 gradient polymer is obtained.

[0132] In a particular mode according to the invention, the PG2 gradient polymer is left to age between 5 and 60 min, preferably between 10 and 30 min.

[0133] Step e), adding a third fraction (F3) to the solution comprising PG2 Fraction F3

[0134] Advantageously, fraction F3 comprises between 5 and 40% by weight of monomer (A and / or B + optionally C) relative to the total weight of monomer (A + B + optionally C) of the anionic water-soluble polymer, preferably between 10 and 30%.

[0135] The fraction F3 advantageously comprises between 0 and 50 mol% of anionic monomers A, preferably between 0 and 35 mol%, relative to the total number of moles of monomers in the fraction F3.

[0136] The fraction F3 advantageously comprises between 50 and 100 mol% of non-ionic monomers B, preferably between 65 and 100 mol%, relative to the total number of moles of monomers in the fraction F3.

[0137] The fraction F3 advantageously comprises between 0 and 10,000 ppm of compounds I relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 10 and 5,000 ppm, more preferably between 20 and 1,000 ppm.

[0138] The fraction F3 advantageously comprises between 0 and 10,000 ppm of compounds II relative to the total weight of monomers A and B (+ optionally monomer C) of the anionic water-soluble polymer, preferably between 0 and 1,000 ppm.

[0139] The various monomers and compounds comprising F3 are advantageously added in the form of solutions. These solutions can be added separately or mixed together in the polymer vat, all at once, in several stages, or by pouring, i.e., drop by drop. Preferably, the addition is carried out by mixing and pouring.

[0140] The pouring of fraction F3 advantageously lasts between 10 minutes and 100 minutes, preferably between 30 minutes and 90 minutes.

[0141] In a preferred mode, the fraction F3 contains at least one monomer B and at least one compound I.

[0142] Step f), polymerization of fraction F3 on PG2 to form the anionic water-soluble polymer Polymerization (P3)

[0143] The P3 polymerization takes place in continuity with the P2 polymerization, it takes place under the same time and temperature conditions as P2 (advantageously 70 to 90 °C for 10 to 100 minutes, preferably between 30 and 90 minutes).

[0144] The P3 polymerization begins with the addition of the first monomers of the F3 fraction.

[0145] Advantageously, the polymerization time P3 corresponds to the pouring time of fraction F3.

[0146] At the end of the P3 polymerization, the anionic water-soluble polymer is obtained.

[0147] In a particular mode according to the invention, the anionic water-soluble polymer is left to age between 5 minutes and 60 minutes before the removal of residual monomers, preferably between 10 minutes and 30 minutes.

[0148] The reaction is advantageously stopped by adding an excess of initiator and / or water; this step is used to eliminate any residual monomers present in the solution comprising the anionic water-soluble polymer. Optional step(s)

[0149] The method according to the invention may further comprise additional steps and is not limited to the steps described above.

[0150] In a particular mode according to the invention, the polymerization process according to the invention may include the addition of additional fractions constituting the final anionic water-soluble polymer.

[0151] In a preferred mode according to the invention, the anionic water-soluble polymer is allowed to age for between 10 and 100 minutes after polymerization step f) P3, preferably between 30 and 90 minutes. In the case of the addition of additional fractions, the aging is carried out after the last polymerization step.

[0152] In a particular mode according to the invention, a crosslinking agent and / or a transfer agent is added during at least one of the steps described above.

[0153] In a preferred mode according to the invention, a crosslinking agent is added to the Fl fraction and / or to the F2 fraction.

[0154] When a crosslinking agent is added, it is advantageously chosen from among the crosslinking agents previously mentioned.

[0155] When a crosslinking agent is added, its quantity is advantageously between 5 and 5,000 ppm relative to the total weight of the anionic water-soluble polymer (monomers A, B and optionally C), preferably between 50 and 3,000 ppm.

[0156] In a preferred mode according to the invention, a transfer agent is added to fraction Fl and / or to fraction F2.

[0157] When a transfer agent is added, it is advantageously chosen from among the previously mentioned transfer agents.

[0158] When a transfer agent is added, its quantity is advantageously included between 10 and 10,000 ppm relative to the total weight of the anionic water-soluble polymer (monomers A, B and optionally C), preferably between 50 and 5,000 ppm.

[0159] Advantageously, the anionic water-soluble polymer obtained according to the process of the invention is used without post-treatment other than the salification of said polymer. It can be used immediately after step f) or after one or more optional steps, in solution (without prior drying or purification), or after having been dried. Papermaking process

[0160] The present invention also relates to a method for manufacturing paper or board comprising (1) adding a water-soluble anionic polymer according to the invention to an aqueous suspension of fibers (advantageously cellulosic fibers) and (2) forming a sheet of paper or board. Thus, the invention relates to the use of a water-soluble anionic polymer in a papermaking process.

[0161] The various stages of the paper, cardboard or similar manufacturing process are known and conform to techniques requiring the knowledge of a person skilled in the art; it is not necessary to describe them in more detail as they remain known and classic to what a person skilled in the art knows; if necessary, he may refer to the document: Handbook for Pulp & Paper Technologists, 3rd Edition, GASmook.

[0162] According to the invention, the anionic water-soluble polymer is added in the papermaking process, before or after the formation of the sheet of paper, cardboard, or similar material. Thus, the contact between the cellulosic material and the polymer of the invention can be carried out in various ways, including according to typical methods known to those skilled in the art.

[0163] The anionic water-soluble polymer can be added to the cellulosic material in the form of a dilute or undiluted aqueous solution. It can be applied by an impregnation technique, or can be added directly to the fibrous suspension at any point in the papermaking process where dry strength agents are normally introduced.

[0164] Thus, the polymer according to the invention can be introduced into the thick stock or the thin stock. It can be added at the mixing pump, before the headbox or the filter screen. Preferably, the polymer is introduced before the headbox.

[0165] Preferably, the polymer according to the invention is industrially injected into the fibrous suspension, i.e., before its dilution by white water (thick paste). The consistency of the paste is on the order of 1 to 5% by mass of cellulosic fibers.

[0166] The papermaking process according to the invention can be implemented with any type of paper pulp, such as virgin fiber pulps (Kraft, Bisulfite), recycled fiber pulps, deinked pulps, mechanical and thermomechanical pulps.

[0167] In a preferred mode according to the invention, the anionic water-soluble polymer according to the invention is added in combination with a cationic water-soluble polymer in order to enhance the dry strength properties of the paper while maintaining good drainage performance.

[0168] The cationic water-soluble polymers are advantageously chosen from among PAEs (polyaminopolyamide-epichlorohydrin), polyvinylamines, glyoxalated polyacrylamides, PEIs (polyethyleneimine), PAs (polyamines, epichlorohydrin-dimethylamine resins), polymers resulting from Hofmann degradation, polyacrylamides, starches and mixtures thereof. Preferably, they are polymers resulting from Hofmann degradation.

[0169] Advantageously, the mass ratio between the anionic water-soluble polymer of the invention and the cationic water-soluble polymer is between 1 / 10 and 10 / 1.

[0170] Water-soluble anionic and cationic polymers are advantageously added before the formation of the sheet, directly to the fibrous suspension.

[0171] They can be added separately or in a mixture, in any order of introduction, at one point or at two points of injection.

[0172] The papermaking process according to the invention may also include the addition of other additives and / or polymers as required; by way of example and without limitation, these may include: biocides, coagulants, retention agents, flocculants, starch... Use

[0173] The present invention also relates to the use of the anionic water-soluble polymer in hydrocarbon recovery (oil and / or gas); in well drilling or cementing; in the stimulation of hydrocarbon (oil and / or gas) wells, for example hydraulic fracturing, conformance, diversion; in open, closed or semi-closed water treatment; in the treatment of fermentation musts; in sludge treatment; in construction; in wood processing; in the treatment of hydraulic compositions (concrete, cement, mortar and aggregates); in the mining industry; in the formulation of cosmetic products; in the formulation of detergents; in textile manufacturing; in geothermal energy; in the manufacture of sanitary diapers; or in agriculture.

[0174] The present invention also relates to the use of the anionic water-soluble polymer as a flocculant, coagulant, binding agent, fixing agent, viscosity reducing agent, thickening agent, absorbent agent, friction reducing agent, draining agent, charge retention agent, dehydrating agent, conditioning agent, stabilizing agent, fixing agent, film-forming agent, sizing agent, superplasticizing agent, clay inhibitor or dispersant.

[0175] The invention and its advantages will be more clearly illustrated by the examples The following are given to illustrate the invention, and not in a limiting manner. Examples

[0176] List of abbreviations: AMD: Acrylamide (monomer B) AA: Acrylic acid (monomer A) DM AM: Dimethylacrylamide (compound II) SMS: Sodium methylsulfonate (compound I) SPS: Sodium persulfate (polymerization initiator) ATBS: 2-Acrylamido-2-methylpropanesulfonic acid (monomer A) AI: Itaconic acid (monomer A)

[0177] Description of the GPC-Malls molecular weight characterization

[0178] Permeable gel chromatography is a method for separating macromolecules according to their hydrodynamic volume; it is coupled to a Malls detector, allowing the light scattering to be measured at several angles.

[0179] The synthesized polymers are analyzed under the following conditions: - Instrument: GPC-2 - Columns: Shodex SB-807-HQ & SB-805 custom - Method : * Temperature: 30°C * Mobile phase: 0.5M NaNO3, HEPES (pH=8), 1OOppm NaN3 * Injection: lOOpL * Flow rate: 0.3 mL / min * Detection: (i) Light scattering detector (MALS): Absolute molar mass (ii) Refractometry (RI): Concentration

[0180] Viscosity is measured using a Brookfield viscometer, at 25°C with a Brookfield LV3 module speed 6 rpm. Polymer preparation Polymer 1

[0181] In a 1-liter reactor equipped with a mechanical stirrer, a thermometer, a condenser, and a nitrogen gas dip tube, a first fraction Fl is introduced at the bottom of the tank. This fraction consists of 165.6 g of water, 71.2 g of acrylamide (50% by weight in water), 1 g of citric acid, 0.5 g of dimethylacrylamide, and 0.68 g of sodium methyl sulfonate. The mixture is heated and maintained at a temperature between 79 and 81°C using a water bath. The addition of 0.05 g of sodium persulfate primes this starter and initiates the polymerization of the monomers (PI) for To form a first PG1 gradient polymer, once the exothermic reaction is complete, the following steps are initiated: a starter (30g of SPS at 0.33 wt% in water) is poured for 130 minutes, and simultaneously a second fraction F2, composed of 28.8g of water, 124.9g of acrylamide (50 wt% in water), 23g of 100% acrylic acid, 0.5g of dimethylacrylamide, and 0.33g of sodium methyl sulfonate, is poured for 50 minutes. After the F2 fraction has been poured, the PG2 gradient polymer is allowed to age for 10 minutes (the P2 polymerization to form the PG2 gradient polymer occurs during the pouring of the F2 fraction and during the aging process). We then begin to pour a third fraction F3, composed of 136.8g of water, 61.1g of acrylamide (50% by weight in water), 0.01g of sodium methyl sulfonate, over 60 minutes.At the end of the addition of fraction F3, the polymer is allowed to age for 10 minutes (the P3 polymerization to form the polymer takes place during the pouring of fraction F3 and during aging). Once aging is complete, 165.3 g of water and 0.15 g of sodium persulfate are added. When the desired viscosity is reached, the reaction is stopped by adding 2.4 g of sodium bisulfite (40 wt% in water) and 165.2 g of water. A further aging of 60 minutes is applied before cooling. The resulting polymer 1 has a pH of 3.5, an active ingredient content of 15 wt%, a viscosity of 8900 cps, and a molecular weight obtained by GPC-Malls of 4,580,000 Da. Polymers 2-5

[0182] The protocol for preparing polymer 1 is reproduced by varying the composition of the different fractions in order to produce polymers 2 to 5; the compositions are summarized in Table 1. Polymer 6

[0183] In a 1-liter reactor equipped with a mechanical stirrer, a thermometer, a condenser, and a nitrogen gas dip tube, 663.7 g of water, 262.9 g of acrylamide (50 wt. in water), 23.5 g of 100% acrylic acid, 0.5 g of dimethylacrylamide, and 0.65 g of sodium methylsulfonate are introduced. The pH is adjusted to 6 by adding 23 g of NaOH (50 wt. in water). The reactor is heated to 35°C. The reaction is initiated with the addition of 0.16 g of VA 044.

[0184] When the maximum temperature is reached, the mixture is aged for 60 minutes before the addition of 2.4 g of sodium bisulfite (40 wt% in water). A further 60 minutes of aging is applied before cooling. The resulting polymer 6 has a pH of 7, an active substance content of 15 wt%, a viscosity of 7000 cps, and a molecular weight obtained by GPC-Malls of 1,400,000 Da. Polymer 7

[0185] Polymer 7 is produced according to the same protocol as polymer 6, by making vary the monomeric composition of the polymer. Polymer 8

[0186] Polymer 8 is produced according to the same protocol as polymer 1, with the difference that polymer is obtained without compound II (DMAM). Polymer 9

[0187] Polymer 9 is produced according to the preparation protocol of polymer 1, with the difference that the polymer is obtained without compounds I (SMS) and II (DMAM), but in the presence of a transfer agent, sodium hypophosphite (Hypo). Composition globale (mol%) Composition F1 (ppm en poids) Composition F2 (ppm en poids) Composition F3 (ppm en poids) Visco sité (cps) Poids moléculaire (Da) Pi (INV) AMD / AA 85 / 15 AMD DMAM SMS 28% 3298ppm 4485ppm AMD AA DMAM SMS 48% 100% 3298ppm 2177 ppm AMD SMS 24% 66ppm 8900 4580000 P2 (INV) AMD / AA 85 / 15 AMD AA DMAM SMS 28% 50% 3298ppm 4485ppm AMD AA DMAM SMS t'-J Cm •O MO r 4^ <1 GO 0 00 X® o- o-, S B AMD SMS 24% 66ppm 7450 4400000 P3 (INV) AMD / ATBS 85 / 15 AMD DMAM SMS 28% 3187ppm 3569ppm AMD ATBS DMAM SMS 48% 100% 3187ppm 1721ppm AMD SMS 24% 64ppm 6200 4560000 P4 (INV) AMD / AI 92,5 / 7.5 AMD DMAM SMS 28% 3306ppm 429§ppm AMD AI DMAM SMS 48% 100% 3306ppm 2050ppm AMD SMS 24% 66ppm 7800 4300000 P5 (INV) AMD / AA 70 / 30 AMD DMAM SMS 28% 3299ppm 3629ppm AMD AA DMAM SMS 48%: 100% 3299ppm 1716ppm AMD SMS 24% 66ppm 7900 3900000 P6 (CE) AM AA DMAM SMS 4 D 85% 15% 3227 ppm 195 ppm 7000 1400000 P7 (LE) AMI AA DMAM SMS 4 9 70% 30% 3333 ppm 067 ppm 8000 1 000000 PS (CE) AMD / AA 85 / 15 AMD SMS 28% 4578ppm AMD AA SMS 48% 100% 2221 ppm AMD SMS 24% 67ppm 8100 1350000 P9 (CL) AMD / AA 85 15 AMD Hypo 28%. 212ppm AMD AA Hypo 48%. 100% lOOppm AMD Hypo 24% 3 ppm 8400 1280000 .

[0189] Table 1: Synthesis of polymers 1 to 9 (P1-P9: polymers 1 to 9; INV = invention; CE = comparative example)

[0190] Table 2 summarizes the composition of the different fractions (monomers A and B, compounds I and II). Composition F1 Composition F2 Composition F3 PI (INV) B -I-II ABI II BI P2 (INV) ABI-II ABI-II BI P3 (INV) BI - II ABI-II BI P4 (INV) B — I — II ABI-II BI P5 (INV) BI - II ABI-II BI P6 (CE) ABI-II P7 (CE) ABI-II PS (CE) BI ABI BI P9 (CE) B AB B

[0192] Table 2: Composition of fractions in the synthesis of polymers 1 to 9. Application test

[0193] Polymers 1 to 9 are used in combination with the following cationic polymers:

[0194] HF 31: SNF range polymer, polyvinylamine from Hofmann degradation, cationic, having a viscosity of 200 cps and a dry extract of 21% by weight.

[0195] VP 450: SNF range polymer, polyvinylamine from the hydrolysis of poly-vinylformamide, cationic, having a viscosity of 1380 cps and a dry extract of 19.2% by weight.

[0196] The drainage and dry strength performance of polymers 1 to 9 in combination with HF 31 and VP 450 are evaluated under the conditions described below.

[0197] The wet pulp used in all application examples is obtained by disintegrating dry pulp to obtain a final aqueous concentration of 1% by mass. It is a pH-neutral pulp composed of 100% recycled cardboard fibers.

[0198] Evaluation of vacuum draining performance (DDA)

[0199] The DDA (Dynamic Drainage Analyzer) automatically determines the time (in seconds) required to drain a fibrous suspension under vacuum onto a cloth. The polymers are added to the wet paste (0.6 liters of paste at 1.0 wt%) in the DDA cylinder while being stirred at 1000 rpm: T=0s: paste stirring begins; T=10s: polymer(s) added. T=30s: agitation stopped and draining under vacuum at 200mBar for 60s

[0200] The pressure under the canvas is recorded as a function of time. When all the water is Once the air is evacuated from the fibrous mat, it passes through, creating a break in slope on the curve representing the pressure under the fabric as a function of time. The time, expressed in seconds, recorded at this break in slope corresponds to the drainage time. The shorter the time, the better the vacuum drainage.

[0201] Performance in dry resistance application, basis weight at 80g.m2

[0202] The necessary quantity of pulp is taken so as to obtain in the end a sheet with a weight of 80g.m2.

[0203] The wet paste is introduced into the dynamic mold vat and kept under agitation. The various components of the system are injected into this paste according to the predefined sequence. A contact time of 30 to 45 seconds is generally observed between each addition of polymer.

[0204] Paper molds are produced using an automatic dynamic mold: blotting paper and the forming cloth are placed in the bowl of the dynamic mold before starting the bowl's rotation at 1000 rpm and building the water wall. The processed pulp is spread over the water wall to form the fibrous mat on the forming cloth.

[0205] Once the water has been drained, the fibrous mat is recovered, pressed under a press delivering 4 bars, and then dried at 117°C. The resulting sheet is conditioned overnight in a room with controlled humidity and temperature (50% relative humidity and 23°C). The dry strength properties of all the sheets obtained by this procedure are then measured.

[0206] Bursting force is measured with a Messmer Buchel M 405 burst gauge according to TAPPI T403 om-02 standard. The result is expressed in kPa. The bursting index, expressed in kPa.m2 / g, is determined by dividing this value by the basis weight of the tested sheet.

[0207] The breaking length in the dry state is measured in the machine direction with a Testometric AX tensile testing device according to TAPPI T494 om-01. The result is expressed in km.

[0208] [Tables3] Example Composition Percentage Increase Burst Percentage Increase *DBL Percentage Increase DDA White - - - - Example 1 (INV) HF 31 Polymer 1 36.4 27.0 53.3 Example 2 (INV) HF 31 Polymer 2 34.0 26.1 55.7 Example 3 (INV) HF 31 Polymer 3 30.7 21.6 49.7 Example 4 (INV) HF 31 Polymer 4 33.6 24.5 54.8 Example 5 (INV) HF 31 Polymer 5 38.4 28.0 54.3 Example 6 (CE) HF 31 Polymer 6 2? Example 7 (CE) HF 31 Polymer 7 24.7 12.9 28.4 Example 8 (CE) HF 31 Polymer 8 77 5 11.8 29.8 Example 9 (CE) HF 31 Polymer 9 22.8 12.0 30.5 Example 10 (INV) VP 450 Polymer 1 43.4 30.8 57.5 Example 11 (INV) VP 450 Polymer 2 41.7 27.7 61.1 Example 12 (INV) VP 450 Polymer 3 40.8 24.0 58.1 Example 13 (INV) VP 450 Polymer 4 42.2 28.2 59.0 Example 14 (INV) VP 450 Polymer 5 44.7 32.9 58.1 Example 15 (CE) VP 450 Polymer 6 28.0 13.8 43.4 Example 16 (CE) VP 450 Polymer 7 29.0 14.9 41.8 Example 17 (CE) VP 450 Polymer 8 27.1 13.2 42.4 Example 18 (CE) VP 450 Polymer 9 28.3 13.6 44.4 .

[0209] Table 3: (INV = invention; CE = comparative example)

[0210] It is interesting to note that the polymers of the invention (1 to 5), in combination with a cationic polymer, exhibit improved drainage performance (DDA) and mechanical characteristics (Burst: bursting; DBL: dry break) compared to a polymer prepared with a conventional process (polymer 6 and 7), or in the absence of a structuring system (polymer 8 and 9).

Claims

Demands

1. Anionic water-soluble polymer comprising: - at least one anionic monomer A; - at least one non-ionic monomer B; - at least one structuring system comprising: (i) at least one compound I, different from at least one monomer A and selected from: allylsulfonic acid, methallylsulfonic acid, allyl disulfonic acid, methallyl disulfonic acid, their salts and mixtures thereof; (ii) at least one compound II of formula I, different from at least one monomer B: [Chem.l] Formula I Ri and R2 being, independently of each other, a hydrogen atom, a methyl group, an ethyl group, an isopropyl group or a CH2-OH group; Ri and R2 are not both hydrogen atoms; said polymer being devoid of cationic monomer and zwitterionic monomer; said anionic water-soluble polymer being obtained according to the following steps: a) formation of a solution (SI) comprising a first fraction (Fl) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; b) polymerization 1 (PI) of the Fl fraction to form a solution of a first gradient polymer (PG1); c) addition, to the solution comprising PG1, of a second fraction (F2) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; d) polymerization 2 (P2) of fraction F2 on PG1 to form a solution of a second gradient polymer (PG2); e) addition, to the solution comprising PG2, of a third fraction (F3) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; f) polymerization 3 (P3) of fraction F3 on PG2 to form a solution comprising an anionic water-soluble polymer.

2. Anionic water-soluble polymer according to claim 1, characterized in that the at least anionic monomer A is selected from acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, acrylamidoundecanoic acid, 3-acrylamido-3-methylbutanoic acid, maleic anhydride, 2-acrylamido-2-methylpropane sulfonic acid (ATBS), vinylsulfonic acid, vinylphosphonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropylacrylate, allylphosphonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane disulfonic acid, their salts and mixtures thereof.

3. Anionic water-soluble polymer according to claim 1 or 2, characterized in that the at least nonionic monomer B is selected from acrylamide, methacrylamide, N-vinylformamide (NVF), N-vinyl acetamide, N-vinylpyrrolidone (NVP), N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), acryloyl chloride, glycidyl methacrylate, glyceryl methacrylate, acrylamide diacetone, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate and mixtures thereof; the alkyl being in Ci-C3.

4. Anionic water-soluble polymer according to any one of the preceding claims, characterized in that it comprises between 500 and 50,000 ppm of compound I, relative to the total weight of monomers A and B.

5. Anionic water-soluble polymer according to any one of the preceding claims, characterized in that it comprises between 500 and 50,000 ppm of compound II, relative to the total weight of monomers A and B.

6. Anionic water-soluble polymer according to any one of the preceding claims, characterized in that compound II is selected from: N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-isopropylacrylamide, N-methylolacrylamide and mixtures thereof.

7. Anionic water-soluble polymer according to any one of the preceding claims, characterized in that the mass ratio between compound I and compound II is between 0.01 and 100.

8. A process for the sequential preparation of an anionic water-soluble polymer comprising: - at least one anionic monomer A; - at least one non-ionic monomer B; - at least one structuring system comprising: (i) at least one compound I, different from at least one monomer A and selected from: allylsulfonic acid, methallylsulfonic acid, allyl disulfonic acid, methallyl disulfonic acid, their salts and mixtures thereof; (ii) at least one compound II of formula I, different from at least one monomer B: [Chem.l] Formula I Ri and R2 being, independently of each other, a hydrogen atom, a methyl group, an ethyl group, an isopropyl group or a CH2-OH group; Ri and R2 are not both hydrogen atoms (Ri^H when R2 = H; R2^H when Ri = H); said polymer being devoid of cationic monomer and zwitterionic monomer, The process includes the following steps: a) formation of a solution (SI) comprising at least a first fraction (Fl) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; b) polymerization 1 (PI) of the Fl fraction to form a solution of a first gradient polymer (PG1); c) addition, to the solution comprising PG1, of a second fraction (F2) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; d) polymerization (P2) of fraction F2 on PG1 to form a solution of a second gradient polymer (PG2); e) addition, to the solution comprising PG2, of a third fraction (F3) containing (1) at least one monomer selected from monomers A and B and (2) at least one compound selected from compounds I and II; f) polymerization (P3) of fraction F3 on PG2 to form a solution comprising an anionic water-soluble polymer.

9. A process according to claim 8, characterized in that an initiator is added continuously throughout the process.

10. A process according to claim 8 or 9, characterized in that, after polymerization step f) (P3), the process includes an aging step of 10 minutes to 100 minutes.

11. A method for manufacturing paper or board comprising adding an anionic water-soluble polymer according to any one of claims 1 to 7, into an aqueous suspension of fibers and forming a sheet of paper or board.

12. Use of the anionic water-soluble polymer according to any one of claims 1 to 7, in hydrocarbon recovery; in well drilling or cementing; in hydrocarbon well stimulation; in open, closed or semi-closed circuit water treatment; in fermentation must treatment; in sludge treatment; in construction; in wood processing; in hydraulic composition processing; in the mining industry; in cosmetic formulation; in detergent formulation; in textile manufacturing; in geothermal energy; in the manufacture of sanitary diapers; or in agriculture.

13. Use of the anionic water-soluble polymer according to any one of claims 1 to 7, as a flocculant, coagulant, binding agent, fixing agent, viscosity reducing agent, thickening agent, absorbent agent, friction reducing agent, draining agent, charge retaining agent, dehydrating agent, conditioning agent, stabilizing agent, fixing agent, film-forming agent, sizing agent, superplasticizing agent, clay inhibitor or dispersant.