CONTINUOUS PREPARATION OF POLYETHER COMPOUND

Abstract

The invention relates to a thickening copolymer and its continuous preparation method by reactive extrusion. The preparation method comprises a polymerization reaction of a dihalogenated compound and a polyhydroxylated monomer. This copolymer allows for viscosity control of a versatile aqueous composition usable in numerous technical fields.

Description

Title of the invention: CONTINUOUS PREPARATION OF POLYETHER COMPOUND

[0001] The invention relates to a thickening copolymer and its continuous reactive extrusion preparation method. The preparation method comprises a polymerization reaction of a dihalogenated compound and a polyhydroxylated monomer. This copolymer allows for viscosity control of a versatile aqueous composition usable in numerous technical fields.

[0002] Many technical fields require control of the rheology of the compositions used, particularly aqueous compositions. Having a variety of effective thickening agents is therefore very useful. Some technical fields also require effective control of the dispersion or coagulation of matter in aqueous media, particularly mineral matter, or the improvement of the antistatic properties of an aqueous composition.

[0003] Controlling particle size or reducing friction within an aqueous composition is also important in certain technical fields. In particular, such properties may be sought in the paper industry (pulp dispersion quality for papermaking, pulp dispersion, reduced friction resistance, improved yield for newsprint and cardboard), in the textile industry (sizing or coating), in the glass industry (fiber sizing, sizing or screening), in civil engineering or construction (material transport, reduced friction resistance, modified fluidity, extrusion molding, improved sliding properties), in the ceramics industry, in the adhesives industry, and in the coating materials industry (improved viscosity, particularly for emulsion paints).in the metals and mining industry (viscosity reduction, collection of airborne mineral phosphate, coagulation), in the polymer industry, in the beauty products industry (formulation or release of cosmetic or moisturizing compounds), in the detergent industry (formulation or release of surfactant, fabric softener, and perfume compounds), in the pharmaceutical or phytopharmaceutical industry (protection or delivery of active compounds, administration or controlled release), in shipbuilding (drag reduction).

[0004] Specific polymers can therefore be used to impart such properties to aqueous compositions. These polymers should possess high solubility in water or in polar solvents. They should also possess a capacity for hydration or rapid swelling or facilitating the formation of hydrogel.

[0005] These polymers should be insensitive to pH variations.

[0006] Generally, methods for preparing thickening compositions comprising a hydrophilic polymer, advantageously water-soluble, that are flexible and reproducible are sought. Improving the thickening efficiency of the resulting thickening agent is also desired. According to the invention, a water-soluble polymer is understood to be a polymer that is totally miscible with water at a temperature above its melting point.

[0007] These thickening copolymers can in particular be used to control the rheology of detergent compositions, cosmetic compositions, paper coating compositions, and coating compositions.

[0008] Hydrophobic compounds, particularly hydrophobically modified compounds such as associative non-ionic thickening agents, are known as rheology-modifying agents. However, known compounds do not always provide a satisfactory solution.

[0009] Furthermore, it is also important to have access to improved copolymer preparation methods. Indeed, known methods, particularly discontinuous or batch preparation methods, generate numerous problems that make them difficult to implement. It may prove impossible to efficiently implement certain thickening agent preparation methods because the problems encountered can be so difficult to overcome, especially problems related to viscosity drift in the reaction medium for preparing thickening agents.For example, the preparation of polymers by polymerization of polyethylene glycol often produces a reaction mixture whose viscosity increases significantly during the reaction. This can lead to a sharp increase in energy consumption for stirring, heating of the reaction medium due to stirring exothermics, or even blockage if the viscosity drift is too great. The preparation of such polymers therefore precludes the use of stirred reactors. The preparation of these polymers may also require significant dilution of the reaction medium with a solvent that must then be separated. Nevertheless, the use of solvents should always be limited or eliminated.

[0010] It is also important to have flexible preparation methods available, particularly methods that allow for varying the reagents introduced (nature, quantity) into the feed zones during synthesis. Improving the reproducibility of copolymer preparation methods should also be a priority.

[0011] There is therefore a need for a method of preparing a thickening copolymer that provides a solution to all or part of the problems of known methods.

[0012] Thus, the invention provides a method for the continuous preparation of a copolymer P by reactive extrusion comprising the polymerization reaction in the presence of a base: a) of at least one polyhalogenated compound a; b) of at least one polyhydroxylated monomer b used in a molar quantity providing a number of hydroxyl groups (OH) greater than the number of halides provided by compound a.

[0013] For the method according to the invention to be effective, the presence of a base is essential to allow the reaction of the polyhydroxylated monomer b with the dihalogenated compound a. Preferably according to the invention, the base is used in a molar excess relative to the molar amount of OH groups of monomer b. More preferably, the base is used in a molar amount of 1.05 to 10, preferably 1.1 to 6, molar equivalents relative to the molar amount of OH groups of monomer b.

[0014] The base used leads to an increase in pH during the implementation of the method according to the invention. Preferably, the polymerization is carried out at a pH greater than 10 or greater than 12.

[0015] According to the invention, numerous bases can be used. Preferably, according to the invention, the base is a strong mineral base or a strong organic base. More preferably, the base is selected from sodium hydride, potassium hydride, NaOH, KOH, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butanolate, and potassium tert-butanolate. Sodium hydroxide is the preferred base.

[0016] Generally, according to the invention, the base allows the alkoxide derivative of compound b to be obtained. Advantageously, the treatment, total or partial, with the base of compound b, prior to carrying out the reactive extrusion, can allow this alkoxide derivative of compound b to be introduced directly. The alkoxide derivative of compound b can optionally be stored separately and then introduced during the reactive extrusion in the presence of compound a.

[0017] The method according to the invention comprises the polymerization of the polyhydroxylated monomer b and the polyhalogenated compound a. Preferably, the method according to the invention uses a single polyhalogenated compound a or two or three different polyhalogenated compounds a. According to the invention, the polyhalogenated compound can be selected from a dihalogenated compound a1, a trihalogenated compound a2, a tetrahalogenated compound a3, and combinations thereof. Preferably according to the invention, the polyhalogenated compound a is a dihalogenated compound a1 of formula I: [Chem I] dx>2 (I) in which: - D independently represents a divalent hydrocarbon group, preferably a Ci-Cio-alkylene group, more preferably a Ci-C2-alkylene group, much more preferably CH2; - X1 independently represents Br, Cl or I, preferably Br.

[0018] Also preferably according to the invention, the polyhalogenated compound a is a trihalogenated compound a2 of formula II: [Chem II] T-X23 (II) in which: - T independently represents a trivalent hydrocarbon group, preferably a Ci-Cio-alkylene group, more preferably a Ci-C2-alkylene group, much more preferably CH; - X2 independently represents Br, Cl or I, preferably Br

[0019] Preferably according to the invention, T represents a saturated trivalent hydrocarbon group. According to the invention, the polyhalogenated compound can also be a tetrahalogenated compound selected from 1,1,2,2-tetrabromoethane, 1,2,4,5-tetrabromobenzene, tetrabromobisphenol A, tetrachloro-m-xylene, tetrachloro-O-benzoquinone.

[0020] Preferably, the method according to the invention uses a single polyhydroxyl compound b or two or three different polyhydroxyl compounds b. More preferably according to the invention, the polyhydroxyl compound b is a compound comprising two, three, or four hydroxyl groups. More preferably, the polyhydroxyl compound b is a compound bl of formula III: [Chem III] HO-Qn-OH (III) in which: - Q independently represents an oxyalkylene group, preferably chosen from oxyethylene, oxyethylene-oxypropylene comprising at most 40 mol% oxypropylene, oxyethylene-oxybutylene comprising at most 20 mol% oxybutylene, and their combinations, - n independently represents a number ranging from 20 to 800.

[0021] In order for the oxyethylene-oxypropylene copolymer to retain its water-soluble character, its oxypropylene content is less than 40 mol%, advantageously less than 35 mol%. In order for the oxyethylene-oxybutylene copolymer to retain its water-soluble character, its oxybutylene content is less than 20 mol%, advantageously less than 15 mol%.

[0022] The preferred polyhydroxylated compound bl of formula II comprises oxyethylene Q groups. Preferably according to the invention, the polyhydroxylated compound ba has a molar mass (Mw) ranging from 800 to 40,000 g / mol, preferably from 2,000 to 20,000 g / mol, and more preferably from 2,000 to 15,000 g / mol. According to the invention, the molar mass of compound b is determined by Size Exclusion Chromatography (SEC).

[0023] According to the invention, the copolymer P is advantageously prepared by reactive extrusion, with respect to the total molar quantity of compounds a and b, by means of: * 5 mol% to less than 50 mol% of polyhalogenated compound a; * 50 molar to 95 molar polyhydroxylated monomer b.

[0024] According to the invention, the copolymer P can advantageously be prepared by reactive extrusion, with respect to the total molar quantity of compounds a and b, by means of: * 15 mol% to less than 50 mol% of polyhalogenated compound a; * 50 molar to 85 molar polyhydroxylated monomer b.

[0025] According to the invention, the copolymer P can advantageously be prepared by reactive extrusion, with respect to the total molar quantity of compounds a and b, by means of: * 30 mol% to less than 50 mol% of polyhalogenated compound a; * 50 molar to 70 molar polyhydroxylated monomer b.

[0026] According to the invention, the copolymer P can advantageously be prepared by reactive extrusion, with respect to the total molar quantity of compounds a and b, by means of: * 40 mol% to less than 50 mol% of polyhalogenated compound a; * 50 molar to 60 molar polyhydroxylated monomer b.

[0027] Particularly advantageously, especially compared to a batch process which requires dilution of the reaction medium, the method according to the invention can be carried out with or without a solvent, for example in a solvent chosen from water, an organic solvent and combinations thereof, preferably water. Preferably according to the invention, the preparation method can be carried out in the absence of a solvent.

[0028] Advantageously, the preparation method according to the invention may also include a final acid treatment of the copolymer P leading to a pH below 8, preferably to a pH above 6, for example by means of an acid, in particular a carboxylic acid such as acetic acid or lactic acid.

[0029] The preparation method according to the invention comprises the reaction according to a continuous reactive extrusion process. Reactive extrusion is a method generally known for the preparation of thermoplastic polymers that have high temperatures Glass transition or melting temperatures. Reactive extrusion generally allows all steps (mixing, polymerization, and purification or devolatilization) to be carried out within the extruder. Although the polyhydroxylated compound may be heat-sensitive, no degradation is usually observed. Various types of extruders can be used for mixing the reagents: single-screw, two-stage or co-kneader, twin-screw, planetary gear, and ring extruders. Twin-screw extruders are generally preferred. The L / D (length / diameter) ratio of the extruder is adjusted according to the polymerization, polycondensation, or polyaddition time, which depends on the flow rate and residence time. The L / D ratio can, for example, be greater than or equal to 20, or more advantageously greater than or equal to 30.The implementation parameters can be adapted, including the rotation speed of the extruder screws and its design in the mixing zones, for example, depending on the desired mixing.

[0030] The extruder may include one or more feeding zones. It is possible to premix the components before introducing them into the extruder. It is also possible to include in the extruder a melting zone for some of the compounds before the addition of the other compounds, in particular compound b. The extruder may include one or more heating zones. Advantageously, it includes several heating zones. The polymerization, polycondensation, or polyaddition reaction is advantageously conducted at a temperature ranging from 50°C to 350°C, more advantageously from 70°C to 300°C. The pressure can vary from 50 mbar (5 x 10³ Pa) up to 50 bar (5 MPa). The polymerization, polycondensation, or polyaddition reaction is advantageously conducted under an inert atmosphere, for example, by purging with nitrogen or argon.It can also be carried out in the presence of radical inhibitors that will contribute to the thermal stabilization of compound b or the polymerization product. The method according to the invention may include one or more evaporation steps for the unreacted volatile components. The method according to the invention makes it possible to obtain the copolymer P with high conversion rates, in times compatible with industrial use. Furthermore, the method according to the invention, compared to a batch reactor process, allows for faster homogenization of the compounds with an increased diffusion rate of the compounds and thus improved mixing.

[0031] According to the invention, the reactants are generally pumped to the reactor at a temperature between 70°C and 120°C. Hot water or steam can be used as a heat transfer fluid to control the reactor temperature within the range of 70°C to 120°C. The reactor can include separate heating zones so that different zones can be maintained at different temperatures. depending on the preparation requirements of the copolymer P being prepared. Similarly, the residence time in the reactor can be controlled, for example, from less than one hour to more than six hours. A twin-screw extruder can be fitted to the end of the reactor.

[0032] The preparation method according to the invention is particularly advantageous both in itself and for enabling the production of a specific copolymer P. Thus, the invention also relates to a copolymer P obtained according to the continuous reactive extrusion preparation method defined according to the invention. Preferably, the copolymer P is in solid form at 25°C, preferably in molten form or in solid form at 25°C or at a temperature below its melting point, for example, in a solid form selected from pellets, flakes, granules, chips, powder, and combinations thereof.

[0033] Surprisingly, the preparation method according to the invention also improves the viscosifying properties of the copolymer P according to the invention. Thus, the same quantity of copolymer P obtained by the method according to the invention will be thicker than an identical quantity of polymer obtained by reacting the same compounds, in the same proportions, but according to a batch process in a reactor.

[0034] Also, the method according to the invention makes it possible to obtain copolymers P with higher molar masses (Mw) than those of polymers that can be obtained in a batch process in a reactor, whereas the increase in viscosity would impose a maximum molar mass limit. Reactive extrusion is particularly advantageous for the preparation of copolymer P despite the sensitivity of compound b to heat. Reactive extrusion allows for time savings, with shorter cycle times compared to a batch process in a reactor. It is then possible to use higher temperatures, for example when using polyalkylene glycols. The risk of thermal degradation of these compounds is then reduced, notably thanks to shorter residence times.

[0035] The method according to the invention makes it possible to obtain copolymers P with a high molar mass (Mw). Preferably according to the invention, the molar mass (Mw) of the copolymer P is greater than 50,000 g / mol, preferably greater than 100,000 g / mol or greater than 200,000 g / mol. Advantageously according to the invention, the molar mass (Mw) of the copolymer P is less than 10,000,000 g / mol, preferably less than 5,000,000 g / mol or less than 1,000,000 g / mol. Preferably according to the invention, the molar mass (Mw) of the copolymer P ranges from 50,000 g / mol to 10,000,000 g / mol or from 100,000 g / mol to 5,000,000 g / mol, preferably from 200,000 g / mol to 1,000,000 g / mol.

[0036] According to the invention, the molar mass of the copolymer P or of the compound b is determined by Size Exclusion Chromatography (SEC) or in English “Gel Permeation Chromatography (GPC). This technique uses a Waters liquid chromatography system equipped with a detector. This detector is a Waters 2414 refractometric concentration detector. This liquid chromatography system has two size-exclusion columns to separate the different molecular weights of the polymers or compounds being studied. The elution liquid phase is an organic phase composed of THF (HPLC grade, unstabilized).

[0037] In a first step, approximately 25 mg of copolymer or compound is solubilized in 5 mL of THF, to which 0.1 mol% water is added as an internal flow marker. The solution is then filtered to 0.2 µm. 50 pL is then injected into the chromatography apparatus (eluent: THF, HPLC grade, unstabilized).

[0038] The liquid chromatography apparatus includes an isocratic pump (Waters 515) with a flow rate set at 0.3 mL / min. The chromatography apparatus also includes a furnace comprising a series column system: a 250 mm long and 4.6 mm diameter Agilent PLgel MiniMIX-A column followed by a 250 mm long and 4.6 mm diameter Agilent PLgel MiniMIX-B column. The detection system consists of a Waters 2414 RI refractometer detector. The columns are maintained at 35°C and the refractometer is also heated to 35°C.

[0039] The chromatography apparatus is calibrated using polymethyl methacrylate standards certified by the supplier “Agilent” (“EasiVial” PMMA).

[0040] The copolymer P according to the invention can be used directly or it can be combined with other substances in a composition. When used directly, the copolymer P according to the invention can be in a molten state, in particular at a temperature above its melting point and compatible with the intended use. It can also be used directly after cooling, in particular after cooling to a temperature below its melting point. It can then be used in various solid forms, for example in a form selected from pellets, flakes, granules, chips, powder, and combinations thereof.

[0041] The invention also provides a rheological control composition comprising at least one copolymer P according to the invention. The composition according to the invention can optionally be acidified, leading to a pH below 8, preferably above 6, for example by means of an acid, in particular a carboxylic acid such as acetic acid or lactic acid.

[0042] Preferably, in the rheological control composition according to the invention, the copolymer P according to the invention is combined with at least one solvent, in particular water or a coalescing solvent, for example glycol, butyl glycol, butyldiglycol, monopropylene glycol, ethylene glycol, ethylenediglycol, "Dowanol" products, the CAS number is 34590-94-8, "Texanol" products whose CAS number is 25265-77-4; or combined with at least one additive selected from an amphiphilic compound, including a surfactant compound, preferably a hydroxylated surfactant compound, for example alkyl-polyalkyleneglycol, including alkyl-polyethylene glycol and alkyl-polypropyleneglycol; a polysaccharide derivative, for example cyclodextrin, cyclodextrin derivative, polyethers, alkyl-glucosides; a hydrotropic compound, an antifoaming agent, a biocidal agent and combinations thereof.

[0043] The invention also provides an aqueous formulation that can be used in many technical fields. The aqueous formulation according to the invention comprises: - at least one composition according to the invention; optionally - at least one organic or mineral pigment or organic, organometallic or mineral particles, for example calcium carbonate, talc, kaolin, mica, silicates, silica, metal oxides, in particular titanium dioxide, iron oxides; and possibly - at least one agent selected from a particle spacer, a dispersing agent, a steric stabilizer, an electrostatic stabilizer, an opacifying agent, a coloring agent, a solvent, a coalescing agent, an antifoaming agent, a preservative, a biocidal agent, a spreading agent, a thickening agent, a film-forming copolymer and mixtures thereof.

[0044] The aqueous formulation according to the invention may also include at least one composition according to the invention, a binding agent, and an inkjet coloring agent. The aqueous formulation according to the invention may also include at least one composition according to the invention and a cosmetic agent, in particular a sunscreen or a moisturizing agent. The aqueous formulation according to the invention may also include at least one composition according to the invention, a binding agent, and a pigment, in particular a pigment for paper coating.

[0045] Depending on the particular copolymer P or the additives it comprises, the formulation according to the invention can be implemented in numerous technical fields. Thus, the formulation according to the invention can be a coating formulation. Preferably, the formulation according to the invention is an ink formulation, an adhesive formulation, a varnish formulation, a paint formulation, for example, decorative or industrial paint. The formulation according to the invention can also be an inkjet ink composition, a cosmetic composition, or a paper coating slurry.

[0046] The invention also provides a concentrated aqueous pigment paste comprising at least one copolymer P and at least one organic or mineral colored pigment.

[0047] The copolymer P and the formulation according to the invention possess properties enabling them to be used to modify or control the rheology of the medium. including. Thus, the invention also provides a method for controlling the viscosity of an aqueous composition. This method of viscosity control according to the invention comprises the addition of at least one copolymer P, obtained according to the invention, to an aqueous composition.

[0048] Preferably, the viscosity control method according to the invention is implemented for an aqueous composition which is a formulation according to the invention.

[0049] The advantageous, particular or preferred characteristics of the preparation method according to the invention define copolymers P, aqueous compositions, formulations, pigment pastes as well as viscosity control methods according to the invention which are also advantageous, particular or preferred.

[0050] The following examples illustrate the different aspects of the invention. EXAMPLES

[0051] Example 1: Preparation of PI and P2 copolymers according to the invention

[0052] A twin-screw co-rotating extruder with the following geometric parameters is used: Diameter = 26 mm and Length / Diameter ratio = 80, equipped with a gas introduction device (for example, nitrogen or depleted air) and a gas evacuation system. The tests are carried out under an uncontrolled atmosphere and at atmospheric pressure.

[0053] The twin-screw extruder has 16 independently temperature-controlled zones. These zones can be electrically heated and cooled by circulating water. Zone 1 is located below the hopper, and zone 16 corresponds to the die. The other zones are numbered 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15, in that order from zone 1 to zone 16. Each zone has a length equal to 5 screw elements. The reagents can be stored in heated, agitated, nitrogen-filled tanks equipped with pumps that allow direct injection of the reagents into the extruder. The flow rates of each pump can be independently controlled to regulate the ratios between the different reagents as well as the overall flow rate. This allows adjustment of the residence time in the extruder. Residence time can be measured by adding a colored tracer.

[0054] For the preparation of the copolymers, the following compounds a, b and c are used: - compound al: dibromomethane, - compound bl: polyethylene glycol with a molecular mass of 8,000 g / mol.

[0055] In a sealed tank heated to 90°C, under vacuum, and dehydrated to a water content below 800 ppm, compound bl is placed. This tank is then purged with nitrogen. Compound bl is injected into zone 1 of the extruder, which is heated to 80°C. Sodium hydroxide is also added to zone 1. Zones 2, 3, 4, and 5 of the extruder are heated to 100°C, 100°C, 150°C, and 150°C, respectively. Compound al is added to zone 6 of the extruder. Zones 6 to 10 are The areas are heated to 200°C to produce a copolymer of compounds al and bl. Zones 11 to 14 are maintained at this temperature. Zone 15 is cooled to 80°C. The residence time of the reaction mixture in the extruder is approximately 9 minutes for a throughput of 3 kg / h.

[0056] The PI copolymer obtained at the extruder outlet is in molten form. To obtain a rheological control composition (CRI) according to the invention, the PI copolymer is introduced directly at the extruder die outlet into an aqueous composition whose final pH is adjusted to approximately 7 using an aqueous solution of acetic acid. The CRI composition comprises 40% by weight of PI copolymer and 60% by weight of aqueous solution comprising acetic acid.

[0057] Similarly, the copolymer P2 and the rheological control composition CR2 according to the invention comprising the copolymer P2 are prepared and characterized. The compounds and molar quantities of the compounds used are presented in Table 1.

[0058] [Table 1] s. < is :>>t __________________________ ŒnFu "............................ CwKpCs&èS: 220 30 J [ 1 lï F CR2 cm 34; 38; 220

[0059] Example 2: Preparation and characterization of aqueous formulations comprising PI and P2 copolymers according to the invention

[0060] The CRI and CR2 compositions of PI and P2 copolymers according to the invention are used as thickening agents in an aqueous formulation. The CRI and CR2 compositions, comprising the thickening PI and P2 copolymers respectively, have a dry extract of 40% by weight of active ingredient. Each formulation is prepared by mixing the different ingredients.

[0061] For each formulation, the resulting low-gradient viscosity is determined: Brookfield viscosity at 10 rpm, denoted VB10 (mPa·s). These measurements are taken 24 hours after preparation of the formulation. The formulations are thermostated at 25 ± 0.5°C. The results are presented in Table 2.

[0062] [Table 2] < iikî't - \ fc'Cf'îk' VB UiîPj.s) CRHPU.............................. ]...................7,590........................] f Œ2 < P2 J............................................................................34 660........................

[0063] The copolymers according to the invention allow for the efficient thickening of these aqueous formulations with low shear gradients. These copolymers can be used effectively as rheology-modifying additives.

Claims

Demands

1. Method of continuous preparation of a copolymer P by reactive extrusion comprising the polymerization reaction in the presence of a base of: a) at least one polyhalogenated compound a; b) at least one polyhydroxylated monomer b used in a molar quantity providing a number of hydroxyl groups (OH) greater than the number of halides provided by compound a.

2. A preparation method according to claim 1 wherein: * the base is used in a molar excess relative to the molar amount of OH groups of monomer b, preferably used in a molar amount of 1.05 to 10, preferably 1.1 to 6, molar equivalents relative to the molar amount of OH groups of monomer b; or * the polymerization is carried out at a pH greater than 10 or greater than 12; or * the base is a strong mineral base or a strong organic base, preferably a base selected from sodium hydride, potassium hydride, NaOH, KOH, sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, sodium tert-butanolate, potassium tert-butanolate.

3. A preparation method according to any one of claims 1 or 2 wherein: * a single polyhalogenated compound a is used or wherein 2 or 3 different polyhalogenated compounds a are used; or * the polyhalogenated compound a is selected from a dihalogenated compound al, a trihalogenated compound a2, a tetrahalogenated compound a3 and their combinations; or * the polyhalogenated compound a is a dihalogenated compound al of formula I [Chem I] dx>2 (I) in which: - D independently represents a divalent hydrocarbon group, preferably a Ci-Cio-alkylene group, more preferably a Ci-C2-alkylene group, much more preferably CH2; - X1 independently represents Br, Cl or I, preferably Br; or * the polyhalogenated compound a is a trihalogenated compound a2 of formula II: [Chem II] T-X23 (II) in which: - T independently represents a trivalent hydrocarbon group, preferably a Ci-Cio-alkylene group, more preferably a Ci-C2-alkylene group, much more preferably CH; - X2 independently represents Br, Cl or I, preferably Br; or * the polyhalogenated compound a is a tetrahalogenated compound a3 selected from 1,1,2,2-tetrabromoethane, 1,2,4,5-tetrabromobenzene, tetrabro-mobisphenol A, tetrachloro-m-xylene, tetrachloro-O-benzoquinone.

4. A preparation method according to any one of claims 1 to 3 wherein: * a single polyhydroxyl compound b is used or wherein 2 or 3 different polyhydroxyl compounds b are used; or * the polyhydroxyl compound b is a compound comprising 2, 3 or 4 hydroxyl groups; or * the polyhydroxylated compound b is a compound bl of formula III: [Chem III] HO-Qn-OH (HD in which: - Q independently represents an oxyalkylene group, preferably selected from oxyethylene, oxyethylene-oxypropylene comprising at most 40 mol% oxypropylene, oxyethylene-oxybutylene comprising at most 20 mol% oxybutylene, and their combinations; - n independently represents a number from 20 to 800; or * the polyhydroxylated compound ba a molar mass by mass (Mw) from 800 to 40,000 g / mol, preferably from 2,000 to 20,000 g / mol, more preferably from 2,000 to 15,000 g / mol.

5. A preparation method according to any one of claims 1 to 4 wherein the copolymer P is prepared by reactive extrusion, relative to the total molar amount of compounds a and b, using: * 5 mol% to less than 50 mol% of polyhalogenated compound a; * 50 molar to 95 molar polyhydroxylated monomer b.

6. A preparation method according to any one of claims 1 to 5 carried out in the absence of solvent or in a solvent selected from water, an organic solvent and combinations thereof, preferably water.

7. A preparation method according to any one of claims 1 to 6 also comprising a final acid treatment of the copolymer P leading to a pH below 8, preferably above 6, for example by means of an acid, in particular a carboxylic acid such as acetic acid or lactic acid.

8. Copolymer P obtained according to the continuous preparation method by reactive extrusion defined according to any one of claims 1 to 7, preferably in molten form or in solid form at 25 °C or at a temperature below its melting point, for example in a solid form selected from pellet, flake, ground, chip, powder and combinations thereof.

9. Copolymer P according to claim 8 having a molar mass Mw, measured by CES, of: * greater than 50,000 g / mol, preferably greater than 100,000 g / mol or greater than 200,000 g / mol, or * less than 10,000,000 g / mol, preferably less than 5,000,000 g / mol or less than 1,000,000 g / mol, or * in the range of 50,000 g / mol to 10,000,000 g / mol or of 100,000 g / mol to 5,000,000 g / mol, preferably of 200,000 g / mol to 1,000,000 g / mol.

10. Rheological control composition comprising at least one copolymer P according to any one of claims 8 or 9, optionally acid-treated leading to a pH below 8, preferably above 6, for example by means of an acid, in particular a carboxylic acid such as acetic acid or lactic acid.

11. Rheological control composition comprising at least one copolymer P according to any one of claims 8 or 9 combined with at least one solvent, in particular water or a coalescing solvent.

12. Method for controlling the viscosity of an aqueous composition comprising the addition of at least one copolymer P according to one of claims 8 or 9 in an aqueous composition.