METHOD FOR PREPARING STRUCTURED POLYMERS IN POWDER FORM BY THE GEL PROCESS

Abstract

This invention relates to a method for preparing a structured water-soluble polymer having a weight average molecular weight greater than 1 million Daltons and a Huggins Coefficient K.sub.H greater than 0.4, the method comprising the following successive steps: a) Preparing a polymer, in the form of a gel, by free-radical polymerization in aqueous solution at an initiation temperature between −20° C. and +50° C. of at least one water-soluble monounsaturated ethylenic monomer, the total weight concentration of monomer(s) in relation to the polymerization charge being between 10 and 60%; b) Granulating the resulting polymer gel; c) Drying the polymer gel to obtain a polymer in powder form; d) Grinding and sifting the powder; at least 10% by weight of water-soluble polymer, based on the total weight of the water-soluble monounsaturated ethylenic monomer or monounsaturated ethylenic monomers used in step a), being added during the polymerization step a) and optionally during the granulation step b), the water-soluble polymer being structured and added as a water-in-oil inverse emulsion or dispersion in oil.

Claims

1. A method for preparing a structured water-soluble polymer of weight-average molecular weight greater than 1 million Daltons and having a Huggins coefficient K.sub.H greater than 0.4, the Huggins coefficient K.sub.H being measured at a polymer weight concentration of 5 g.L.sup.−1, in a 0.4 N aqueous solution of sodium nitrate, at pH 3.5 and a temperature of 25° C., the method comprising the following successive steps: a) preparing a polymer, in the form of a gel, by free-radical polymerization in aqueous solution at an initiation temperature between −20° C. and +50° C. of at least one water-soluble monounsaturated ethylenic monomer, the total weight concentration of monomer(s) in relation to polymerization charge being between 10 and 60%; b) granulating the resulting polymer gel; c) drying the polymer gel to obtain a polymer in powder form; d) grinding and sifting the powder; at least 10% by weight of water-soluble polymer, based on the total weight of the water-soluble monounsaturated ethylenic monomer or monounsaturated ethylenic monomers used in step a), being added during the polymerization step a) and optionally during the granulation step b), the water-soluble polymer being structured and added as a water-in-oil inverse emulsion or dispersion in oil.

2. The method according to claim 1, wherein between 10 and 50% by weight, based on the total weight of free monomers involved, of water-soluble polymer in the form of a water-in-oil inverse emulsion or dispersion in oil, containing at least one structured water-soluble polymer, is added during the polymerization step a) and optionally during the granulation step b).

3. The method according to claim 1, wherein between 10 and 50% by weight, based on the total weight of the free monomers involved, of water-soluble polymer in the form of a water-in-oil inverse emulsion or in dispersion oil, containing at least one structured water-soluble polymer, are added in a proportion of between ⅔ and ¾ during the polymerization step a) and of between ¼ and ⅓ during the granulation step b).

4. The method according to claim 1, wherein between 10 and 30%, based on the total weight of the free monomers involved, of water-soluble polymer in the form of a water-in-oil inverse emulsion or dispersion in oil, containing at least one structured water-soluble polymer, is added during the polymerization step a).

5. The method according to claim 1, wherein the Brookfield viscosity of the polymerization charge at the polymerization temperature is less than 100 centipoise (Brookfield modulus: LV1, speed of rotation: 60 rpm.sup.−1).

6. The method according to claim 1, wherein the Huggins coefficient of the water-soluble structured polymer of the water-in-oil inverse emulsion or of the dispersion in oil at a polymer weight concentration of 5 g L.sup.−1 in a 0.4 N aqueous solution of sodium nitrate at pH 3.5 and a temperature of 25° C. is greater than 0.4.

7. The method according to claim 1, wherein step a) involves the polymerization of at least one nonionic water-soluble monounsaturated ethylenic monomer and at least one anionic or cationic water-soluble unsaturated ethylenic monomer.

8. The method according to claim 7, wherein the at least one nonionic monomers is selected from acrylamide, methacrylamide, N,N-dimethylacrylamide, N-vinyl formamide, N-vinyl acetamide, N-vinyl pyridine and N-vinylpyrrolidone, acryloyl morpholine (ACMO) and diacetone acrylamide.

9. The method according to claim 7, wherein the anionic monomer is selected from acrylic acid, methacrylic acid, itaconic acid, maleic acid, 2-acrylamido-2-methyl propane sulfonic acid, vinylsulphonic acid, and vinyl phosphonic acid, said anionic monomer being not salified, or partially, or totally salified.

10. The method according to claim 7, wherein the cationic monomer is selected from quaternized dimethyl amino ethyl acrylate, quaternized dimethyl amino ethyl methacrylate, dimethyl diallyl ammonium chloride, acrylamido propyl trimethyl ammonium chloride, and methacryl amido propyl trimethyl ammonium chloride.

11. The method according to claim 1, wherein the water-in-oil inverse emulsion or the dispersion in oil contains between 10 and 70% by weight of structured water-soluble polymer.

12. The method according to claim 1, wherein the structured water-soluble polymer contained in the inverse emulsion or in the dispersion in oil is composed of the same monounsaturated ethylenic monomers as those polymerized in step a).

13. The method according to claim 12, wherein the proportion of each monomer constituting the structured water-soluble polymer contained in the inverse emulsion or dispersion in oil is composed of the same proportions of monounsaturated ethylenic monomers as those polymerized in step a).

14. The method according to claim 1, wherein the structured water-soluble polymer contained in the inverse emulsion or the dispersion is structured with ethylenic monomers having at least two unsaturations.

15. The method according to claim 1, wherein the oil in the inverse emulsion or the dispersion has a flash point above 60° C.

16. The method according to claim 1, wherein the water-in-oil inverse emulsion of the structured water-soluble polymer comprises: a hydrophilic phase comprising at least one structured water-soluble (co)polymer; a lipophilic phase; at least one interfacial polymer composed of at least one monomer of formula (I): ##STR00002## wherein, R1, R2, R3 are independently selected from the group consisting of a hydrogen atom, a methyl group, a carboxylate group and Z—X, Z is selected from the group consisting of C(═O)—O; C(═O)—NH; O—C(═O); NH—C(═O)—NH; NH—C(═O)—O; and a saturated or unsaturated carbon chain comprising from 1 to 20 carbon atoms, substituted or unsubstituted, possibly comprising one or more heteroatoms chosen from nitrogen and oxygen, X is a group chosen from alkanolamides, sorbitan esters, ethoxylated sorbitan esters, glyceryl esters, and polyglycosides; X comprising a hydrocarbon chain, saturated or unsaturated, linear, branched or cyclic, optionally aromatic.

17. The method according to claim 1, consisting for step a) of polymerizing by the radical route, by means of redox initiators and azo compounds, at an initiation temperature of between 0 and 20° C. at least one monounsaturated ethylenic monomer soluble in aqueous solution, the concentration by total weight of monomer relative to the polymerization charge being between 25 and 50%, in the presence of 20 to 30% by weight, relative to the total weight of the free monomers involved, of an inverse emulsion containing between 30 and 60% by weight of a copolymer composed of acrylamide and 40 to 90 mol % of dimethylaminoethyl acrylate quaternized with methyl chloride, structured with less than 0.05% of methylenebisacrylamide, of which the Huggins coefficient, at a concentration by weight of polymer of 5 gL.sup.−1 in deionized water and at a temperature of 25° C., is greater than 0.4, and the Brookfield viscosity of the polymerization charge at the temperature of polymerization being less than 100 centipoise (Brookfield modulus: LV1, speed of rotation: 60 rpm.sup.−1) and for step b) to granulate the gel thus obtained in the presence of 5 to 10% by weight of this polymer in the form of an inverse emulsion.

18. The method according to claim 2, wherein the Brookfield viscosity of the polymerization charge at the polymerization temperature is less than 100 centipoise (Brookfield modulus: LV1, speed of rotation: 60 rpm.sup.−1).

19. The method according to claim 18, wherein the Huggins coefficient of the water-soluble structured polymer of the water-in-oil inverse emulsion or of the dispersion in oil at a polymer weight concentration of 5 g L.sup.−1 in a 0.4 N aqueous solution of sodium nitrate at pH 3.5 and a temperature of 25° C. is greater than 0.4.

20. The method according to claim 19, wherein step a) involves the polymerization of at least one nonionic water-soluble monounsaturated ethylenic monomer and at least one anionic or cationic water-soluble unsaturated ethylenic monomer.

Description

EXAMPLES

Example 1: Gel Synthesis of a Quaternized Acrylamide/Dimethyl Amino Ethyl Acrylate Copolymer (Adame Quat) by Adding to the Polymerization Charge 20% by Weight of Structured Polymer in Reverse Emulsion Form

[0117] In a 2 L beaker, an aqueous charge comprising 113 g of acrylamide at 50% by weight in water, 773 g of Adame Quat (Adame Quat=dimethyl amino ethyl acrylate quaternized with methyl chloride) at 80% by weight in water and 177 g of water is prepared at room temperature, then the pH is adjusted between 3 and 4 using phosphoric acid. This charge is then cooled to 10° C., then placed in a Dewar. 1.5 g of azobisisobutyronitrile are introduced into the charge as well as 420 g of an inverse emulsion (EM1) containing 41% by weight of an acrylamide/Adame Quat copolymer (20/80 mol %), the proportion of aqueous phase/oily phase synthetic (Exxsol D100) being 70/30. The copolymer of the inverse emulsion is crosslinked with MBA and has a Huggins coefficient (at a polymer concentration by weight of 5 gL.sup.−1, in a 0.4 N aqueous solution of sodium nitrate, at pH 3.5 and at a temperature of 25° C.) of 0.8.

[0118] The homogenization of the charge is carried out using a hand mixer at a speed of 500 rpm for 20 s. This charge comprising the monomers and the branched polymer in the form of an inverse emulsion is then degassed with nitrogen bubbling for 20 minutes. The viscosity measured after degassing is 82 cP (Brookfield modulus: LV1, speed of rotation: 60 rpm.sup.−1). 1.3×10.sup.−3 mole % of sodium hypophosphite is then added to the charge, expressed relative to the total amount of monomers involved, then the reaction is initiated by successive additions of 3.2×10.sup.−3 mole % of sodium persulfate then 1.9×10.sup.−3 mole % of Mohr's salt. The reaction time is 45 min, for a final temperature of 80° C. The polymer obtained is in the form of a gel having a texture allowing it to be granulated and then to be dried in an air flow at 70° C. for 60 min. The dry polymer grains are then ground in order to obtain a particle size of less than 1.7 mm. The product obtained, which is 100% water soluble, has a weight average molecular weight of 1.9 million Daltons and a K.sub.H (at a polymer weight concentration of 5 gL.sup.−1, in an aqueous solution of 0.4 N sodium nitrate, at pH 3.5 and at a temperature of 25° C.) of 0.69.

Example 2: Synthesis by RAFT-Type Gel Route of an Acrylamide/Adame Quat Copolymer by Adding to the Polymerization Charge 20% by Weight of Structured Polymer in the Form of an Inverse Emulsion

[0119] In a 2 L beaker, an aqueous charge comprising 113 g of acrylamide at 50% by weight in water, 773 g of Adame Quat at 80% by weight in water and 177 g of water is prepared at room temperature, then the pH is adjusted between 3 and 4 using phosphoric acid. This charge is then cooled to 10° C., then placed in a Dewar. 1.5 g of azobisisobutyronitrile (AIBN) are introduced into the charge as well as 420 g of the inverse emulsion (EM1) used in Example 1. The homogenization of the charge is carried out using a hand mixer at a speed of 500 rpm for 20 seconds. This charge comprising the monomers and the branched polymer in the form of an inverse emulsion is then degassed with nitrogen bubbling for 20 minutes. The viscosity measured after degassing is 82 cP (Brookfield modulus: LV1, speed of rotation: 60 rpm.sup.−1). 5.2×10.sup.−3 mole % of sodium hypophosphite is then added to the charge, expressed relative to the total amount of monomers involved, 5.2×10−4 mol % of O-ethyl-S-(1-methoxy carbonyl ethyl) xanthate (RAFT transfer agent), then the reaction is initiated by successive additions of 3.2×10−3 mole % of sodium persulfate then 1.9×10−3 mole % of Mohr's salt. The reaction time is 60 min, for a final temperature of 80° C. The polymer obtained is in the form of a gel having a texture allowing it to be granulated and then to be dried in an air flow at 70° C. for 60 minutes. The dry polymer grains are then ground in order to obtain a particle size of less than 1.7 mm. The product obtained, which is 100% water soluble, has a weight average molecular weight of 2.1 million Daltons and a K.sub.H (at a polymer weight concentration of 5 gL.sup.−1, in an aqueous solution of 0.4 N sodium nitrate, at pH 3.5 and at a temperature of 25° C.) of 0.73.

Example 3 (Counter-Example): Gel Synthesis of a Branched Acrylamide/Adame Quat Copolymer Using N,N′-Methylenebis(Acrylamide) (MBA)

[0120] In a 2 L beaker, an aqueous charge comprising 126 g of acrylamide at 50% by weight in water, 858 g of Adame Quat at 80% by weight in water and 534 g of water is prepared at room temperature, then the pH is adjusted between 3 and 4 using phosphoric acid. This charge is then cooled to 0° C., then placed in a Dewar. 1.5 g of azobisisobutyronitrile are introduced into the charge which is degassed under nitrogen bubbling for 20 minutes. During bubbling, 2.1×10.sup.−2 mol % of sodium hypophosphite and 6.6×10.sup.−3 mol % of MBA are introduced, based on the total amount of monomers involved. The reaction is then initiated at a temperature of 0° C. by successively adding, always expressed with respect to the total amount of monomers involved, 3.4×10.sup.−3 mol % of sodium persulfate and 3.4×10.sup.−4 mol % of Mohr's salt. The reaction time is 30 min, for a final temperature of 70° C. The polymer obtained is in the form of a gel having a texture allowing it to be granulated and then to be dried in an air flow at 70° C. for 60 minutes. The dry polymer grains are then ground in order to obtain a particle size of less than 1.7 mm. The product obtained, which is 100% water soluble, has a weight-average molecular weight of 2.4 million Daltons and a K.sub.H (at a polymer weight concentration of 5 gL.sup.−1, in an aqueous solution of 0.4 N sodium nitrate, at pH 3.5 and at a temperature of 25° C.) of 0.24.

[0121] When the structured polymers are obtained by the method of the invention (examples 1 and 2) their K.sub.H is higher than 0.4, whereas by directly adding the structuring agent (MBA) to the charge of a gel polymerization, the K.sub.H remains lower than 0.3 (example 3: counter-example).