Hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid

Abstract

The present invention relates to a hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid having a 2-theta powder X-ray diffraction diagram comprising peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, 46.04° degrees (+/−0.1°). The present invention also relates to a production method for this form of 2-acrylamido-2-methylpropane sulfonic acid and a preparation method for an aqueous solution A of a salt of this form of 2-acrylamido-2-methylpropane sulfonic acid, and the (co)polymer of this form of -acrylamido-2-methylpropane sulfonic acid.

Claims

1. A (co)polymer of 2-acrylamido-2-methylpropanesulfonic acid, in its acidic and/or salified form, wherein at least a portion of the 2-acrylamido-2-methylpropanesulfonic acid is in hydrated crystalline form and has a powder X-ray diffraction pattern including peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, and 46.04° degrees 2-theta, all peak values being +/−0.1°.

2. The (co)polymer according to claim 1, wherein the (co)polymer comprises one or more additional monomers selected from the group consisting of non-ionic monomers, cationic monomers, zwitterionic monomers, anionic monomers distinct from 2-acrylamido-2-methylpropanesulfonic acid being in hydrated crystalline form and having a powder X-ray diffraction pattern including peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, and 46.04° degrees 2-theta, all peak values being +/−0.1°, and mixtures thereof.

3. The (co)polymer according to claim 1, wherein the (co)polymer is a copolymer of the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid and at least one non-ionic monomer.

4. The (co)polymer according to claim 1, wherein the (co)polymer is a copolymer of the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid and at least one non-ionic monomer selected from the group consisting of acrylamide; N-isopropylacrylamide; N,N-dimethylacrylamide; N-vinylformamide; acryloyl morpholine; N,N-diethyl acrylamide; N-tert-butyl acrylamide; N-tert-octylacrylamide; N-vinylpyrrolidone; N-vinylcaprolactam; N-vinyl-imidazole, hydroxyethyl methacrylamide, hydroxypropylacrylate, isoprenoln diacetone acrylamide, and mixture thereof.

5. The (co)polymer according to claim 2, wherein the anionic monomer is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, acrylamide undecanoic acid, acrylamide 3-methylbutanoic acid, maleic anhydride; vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethylmethacrylate, sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid, styrene sulfonic acid, 2-acrylamido-2-methypropane disulfonic acid, salts of these monomers, and mixture thereof.

6. The (co)polymer according to claim 2, wherein the cationic monomer is selected from the group consisting of quaternized dimethylaminoethyl acrylate, quaternized dimethylaminoethyl methacrylate, dimethyldiallylammonium chloride, acrylamido propyltrimethyl ammonium chloride, methacrylamido propyltrimethyl ammonium chloride, and mixture thereof.

7. The (co)polymer according to claim 2, wherein the zwitterionic monomer is selected from the group consisting of 2-((2-(acryloyloxy)ethyl) dimethylammonio) ethane-1-sulfonate, 3-((2-(acryloyloxy)ethyl) dimethylammonio) propane-1-sulfonate, 4-((2-(acryloyloxy)ethyl) dimethylammonio) butane-1-sulfonate, [2-(acryloyloxy)ethyl)] (dimethylammonio) acetate, 2-((2-(methacryloyloxy) ethyl) dimethylammonio) ethane-1-sulfonate, 3-((2-(methacryloyloxy) ethyl) dimethylammonio) propane-1-sulfonate, 4-((2-(methacryloyloxy) ethyl) dimethylammonio) butane-1-sulfonate, [2-(methacryloyloxy)ethyl] (dimethylammonio) acetate, 2-((3-acrylamidopropyl) dimethylammonio) ethane-1-sulfonate, 3-((3-acrylamidopropyl) dimethylammonio) propane-1-sulfonate, 4-((3-acrylamidopropyl) dimethylammonio) butane-1-sulfonate, [3-(acryloyloxy) propyl] (dimethylammonio) acetate, 2-((3-methacrylamidopropyl) dimethylammonio) ethane-1-sulfonate, 3-((3-methacrylamidopropyl) dimethylammonio) propane-1-sulfonate, 4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate, [3-(methacryloyloxy)propyl)] (dimethylammonio) acetate, and mixture thereof.

8. The (co)polymer according to claim 1, wherein the (co)polymer is linear, structured or crosslinked.

9. The (co)polymer according to claim 1, wherein the (co)polymer comprises at least one LCST group.

10. The (co)polymer according to claim 1, wherein the (co)polymer comprises at least one UC ST group.

11. The (co)polymer according to claim 1, wherein the (co)polymer has an average molecular weight by weight of between 1 and 40 millions g/mol.

12. The (co)polymer according to claim 1, wherein the hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid presents a Fourier transform infrared spectrum comprising peaks at 3280 cm.sup.−1, 3126 cm.sup.−1, 1657 cm.sup.−1, 1595 cm.sup.−1, 1453 cm.sup.−1, 1395 cm.sup.−1, 1307 cm.sup.−1, 1205 cm.sup.−1, 1164 cm.sup.−1, 1113 cm.sup.−1, 1041 cm.sup.−1, 968 cm.sup.−1, 885 cm.sup.−1, 815 cm.sup.−1, and 794 cm.sup.−1, all peak values being +/−8 cm.sup.−1.

13. The (co)polymer according to claim 1, wherein the hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid presents minimum ignition energy greater than 400 mJ.

14. The (co)polymer according to claim 1, wherein the hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid presents 4 thermal phenomena with the Differential Scanning calorimetry technique at 70° C., 100° C., 150° C. and 190° C., all +/−10° C.

15. The (co)polymer according to claim 1, wherein the hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid has a water/2-acrylamido-2-methylpropane sulfonic acid molar ratio of 1:1.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1 illustrates the proton NMR spectrum of the 2-acrylamido-2-methylpropane sulfonic acid crystals obtained according to examples 1 and 2.

(2) FIG. 2 illustrates the X-ray diffraction diagram of the crystals obtained according to example 1.

(3) FIG. 3 illustrates the X-ray diffraction diagram of the crystals obtained according to example 2.

(4) FIG. 4 illustrates the Fourier transform infrared spectrum of the crystals obtained in example 1.

(5) FIG. 5 illustrates the X-ray diffraction diagram of the crystals obtained according to example 2.

(6) FIG. 6 illustrates the thermogram of the crystals obtained according to example 1.

(7) FIG. 7 illustrates the thermogram of the crystals obtained according to example 2.

(8) FIG. 8 illustrates the particle size graph of the crystals obtained according to example 1.

(9) FIG. 9 illustrates the particle size graph of the crystals obtained according to example 2.

(10) FIG. 10 corresponds to the optical microscope observation of the crystals obtained according to example 1.

(11) FIG. 11 corresponds to the optical microscope observation of the crystals obtained according to example 2.

(12) FIG. 12 corresponds to the scanning electron microscope observation of the crystals obtained according to example 1.

(13) FIG. 13 corresponds to the scanning electron microscope observation of the crystals obtained according to example 2.

(14) FIG. 14 illustrates the loss of viscosity as a function of ATBS form and iron content for a copolymer.

(15) FIG. 15 illustrates the viscosity loss as a function of ATBS form at 90° C. aging for a copolymer.

(16) FIG. 16 illustrates the loss of viscosity as a function of ATBS form and iron content for a homopolymer.

EXAMPLE EMBODIMENTS OF THE INVENTION

Example 1: Synthesis of 2-acrylamido-2-methylpropane Sulfonic Acid

(17) To a stirred 2000-mL jacketed reactor, 1522 grams of acrylonitrile was added containing 0.4% of water by weight and 180 grams of fuming sulfuric acid titrating at 104% H.sub.2SO.sub.4 (18% Oleum). The mixture was stirred for 1 hour and cooled via the reactor jacket, which held the temperature of the sulfonating mixture at −20° C.

(18) To the previous sulfonating mixture, 97 grams of isobutylene was added, at a flow rate of 1.6 grams/minute.

(19) The temperature of the mixture was controlled at 45° C. while isobutylene was added. The particles of 2-acrylamido-2-methylpropane sulfonic acid precipitate in the mixture and the solid content was about 20% by weight. The reaction mixture was filtered on a Buchner filter and dried under vacuum at 50° C. The solid obtained was 2-acrylamido-2-methylpropane sulfonic acid; it was present in the form of a very fine white powder.

(20) From observations made with an optical microscope (FIG. 10) and a scanning electron microscope (FIG. 12), the crystals were needle-shaped.

Example 2: Formation of the Hydrated Crystalline form of 2-acrylamido-2-methylpropane Sulfonic Acid

(21) To a 2000-mL jacketed reactor, 500 grams of 2-acrylamido-2-methylpropane sulfonic acid obtained in example 1 and 460 grams of sulfuric acid at a concentration of 10% H.sub.2SO.sub.4 were added.

(22) 250 mg of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl was added to the preceding mixture.

(23) The mixture was stirred for 10 minutes, at 20° C., to form suspension A.

(24) Suspension A was heated to a temperature of 60° C. and maintained at this temperature for 20 minutes to form solution B.

(25) Solution B was cooled to a temperature of 10° C. The cooling time between 60° C. and 10° C. was 6 hours. Suspension C of crystals of 2-acrylamido-2-methylpropane sulfonic acid was obtained. Suspension C was filtered on a vertical Robatel centrifugal dryer. A solid of composition 1 was obtained, containing 80% by weight of 2-acrylamido-2-methylpropane sulfonic acid crystals.

(26) From observations made with an optical microscope (FIG. 11) and a scanning electron microscope (FIG. 13), the crystals were cubic-shaped.

Example 3: NMR Analysis of Products from Examples 1 and 2

(27) The 2-acrylamido-2-methylpropane sulfonic solid obtained in example 1 and its hydrated crystalline form obtained in example 2 were analyzed by proton nuclear magnetic resonance (NMR).

(28) The samples were dissolved in D.sub.2O. The Bruker NMR machine had a frequency of 400 MHz, and was equipped with a 5 mm BBO BB-.sup.1H probe.

(29) The two proton spectra (FIG. 1) were identical and the peak assignments conformed to the molecular structure of 2-acrylamido-2-methylpropane sulfonic acid.

Example 4: X-Ray Diffraction Analysis

(30) The solids obtained in examples 1 and 2 were previously ground to form powders and were analyzed by X-ray diffraction over an angular range from 10 to 90°. The equipment used was a Rigaku miniflex II diffractometer equipped with a copper source.

(31) We observed that the solid obtained from example 2 (FIG. 3) has a 2-theta X-ray diffraction diagram with the following characteristic peaks:

(32) 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, 46.04° 2-Theta degrees (+/−0.1°).

Example 5: Fourier Transform Infrared Measurement

(33) The equipment for Fourier transform infrared measurement was the Perkin Elmer Spectrum 100, whose precision is 8 cm.sup.−1.

(34) The solids obtained in examples 1 and 2 were sieved at 100 μm. The particles remaining on the sieve were dried and put in the oven at 60° C. for at least 4 hours.

(35) 10 mg of solid was weighed precisely and mixed with 500 mg of potassium bromide (KBr). The mixture was then compacted in a hydraulic press under a pressure of at least 10 bars.

(36) We observed that the following bands (FIG. 5) are characteristic of the hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid:

(37) 3280 cm.sup.−1, 3126 cm.sup.−1, 1657 cm.sup.−1, 1595 cm.sup.−1, 1453 cm.sup.−1, 1395 cm.sup.−1, 1307 cm.sup.−1, 1205 cm.sup.−1, 1164 cm.sup.−1, 1113 cm.sup.−1, 1041 cm.sup.−1, 968 cm.sup.−1, 885 cm.sup.−1, 815 cm.sup.−1, 794 cm.sup.−1.

(38) The infrared spectrum of the solid according to example 1 (FIG. 4) did not present the same peaks.

Example 6: Differential Scanning Calorimetry (DSC)

(39) The device used was a DSC131 EVO by Setaram.

(40) The solids obtained in examples 1 and 2 were analyzed with a 10° C./minute heating ramp under a flow of nitrogen. The initial temperature was 30° C.; the product was heated to 220° C.

(41) The thermogram of the crystals in example 1 (FIG. 6) showed a thermal effect at a temperature of 191.5° C., which is generally considered as the melting/degradation point of 2-acrylamido-2-methylpropane sulfonic acid.

(42) The thermogram of the crystals from example 2 (FIG. 7) showed 3 additional thermal phenomena visible at 70.8; 103.4 and 152.2° C. The peak at 187.4° C. is related to the degradation of the molecule of 2-acrylamido-2-methylpropane sulfonic acid.

(43) As a comparison, the thermogram of the crystals from example 1 did not present a degradation peak at 191.5° C. (FIG. 6).

Example 7: Acid-Base Titration

(44) To a 1000-mL beaker, 500 mL of demineralized water and 100 g of the obtained from example 1 were added. A magnetic bar was added to be able to mix the solution.

(45) A graduated burette was filled with 30% sodium hydroxide.

(46) A pH meter was added to be able to monitor the pH during the sodium hydroxide addition.

(47) Initially the pH of the aqueous solution was less than 1 Sodium hydroxide was added until a pH of 7 was obtained.

(48) 64 g of 30% sodium hydroxide was added.

(49) The molar mass of 2-acrylamido-2-methylpropane sulfonic acid was 207 g/mol. Calculating the equivalence point showed that the solid obtained in example 1 contained 99% by weight of 2-acrylamido-2-methylpropane sulfonic acid (titration of the acid function).

(50) The solid obtained in example 2 was titrated using the same protocol. 59 g of sodium hydroxide was added to 100 g of the solid obtained from example 2. Calculating the equivalence point showed that the solid obtained in example 2 contained 92% by weight of 2-acrylamido-2-methylpropane sulfonic acid.

(51) The remaining 8% was water. This 2-acrylamido-2-methylpropane sulfonic acid/H.sub.2O mass ratio (92/8) corresponded to a 1:1 molar ratio.

(52) The solid obtained in example 2 was therefore a hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid.

Example 8: Measurement of the Minimum Ignition Energy (MIE)

(53) Minimum ignition energy was measured according to standard NF EN 13821.

(54) The explosimeter was a vertical Hartmann tube. The dust dispersion system was a mushroom system.

(55) The total induction was less than 25 microhenry. The discharge voltage was comprised between 5 kV and 15 kV. The electrodes were made of brass and spaced at least 6 mm apart.

(56) Different energies and dispersed mass were tested and summarized in the following tables.

(57) It appears clearly that the hydrated crystalline form presents a substantially lower explosion risk than the needle-shaped form obtained in example 1.

(58) TABLE-US-00001 TABLE 1 Determination of the solid MIE from example 1 Mass of Ignition? Energy dispersed Number of Yes (Y) (mJ) solid (g) dispersions No (N) Flame Pressure 1000 0.5 2 Y Small Small 500 0.5 3 Y Average Average 300 0.5 3 Y Average Average 100 0.5 20 N 200 0.5 20 N 200 1 20 N 200 2 20 N 200 3 7 Y Average Small 100 3 20 N 100 5 20 N 100 7 20 N 100 10 20 N 100 1 20 N 100 2 20 N

(59) TABLE-US-00002 TABLE 2 Determination of the solid MIE from example 2 Mass of Ignition? Energy dispersed Number of Yes (Y) (mJ) solid (g) dispersions No (N) Flame Pressure 1000 0.5 20 N 1000 1 20 N 1000 2 20 N 1000 3 20 N 1000 5 20 N 1000 7 20 N 1000 10 20 N 1000 15 13 Y Small Average 500 15 20 N 500 20 20 N 500 10 20 N 500 7 20 N 500 5 20 N 500 3 20 N 500 2 20 N 500 1 20 N 500 0.5 20 N

Example 9: Particle Size Measurement

(60) The solids obtained in examples 1 and 2 were analyzed by laser diffraction to determine their particle size distribution.

(61) The equipment used was a Cilas 1190.

(62) For the crystals in example 1, the d.sub.50 value was about 40 μm and 90% of the particles were smaller than 200 μm (FIG. 8).

(63) For the crystals in example 2, the d.sub.50 value was about 600 μm and 90% of the particles were smaller than 1500 μm (FIG. 9). The crystals contained less than 10% of particles smaller than 300 μm.

Example 10: Measurement of Specific Surface Area

(64) The solids obtained in examples 1 and 2 were degassed at ambient temperature for 24 hours.

(65) The device for measuring specific surface area by sorptometry was a TriStar II Micromeritics device coupled with a Micromeritics Smart VacPrep. The measurement temperature was −196° C.

(66) TABLE-US-00003 TABLE 3 Specific surface area of 2-acrylamido- 2-methylpropane sulfonic acids Origin of the Specific surface 2-acrylamido-2-methylpropane sulfonic acid area (m.sup.2/g) Example 1 (counter-example) 1.32 +/− 0.14 Example 2 (invention) 0.06 +/− 0.01

Example 11: Preparation Protocol for the Sodium Salt of the Hydrated Crystalline Form of 2-acrylamido-2-methylpropane Sulfonic Acid

(67) To a jacketed 2000-mL reactor equipped with a condenser, a pH meter and a stirrer, 500 grams of the hydrated crystalline form of acrylamido-2-methylpropane sulfonic acid from example 2 and 770 grams of water were added. The mixture had a pH of less than 1.

(68) A solution of 50% concentration by weight sodium hydroxide was prepared in a dropping funnel. The caustic solution was added to the reaction mixture for 120 minutes. The temperature was controlled to be less than 30° C.

(69) During the sodium hydroxide addition, the pH remained under 5.

(70) 175 grams of 50% concentration by weight sodium hydroxide solution was added.

(71) The mixture obtained was a solution of the 2-acrylamido-2-methylpropane sulfonic acid sodium salt at a concentration of 35% by weight.

Example 12 Preparation of Copolymer P1 of acrylamide/2-acrylamido-2-methylpropane Sulfonic Acid of Hydrated Crystalline Form (75/25 Mole %)

(72) 549.5 g of deionized water, 520.5 of acrylamide in 50% solution, 97.6 g of 50% sodium hydroxide solution, 16.2 g of urea and 316.2 g of 2-acrylamido-2-methylpropanesulfonic acid crystals obtained in Example 2g are added to a 2000 ml beaker.

(73) The solution thus obtained is cooled between 0 and 5° C. and transferred to an adiabatic polymerization reactor, nitrogen bubbling is carried out for 30 minutes to remove any trace of dissolved oxygen.

(74) Then added in the reactor:

(75) 0.75 g of 2,2′-azobisisobutyronitrile,

(76) 1.5 ml of a solution containing 5 g/l of 2,2′-azobis [2-(2-imidazolin-2-yl) propane dihydrochloride],

(77) 1.5 ml of a solution containing 3 g/l of sodium hypophosphite,

(78) 2.25 ml of a solution containing 1 g/l of tert-butyl hydroperoxide,

(79) 2.25 ml of a 1 g/l solution of ammonium sulfate and iron (II) hexahydrate (Mohr salt).

(80) After a few minutes the nitrogen inlet is closed and the reactor is closed. The polymerization reaction takes place for 1 to 5 hours until a peak temperature is reached. The rubbery gel obtained is chopped into particles with a size of between 1 and 6 mm.

(81) The gel is then dried and milled to obtain the polymer in powder form.

Example 13 Preparation of Copolymer P′1 of acrylamide/2-acrylamido-2-methylpropanesulfonic Acid that is not the Hydrated Crystalline Form (75/25 Mole %)

(82) The copolymer is prepared as in Example 12, replacing the crystalline form 2-acrylamido-2-methylpropane sulfonic acid hydrate (Example 2) with the non hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid obtained in Example 1.

Example 14 Measurement of the Resistance to Chemical Degradation of Solutions of Copolymers P1 and P′1 of Equivalent Molecular Weight

(83) Resistance to chemical degradation tests of polymers P1 and P′1 with a molecular weight of 9 million were carried out under aerobic conditions in the presence of different concentrations of iron (II) (2, 5, 10 and 20 ppm) in a brine composed of water, 37000 ppm NaCl, 5000 ppm Na.sub.2SO.sub.4 and 200 ppm NaHCO.sub.3. These tests were carried out on a polymer prepared from the non-crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or of at least one of its salts (P′1) and on a polymer prepared from the crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts (P1). Both polymers have the same chemical composition. The results obtained after 24 hours of bringing the polymer solution into contact with the contaminant are shown in FIG. 14.

(84) We can observe that, for each concentration of iron (II), the polymer P1 loses less viscosity than the polymer P′1 equivalent.

Example 15 Measurement of Resistance to Thermal Degradation of Solutions of Polymers of Equivalent Molecular Weight

(85) Tests of resistance to thermal degradation of polymers P1 and P′ 1 with a molecular weight of 9 million were carried out anaerobically at an active concentration of 2000 ppm in a brine composed of water, 30000 ppm of NaCl and 3000 ppm CaCl.sub.2.2H.sub.2O. These tests were carried out on a polymer made from the non-crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts (P′1) and on a polymer made from the crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts (P1). Both polymers have the same chemical composition. The polymer solutions were aged for 6 months at 90° C. The results obtained are shown in FIG. 15 in terms of loss of viscosity. We can observe that the polymer P1 loses less viscosity than the polymer P′1 equivalent.

Example 16 Preparation of Homopolymers P2 from the Hydrated Crystalline Form of 2-acrylamido-2-methylpropanesulfonic Acid

(86) 390.5 g of deionized water, 262 g of 50% sodium hydroxide solution and 847.5 g of 2-acrylamido-2-methylpropanesulfonic acid crystals obtained in Example 2 are added to a 2000 ml beaker.

(87) The solution thus obtained is cooled between 5 and 10° C. and transferred to an adiabatic polymerization reactor, a nitrogen bubbling is carried out for 30 minutes to remove any trace of dissolved oxygen.

(88) Then added in the reactor:

(89) 0.45 g of 2,2′-azobisisobutyronitrile,

(90) 1.5 ml of a solution containing 2.5 g/l of 2,2′-azobis [2-(2-imidazolin-2-yl) propane dihydrochloride],

(91) 1.5 ml of a 1 g/l solution of sodium hypophosphite,

(92) 1.5 ml of a solution containing 1 g/l of tert-butyl hydroperoxide,

(93) 1.5 ml of a 1 g/l solution of ammonium sulfate and iron (II) hexahydrate (Mohr salt).

(94) After a few minutes the nitrogen inlet is closed and the reactor is closed. The polymerization reaction takes place for 2 to 5 hours until a peak temperature is reached. The rubbery gel obtained is chopped and dried to obtain a coarse powder which is itself ground and sieved to obtain the polymer in powder form.

Example 17 Preparation of Homopolymers P′2 from 2-acrylamido-2-Methylpropane Sulfonic Acid that is not the Hydrated Crystalline Form

(95) The polymers are prepared as in Example 16, replacing the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid with 2-acrylamido-2-methylpropanesulfonic acid synthesized in example 1 that is not the hydrated crystalline form.

Example 18 Measurement of Resistance to Chemical Degradation of Solutions of Polymers P2 and P′2

(96) Resistance tests to chemical degradation of polymers P2 and P′2 with a molecular weight of 5.3 million Da were performed under aerobic conditions in the presence of various iron (II) concentrations (2, 5, 10 and 20 ppm) in brine composed of water, 37000 ppm NaCl, 5000 ppm Na.sub.2SO.sub.4 and 200 ppm NaHCO.sub.3. These tests were carried out on a polymer prepared from the non-crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or of at least one of its salts (P′2) and on a polymer prepared from the crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts (P2). Both polymers have the same chemical composition. The results obtained after 24 hours of bringing the polymer solution into contact with the contaminant are shown in FIG. 16.

(97) We can observe that for each iron (II) concentration, the polymer P2 loses less viscosity than the equivalent polymer P′2.

Example 19 Preparation of post Hydrolyzed Copolymer P3 of acrylamide/2-acrylamido-2-Methylpropane Sulfonic acid of Hydrated Crystalline Form (75/25 Mole %)

(98) In a 2000 ml beaker are added 761.9 g of deionized water, 574.2 g of acrylamide in 50% solution, 35.9 g of 50% sodium hydroxide solution, 11.7 g of urea and 116.3 g 2-acrylamido-2-methylpropanesulfonic acid crystals obtained in Example 2.

(99) The solution thus obtained is cooled between 0 and 5° C. and transferred to an adiabatic polymerization reactor, nitrogen bubbling is carried out for 30 minutes to remove any trace of dissolved oxygen.

(100) Then added in the reactor:

(101) 0.45 g of 2,2′-azobisisobutyronitrile,

(102) 1.5 ml of a solution containing 5 g/l of 2,2′-azobis [2-(2-imidazolin-2-yl) propane dihydrochloride],

(103) 1.5 ml of a 1 g/l solution of sodium hypophosphite,

(104) 2.25 ml of a solution containing 1 g/l of tert-butyl hydroperoxide,

(105) 3.0 ml of a 1 g/l solution of ammonium sulfate and iron (II) hexahydrate (Mohr salt).

(106) After a few minutes the nitrogen inlet is closed and the reactor is closed. The polymerization reaction takes place for 2 to 5 hours until a peak temperature is reached. The rubbery gel obtained is chopped into particles with a size of between 1 and 6 mm.

(107) 500.0 g of previously minced gel are then mixed with 18.0 g of 50% sodium hydroxide solution, the mixture is heated and maintained at a temperature of 90° C. for a duration of 90 minutes.

(108) The gel is then dried and milled to obtain the polymer in powder form.

Example 20 Preparation of Post Hydrolyzed P′3 copolymer of acrylamide/2-acrylamido-2-methylpropanesulfonic Acid that is not the Hydrated Crystalline Form (75/25 Mole %)

(109) The copolymer is prepared as in Example 19, replacing the 2-acrylamido-2-methylpropanesulfonic acid of hydrated crystalline form (Example 2) with 2-acrylamido-2-methylpropanesulfonic acid synthesized in example 1 that is not the hydrated crystalline form.