Preparation of hydrophilic polymers of high mass by controlled radical polymerization

Abstract

The present invention concerns a process for preparing a polymer comprising at least one gel polymerization step (E) in which the following are contacted: ethylenically unsaturated water-soluble monomers, the same or different; a source of free radicals adapted to the polymerization of the said monomers, typically a redox system; and a radical polymerization control agent, preferably comprising a thiocarbonylthio S(CS) group;
with a concentration of monomers in the reaction medium of step (E) sufficiently high to cause gelling of the medium if polymerization was conducted without the control agent.

Claims

1. A process for preparing a polymer comprising at least one polymerization in a reaction medium wherein the polymerization comprises contacting: ethylenically unsaturated water-soluble monomers, the same or different; a source of free radicals adapted to the polymerization of said monomers; and a radical polymerization control agent, wherein said control agent is a reversible transfer agent; wherein the polymerization is performed without any cross-linking agent and the concentration of monomers in the reaction medium of the polymerization is sufficiently high to cause gelling of the medium and lead to a non-covalent gel if polymerization was conducted without the control agent, wherein in the polymerization, the initial concentration of control agent in the medium is chosen so that the number-average molecular weight M.sub.n of the synthesized polymer is higher than 100,000 g/mol; wherein the control agent is a compound carrying an S(CS)O xanthate function; and wherein number-average molecular weight M.sub.n of the synthesized polymer is of 500 000 g/mol or higher.

2. The process according to claim 1 wherein the monomers, the source of free radicals and the control agent are contacted in an aqueous medium.

3. The process according to claim 1 wherein the monomers comprise acrylamido monomers.

4. The process according to claim 1 wherein the initial concentration of monomers in the reaction medium is between 10 and 40% by weight relative to the total weight of the reaction medium.

5. The process according to claim 1 wherein the source of free radicals used is a redox initiator.

6. The process according to claim 5 wherein the source of free radicals is a redox system which is an association of ammonium persulfate and sodium formaldehyde sulfoxylate.

7. The process according to claim 1 wherein the reaction medium is free of copper.

8. The process according to claim 1, wherein the control agent is a compound carrying an O-ethyl xanthate function of formula S(CS)OCH.sub.2CH.sub.3.

Description

EXAMPLE 1: SYNTHESIS OF A POLYACRYLAMIDE ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING PRE-POLYMER WITH XANTHATE FUNCTION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(1) 1.1: Synthesis of a Living Polyacrylamide Pre-Polymer P1

(2) To a 50 mL flask were added at ambient temperature (20 C.), 6 g of powdered acrylamide (the acrylamide powder used in all the examples was free of copper), 15.2 g of distilled water, 2.53 g of O-ethyl-S-(1-methoxycarbonyl ethyl) xanthate of formula (CH.sub.3CH(CO.sub.2CH.sub.3))S(CS)OEt, 8 g of ethanol and 150 mg of V-50 initiator (2,2-Azobis(2-methylpropionamidine)dihydrochloride). The mixture was degassed by bubbling extra-pure argon for 30 minutes. The flask was then placed in a thermostat-controlled oil bath at 60 C., and the polymerization reaction left to take place under agitation for 3 hours at 60 C. 100% conversion was obtained (determined by .sup.1H NMR). The number-average molecular weight of the pre-polymer P1, determined by .sup.1H NMR, was 750 g/mol.

(3) 1.2: Gel Polymerization of the Acrylamide (Using P1 as Control Agent)

(4) After step 1.1, the reaction mixture was dried in vacuo to evaporate the ethanol and the extract was readjusted by adding distilled water to obtain an aqueous 50 weight % solution 51 of the pre-polymer P1.

(5) To a 200 mL flask, at ambient temperature, were added 20 g powdered acrylamide, 56 g distilled water and 30 mg of solution 51. The mixture was degassed by bubbling extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition in the form of two 0.6 weight % aqueous solutions, 2 mL of each of the solutions being added. These two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(6) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(7) After a reaction time of 24 hours, 98% conversion was obtained (determined by .sup.1H NMR). Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index values: M.sub.n=1 062 000 g/mol M.sub.w/M.sub.n=1.89.

(8) For comparison, the theoretical number-average molecular weight is 990 00 g/mol

EXAMPLE 2: SYNTHESIS OF A POLYACRYLAMIDE ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING PRE-POLYMER WITH XANTHATE FUNCTION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(9) The same pre-polymer P1 as for Example 1 was used in this Example, prepared under the conditions of step 1.1 in Example 1 and used in the form of the same aqueous solution et S1 as in step 1.2 of Example 1.

(10) To a 200 mL flask, at ambient temperature, were added 20 g acrylamide powder, 56 g distilled water and 35 mg of solution S1. The mixture was degassed by bubbling extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition, in the form of two 0.6 wt. % aqueous solutions, 2 mL of each of the solutions being added. As in Example 1, the two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(11) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(12) After the reaction time of 24 hours, 96% conversion was obtained (determined by .sup.1H NMR). Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=846 000 g/mol M.sub.w/M.sub.n=1.89.

(13) For comparison, the theoretical number-average molecular weight is 812 00 g/mol.

EXAMPLE 3: SYNTHESIS OF A POLYACRYLAMIDE ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING PRE-POLYMER WITH XANTHATE FUNCTION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(14) Here again, the same pre-polymer P1 as the one in Example 1 was used prepared under the conditions of step 1.1 in Example 1 and used in the form of the same aqueous solution S1 as in step 1.2 of Example 1.

(15) To a 200 mL flask, at ambient temperature, were added 20 g of powder acrylamide, 56 g distilled water and 50 mg of solution S1. The mixture was degassed by bubbling extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition, in the form of two 0.6 wt. % aqueous solutions, 2 mL of each of the solutions being added. As in Example 1, the two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(16) The polymerization reaction was then left to take place under agitation for 24 hours at ambient temperature (20 C.).

(17) After the reaction time of 24 hours, 88% conversion was obtained (determined by .sup.1H NMR). Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=640 000 g/mol M.sub.w/M.sub.n=1.81.

(18) For comparison, the theoretical number-average molecular weight is 530 000 g/mol.

EXAMPLE 4: SYNTHESIS OF A POLYACRYLAMIDE ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING PRE-POLYMER WITH XANTHATE FUNCTION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(19) The same pre-polymer P1 as in Example 1 was used, prepared under the conditions of step 1.1 in Example 1 and used in the form of the same aqueous solution S1 as in step 1.2 of Example 1.

(20) To a 200 mL flask, at ambient temperature, were added 10 g of powder acrylamide, 26 g distilled water and 35 mg of solution S1. The mixture was degassed by bubbling extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition, in the form of two 0.6 wt. % aqueous solutions, 1 mL of each of the solutions being added. As in Example 1, the two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(21) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(22) After the reaction time of 24 hours, 100% conversion was obtained, determined by .sup.1H NMR. Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=452 700 g/mol M.sub.w/M.sub.n=1.59.

(23) For comparison, the theoretical number-average molecular weight is 410 000 g/mol

EXAMPLE 5: SYNTHESIS OF A POLYACRYLAMIDE ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING PRE-POLYMER WITH XANTHATE FUNCTION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(24) The same pre-polymer P1 as in Example 1 was used, prepared under the conditions of step 1.1 in Example 1 and used in the form of the same aqueous solution 51 as in step 1.2 of Example 1.

(25) To a 200 mL flask, at ambient temperature, were added 10 g of powder acrylamide, 26 g distilled water and 150 mg of solution 51. The mixture was degassed by bubbling with extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition, in the form of two 0.6 wt. % aqueous solutions, 1 mL of each of the solutions being added. As in Example 1, the two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(26) The polymerization reaction was then left to take place under agitation for 24 hours at ambient temperature (20 C.).

(27) After the 24-hour reaction time 100% conversion was obtained, determined by .sup.1H NMR. Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=103 700 g/mol M.sub.w/M.sub.n=1.59.

(28) For comparison, the theoretical number-average molecular weight is 100 000 g/mol Although Examples 1 to 5 were conducted with a non-stabilized acrylamide, similar results were obtained with stabilized acrylamides, using copper salts for example (with the addition of a complexing agent of EDTA type to prevent exothermicity) or else using MEHQ.

EXAMPLE 6: SYNTHESIS OF A POLY(ACRYLIC ACID)-B-POLY(ACRYLAMIDE) DIBLOCK COPOLYMER: SYNTHESIS OF THE POLYACRYLAMIDE BLOCK ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING POLYACRYLATE WITH XANTHATE TERMINATION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(29) 6.1: Synthesis of a Living Poly(Acrylic Acid) with Xanthate Termination (Polymer P6)

(30) To a 15 mL flask, at ambient temperature, were added 4 g acrylic acid, 3.2 g distilled water, 0.8 g ethanol, 87 mg O-ethyl-S-(1-methoxycarbonyl ethyl) xanthate of formula (CH.sub.3CH(CO.sub.2CH.sub.3))S(CS)OEt and 25 mg 4,4-Azobis(4-cyanovaleric acid). The mixture was degassed by bubbling extra-pure argon for 30 minutes.

(31) The flask was then placed in a thermostat-controlled oil bath at 60 C., and the reaction medium left under agitation for 2 hours at 60 C.

(32) After these two hours, 99% conversion was determined by .sup.1H NMR.

(33) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values for the P6 polymer thus obtained: M.sub.n=13 000 g/mol M.sub.w/M.sub.n=1.52.
6.2: Synthesis of the Diblock Copolymer

(34) After step 6.1, the reaction mixture was dried in vacuo then dissolved in ethanol and precipitated in diethylether. The precipitate obtained was dried in vacuo for 24 hours to remove the residual solvents, after which the P6 polymer was obtained in the form of a dried powder.

(35) 20 mg of this dried powder of the P6 polymer were added to a 15 mL flask, at ambient temperature, and 2 g of powder acrylamide and 5.6 g of distilled water were added to the flask.

(36) The mixture was degassed by bubbling extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition, in the form of two 0.6 wt. % aqueous solutions, 0.2 mL of each of the solutions being added. The two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(37) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(38) After the 24-hour reaction time, 96% conversion was obtained, such as determined by .sup.1H NMR.

(39) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=682 000 g/mol M.sub.w/M.sub.n=2.18.

(40) For comparison, the theoretical number-average molecular weight is 890 000 g/mol

EXAMPLE 7: SYNTHESIS OF A POLY(ACRYLIC ACID-B-POLY(ACRYLAMIDE) DIBLOCK COPOLYMER; SYNTHESIS OF THE POLYACRYLAMIDE BLOCK ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING POLYACRYLATE WITH XANTHATE TERMINATION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(41) The same polymer P6 as the one in Example 6 was used for this Example, used in the form of a powder prepared under the conditions of step 6.2 in Example 6.

(42) 210 mg of P6 polymer powder were placed in a 15 mL flask, at ambient temperature, and 2 g of powder acrylamide and 5.6 g of distilled water were added to the flask.

(43) The mixture was degassed by bubbling with extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition in the form of two 0.6 wt. % aqueous solutions, 0.2 mL of each of the solutions being added. The two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(44) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(45) After the 24-hour reaction time, 99% conversion was obtained as determined by .sup.1H NMR.

(46) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=108 000 g/mol M.sub.w/M.sub.n=1.46.

(47) For comparison, the theoretical number-average molecular weight is 100 000 g/mol

EXAMPLE 8: SYNTHESIS OF A POLY(2-ACRYLAMIDO-2-METHYLPROPANE SULFONIC ACID)-B-POLY(ACRYLAMIDE) DIBLOCK COPOLYMER; SYNTHESIS OF THE POLYACRYLAMIDE BLOCK ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING POLY(AMPS) WITH XANTHATE TERMINATION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(48) 8.1 Synthesis of a Living Poly(2-Acrylamido-2-methylpropane Sulfonic Acid) with Xanthate Termination (Polymer P8)

(49) To a 25 mL flask at ambient temperature, were added 8 g of an aqueous solution of 2-acrylamido-2-methylpropane sulfonic acid (AMPS; concentration: 50 weight %), 1.4 g distilled water, 1.2 g ethanol, 90 mg of O-ethyl-S-(1-methoxycarbonyl ethyl) xanthate of formula (CH.sub.3CH(CO.sub.2CH.sub.3))S(CS)OEt and 40 mg of 4,4-Azobis(4-cyanovaleric acid). The mixture was degassed by bubbling with extra-pure argon for 30 minutes.

(50) The flask was then placed in a thermostat-controlled oil bath at 60 C., and the reaction medium was left under agitation for 2 hours at 60 C.

(51) After these two hours, 99% conversion was determined by .sup.1H NMR.

(52) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angel MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=10 700 g/mol M.sub.w/M.sub.n=1.45.
8.2: Synthesis of the Diblock Copolymer

(53) After step 8.1, the reaction mixture was dried in vacuo then dissolved in ethanol and precipitated in diethylether. The precipitate obtained was dried in vacuo for 24 hours to remove residual solvents, after which the P8 polymer was obtained in the form of a dried powder.

(54) 20 mg of this dried P8 polymer powder were placed in a 15 mL flask, at ambient temperature, and 2 g of powder acrylamide and 5.6 g of distilled water were added.

(55) The mixture was degassed by bubbling with extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition in the form of two 0.6 wt. % aqueous solutions, 0.2 mL of each of the solutions being added. The two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(56) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(57) After the 24-hour reaction time, 96% conversion was obtained as determined by .sup.1H NMR.

(58) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=730 000 g/mol M.sub.w/M.sub.n=2.51.

(59) For comparison, the theoretical number-average molecular weight is 950 000 g/mol

EXAMPLE 9: SYNTHESIS OF A POLY(2-ACRYLAMIDO-2-METHYLPROPANE SULFONIC ACID)-B-POLY(ACRYLAMIDE) DIBLOCK COPOLYMER; SYNTHESIS OF THE POLYACRYLAMIDE BLOCK ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING POLY(AMPS) WITH XANTHATE TERMINATION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(60) The same P8 polymer as in Example 8 was used for this Example, used in the form of a powder prepared under the conditions of step 8.2 in Example 8.

(61) 215 mg of the P8 polymer powder were placed in a 15 mL flask, at ambient temperature, and 2 g of powder acrylamide and 5.6 g of distilled water were added.

(62) The mixture was degassed by bubbling with extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition in the form of two 0.6 wt. % aqueous solutions, 0.2 mL of each of the solutions being added. The two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(63) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(64) After the 24-hour reaction time, 100% conversion was obtained as determined by .sup.1H NMR.

(65) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) and using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=105 000 g/mol M.sub.w/M.sub.n=2.44.

(66) For comparison, the theoretical number-average molecular weight is 100 000 g/mol

EXAMPLE 10: SYNTHESIS OF A POLY(ACRYLAMIDOPROPYLTRIMETHYLAMMONIUM CHLORIDE)-B-POLY(ACRYLAMIDE) DIBLOCK COPOLYMER; SYNTHESIS OF THE POLYACRYLAMIDE BLOCK ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING POLYMER WITH XANTHATE TERMINATION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(67) 10.1: Synthesis of the Living Poly(Acrylamidopropyltrimethylammonium Chloride) Polymer with Xanthate Termination (Polymer P10)

(68) To a 25 mL flask, at ambient temperature, were added 8 g of acrylamidopropyltrimethylammonium chloride solution (75 wt. % solution in water), 3.9 g distilled water, 1.3 g ethanol, 130 mg of O-ethyl-S-(1-methoxycarbonyl ethyl) xanthate of formula (CH.sub.3CH(CO.sub.2CH.sub.3))S(CS)OEt and 30 mg of V-50 initiator (2,2-Azobis(2-methylpropionamidine) dihydrochloride). The mixture was degassed by bubbling with extra-pure argon for 30 minutes.

(69) The flask was then placed in a thermostat-controlled oil bath at 60 C., and the reaction medium was left under agitation for 2 hours at 60 C.

(70) After these two hours, 99% conversion was determined by .sup.1H NMR.

(71) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) using an eighteen-angle MALLs detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=13 100 g/mol M.sub.w/M.sub.n=1.64.
10.2: Synthesis of the Diblock Copolymer

(72) After step 10.1, the reaction medium was dried in vacuo then dissolved in ethanol and precipitated in diethylether. The precipitate obtained was dried in vacuo for 24 hours to remove the residual solvents after which the P10 polymer was obtained in the form of a dried powder.

(73) 20 mg of this dried P10 polymer powder were placed in a 15 mL flask, at ambient temperature, and 2 g of powder acrylamide and 5.6 g of distilled water were then added.

(74) The mixture was degassed by bubbling with extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition in the form of two aqueous 0.6 wt. % solutions, 0.2 mL of each of the solutions being added. The two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(75) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(76) After the 24-hour reaction time, 99% conversion was obtained as determined by .sup.1H NMR.

(77) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=806 000 g/mol M.sub.w/M.sub.n=3.25.

(78) For comparison, the number-average molecular weight is 900 000 g/mol

EXAMPLE 11: SYNTHESIS OF A POLY(ACRYLAMIDOPROPYLTRIMETHYLAMMONIUM CHLORIDE)-B-POLY(ACRYLAMIDE) DIBLOCK COPOLYMER; SYNTHESIS OF THE POLYACRYLAMIDE BLOCK ACCORDING TO THE INVENTION (CONTROL AGENT: LIVING POLYMER WITH XANTHATE TERMINATION; INITIATOR PAIR: AMMONIUM PERSULFATE/SODIUM FORMALDEHYDE SULFOXYLATE)

(79) Step 1: Synthesis of the Poly(Acrylamidopropyltrimethylammonium Chloride) Block.

(80) The same polymer prepared in Example 8 was used.

(81) Step 2: Synthesis of the Diblock Copolymer

(82) The same P10 polymer as in Example 10 was used for this Example, used in the form of a powder prepared under the conditions of step 10.2 in Example 10.

(83) 215 mg of the P8 polymer powder were placed in a 15 mL flask, at ambient temperature and 2 g of powder acrylamide and 5.6 g of distilled water were added.

(84) The mixture was degassed by bubbling with extra-pure argon for 30 minutes, after which the temperature of the solution was lowered to 10 C. Ammonium persulfate and sodium formaldehyde sulfoxylate were added to the medium in a single addition, in the form of two aqueous 0.6 wt. % solutions, 0.2 mL of each of the solutions being added. The two aqueous solutions of ammonium persulfate and sodium formaldehyde sulfoxylate were previously degassed by bubbling argon.

(85) The polymerization reaction was left to take place under agitation for 24 hours at ambient temperature (20 C.).

(86) After the 24-hour reaction time, 98% conversion was obtained as determined by .sup.1H NMR.

(87) Analysis by size exclusion chromatography in water with the addition of NaNO.sub.3 (0.1N) using an eighteen-angle MALLS detector gave the following number-average molecular weight (M.sub.n) and polymolecularity index (M.sub.w/M.sub.n) values: M.sub.n=160 500 g/mol M.sub.w/M.sub.n=2.0.

(88) For comparison, the theoretical number-average molecular weight is 100 000 g/mol.