Method for synthesizing polymers from acrylic acid, one of the salts of same or the mixture thereof

1. A process for preparing a polymer comprising a step of radical polymerization of monomers comprising at least monomers (M1) selected from a group consisting of acrylic acid, a salt thereof, and a mixture thereof, wherein said radical polymerization step is carried out:

continuously;

at a pH which remains included from 3 to 5 during the polymerization step;

in the presence of a metabisulfite/persulfate redox couple, as a radical initiator, with a metabisulfite/persulfate molar ratio included from 1 to 3.5 and an initiator/monomer molar percentage included from 5% to 18%.

2. The process as claimed in claim 1 , wherein the pH is included from 3.5 to 5.

3. The process as claimed in claim 1 , wherein the sodium metabisulfite/sodium persulfate molar ratio is included from 1 to 2.5.

4. The process as claimed in claim 1 , wherein the molar percentage is included from 3% to 10%.

5. The process as claimed in claim 1 , wherein the polymerization step is carried out at a temperature which remains included from 30° C. to 100° C. throughout the polymerization.

6. The process as claimed in claim 1 , wherein the polymerization is carried out in a tubular reactor, a plate reactor or a microreactor which is appropriate.

7. The process as claimed in claim 6 , wherein the tubular reactor comprises at least one static mixer.

8. The process as claimed in claim 1 , wherein the polymerization step is carried out with a residence time of less than 5 minutes.

9. The process as claimed in claim 1 , wherein the polymer obtained has a weight-average molar mass included from 1000 g/mol to 10 000 g/mol.

10. The process as claimed in claim 1 , wherein the polymer obtained is subjected to an additional post-treatment step in the presence of additives, of biocides or of bases.

11. The process as claimed in claim 1 , wherein the radical polymerization reaction is carried out in the presence of at least one monomer (M2), said monomer (M2) being different than the monomer (M1).

12. The process as claimed in claim 11 , wherein the monomer (M2) is a monomer which has one or more functions or groups selected from the group consisting of: carboxylic acid; sulfonate; sulfate; phosphonate; phosphate; hydroxyl; primary, secondary, tertiary or quaternary amine; lactam; amide; ethylene glycol or polyalkylene oxide; carboxybetaine, sulfobetaine and phosphobetaines.

13. The process as claimed in claim 1 , wherein said metabisulfite/persulfate redox couple is the sodium metabisulfite/sodium persulfate couple.

14. The process as claimed in claim 1 , wherein the pH is included from 4.0 to 5.

15. The process as claimed in claim 1 , wherein the pH is included from 4.4 to 4.9.

16. The process as claimed in claim 1 , wherein the sodium metabisulfite/sodium persulfate molar ratio is less than or equal to 2.

17. The process as claimed in claim 1 , wherein the molar percentage is included from 6% to 8.5%.

18. The process as claimed in claim 1 , wherein the polymerization step is carried out with a residence time of less than 2 minutes.

19. The process as claimed in claim 1 , wherein the polymer obtained has a weight-average molar mass included from 1500 g/mol to 7500 g/mol.

20. The process as claimed in claim 1 , wherein the polymer obtained has a weight-average molar mass included from 2000 g/mol to 6000 g/mol.