Amphiphilic multiblock polymers

1. A process for preparing a polymer, the process comprising a polymerization step (E) in which the following are placed in contact in an aqueous medium (M) containing dispersed surfactant micelles:

ethylenically unsaturated monomers M1 predominantly present in the aqueous medium, referred to as “hydrophilic monomers”;

ethylenically unsaturated monomers M2 different from the hydrophilic monomers, at least partly present in the surfactant micelles, and having a solubility in the aqueous medium (M) at the implementation temperature of step (E) at least equal to that of hexyl acrylate, referred to as “partially water-soluble hydrophobic monomers”;

at least one radical polymerization initiator; and

at least one radical polymerization control agent; thereby preparing a polymer having a mass of greater than 100 000 g/mol and less than 300 000 g/mol; and,

after step (E), a step (E2) of grafting an ethylenically unsaturated group onto the polymer as obtained on conclusion of step (E), whereby a polymer bearing an ethylenically unsaturated function is obtained.

2. The process as claimed in claim 1 , wherein the radical polymerization control agent is a compound which comprises at least one thiocarbonylthio group —S(C═S)—.

3. The process according to claim 2 , wherein the thiocarbonylthio group is a xanthate.

4. The process as claimed in claim 1 , wherein the radical polymerization control agent is a prepolymer bearing at least one thiocarbonylthio group —S(C═S)— obtained on conclusion of a step (E 0 ), prior to step (E), said step (E 0 ) placing in contact

monomers M0 bearing hydrophilic groups;

a radical polymerization initiator; and

a control agent bearing at least one thiocarbonylthio group —S(C═S)—.

5. The process as claimed in claim 4 , wherein the monomers (M0) are (meth)acrylic acid monomers, whereby the control agent is a poly(meth)acrylic acid bearing at least one xanthate group and the polymer having the specific structure obtained according to step (E) also with a poly(meth)acrylic acid block linked at one of its ends.

6. The process according to claim 4 , wherein the monomers M0 bearing hydrophilic groups are identical to the hydrophilic monomers of step (E).

7. The process according to claim 4 , wherein the at least one thiocarbonylthio group —S(C═S)— of the control agent is a xanthate.

8. The process as claimed in claim 1 , wherein the radical polymerization control agent is a water-soluble or water-dispersible oligomer bearing a thiocarbonylthio group —S(C═S)—, which

is soluble or dispersible in the aqueous medium (M) used in step (E);

and/or

is not capable of penetrating into the micelles of the micellar solution.

9. The process as claimed in claim 1 , wherein the hydrophilic monomers of step (E) are (meth)acrylic acid monomers or acrylamido or methacrylamido monomers.

10. The process as claimed in claim 1 , wherein the hydrophilic monomers of step (E) are 2-acryloylamino-2-methylpropane-1-sulfonic acids (AMPS) or acrylamide or acrylic acid.

11. The process according to claim 1 , wherein the at least one radical polymerization initiator is water-soluble or water-dispersible.

12. A polymer with a mass of greater than 100 000 g/mol and less than 300 000 g/mol obtained according to the process of claim 1 .

13. A method

for modifying a liquid/liquid, liquid/solid or liquid/gas interface;

for regulating the rheology of a liquid medium; and/or

for dispersing organic or mineral pigments

comprising using the polymer as claimed in claim 12 .

14. A method for radical polymerization comprising using the polymer as claimed in claim 12 as an ethylenically unsaturated monomer.