Synthesis of acylureas and composition comprising acylureas

1. A process for the synthesis of a polyisocyanate composition comprising acylureas, comprising the step of reacting a starting composition comprising at least one compound having at least two isocyanate functional groups with either:

(1) an acid having at least two acid functional groups, at least one of said acid functional groups having a pKa value of less than or equal to 3, and at least one acid functional group having a pKa value of more than 3 and less than or equal to 6, or

(2) a first acid having at least one acid functional group having a pKa value of less than or equal to 3, and a second acid having at least one acid functional group having a pKa value of more than 3 and less than or equal to 6, at a temperature at least equal to 50° C.

2. The process as claimed in claim 1 , wherein at least one compound having at least two isocyanate functional groups is a monomer.

3. The process as claimed in claim 2 , wherein the at least one compound having at least two isocyanate functional groups represent at least ⅓, by weight of said starting composition.

4. The process as claimed in claim 2 , wherein the monomer derivatives represent at least ½, by weight of said starting composition.

5. The process as claimed in claim 2 , wherein the at least one compound having at least two isocyanate functional groups represents at least 90%, by weight of said starting composition.

6. The process as claimed in claim 1 , wherein the at least one compound having at least two isocyanate functional groups is at least partially aliphatic.

7. The process as claimed in claim 1 , wherein said polyisocyanate composition further comprises a compound having a biuret functional group, synthesized by bringing said starting composition into contact with an amine or an amine-generating reactant.

8. The process as claimed in claim 7 , wherein said amine-generating reactant is water in the form of a fluid.

9. The process as claimed in claim 7 , wherein said at least one compound is a monomer and wherein the molar ratio of the amine generated or added to the total amount of the monomer, expressed in moles, is from ½ to 1/50.

10. The process as claimed in claim 7 , wherein said at least one compound is a monomer and wherein the molar ratio of the amine generated or added to the total amount of the monomers, expressed in moles, is from ⅓ to 1/25.

11. The process as claimed in claim 7 , wherein said starting composition is brought into contact with water in the presence of (1) an acid having at least two acid functional groups, at least one of said acid functional groups having a pKa value of less than or equal to 3, and at least one acid functional group having a pKa value of more than 3 and less than or equal to 6, or (2) a first acid having at least one acid functional group having a pKa value of less than or equal to 3, and a second acid having at least one acid functional group having a pKa value of more than 3 and less than or equal to 6.

12. The process as claimed in claim 1 , wherein the acid having at least one acid functional group having a pKa value of less than or equal to 3 is an aliphatic sulfonic acid, an aromatic sulfonic acid, an aliphatic phosphonic acid , an aromatic phosphonic acid, a carboxylic-phosphonic acid, a phosphoric ester or a perhaloalkanoic acid.

13. The process as claimed in claim 1 , wherein the acid having at least one acid functional group having a pKa value of more than 3 and less than or equal to 6 is an aliphatic or aromatic carboxylic acid.

14. The process as claimed in claim 1 , wherein the acid having an acid functional group having a pKa value of more than 3 and less than or equal to 6 is at least partially added to the reaction medium in the form of a precursor.

15. The process as claimed in claim 1 , wherein the acid having an acid functional group having a pKa value of less than or equal to 3 is at least partially introduced into the reaction medium in the form of a precursor.

16. The process as claimed in claim 2 , wherein the molar ratio of the sum of the acid functional group having a pKa value of less than or equal to 3, expressed as equivalents, to the total amount of the monomers, expressed as moles, is at least equal to 0.1%.

17. The process as claimed in claim 2 , wherein the molar ratio of the sum of the acid functional group having a pKa value of less than or equal to 3, expressed as equivalents, to the total amount of the monomers, expressed as moles, is at most equal to 2%.

18. The process as claimed in claim 2 , wherein the molar ratio of the sum of the acid functional group having a pKa value of more than 3 and less than or equal to 6, expressed as equivalents, to the total amount of the monomers, expressed as moles, is at least equal to 2%.

19. The process as claimed in claim 18 , wherein the molar ratio of the sum of the acid functional group having a pKa value of more than 3 and less than or equal to 6, expressed as equivalents, to the total amount of the monomers, expressed as moles, is at most equal to 10%.

20. The process as claimed in claim 1 , wherein said acid having a pKa value of less than or equal to 3 is added in a dilute form.

21. The process as claimed in claim 20 , wherein said diluent is water or a C1 to C14 alcohol.

22. The process as claimed in claim 1 , wherein said acid having a pKa value of less than or equal to 3 is present in a first compound and said acid having a pKa value of more than 3 and less than or equal to 6 is present in a second compound.

23. The process as claimed in claim 1 , wherein said acid functional group having a pKa value of less than or equal to 3 and said acid functional group having a pKa value of more than 3 and less than or equal to 6 are present in the same compound.

24. The process as claimed in claim 22 , wherein said acid having a pKa value of less than or equal to 3 is diluted in said acid having a pKa value of more than 3 and less than or equal to 6.