1,3-dipolar compound bearing a phosphorus-containing group and a dipole containing a nitrogen atom

1. A 1,3-dipolar compound comprising a phosphorus-containing group of formula (I) and a dipole containing a nitrogen atom,

—OP(O)(OR′)(OR″)  (I)

R′ and R″, which may be identical or different, representing a hydrogen or a carbon-containing group, and wherein the dipole containing a nitrogen atom is a dipole having the formula —C≡N→O.

2. The compound according to claim 1 , in which the carbon-containing group is selected from the group consisting of an alkyl group, an aryl group, and an alkaryl group.

3. The compound according to claim 1 , in which at least one of R′ and R″ is different from hydrogen.

4. The compound according to claim 2 , in which R′ and R″ represent independently an alkyl group.

5. The compound according to claim 4 , in which R′ and R″ represent independently methyl or ethyl.

6. A 1,3-dipolar compound comprising a unit of formula (II):

in which:

four of the five symbols R 1 to R 5 , which may be identical or different, are each an atom or a group of atoms, and the fifth symbol denotes a direct or indirect attachment to a phosphorus-containing group, and R 1 and R 5 are both different from H, and wherein the phosphorus-containing group is represented by formula (I)

—OP(O)(OR′)(OR″)  (I)

R′ and R″, which may be identical or different, representing a hydrogen or a carbon-containing group.

7. The compound according to claim 6 , in which R 2 or R 4 represents a direct attachment to the phosphorus-containing group.

8. The compound according to claim 6 , in which R 1 , R 3 and R 5 are identical.

9. The compound according to claim 6 , in which R 1 , R 3 and R 5 are each an alkyl group with 1 to 6 carbon atoms.

10. The compound according to claim 9 , in which R 1 , R 3 and R 5 are each a methyl or an ethyl.

11. A 1,3-dipolar compound comprising a unit of formula (III)

12. A method for modifying, by a grafting reaction, an unsaturated polymer that has at least one unsaturation, said method comprising reacting the 1,3-dipolar compound defined according to claim 1 on at least one unsaturation of the unsaturated polymer.

13. The method according to claim 12 , in which the unsaturated polymer is a diene polymer.

14. A rubber composition comprising:

a diene elastomer,

a reinforcing filler, the reinforcing filler comprising an inorganic reinforcing filler, and the 1,3-dipolar compound defined according to claim 1 .

15. The rubber composition according to claim 14 , in which the inorganic reinforcing filler is a silica.

16. The rubber composition according to claim 14 , in which the amount of 1,3-dipolar compound is between 1 and 5 molar equivalents of phosphorus-containing group per 100 moles of monomer units constituting the diene elastomer.

17. The rubber composition according to claim 14 , said composition further comprising a silane coupling agent for binding the inorganic reinforcing filler to the diene elastomer.

18. The rubber composition according to claim 14 , in which the 1,3-dipolar compound is pre-grafted on the diene elastomer by a method comprising reacting the 1,3-dipolar compound on at least one unsaturation of the diene elastomer.

19. The rubber composition according to claim 14 , said composition further comprising a crosslinking system.

20. A tire comprising the rubber composition according to claim 14 .

21. The tire according to claim 20 , wherein the rubber composition is in a tread of the tire.