Functional diene elastomer with a low pi and improved cold flow, and rubber composition containing same

1. An elastomer composed:

a) of a functionalized diene elastomer, at the chain end or in the middle of the chain, by a tin functional group, exhibiting a monomodal distribution of molecular weights before functionalization and a polydispersity index before functionalization of less than or equal to 1.3,

b) of a star-branched diene elastomer being branched with a tin-comprising compound, exhibiting a monomodal distribution of molecular weights before star-branching and a polydispersity index before star-branching of less than or equal to 1.3, and

c) of a content of less than 15% by weight, with respect to the total weight of the elastomer, of a non-tin-functional diene elastomer,

wherein the diene elastomer a) before functionalization, the diene elastomer b) before star-branching, and the diene elastomer c) being the same in nature.

2. An elastomer according to claim 1 , wherein the functionalized diene elastomer a) comprises an amine functional group at one or all of the ends of chains not functionalized by tin.

3. An elastomer according to claim 1 , wherein the star-branched diene elastomer b) comprises an amine functional group at the ends of chains not star-branched by tin.

4. An elastomer according to claim 1 , wherein the non-tin-functional diene elastomer c) comprises an amine functional group at one of the chain ends.

5. An elastomer according to claim 1 , wherein the functionalization of the functionalized diene elastomer a) is obtained with a monohalotin functionalization agent or a dihalotin coupling agent.

6. An elastomer according to claim 1 , wherein the star-branching of the stand-branched elastomer b) is obtained with a tri- or tetrahalotin star-branching agent.

7. An elastomer according to claim 1 , wherein the functionalized diene elastomer a) is a diene elastomer functionalized by a tin functional group in the middle of the chain and the star-branched diene elastomer b) is a diene elastomer star-branched by tin having 4 branches.

8. An elastomer according to claim 1 , wherein the diene elastomers a), b), and c) are chosen from polybutadienes, butadiene-styrene copolymers, butadiene-isoprene copolymers, isoprene-styrene copolymers, butadiene-styrene-isoprene terpolymers and synthetic polyisoprene.

9. An elastomer according to claim 1 , comprising from 5% to 45% by weight, with respect to the total weight of the elastomer, of the star-branched diene elastomer b).

10. An elastomer according to claim 9 , comprising from 10% to 30% by weight, with respect to the total weight of the elastomer, of the star-branched diene elastomer b).

11. An elastomer according to claim 1 , comprising a content of greater than 0% by weight and of less than 10% by weight, with respect to the total weight of the elastomer, of the non-tin-functional diene elastomer c).

12. An elastomer according to claim 11 , comprising a content of less than 5% be weight, with respect to the total weight of the elastomer, of the non-tin-functional diene elastomer c).

13. A reinforced rubber composition based on at least one reinforcing filler and on an elastomer matrix, wherein the elastomer matrix comprises at least one elastomer as defined in claim 1 .

14. A reinforced rubber composition according to claim 13 , wherein the elastomer matrix also comprises at least one diene elastomer other than the elastomer.

15. A reinforced rubber composition according to claim 13 , wherein the reinforced rubber composition further comprises a chemical crosslinking agent.

16. A semi-finished article made of rubber for a tire, wherein the rubber comprises a crosslinkable or crosslinked rubber composition as defined in claim 13 .

17. A semi-finished article according to claim 16 , wherein the article is a tread.

18. A tire, wherein the tire comprises a semi-finished article as defined in claim 16 .