Rubber composition comprising a diene elastomer bearing imidazole functional groups randomly distributed along the chain
A rubber composition comprises a reinforcing filler and a diene elastomer bearing imidazole functional groups along the chain which are randomly distributed along the chain. Such a composition exhibits an improved compromise in certain properties such as stiffness in the cured state and hysteresis.
1. A rubber composition comprising at least one diene elastomer and a reinforcing filler,
wherein the diene elastomer comprises imidazole rings of formula (I) which are randomly distributed along the chain of the diene elastomer:
wherein three of the four symbols Z, Y, R and R′, which are identical or different, each represent an atom or a group of atoms, it being possible for Z and Y to form, together with the carbon atoms to which they are attached, a ring, and the fourth symbol Z, Y, R or R′ denotes a direct or indirect attachment to the diene elastomer.
2. The rubber composition according to claim 1 , wherein R′ denotes a direct or indirect attachment to the elastomer.
3. The rubber composition according to claim 2 , wherein Z and Y are each a hydrogen atom.
4. The rubber composition according to claim 2 , wherein Z and Y form, together with the carbon atoms to which they are attached, a ring.
5. The rubber composition according to claim 1 , wherein R represents a hydrogen atom or a carbon-based group which can contain at least one heteroatom.
6. The rubber composition according to claim 5 , wherein R is an alkyl group that contains from 1 to 12 carbon atoms.
7. The rubber composition according to claim 1 , wherein the imidazole rings are groups grafted to the diene elastomer.
8. The rubber composition according to claim 7 , wherein the imidazole rings are groups attached to the diene units of the diene elastomer.
9. The rubber composition according to claim 7 , wherein the imidazole rings are grafted to the diene elastomer via groups resulting from grafting a 1,3-dipolar compound to the diene elastomer,
wherein the 1,3-dipolar compound is of formula (II):
Q-A-B (II),
wherein Q comprises a dipole containing at least one nitrogen atom,
wherein A is an atom or a group of atoms connecting Q to B, and
wherein B comprises the imidazole ring of formula (I) in which the fourth symbol denoting an indirect attachment to the diene elastomer denotes a direct attachment to A.
10. The rubber composition according to claim 9 , wherein A is an aliphatic group or an aromatic group.
11. The rubber composition according to claim 10 , wherein A is an alkylene group or an arylene group.
12. The rubber composition according to claim 9 , wherein the 1,3-dipolar compound is selected from the group consisting of nitrile oxides, nitrile imines and nitrones.
13. The rubber composition according to claim 12 , wherein Q contains a —C≡N→O unit.
14. The rubber composition according to claim 13 , wherein Q comprises a unit of formula (III):
wherein four of the five symbols R 1 to R 5 , which are identical or different, are each an atom or a group of atoms and the fifth symbol denotes a direct attachment to A, and
wherein neither of R 1 and R 5 are H.
15. The rubber composition according to claim 14 , wherein R 1 , R 3 and R 5 are each an alkyl group of 1 to 6 carbon atoms.
16. The rubber composition according to claim 15 , wherein the 1,3-dipolar compound is 2,4,6-trimethyl-3-((2-methyl-1H-imidazol-1-yl)methyl)benzonitrile oxide or 2,4,6-triethyl-3-((2-methyl-1H-imidazol-1-yl)methyl)benzonitrile oxide.
17. The rubber composition according to claim 12 , wherein Q contains a —C═N(→O)— unit.
18. The rubber composition according to claim 17 , wherein Q comprises a unit of formula (IV) or (V):
wherein Y 1 is an aliphatic group or an aromatic group containing from 6 to 20 carbon atoms, and
wherein Y 2 , comprising a direct attachment to A, is an aliphatic group or an aromatic group comprising, on its benzene nucleus, the direct attachment to A.
19. The rubber composition according to claim 18 , wherein the 1,3-dipolar compound is a compound of formula (IVa), (IVb), (Va) or (Vb):
20. The rubber composition according to claim 1 , wherein the diene elastomer is an essentially unsaturated elastomer selected from the group consisting of polybutadienes, polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures thereof.
21. The rubber composition according to claim 1 , wherein the diene elastomer comprises between 0 and 3 moles of imidazole rings per 100 moles of monomer units constituting the diene elastomer.
22. The rubber composition according to claim 1 , wherein the reinforcing filler comprises a reinforcing inorganic filler.
23. The rubber composition according to claim 22 , wherein the reinforcing inorganic filler is a silica.
24. The rubber composition according to claim 22 , further comprising a silane coupling agent for bonding the reinforcing inorganic filler to the diene elastomer.
25. The rubber composition according to claim 1 , further comprising a crosslinking system.
26. A process for preparing a rubber composition according to claim 1 , based on at least one diene elastomer, a reinforcing filler and a crosslinking system, the process comprising the steps of:
(a) incorporating, in the diene elastomer, during a first non-productive stage, the reinforcing filler and, if appropriate, the coupling agent, by kneading thermomechanically until a maximum temperature of between 130° C. and 200° C. is reached;
(b) cooling the combined mixture to a temperature of less than 100° C.;
(c) subsequently incorporating the crosslinking system; and
(d) kneading up to a maximum temperature of less than 120° C.,
wherein the diene elastomer comprises imidazole rings of formula (I) which are randomly distributed along the chain of the diene elastomer.
27. The process according to claim 26 , wherein step (a) is preceded by a step of reacting a 1,3-dipolar compound with a diene elastomer by a bulk or solution grafting reaction,
wherein the 1,3-dipolar compound is of formula (II):
Q-A-B (II),
wherein Q comprises a dipole containing at least one nitrogen atom,
wherein A is an atom or a group of atoms connecting Q to B, and
wherein B comprises the imidazole ring of formula (I) in which the fourth symbol denoting an indirect attachment to the diene elastomer denotes a direct attachment to A.
28. A tread comprising the rubber composition according to claim 1 .
29. A tire comprising the rubber composition according to claim 1 .