Rubber composition and pneumatic tire

1. A rubber composition comprising:

a bifunctionalized elastomer comprising the reaction product of 1) a living anionic elastomeric polymer initiated with a functional initiator and 2) a functional polymerization terminator, wherein

1) the living anionic elastomeric polymer initiated with a functional initiator is of formula AYLi where Y is a divalent polymer radical, Li is a lithium atom bonded to a carbon atom of Y, and A is an amine-containing radical having the formula X

wherein R 15 and R 16 independently have from 1 to 20 carbon atoms and each are independently an alkyl group, a cycloalkyl group, an aromatic group, a substituted alkyl group, a substituted cycloalkyl group or a substituted aromatic group, or R 15 and R 16 taken together with the nitrogen to which both R 15 and R 16 are attached comprise a heterocyclic amine group wherein R 15 and R 16 taken together form an alkanediyl group of from 4 to 20 carbon atoms or a substituted alkanediyl group of from 4 to 20 carbon atoms, and R 17 is a covalent bond, an alkanediyl group of from 1 to 20 carbon atoms or a substituted alkanediyl group of from 1 to 20 carbon atoms; and

2) the functional polymerization terminator is of formula I

wherein R 1 is C1 to C4 linear alkyl, or C1 to C4 branched alkanediyl;

X 1 , X 2 , X 3 are independently O, S, or a group of formula (II) or (III)

where R 2 is C1 to C18 linear or branched alkyl;

Z is R 3 , —OR 4 , or —R 5 —X 4 ; R 3 , R 4 are independently C1 to C18 linear or branched alkyl; R 5 is C1 to C18 alkanediyl or dialkyl ether diyl;

X 4 is halogen or a group of structure IV, V, VI, VII or VIII

wherein R 6 , R 7 , R 8 , R 9 , and R 10 are independently H or C1 to C8 alkyl; R 11 is C2 to C8 alkanediyl; R 12 and R 13 are independently H, aryl or C1 to C8 alkyl;

Q is N or a group of structure IX

wherein R 14 is C1 to C8 alkyl.

2. The rubber composition of claim 1 , wherein the filler comprises from 10 to 100 phr of silica.

3. The rubber composition of claim 1 , wherein the filler further comprises carbon black, and the weight ratio of silica to carbon black is greater than or equal to one.

4. The rubber composition of claim 1 , wherein the filler comprises from 10 to 100 phr of silica, and carbon black wherein the weight ratio of silica to carbon black is greater than or equal to one.

5. The rubber composition of claim 1 , further comprising at least one additional diene based elastomer selected from the group consisting of styrene-butadiene rubber, polybutadiene, natural rubber, and synthetic polyisoprene.

6. The rubber composition of claim 1 , wherein the living anionic elastomer is derived from at least one diene monomer and optionally at least one vinyl aromatic monomer.

7. The rubber composition of claim 1 , wherein the living anionic elastomer is derived from at least one of isoprene and butadiene, and optionally from styrene.

8. The rubber composition of claim 1 , wherein the living anionic elastomer is derived from butadiene and styrene.

9. The rubber composition of claim 1 , wherein the polymerization terminator of formula I is ESTI, 1-ethoxy-3,7,10-trimethylsilatrane.

10. The rubber composition of claim 1 , wherein the polymerization terminator of formula I is CSTI, 1-(3-chloropropyl)-3,7,10-trimethylsilatrane.

11. The rubber composition of claim 1 , wherein the polymerization terminator of formula I is BSTI, 1-isobutyl-3,7,10-trimethylsilatrane.

12. The rubber composition of claim 1 , wherein the polymerization terminator of formula I is OSTI, 1-octyl-3,7,10-trimethylsilatrane.

13. The rubber composition of claim 1 , wherein the polymerization terminator of formula I is BIPOS, 1,2-bis(3,7,10-trimethylsilatrane)ethane.

14. The rubber composition of claim 1 , wherein the polymerization terminator of formula I is selected from the group consisting of the following structures

15. The rubber composition of claim 1 , wherein the polymerization terminator of formula I has the structure

16. The rubber composition of claim 1 , wherein the polymerization terminator of formula I has the structure

17. The rubber composition of claim 1 , wherein the structure of formula X is selected from the group consisting of 3-(N, N-dimethylamino)-1-propyl, 3-(N, N-dimethylamino)-2-methyl-1-propyl, 3-(N, N-dimethylamino)-2,2-dimethyl-1-propyl, 4-(N, N-dimethylamino)-1-butyl, 5-(N, N-dimethylamino)-1-pentyl, 6-(N, N-dimethylamino)-1-hexyl, and 8-(N, N-dimethylamino)-1-propyl.

18. The rubber composition of claim 1 , wherein the structure of formula X is selected from the group consisting of 3-piperidino-1-propyl and 3-pyrrolidino-1-propyl.

19. The rubber composition of claim 18 , further comprising silica.

20. A pneumatic tire comprising the rubber composition of claim 19 .