Process for producing modified conjugated diene polymer, modified conjugated diene polymer obtained by the process, and rubber composition containing the same

1. A process for producing a modified conjugated diene polymer comprising subjecting an active terminal of a conjugated diene polymer having a vinyl content of less than 10% and a cis-1,4 bond content of 75% or more to a modification reaction with an alkoxysilane compound, and subjecting the alkoxysilane compound (residue) to a condensation reaction in an aqueous solution at a pH of 9 to 14 and a temperature of 85 to 180° C. in the presence of a condensation accelerator comprising a compound containing titanium.

2. The process according to claim 1 , further comprising adding an alkoxysilane compound having a functional group.

3. The process according to claim 1 , wherein the condensation accelerator is an alkoxide, a carboxylate, or an acetylacetonate complex of titanium.

4. The process according to claim 1 , wherein the alkoxysilane compound used for the modification reaction is an alkoxysilane compound comprising at least one functional group selected from (a) an epoxy group, (b) an isocyanate group, and (c) a carboxyl group.

5. The process according to claim 1 , further comprising adding a compound comprising at least one functional group selected from (d) an amino group, (e) an imino group, and (f) a mercapto group.

6. The process according to claim 1 , wherein a conjugated diene compound which forms the modified conjugated diene polymer is at least one conjugated diene compound selected from 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene.

7. The process according to claim 1 , wherein the conjugated diene polymer is prepared by polymerizing a conjugated diene compound using a catalyst mainly containing (g) a compound containing a rare earth element having an atomic number of 57 to 71 in the periodic table or a reaction product of the compound with a Lewis base, (h) an alumoxane and/or an organoaluminum compound represented by AlR 1 R 2 R 3 (wherein R 1 and R 2 individually represent a hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom, and R 3 represents a hydrocarbon group having 1 to 10 carbon atoms and may be the same as or different from R 1 or R 2 ), and (i) a halogen-containing compound.

8. A modified conjugated diene polymer produced by the process according to claim 1 .

9. A rubber composition comprising the modified conjugated diene polymer according to claim 8 .

10. The rubber composition according to claim 9 , wherein the rubber composition includes a rubber component comprising the modified conjugated diene polymer in an amount of 20 mass % or more, and silica and/or carbon black in an amount of 20 to 120 parts by mass per 100 parts by mass of the rubber component.

11. The rubber composition according to claim 9 , wherein the rubber component comprises 20 to 100 mass % of the modified conjugated diene polymer, and 0 to 80 mass % of at least one rubber other than the modified conjugated diene polymer selected from the group consisting of a natural rubber, a synthetic isoprene rubber, a butadiene rubber, a styrene-butadiene rubber, an ethylene-α-olefin copolymer rubber, an ethylene-α-olefin-diene copolymer rubber, an acrylonitrile-butadiene copolymer rubber, a chloroprene rubber, and a halogenated butyl rubber (provided that the modified conjugated diene polymer+the rubber other than the modified conjugated diene polymer=100 mass %).

12. The rubber composition according to claim 10 , wherein the rubber component comprises 20 to 100 mass % of the modified conjugated diene polymer, and 0 to 80 mass % of at least one rubber other than the modified conjugated diene polymer selected from the group consisting of a natural rubber, a synthetic isoprene rubber, a butadiene rubber, a styrene-butadiene rubber, an ethylene-α-olefin copolymer rubber, an ethylene-α-olefin-diene copolymer rubber, an acrylonitrile-butadiene copolymer rubber, a chloroprene rubber, and a halogenated butyl rubber (provided that the modified conjugated diene polymer+the rubber other than the modified conjugated diene polymer=100 mass %).

13. The process according to claim 2 , wherein the condensation accelerator is an alkoxide, a carboxylate, or an acetylacetonate complex of titanium.

14. The process according to claim 2 , the process further comprising adding a compound having at least one functional group selected from (d) an amino group, (e) an imino group, and (f) a mercapto group.

15. The process according to claim 3 , the process further comprising adding a compound having at least one functional group selected from (d) an amino group, (e) an imino group, and (f) a mercapto group.

16. The process according to claim 13 , the process further comprising adding a compound having at least one functional group selected from (d) an amino group, (e) an imino group, and (f) a mercapto group.

17. The process according to claim 4 , the process further comprising adding a compound having at least one functional group selected from (d) an amino group, (e) an imino group, and (f) a mercapto group.

18. The process according to claim 6 , wherein the conjugated diene polymer is prepared by polymerizing a conjugated diene compound using a catalyst mainly containing (g) a compound containing a rare earth element having an atomic number of 57 to 71 in the periodic table or a reaction product of the compound with a Lewis base, (h) an alumoxane and/or an organoaluminum compound represented by AlR 1 R 2 R 3 (wherein R 1 and R 2 individually represent a hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom, and R 3 represents a hydrocarbon group having 1 to 10 carbon atoms and may be the same as or different from R 1 or R 2 ), and (i) a halogen-containing compound.

19. The process according to claim 2 , wherein the alkoxysilane compound having a functional group is added after the modification reaction, but before the condensation reaction.