Process for producing conjugated diene polymer, conjugated diene polymer, and rubber composition

1. A process for producing a conjugated diene polymer comprising a polymerization wherein a conjugated diene polymer having a cis-1,4-bond content of 98.5 mass % or more and a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography of 2.5 or less is obtained by carrying out a polymerization reaction in conjugated diene compounds using a catalyst composition comprising the following components (a) to (c):

component (a): a rare earth element comprising compound which comprises at least a rare earth element of an atomic number of 57 to 71 in the periodic table, or a reaction product of the rare earth element comprising compound with a Lewis base,

component (b): an aluminoxane and organoaluminum compound shown by a general formula AlR 1 R 2 R 3 , wherein R 1 and R 2 individually represent a same or different 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 which is the same as or different from R 1 and R 2 , and

component (c): iodine.

2. The process for producing a conjugated diene polymer according to claim 1 , wherein the 1,2-vinyl content of the obtained conjugated diene polymer is 0.3 mass % or less.

3. The process for producing a conjugated diene polymer according to claim 1 , wherein the polymerization reaction is carried out at a temperature of 10° C. or higher.

4. The process for producing a conjugated diene polymer according to claim 1 , wherein the molar ratio of the iodine atom contained in the component (c) to the component (a), (iodine atom)/(component (a)), is 0.5 to 3.

5. A conjugated diene polymer produced by the process for producing a conjugated diene polymer according to claim 1 .

6. A rubber composition comprising a rubber component (A) which contains the conjugated diene polymer according to claim 5 .

7. The rubber composition according to claim 6 , comprising the rubber component (A) and silica and/or carbon black (B).

8. The rubber composition according to claim 7 , wherein the rubber component (A) contains the conjugated diene polymer in an amount of 20 mass % or more, and the rubber composition contains silica and/or carbon black of the component (B) in an amount of 20 to 120 parts by mass per 100 parts by mass of the rubber component (A).

9. The process of claim 1 , wherein in the process, the rare earth element-comprising compound comprises neodymium.

10. The process of claim 1 , wherein in the process, the rare earth element-comprising compound comprises praseodymium.

11. The process of claim 1 , wherein in the process, the rare earth element-comprising compound comprises cerium.

12. The process of claim 1 , wherein in the process, the rare earth element-comprising compound comprises lanthanum.

13. The process of claim 1 , wherein in the process, the rare earth element-comprising compound comprises gadolinium.

14. The process of claim 1 , wherein in the process, the rare earth element-comprising compound is a phosphate.

15. The process of claim 1 , wherein in the process, the rare earth element-comprising compound is a carboxylate.

16. The process of claim 1 , wherein in the process, the component (a) comprises the product obtained by the reaction of the rare earth element-comprising compound with a Lewis base.

17. The process of claim 1 , wherein in the process, in the component (b), R 1 is a hydrogen atom.

18. The process of claim 1 , wherein in the process, in the component (b), R 2 is a hydrogen atom.