Process for producing modified polymer, modified polymer obtained by the process, and rubber composition thereof

1. A process for producing a modified polymer comprising a step of carrying out a modification reaction on an active end of a conjugated diene polymer having a vinyl content of less than 10%, a cis-1,4 bond content of 75% or higher, and an active end using an alkoxysilane compound, and a step of carrying out a condensation reaction in the presence of a condensation accelerator comprising a compound of zirconium (Zr), bismuth (Bi), or aluminum (Al).

2. The process according to claim 1 , wherein the compound constituting the condensation accelerator is an alkoxide, a carboxylate, or an acetylacetonate complex salt of the above-mentioned element.

3. The process according to claim 1 , wherein the alkoxysilane compound comprises at least one functional group selected from the following (a) to (c):

(a) an epoxy group;

(b) an isocyanate group; and

(c) a carboxyl group.

4. The process according to claim 1 , wherein the condensation accelerator is at least one compound selected from the following (d) to (h):

(d) a bismuth carboxylate;

(e) a zirconium alkoxide;

(f) a zirconium carboxylate;

(g) an aluminum alkoxide; and

(h) an aluminum carboxylate.

5. The process according to claim 1 , wherein the process further comprises a step of adding a compound containing at least one functional group selected from the following (i) to (k):

(i) an amino group;

(j) an imino group; and

(k) a mercapto group.

6. The process according to claim 1 , wherein the conjugated diene compound is at least one 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 having an active end is a polymer obtained by polymerizing a conjugated diene compound using a catalyst containing the following components (l) to (n) as the main components:

(l) 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;

(m) an alumoxane and/or an organoaluminum compound of the formula AlR 1 R 2 R 3 (wherein R 1 and R 2 , which may be the same or different, are hydrocarbon groups having 1 to 10 carbon atoms or are hydrogen atoms, and R 3 is a hydrocarbon group having 1 to 10 carbon atoms and may be the same as or different from R 1 or R 2 ); and

(n) a halogen-containing compound.

8. A modified polymer produced by carrying out a modification reaction on an active end of a conjugated diene polymer having a vinyl content of less than 10%, a cis-1,4 bond content of 75% or higher, and an active end using an alkoxysilane compound, and a step of carrying out a condensation reaction in the presence of a condensation accelerator comprising a compound of zirconium (Zr), bismuth (Bi), or aluminum (Al).

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

10. A rubber composition comprising a rubber component including at least 20% by mass of the modified polymer according to claim 8 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% by mass of the modified polymer and 80 to 0% by mass of at least one other rubber 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 (with proviso that amount of modified polymer+amount of other rubber(s)=100% by mass).

12. The process according to claim 1 , wherein the condensation reaction is carried out in the presence of a compound of zirconium.

13. The process according to claim 1 , wherein the condensation reaction is carried out in the presence of a compound of bismuth.

14. The process according to claim 1 , wherein the condensation reaction is carried out in the presence of a compound of aluminum.