Block copolymer, method for producing same, rubber composition using said block copolymer, and tire

1. A block copolymer, comprising:

a polymer block A comprising a farnesene-derived monomer unit (a1); and

a random copolymer block comprising a C12 or lower conjugated diene-derived monomer unit (b1) and an aromatic vinyl compound-derived monomer unit (b2),

wherein the block copolymer has an A/B mass ratio of the polymer block A to the random copolymer block B in a range of from 30170 to 0.5/99.5,

wherein the block copolymer has a content of the aromatic vinyl compound-derived monomer unit (b2) in the random copolymer block B in a range of from 1 to 50% by mass,

wherein the block copolymer has a weight average molecular weight as determined by gel permeation chromatography based on polystyrene in a range of from 100,000 to 5,000,000,

wherein at least a part of the block copolymer is a block copolymer in which terminals of linear block copolymer chains are bonded to one another via a coupling agent, and

wherein the coupling ratio is 40% by mass or less.

2. The block copolymer of claim 1 , having a content of the farnesene-derived monomer unit (a1) in the polymer block A of 60% by mass or more.

3. The block copolymer of claim 1 , having a total content of the C12 or lower conjugated diene-derived monomer unit (b1) and the aromatic vinyl compound-derived monomer unit (b2) in the random copolymer block B of 60% by mass or more.

4. The block copolymer of claim 1 , wherein

the coupling ratio is in a range of from 1 to 40% by mass.

5. The block copolymer of claim 1 , wherein at least a part of the block copolymer is a branched block copolymer in which terminals of linear block copolymer chains are bonded to one another via a coupling agent.

6. The block copolymer of claim 1 , wherein the block copolymer has the polymer block A at a terminus of a molecular chain of the block copolymer.

7. A method for producing a block copolymer, the method comprising:

polymerizing a monomer comprising farnesene in the presence of an organic metal initiator to produce a living polymer comprising the polymer block A; and

polymerizing monomers comprising a C12 or lower conjugated diene and an aromatic vinyl compound in the presence of the living polymer comprising the polymer block A to produce a living block copolymer comprising the polymer block A and a random copolymer block B,

wherein the block copolymer comprises a polymer block A comprising a farnesene-derived monomer unit (a1) and the random copolymer block B comprising a C12 or lower conjugated diene-derived monomer unit (b1) and an aromatic vinyl compound-derived monomer unit (b2),

wherein at least a part of the block copolymer is a block copolymer in which terminals of linear block copolymer chains are bonded to one another via a coupling agent, and

wherein the coupling ratio is 40% by mass or less.

8. The method of claim 7 , further comprising:

coupling at least a part of the living block copolymer comprising the polymer block A and the random copolymer block B with a coupling, agent.

9. A method for producing a block copolymer, the method comprising:

polymerizing monomers comprising a C12 or lower conjugated diene and an aromatic vinyl compound in the presence am organic metal initiator to produce a living polymer comprising a random copolymer block B; and

polymerizing a monomer comprising farnesene in the presence of the living polymer comprising the random copolymer block B to produce a living block copolymer comprising a polymer block A and the random copolymer block B,

wherein the block copolymer comprises the polymer block A comprising a farnesene-derived monomer unit (a1) and the random copolymer block B comprising a C12 or lower conjugated diene-derived monomer unit (b1) and an aromatic vinyl compound-derived monomer unit (b2),

wherein at least a part of the block copolymer is a block copolymer in which terminals of linear block copolymer chains are bonded to one another via a coupling agent, and

wherein the coupling, ratio is 40% by mass or less.

10. The method of claim 9 , further comprising:

coupling at least a part of the living block copolymer comprising the polymer block A and the random copolymer block B with a coupling agent.

11. A rubber composition, comprising:

a rubber component (I) comprising the block copolymer of claim 1 ; and

a filler (II),

wherein the rubber composition has a content of the block copolymer in the total amount of the rubber component (I) in a range of from 0.1 to 99.9% by mass, and

wherein the rubber composition comprises the filler (II) in an amount in a range of from 20 to 150 parts by mass, relative to 100 parts by mass of the rubber component (I).

12. A tire, comprising,

the rubber composition of claim 11 .

13. The block copolymer of claim 1 , wherein the coupling ratio is in a range of from 1 to 30% by mass.

14. The block copolymer of claim 1 , wherein the coupling ratio is in a range of from 5 to 28% by mass.

15. The block copolymer of claim 1 , wherein the coup mg ratio is in a range of from 10 to 25% by mass.

16. The block copolymer of claim 1 , wherein the A/B mass ratio of the block copolymer is in a range of from 23/73 to 0.7/99.3.

17. The block copolymer of claim 1 , having a glass transition temperature in a range of from −90 to −10° C.

18. The block copolymer of claim 1 , having a total content of the C12 or lower conjugated diene-derived monomer unit (b1) and the aromatic vinyl compound-derived monomer unit (b2) in the random copolymer block B in a range of from 80 to 100% by mass.

19. The block copolymer of claim 1 , having a total content of the C12 or lower conjugated diene-derived monomer unit (b1) and the aromatic vinyl compound-derived monomer unit (b2) in the random copolymer block B in a range of from 90 to 100% by mass.

20. The block copolymer of claim 1 , having a total content of the C12 lower conjugated diene-derived monomer unit (b1) and the aromatic vinyl compound-derived monomer unit (b2) in the random copolymer block B in a range of from 98 to 100% by mass.