Conjugated diene graft polymer and method for producing the same

A conjugated diene graft polymer composition, comprising:

• a conjugated diene graft polymer, comprising:
• (a) a main chain comprising, in polymerized form, a conjugated diene unit;
• and (b) a side chain comprising, in polymerized form, a conjugated diene unit and/or an aromatic vinyl compound unit;
• and
• a lithium salt,
• wherein the side chain (b) of the conjugated diene graft polymer is bonded to the main chain (a) via one hetero atom serving as a branching point and having a valence of not less than 3,
• wherein the main chain (a) is bonded to the branching point directly or through a linking chain,
• wherein the side chain (b) is directly bonded to the branching point,
• wherein the hetero atom of the branching point comprises Si, Sn, Ge, Pb, P, B, and/or Al,
• wherein a halogen content of a by-product in the conjugated diene graft polymer composition, comprising the lithium salt, is not more than 1000 ppm, and
• wherein an average number X of a functional groups (c) directly bonded to the branching point per molecule of the conjugated diene graft polymer is in a range of from 0 to 10.

A method for producing a conjugated diene graft polymer, the method comprising:

• (A-1) reacting an active end polymer of formula (I):
• P—X (I)
• P being a polymer chain comprising, in polymerized form, a conjugated diene unit and/or an aromatic vinyl compound unit, and X being an active end of anionic polymerization,
• with a functional group-modified conjugated diene polymer comprising, as a branched chain, a moiety comprising a functional group of formula (II):
• V being independently a C1-5 alkoxy group or a hydroxyl group, Z independently being Si, P, or Al, R1 independently being a C6-12 aryl group, a C1-12 alkyl group, or a hydrogen atom, N being a valence of Z, and n being an integer satisfying expression (1):
• 1≤n≤N−1 (1),
• to thereby produce a conjugated diene graft polymer comprising a side chain (b) comprising a polymer comprising, in polymerized form, the conjugated diene unit and/or the aromatic vinyl compound unit, bonded to the main chain (a) via Z, a hetero atom serving as a branching point, the valence of Z being not less than 3 and identical to n, the main chain (a) comprising, in polymerized form, the conjugated diene unit;
• and
• (B) recovering the conjugated diene graft polymer obtained.