Multi-branched styrene-conjugated diene block copolymer and its preparation method

A method for preparing a multi-branched block copolymer having 20,000˜1,000,000 number average molecular weight represented by formula (S-D)m-R-D comprising the steps of;

• i) preparing vinyl aromatic living polymer by reacting alkyl lithium initiator and vinyl aromatic monomer in the presence of inert hydrocarbon solvent;
• ii) preparing vinyl aromatic conjugated-diene diblock copolymer by adding and polymerizing conjugated-diene monomers to obtained vinyl aromatic living polymer in step i);
• and
• iii) preparing multi-branched block copolymer by adding and reacting condensing agent and conjugated-diene monomers to the obtained diblock copolymer in step ii);
• wherein,
• (S-D)m-R-D;
• wherein,
• S represents a polymer of at least one vinyl aromatic monomer selected from the group consisting of styrene, a-methylstyrene, o-methylstyrene, p-methylstyrene and p-tert-butylstyrene;
• D represents a polymer of conjugated-diene monomer;
• R represents a conjugated diene copolymer containing randomly multi-placed condensing agents (Cn), in which C represents a condensing agent with following formula 1 and n represents the number of condensing agents.
• m=nk+1, the ratio of n/m is 1>n/m>1/(k+1)
• wherein,
• Y represents Si or Sn atom;
• R is C1˜C20 alkyl or aryl;
• X is Cl or Br;
• and
• k, 1 is an integer of k+1=3.