Method for preparing modified conjugated diene-based polymer

A method for preparing a modified conjugated diene-based polymer, the method comprising:

• polymerizing a conjugated diene-based monomer in the presence of a catalyst composition in a hydrocarbon solvent to prepare an active polymer;
• reacting the active polymer with a modifier represented by the following Formula 1 to prepare a first polymer;
• and
• adding a sulfur halide to the first polymer and mixing for 15 minutes or more:
• in Formula 1,
• R1 to R3 are each independently a trivalent hydrocarbon group or an unsubstituted divalent hydrocarbon group, wherein the trivalent hydrocarbon group is substituted with one or more substituents selected from the group consisting of a halogen group, an alkyl group of 1 to 20 carbon atoms, a cycloalkyl group of 3 to 20 carbon atoms, an aryl group of 6 to 30 carbon atoms, and —R6COOR7, and wherein the unsubstituted divalent hydrocarbon group has 1 to 10 carbon atoms, where
• all R1 to R3 are not trivalent hydrocarbon groups;
• or unsubstituted divalent hydrocarbon groups at the same time,
• R4 is a single bond, an alkylene group of 1 to 20 carbon atoms, or a cycloalkylene group of 3 to 20 carbon atoms,
• R5 is a silyl group, halogen, a cyano group, or —COR8, wherein the silyl group is unsubstituted or substituted with an alkyl group of 1 to 20 carbon atoms,
• R6 is a single bond, an alkylene group of 1 to 20 carbon atoms, or a cycloalkylene group of 3 to 20 carbon atoms,
• R7 is an alkyl group of 1 to 20 carbon atoms, or a cycloalkyl group of 3 to 20 carbon atoms,
• and R8 is one selected from the group consisting of an alkoxy group of 1 to 10 carbon atoms, an aryl group of 6 to 30 carbon atoms, a heteroaryl group of 2 to 30 carbon atoms, a heterocycloalkyl group of 2 to 10 carbon atoms, a heteroamine group of 2 to 10 carbon atoms, and a disilylamino group of 3 to 10 carbon atoms.