Method for preparing conjugated diene-based copolymer, conjugated diene-based copolymer prepared therefrom, rubber composition comprising the same

A method for preparing a conjugated diene-based copolymer comprising:

• (S10) performing emulsion polymerization on an α-methylstyrene monomer, a conjugated diene-based monomer, and a hydroxyalkyl(meth)acrylate monomer,
• wherein the α-methylstyrene monomer and the conjugated diene-based monomer are added together at one time when a polymerization conversion ratio of the emulsion polymerization is 0%, and the hydroxyalkyl(meth)acrylate monomer is divisionally added two or more times when the polymerization conversion ratio of the emulsion polymerization is 0% to 80%, and
• the α-methylstyrene monomer is added in an amount of 10% by weight to 50% by weight, the conjugated diene-based monomer is added in an amount of 49% by weight to 89% by weight, and the hydroxyalkyl(meth)acrylate monomer is added in an amount of 0.1% by weight to 5% by weight, based on the total monomer amount,
• wherein an amount of the hydroxyalkyl(meth)acrylate monomer-derived repeating unit is maintained within a range of 0.1% by weight to 5% by weight based on the total amount of the respective conjugated diene-based copolymers according to the polymerization conversion ratio of the emulsion polymerization, and
• wherein the hydroxyalkyl(meth)acrylate monomer comprises hydroxypropyl(meth)acrylate or hydroxybutyl(meth)acrylate.