Method for preparing graft copolymer and graft copolymer

A method for preparing a graft copolymer, the method comprising:

• 1) preparing a seed by adding a crosslinking agent, a grafting agent, one or more selected from the group consisting of an alkyl (meth)acrylate-based monomer, an aromatic vinyl-based monomer, and a vinyl cyan-based monomer and carrying out polymerization;
• 2) preparing a core in the presence of the seed by adding an alkyl (meth)acrylate-based monomer, a crosslinking agent and a grafting agent and carrying out polymerization;
• and
• 3) preparing a shell in the presence of the core by adding an aromatic vinyl-based monomer and a vinyl cyan-based monomer and carrying out polymerization,
• wherein an activator including a compound represented by Chemical Formula 1 is added in 3), and wherein the core has an average particle diameter of 320 nm to 520 nm;
• In Chemical Formula 1,
• R1 and R2, which are the same or different from each other, are each independently hydrogen, a C1-C10alkyl group, or *-(C=O)OM2, provided that R1 and R2 are not both hydrogen, and
• M1 and M2, which are the same or different from each other, are each independently an alkali metal.