Method of preparing graft copolymer and method of preparing thermoplastic resin composition including the same

A method of preparing a thermoplastic resin composition, the method comprising:

• adding a polymer particle diameter control agent to a conjugated diene rubber latex to prepare an enlarged conjugated diene rubber latex;
• graft-polymerizing the enlarged conjugated diene rubber latex with an aromatic vinyl compound and a vinyl cyanide compound to prepare a vinyl cyanide compound-conjugated diene compound-aromatic vinyl compound graft copolymer;
• and
• feeding the prepared vinyl cyanide compound-conjugated diene compound-aromatic vinyl compound graft copolymer and an aromatic vinyl compound-vinyl cyanide compound copolymer into an extruder and melt-kneading the same, followed by extrusion,
• wherein the polymer particle diameter control agent is a copolymer comprising:
• 0.1 to 10% by weight of methyl acrylate, 0.1 to 10% by weight of ethyl acrylate, 70 to 85% by weight of butyl acrylate, and 1 to 18% by weight of (meth)acrylic acid;
• a copolymer comprising 75 to 95% by weight of ethyl acrylate, 0.01 to 10% by weight of butyl acrylate, 0 to 10% by weight of methyl acrylate, and 1 to 18% by weight of (meth)acrylic acid;
• a copolymer comprising 82 to 99% by weight of methyl acrylate and 1 to 18% by weight of (meth)acrylic acid;
• or
• a copolymer comprising 0.01 to 10% by weight of methyl acrylate, 75 to 95% by weight of ethyl acrylate, 0.01 to 10% by weight of butyl acrylate, and 1 to 18% by weight of (meth)acrylic acid;
• the polymer particle diameter control agent has a glass transition temperature of 0.5 to 9.6° C., and
• a ratio (PS1/PS2) of an average particle diameter (PS1) of the polymer particle diameter control agent to an average particle diameter (PS2) of the conjugated diene rubber latex is 0.88 to 1.13, and
• wherein an impact strength of the thermoplastic resin composition measured according to ASTM D1238 using a specimen of the thermoplastic resin composition with a thickness of ¼″ is 27 kgf·cm/cm or more.