Thermoplastic resin composition, method of preparing the same, and molded article manufactured using the same

A method of preparing a thermoplastic resin composition, comprising:

• suspension-polymerizing a polymerization solution prepared by mixing 100 parts by weight of a monomer mixture comprising a (meth)acrylate-based monomer, an aromatic vinyl-based monomer, and a maleimide-based monomer, 100 to 200 parts by weight of a reaction solvent, 0.01 to 1 part by weight of an initiator, 1 to 5 parts by weight of a dispersant, and 0.01 to 1 part by weight of a molecular weight regulator to form a polymerization slurry;
• adjusting a pH of the polymerization slurry to 1 to 4 and preparing a styrene-based copolymer;
• and
• mixing 65 to 85% by weight of the styrene-based copolymer, 10 to 30% by weight of a first graft copolymer comprising a first acrylic-based rubber polymer, and 1 to 15% by weight of a second graft copolymer comprising a second acrylic-based rubber polymer and performing kneading and extrusion at 200 to 270° C.,
• wherein the styrene-based copolymer has a residual oligomer content of 0.37% by weight or less, and
• the first acrylic-based rubber polymer and the second acrylic-based rubber polymer of the second graft copolymer have different average particle diameters.