Styrene copolymer, thermoplastic resin composition, and method of preparing styrene copolymer and thermoplastic resin composition

A method of preparing a styrene copolymer, comprising:

• adding a reaction solution comprising 100 parts by weight of a monomer mixture comprising 35 to 65% by weight of a (meth)acrylate-based monomer, 10 to 30% by weight of a vinyl cyanide-based monomer, and 20 to 40% by weight of an aromatic vinyl-based monomer including an alkyl-substituted styrene;
• 100 to 200 parts by weight of a water-based solvent;
• and 0.1 to 10 parts by weight of a dispersant to a reactor to perform polymerization,
• wherein
• some of the aromatic vinyl-based monomer is fed into the reactor batchwise before start of the polymerization, and
• a remainder of the aromatic vinyl-based monomer is continuously fed into the reactor from a time point when a temperature of the reactor reaches 90 to 110° C. to perform the polymerization.