Method for producing copolymer, copolymer produced therefrom, and thermoplastic resin composition including the same

A method for producing a copolymer comprising step (S10) for adding aromatic vinyl-based monomers and vinyl cyan-based monomers to perform polymerization in the presence of polymerization initiators,

• wherein the polymerization initiators comprise at least two different kinds of polymerization initiators, and part of the aromatic vinyl-based monomers are continuously divisionally added while maintaining a constant rate during the polymerization in step (S10),
• wherein all the vinyl cyan-based monomers are added before the polymerization in step (S10),
• wherein the aromatic vinyl-based monomer comprises a styrene monomer substituted with an alkyl group, and
• wherein the polymerization initiators comprise t-butyl peroxybenzoate and at least one selected from the group consisting of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(t-butylperoxy-isopropyl)benzene, t-butyl cumyl peroxide, di-(t-amyl)-peroxide, dicumyl peroxide, butyl 4,4-di(t-butylperoxy)valerate, 2,2-di(t-butylperoxy)butane, t-amyl peroxy-benzoate, t-butylperoxy-acetate, t-butylperoxy-(2-ethylhexyl) carbonate, t-butylperoxy isopropyl carbonate, t-butyl peroxy-3,5,5-trimethyl-hexanoate, 1,1-bis(t-butylperoxy)cyclohexane, t-amyl peroxyacetate, t-amylperoxy-(2-ethylhexyl)carbonate, 1,1-di(t-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-di(t-amylperoxy)cyclohexane, t-butyl-monoperoxy-maleate and 2,2-bis(4,4-di-t-butylperoxycyclohexane)propane).