Poly(amide-imide) copolymer, method of preparing poly(amide-imede) copolymer, and article including poly(amide-imide)copolymer

Provided are a poly(imide-amide) copolymer prepared by making diamine, which contains an oligomer comprising an amide structure unit represented by chemical formula 1, react with dianhydride represented by chemical formula 3; a method for preparing the copolymer; a molded product containing the copolymer; and a display device including the molded product. In the chemical formula 1 and the chemical formula 3, R1, R2, Ar1, Ar2, n0, R10, R12, R13, n7, and n8 are the same as defined in a detailed description of the present invention. According to the present invention, high optical properties and mechanical properties are ensured.