A poly(imide-amide) copolymer includes: an imide structural unit which is a reaction product of a first diamine and a dianhydride, and an amide structural unit which is a reaction product of a second diamine and a diacyl halide, wherein each of the first diamine and the second diamine includes 2,2′-bis-trifluoromethyl-4,4′-biphenyldiamine, and at least one of the first diamine and the second diamine further includes a compound represented by Chemical Formula 1, wherein the dianhydride includes 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-hexafluoroisopropylidene diphthalic anhydride, wherein the diacyl halide includes terephthaloyl chloride (TPCI), and wherein an amount of the compound represented by Chemical Formula 1 is less than or equal to about 10 mole percent based on the total amount of the first diamine and the second diamine: NH2-A-NH2  Chemical Formula 1 wherein in Chemical Formula 1, A is the same as described in the detailed description.