A poly(imide-amide) copolymer including a structural unit represented by Chemical Formula 1; a structural unit represented by Chemical Formula 2; and any one of a structural unit represented by Chemical Formula 3, an amic acid precursor of the structural unit represented by Chemical Formula 3, and a combination thererof; wherein a cured material of the poly(imide-amide) copolymer may have a tensile modulus of greater than or equal to about 5.5 GPa, and a yellowness index of less than or equal to about 5: wherein, groups and variables in Chemical Formulae 1 and 3 are the same as described in the specification.