A graft copolymer (C) having a main chain portion of a precursor polymer (A) and a graft portion from a polymer (B), wherein a core portion of the solid product comprises the main chain portion derived from (A), a shell portion comprises the graft portion derived from (B), and the solid product satisfies: Infrared absorption spectroscopic measurement of a section passing through a center (x) of the solid product, a point (z) on a surface where a distance between the center (x) and the surface is shortest, and a middle point (y) of a line connecting the center (x) and the point (z), absorbance (Abs) satisfies X<0.01, Y<0.01, and Z0.01, wherein X, Y, and Z represent values of Abs (key band of the polymer (B))/Abs (key band of the polymer (A)) at the center (x), the middle point (y) and the point (z).