Abstract: The present disclosure relates to a depolymerization method of a polymer comprising an ester functional group with or without pigments or dyes, a composition for the depolymerization, and a purification method for selectively separating foreign substances from a monomer of the polymer, and is characterized in that a compound represented by formula 1 is added as an additive. The depolymerization method according to the present disclosure enables depolymerization at low temperatures and may increase the yield of a target product. In addition, the purification method according to the present disclosure may remove foreign substances including pigments or dyes from a monomer of the polymer to prepare high-purity monomers.