A thermosensitive copolymer may include a first repeating unit having a temperature-sensitive oligomer and a second repeating unit having an ionic moiety and a counter ion to the ionic moiety. The temperature-sensitive oligomer may be an oligomer including a repeating unit derived from a unsaturated monomer with a moiety represented by Chemical Formula 1 or Chemical Formula 2, or an oligomer including a repeating unit derived from a heterocyclic compound having C, N, O, and a C═N bond in its ring. *—C(═O)N(R2)(R3)  [Chemical Formula 1] R2 and R3 may each independently be hydrogen or a linear or branched C1 to C6 alkyl group, a C3 to C7 cycloalkyl group, or a C6 to C10 aryl group, R2 and R3 may not both be hydrogen, and R2 and R3 may be combined to form a nitrogen containing heterocycle. R4 may be a C2 to C5 alkylene group.