A thermosetting resin including at least one repeating unit represented by the following Chemical Formula 1: wherein, in Chemical Formula 1, A is derived from a phenolic moiety, an anilinic moiety, or a combination thereof, L is C(O)O, C(O)NR′ wherein R′ is hydrogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C6 to C30 aryloxy group, an aromatic ester, an aromatic ester-imide, an aromatic ester-amide, an aromatic amide, or a combination thereof, Z is a substituted or unsubstituted aliphatic group including a double bond or a triple bond, a substituted or unsubstituted alicyclic group including a double bond or a triple bond, a substituted or unsubstituted aryl group including a double bond or a triple bond, (iso)cyanate, a derivative thereof, or a combination thereof, and n is an integer ranging from 1 to about 4.