A monomer is represented by Chemical Formula 1: wherein in Chemical Formula 1, X1 and X2 are independently O, C(═O), or C(═O)O, R1 to R10 are independently hydrogen, a substituted or unsubstituted C1 to C20 alkyl group, a substituted or unsubstituted C1 to C20 alkoxy group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, a substituted or unsubstituted C3 to C20 heterocyclic group, a substituted or unsubstituted silyl group, a hydroxy group, a halogen, a nitro group, or a combination thereof, and n1 and n2 are independently an integer ranging from 0 to 3.