A polymer represented by the following formula (11): ##STR54## wherein R1 is a hydrogen atom, an alkyl group or a halogen atom, and R2 is X--Ar1 ; X is NH, O or S, and Ar1 is a substituted or unsubstituted aromatic ring having a partial structure as set forth in formula (2): ##STR55## or a substituted or unsubstituted heterocyclic ring; each of R3 and R4 is a hydrogen atom, an alkyl group, a subst