FT-IR, UV–visible, ¹Н and ¹³C NМR spectroscopy, thermal and elemental analysis were used in the studies of thermo-oxidative polycondensation of 1,3-bis(4-aminophenoxy)benzene (TPER) in air; structure and properties of the obtained oligomers were investigated. It was demonstrated that prolonged heating of TPER in the temperature range from 180 to 350°C leads to the formation of oligomeric aromatic amines containing benzoid-quinoid sequences with benzoid type units significantly predominating.