Abstract Polyureas with the dibenzylic system on the macromolecular chain are considered. The behaviour of these polyureas during cyclization with oxalyl chloride, leading to polyparabanic derivatives, was studied. The influences of polymer structures and reaction conditions on the heterocyclization is discussed. All the polymers were characterized by elemental analyses, inherent viscosities, i.r. spectra and thermogravimetric analyses.