Polyetherols containing a thermally stable pyrimidine ring were obtained upon the reaction of hydroxymethyl derivatives of barbituric acid with an excess of ethylene or propylene oxide. The reaction was monitored by H-1-NMR and IR spectroscopy for the systems with variable starting molar ratios of reagents. We found that formaldehyde rearranged from N-hydroxymethyl and oxymethylene bridges into the end of the polyetherol chain during the reaction. Simultaneously, the O-hydroxymethyl groups underwent blocking by oxirane. The structures of the polyetherols was deduced on the basis of the course of the reaction and the analytical data. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1601-1606, 2009