A series of waterborne polyurethanes (WPUs) with different contents of reactive organophosphonate were well prepared. Their structures were characterized by Fourier transform infrared and H-1-NMR spectroscopy. Thermogravimetry and derivative thermogravimetry revealed that the WPU films containing phosphorus possessed lower onset and maximum degradation temperatures but higher char yields. Differential scanning calorimetry analysis suggested phase mixing of the hard and soft domains. The mechanical properties decreased with increasing amount of organophosphonate, whereas the limiting oxygen index results of the WPU films indicate that the flame retardancy was improved significantly by the incorporation of organophosphonate. The water uptake values of the organophosphonate-containing WPU films were higher than those of the phosphorus-free ones, whereas the static contact angles of the films indicated that the surface hydrophilic properties were not affected by segmenting in this phosphorus-containing oligomer. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110:3107-3115,2008