A series of polymeric flame retardants (PFRs) containing phosphorus-nitrogen-bromide were synthesized from spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride (SPDPC), 2-methoxyl-4,6-dichloro-1,3,5-triazine (MDCT), and tetrabromobisphenol A (TBBPA). The influence of monomer ratio on their thermal stability was investigated by adjusting the proportion of SPDPC/MDCT (mol/mol) from 80/20 to 20/80. The flammability properties of the PFRs blended with ABS were evaluated using LOI and UL-94 vertical test. The structures of the flame retardants were characterized by means of Fourier transform infrared spectra (FTIR) and proton nuclear magnetic resonance spectroscopy (H-1-NMR). The results show that the initial temperature of decomposition is 274 degrees C and with 35% charring residue at 500 degrees C when the ratio of SPDPC/MDCT is 50/50. V-0 ratings in the UL-94 vertical test were achieved at 20-30% loading of PFRs, when LOI values reached at least 26.9%. The flame retardancy is strongly dependent on the ratio of P, N, and Br. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 957-962, 2010