Deoxybenzoin-based copolymers containing various relative ratios of arylate and phosphonate units in the backbone were synthesized by solution polycondensation. These copolymers were characterized by gel permeation chromatography, Fourier Transform infrared spectrometry, and proton, carbon, and phosphorous nuclear magnetic resonance spectroscopy (H-1, C-13, and P-31 NMR). Pyrolysis combustion flow calorimetry (PCFC) performed on these copolymers revealed their very low heat release capacity, making them attractive for applications in which halogen-free, low flammability materials are desired. Integration of phosphonate units into the polymer backbone is advantageous for achieving high molecular weight polymers with solution processbility while retaining the low flammability inherent to deoxybenzoinbased polymers. Char yields greater than 50% and heat release capacities of 40-60 J/ g K, were observed for these copolymers by PCFC. 2007 Wiley Periodicals, Inc.