Two polyphosphonates having multiple flame-retardant actions were synthesized by interfacial polycondensation of a bisphenol and dichlorophenylphosphine oxide using cetyl trimethyl ammonium chloride as a phase transfer catalyst (PTC) at 0 degreesC. The polyphosphanates thus prepared were characterized by viscometry, elemental analysis, IR, H-1-NMR, P-31-NMR, and X-ray diffraction studies. These polymers are highly soluble in polar solvents such as DMF, DMAc, DMSO, etc., as well as in chlorinated hydrocarbon solvents such as CH2Cl2, CHCl3, etc. The thermal study of polymers was carried out by TGA and DTA analyses. The flammability of the polymers was studied by the limiting oxygen index measurements. The polymers are self-extinguishing, and begin to lose weight at around 252 degreesC.