Potassium diphenyl sulfonate (SSK), poly(sulfonyl phenylene phosphonate) (PSPPP), and their mixtures are proved to be effective flame-retardants for polycarbonates (PCs) by measuring the limited oxygen index values and UL-94 of blends. The flame-retardant systems are characterized by thermogravimetric analysis under dynamic conditions. The resulting data, together with the analysis of the activation energies, demonstrates that the additives accelerate thermodegradation, especially in the early stage, and different additives cause a different process in the final stage. (C) 2003 Wiley Periodicals, Inc.