Sulfonation reactions have been developed that convert aryloxy or arylamino groups linked to phosphazenes to the arylsulfonic acid derivatives. The reactions were developed at three levels-first, with small-molecule phosphazene cyclic trimers; second, with phosphazene high polymers in the solution state; third, at the surfaces of solid polyphosphazenes. The reagents employed included concentrated H2SO4, fuming H2SO4, and ClSO3H. Molecular level products were studied by 31P, C-13, and H-1 NMR spectroscopy, while the surface-reacted materials were examined by XPS, SEM, ATR-IR, contact angle, and optical microscopy. This chemistry is of broad utility for the preparation of hydrophilic and hydrogel surfaces on polymers and for the development of biocompatible or antibacterial materials.