The synthesis of a carboxy-functionalized nitroxide based on the 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy (TIPNO) structure and the synthesis of two difunctional alkoxyamines have been achieved. Because of the presence of the carboxylic acid function, the nitroxide is organo-soluble in its acidic form and water-soluble in its basic form. Polymerizations of styrene and n-butyl acrylate mediated with the functional nitroxide exhibited all the expected features of a controlled system. The presence of an active chain end was demonstrated by reinitiation of a polystyrene block to form a polystyrene-b-poly(n-butyl acrylate) block copolymer. The ability of the new functional nitroxide to mediate polymerization in homogeneous aqueous solution has also been demonstrated. The polymerization of sodium styrenesulfonate was successfully achieved at temperatures below 100 degrees C and led to well-defined polymers, providing the first example of nitroxide-mediated radical polymerization (NMP) in homogeneous aqueous solution below the water boiling point.