The controlled free-radical polymerization of methacrylic acid was performed at 73 and 83 degrees C using a methacrylic acid-based alkoxyamine and the nitroxide SG1 as a mediator in the presence of a small concentration of styrene, without protection of the carboxylic acid groups. The solvent was 1,4-dioxane or ethanol, and no chain transfer to the solvent could be detected. Because of the presence of styrene, the polymerization exhibited the characteristics of a living one. In particular, the polymers could be chain-extended and were used as efficient macroinitiators in the polymerization of styrene, allowing well-defined, amphiphilic diblock copolymers to be synthesized.