This work examines the scope and limitations of the cyanoxyl (OC=N)-mediated free-radical polymerization of acrylic acid (AA) with respect, to the criteria of livingness. Cyanoxyl persistent radicals were generated in situ through the reaction between arenediazonium salts (X-C(6)H(4)Nequivalent toN(circle plus)BF(4)(circle plus), where X is H, OCH3, Cl, or NO2) and sodium cyanate (NaOCN). This article thoroughly discusses the role played by such oxygen-centered radicals in the polymerization process; it. particularly focuses on the influence of the concentration and nature of the diazonium salt. the solvent, and the temperature on features such as the variations of In([M](0)/[M]) versus time (where [M](0) is the initial monomer concentration and [M] is the monomer concentration), the number-average molar mass versus conversion, and the polydispersity versus conversion in cyanoxyl-mediated free-radical polymerizations of AA. Cyanoxyl-terminated samples were used as macroinitiators for the polymerization of methyl methacrylate to generate poly(acrylic acid)-b-poly(methyl methacrylate) block copolymers. (C) 2004 Wiley Periodicals. Inc.