We demonstrated that density functional theory calculations provide a prediction of the trends in C-S bond dissociation energies and atomic spin densities for radicals using two model compounds as diethyldithiocarbamate (DC)-mediated iniferters. On the basis of this information, we synthesized 2-(N,N-diethyldithiocarbamyl)isobutylic acid (DTCA) and (4-cyano-4-diethyldithiocarbamyl)pentanoic acid (CDPA) as DC-mediated iniferters. Free-radical polymerizations of styrene (St) were carried out in benzene initiated by DTCA or CDPA under UV irradiation. The first-order time-conversion plots showed the straight line for the UV irradiation system initiated by CDPA indicating the first order in monomer. The number-average molecular weight (M-n) of the polystyrene (PSt) increased in direct proportion to monomer conversion. The molecular weight distribution (M-w/M-n) of the PSt was in the range of 1.3-1.7. It was concluded this polymerization system proceeded with a controlled radical mechanism. However, photopolymerization of styrene initiated by DTCA showed non-living polymerization consistent with UV initiation. Theoretical predictions supported these experimental results. Methacrylic acid (MA) could also be polymerized in a living fashion with such a PSt precursor as a macroinitiator because PSt exhibited a DC group at its terminal end. This system could be applied to the architecture of block copolymers. (C) 2004 Wiley Periodicals, Inc.