The free radical polymerizations of methyl acrylate have been studied under gamma-ray irradiation in the presence of the dithiocarbamates with different N-groups. The results indicate that the conjugation structure of the N-group of dithiocarbamate plays an important role in living free radical polymerization. The polymerizations reveal good living characteristics in the presence of dithiocarbamates (benzyl 1H-imidazole-l-carbodithioate, benzyl 1H-pyrrole-l-carbodithioate, benzyl 1H-indole1-carbodithioate, and benzyl 9H-carbazole-9-carbodithioate) with N-aryl group. In contrast, the polymerization with benzyl N,N,N-diethyldithiocarbamate cannot be controlled, and the obtained polymer has a broad molecular weight distribution or even crosslink occurs. Moreover, polymerization rate is influenced by the conjugation structure of the N-group of dithiocarbamate, and the aromatic polycyclic structure of the N-group leads to slow polymerization. (C) 2004 Wiley Periodicals, Inc.