Background: Controlled/'living' radical polymerization is a new and robust method to synthesize polymers with predetermined molecular weight, narrow polydispersity and tailored architecture. Several methods have been developed but reversible addition-fragmentation chain transfer (RAFT) has several advantages over the other methods. It has been reported that the effectiveness of RAFT agents depends strongly on the nature of the Z and R groups. Results: Three new dithiocarbamates, namely (2-ethoxy carbonyl)-prop-2-yl-pyrrole-1-carbodithioate (CTA-A), (1-phenyl ethyl) -pyrazole-1-carbodithioate (CTA-B) and (2-ethoxy carbonyl)-prop-2-yl-pyrazole-1-carbodithioate (CTA-C), were synthesized for studying the effect of the Z and R group of a chain transfer agent on the RAFT polymerization of styrene, initiated by 2,2′-azobisisobutyronitrile. Well-controlled molecular weight with narrow polydispersity (1.10-1.46) was achieved. The increase in molecular weight with conversion is linear and follows first-order kinetics. Conclusion: The detailed kinetic results show that the structure of the activating (Z) group of dithiocarbamates has significant effects on the reactivity of dithiocarbamates towards the polymerization of styrene. In the homopolymerization of styrene it was found that, from the polydispersity index of polystyrenes obtained and the kinetic results, the pyrazole-based dithiocarbamates (CTA-B and CTA-C) are very effective compared to the pyrrole-based dithiocarbamate (CTA-A). All the polymerizations show controlled living characters. © 2007 Society of Chemical Industry.