In the present work, the effectiveness of five trithiocarbonates (TTCs) as mediating agents in the reversible addition fragmentation chain transfer (RAFT) polymerization and photopolymerization of styrene (St) were investigated. The five TTCs including S,S'-bis(alpha, alpha'-dimethyl-alpha ''-acetic acid) trithiocarbonate (TTCI), bis(2-oxo-2-phenyl-ethyl) trithiocarbonate (TTC2), 3-(2-carboxyethylsulfanylthiocarbonlylsulfanyl)-propionic acid (TTC3), 2-(2-carboxyethylsulfanylthiocarbonlylsulfanyl)propionic acid (TTC4) , and 2-(2-carboxyethylsulfanylthiocarbonlylsulfanyl)-2-methylpropionic acid (TTC5) were were synthesized, in which the substitution patterns (groups Z and R) of the TTCs were varied. The dynamic behavior of TTC1, TTC2, TTC4, and TTC5-mediated polymerization of St was well described by pseudo first-order kinetics. In the presence of TTC1, TTC2, TTC4, and TTC-5, the polydispersity indices changed with increasing conversion in the range of 1.10-1.25 typical for RAFT-prepared (co)polymers, and were well below the theoretical lower limit of 1.50 for a normal free radical polymerization. Transfer coefficients of TTCs in St Polymerization at 70 degrees C were estimated by using the Mayo method. Density functional theory calculations successfully predicted the effect of the structure of TTCs on the activity of RAFT agents in a qualitative manner. The calculated results for RAFT agents agreed well with the experimental results. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2011-2017, 2009