ortho-Quinones, such as phenanthrenequinone and 3,6-dimethoxyphenanthrenequinone, added with a catalytic amount of metal complexes, impart control to styrene polymerization via the previously reported quinone transfer radical polymerization (QTRP) process. In this study, compounds that mimic the dormant species proposed in the QTRP mechanism have been synthesized and tested as initiators in the presence of cobalt(II) acetylacetonate. These compounds, and particularly 3,6-dimethoxy-10-hydroxy-10-(l-phenyl-ethyl)-phenanthren-9-one, are effective control agents for the radical polymerization of styrene, in agreement with the recently proposed mechanism. Moreover, the induction period, which has been systematically reported in the presence of ortho-quinones, is no longer observed. The end capping of the polystyrene chains by the control agent has been confirmed by H-1 NMR analysis. (c) 2005 Wiley Periodicals, Inc.