2-Mercapto thioxanthone (TX-SH) was used as a chain transfer agent in free-radical polymerization of methyl methacrylate (MMA) and styrene (St), by using 2,2-azobisisobutyronitrile (AIBN) as an initiator at 70 degrees C. Chain transfer constants were found to be 1.41 and 0.12 for St and MMA, respectively. The use of TX-SH as a chain transfer agent leads to the formation of polymers with thioxanthone (TX) end groups. The incorporation TX moiety was confirmed by spectral measurements. Polymers obtained this way were used as triplet photosensitizer in free-radical polymerization of MMA in the presence of a hydrogen donor such as N-methyldiethanolamine (MDEA). (c) 2006 Wiley Periodicals, Inc.