Four new structures (o,o-diethyl dithiobisthioformate, isopropylxanthic disulfide, tetrainethy1dicarbonotrithioic diamide, and phenylacetyl disulfide) are proposed as photoiniferters far controlled photopolymerization reactions. Their photochemical properties, efficiency in controlling the photopolymerization of methyl methacrylate (MMA), and ability to photocrosslink a difunctional acrylate monomer [1,6-hexane diol diacrylate (HDDA)] are investigated. The rates of polymerization of MMA and HDDA and the number-average molecular weights (M.'s) and polydispersity indices (PDIs) of poly(methyl methacrylate) have been determined. The transient absorption spectra and interaction rate constants of the radicals have been measured. Both the (alkyloxythiocarbonyl)thiyl and (benzylcarbonyl)thiyl radicals are efficient in controlling a photopolyinerization process. For a 40% monomer conversion obtained in a few minutes, the M. values range from 6000 to 14,000, and the PDIs can reach 1.6-2.2. A fivefold reduction of the light intensity increases Ma by 25% and reduces PDI by 5%. (C) 2007 Wiley Periodicals, Inc.