The photodecomposition products of (diacetoxyiodo)benzene (DAI) and [bis(trifluoroacetoxy)iodo]benzene (BTI) were found to be efficient initiators for the homopolymerizations of 2-(dimethylaminoethyl)methacrylate (DMAEM) and methyl methacrylate (MMA) and also the copolymerizations of DMAEM with MMA or styrene (St). A free radical mechanism was confirmed. Copolymerization constants for DMAEM-MMA and DMAEM-St were determined ( r DMAEM = 0.35 ± 0.08, r MMA = 0.57 ± 0.08; r DMAEM = 0.14 ± 0.01, r St = 0.20 ± 0.01) and are discussed. DAI and BTI are also cationic photoinitiators for i-butyl vinyl ether (BVE). The efficiencies of DAI and BTI as photoinitiators for radical or cationic polymerization depend on the properties of the solvents and monomers.