The use of DMSO as solvent for transition metal mediated living radical polymerization was investigated using copper (I) bromide/N-(n-propyl)-2-pyridyl-methanimine catalyst system and ethyl-2-bromoisobutyrate as initiator. The best conditions for polymerization in DMSO of different methacrylates (MMA, BMA, DMAEMA, HEMA) were determined. In all cases, the measured number-average molar mass of the product increased linearly with monomer conversion in agreement with the theoretical M-n with low polydispersity products (1.16 < PDI < 1.4) achieved. Solvent was found to play a crucial role in the process. The effect of the polar solvent has been investigated and it was shown that DMSO could coordinate copper (II), increasing the activation process, or copper (I), changing the nature of the copper catalyst by competitive complexation of ligand and DMSO. (C) 2004 Wiley Periodicals, Inc.