The Cu(0)-mediated single electron transfer-living radical polymerization (SET-LRP) of methyl methacrylate (MMA) using ethyl 2-bromoisobutyrate (EMB) as an initiator with Cu(0)/N,N,N',N '',N ''-pentamethyldiethylenetriamine as a catalyst system in 1,1,1,3,3,3-hexafluoro-2-propanoI (HFIP) was studied. The polymerization showed some living features: the measured number-average molecular weight (M-n,GPC) increased with monomer conversion and produced polymers with relatively low polydispersities. The increase of HFIP concentration improved the controllability over the polymerization with increased initiation efficiency and lowered polydispersity values. H-1 NMR, MALDI-TOF-MS spectra, and chain extension reaction confirmed that the resultant polymer was end-capped by EBiB species, and the polymer can be reactivated for chain extension. In contrast, in the cases of dimethyl sulfoxide or N,N-dimethylformamide as reaction solvent, the polymerizations were uncontrolled. The different effects of the solvents on the polymerization indicated that the mechanism of SET-LRP differed from that of atom transfer radical polymerization. Moreover, HFIP also facilitated the polymerization with control over stereoregularity of the polymers. Higher concentration of HFIP and lower reaction temperature produced higher syndiotactic ratio. The syndiotactic ratio can be reached to about 0.77 at 1/1.5 (v/v) of MMAIHFIP at -18 degrees C. In conclusion, using HFIP as SET-LRP solvent, the dual control over the molecular weight and tacticity of PMMA was realized. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6316-6327, 2009