Grafting of tert.-butyl acrylate (tBuA), methyl methacrylate (MMA), and styrene (St) monomers (M) by Cu(I)-mediated ATRP from polystyrene (PSt) macroinitiator (M-n = 5620, polydispersity index, PDI = 1.12), containing initiating 2-bromopropionyloxy groups (1) (bound to 34% of aromatic cores; 11 groups per backbone), was performed using conditions suitable for the respective homopolymerizations. The preparation of PSt-g-PtBuA in bulk using an initial molar ratio [M](0)/[I](0) = 140 had a controlled character up to M-n = (1.32-148) X 10(3) (PDI = 1.08-1.16). With MMA and St and using the same [M](0)/[I](0), preliminary experiments were made; the higher the monomer conversion, the broader was the distribution of molecular weight of the products. Graft copolymerizations of all these monomers at [M]0/[l]0 = 840 or 1680 were successfully conducted up to high conversions. Low-polydispersity copolymers, with very long side chains, in fact star-like copolymers, were obtained mainly by tuning the deactivator amount in the reaction mixture. (PSt-g-PtBuA, DPn,sc (DP of side chain) = 665, PDI = 1.24; PSt-g-PMMA, DPn,sc = 670, PDI = 1.43; PSt-g-PSt, DPn,sc = 324, PDI 1.11). Total suppression of intermolecular coupling was achieved here. However, the low concentrations of initiator required long reaction times, leading sometimes to formation of a small amount (similar to 5%) of low-molecular-weight polymer fraction. This concomitant process is discussed, and some measures for its prevention are proposed. (c) 2006 Wiley Periodicals, Inc.