Novel polyfunctional macroinitiators for atom transfer radical polymerization (ATRP) were obtained via esterification of hyperbranched polyglycerol (PG) (M-n = 4 770 g/mol, (M) over bar(w)/(M) over bar(n) = 1.5) with 2-bromoisobutyryl bromide. Such macroinitiators were used in the presence of CuBr/pentamethyldiethylenetriamine (PMDETA) to initiate methyl acrylate (MA) polymerization, resulting in multi-arm block copolymers with polyether core and 45-55 PMA arms. PMA arm length was controlled via monomer/initiator ratio and conversion (<35%). Polymers were characterized by H-1 NMR, C-13 NMR, SEC, membrane osmometry and DSC.