Novel polyfunctional macroinitiators for atom transfer radical polymerization (ATRP) were obtained via esterification of hyperbranched polyglycerol (PG) (Mn = 4 770 g/mol, Mw/Mn = 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 1H NMR, 13C NMR, SEC, membrane osmometry and DSC.