The one-pot synthesis of a new anionic polyelectrolytic macroinitiator based on esterification of a poly(glycerol monomethacrylate) precursor is described. Electrostatic adsorption of this macroinitiator onto an aminated (cationic) planar substrate is monitored by dual polarization interferometry. Controlled surface-initiated polymerization of five hydrophilic methacrylic monomers from this macroinitiator adsorbed onto aminated silicon wafer surfaces is achieved by atom transfer radical polymerization (ATRP) in protic media. The thickness, uniformity, and hydrophilicity of the resulting polymer brushes are characterized by ellipsometry, atomic force microscopy and contact angle studies, and the hydrophilic surface polymerization kinetics is modeled. Microcontact printing is used to produce patterned surfaces with micrometer-sized features. In summary, polyelectrolytic macroinitiators allow the facile synthesis of well-defined polymer brushes on commercially relevant metal oxide surfaces.