Hyperbranched polymethacrylates were prepared by means of oxyanionic vinyl polymerization of commercially available monomers, including hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEG-MA). Hyperbranched polymethacrylates with high molecular weight were obtained with the complex of potassium hydride and 18-crown-6 as the initiator. The effect of 18-crown-6 is very important, and only oligomer can be obtained in the polymerization without 18-crown-6. The molecular structure of the hyperbranched polymers was confirmed with H-1 NMR and C-13 NMR spectra. The ratio of initiator to monomer significantly affects the architecture of the resultant polymers. When the ratio of initiator to monomer equals 1 in the oxyanionic vinyl polymerization of HEMA, the degree of branching of the resulting polymer was calculated to be around 0.49. (c) 2005 Wiley Periodicals, Inc.