A range of novel cationic star-like polymers (Star-P(MeDMA)s) were synthesized through atom transfer radical polymerization (ATRP) by core-first method, using a beta-cyclodextrin initiator with 21 initiation sites (21Br-beta-CD). Methyl chloride-quaternized 2-(dimethylamino)ethyl methacrylate (MeDMA) was polymerized in an aqueous medium using 21Br-beta-CD, Cu(I)Br, and 2,2'-dipyridyl as an initiator, catalyst, and ligand, respectively. The effects of polymerization temperature and monomer/initiator ratios on the degree and kinetics of polymerization were investigated. The molecular weights, hydrodynamic sizes, and charge densities of the quaternized polymers were characterized using gel permeation chromatography (GPC), dynamic light scattering (DLS), and colloidal titration, respectively. The results demonstrated that the moderate aqueous solubility of the 21Br-beta-CD initiator had significant impact on the physicochemical properties of the obtained star polymers. The polymerization of 500/1/2/5 ([M](0)/[I](0)/ [Cu(I)(0)/[L](0)]) at 90 degrees C for 6 h was found to be the best condition to synthesize the proposed cationic star polymer with well-defined structures in aqueous medium. The nonlinear relationship between the apparent charge density and the particle size of the cationic star polymers was further revealed by GPC and DLS measurements. (c) 2005 Wiley Periodicals, Inc.