Two different polyurethane-based macromonomers, a polyurethane macromonomer with methacrylamide (PUM-M) and a polyurethane macromonomer with acrylamide (PUM-A), were synthesized from poly(ethylene glycol)s (PEGs) of various molecular weights and two different amides, methacrylamide and acrylamide, and they were used for the dispersion polymerization of styrene. The structures of the macromonomers and polystyrene (PS) particles were verified with C-13-NMR and Fourier transform infrared. The weight-average molecular weights of the PS particles increased with the macromonomer concentration but decreased with the PEG molecular weight. The average diameter of the PS particles increased with the PEG molecular weights but decreased with the macromonomer concentration. The thermal stability of PUM-A-PS was enhanced, and its grafting ratio with 30 wt % PUM-A was much higher than that of PUM-M-PS. Thus, this study suggested that the polyurethane-based macromonomers act not only as reactive stabilizers but also as grafting agents in the dispersion polymerization. In addition, the acrylamide end group provided better thermal stability than methacrylamide. (C) 2008 Wiley Periodicals, Inc.