Poly(ethylene oxide) (PEO) macromonomers carrying a methyl, n-butyl, tert-butyl, n-octyl, or n-octadecyl group as the ω-end and a p-vinylbenzyl or methacryloyl group as the α-end were prepared, and their radical polymerizations in water were found to occur unusually rapidly as a result of their organization into micelles. The micelle sizes were estimated by laser light scattering measurements. Significant effects of ω-alkyl groups and the PEO chain lengths on the polymerizability were observed