The synthesis of three different poly(ethylene oxide) macromonomers with a norbornene and oxanorbornene end group is presented. The macromonomers were polymerized to comb-polymers by ring-opening metathesis polymerization (ROMP) using Grubbs' Catalyst G3 to produce water soluble polymers with polydispersities between 1.04 and 1.30 and molecular weights between 14,000 and 50,000 g/mol. Characterization by static and dynamic light scattering reveals that the comb-polymers with norbornene backbone are molecularly disperse in aqueous solution, while the oxanorbornene-backbone polymers form small water-soluble aggregates. (c) 2008 Wiley Periodicals, Inc.