Poly(ethylene glycol) allenyl methyl ether (2) was prepared by the reaction of poly(ethylene glycol) monomethyl ether (the number average molecular weight (M(n)) = 550) with propargyl bromide, followed by the base-catalyzed isomerization reaction. Functionality of end-allenyl groups in the obtained macromonomer was determined as 92% (from H-1-NMR). The radical polymerization of 2 was carried out in bulk and in benzene at 60 or 120 degrees C to yield a polymer with poly(ethylene glycol) side chains. For instance, a polymer (3, M(n) = 3900) was obtained in 39% yield by the polymerization of 2 in bulk at 60 degrees C for 48 h using 6 mol% of alpha,alpha＇-azobisisobutyronitrile (AIBN). The obtained polymer was soluble in organic solvents as well as water.