Radical copolymerizabilities of poly(ethylene glycol) allenyl methyl ether (2a and 2b, the number average molecular weight (M(n)) = 390 and 590, receptively) were evaluated by the copolymerization with styrene monomer (St). The relative reactivities of macromonomers have been decreased as the length of the oxyethylene side chains in the macromonomer increased, and were estimated to be r(1) = 2.5 +/- 0.1, r(2) = 0.96 +/-0.2 for 2a and r(1) = 1.4 +/- 0.1, r(2) = 2.4 +/- 0.3 for 2b.