Prepolymers of poly(ethylene oxide) (Pre-PEG) were synthesized by reacting azoisobutyronitrile (AIBN) with poly(ethylene glycol) (PEG), and their structures were characterized by IR and UV. The molecular weight of pre-PEG was related to the feed ratio and reaction time. These prepolymers can be used to prepare block copolymers - poly(ethylene oxide)-block-poly(butyl acrylate) (PEO-b-PBA) by radical polymerization in the presence of butyl acrylate (BA). Solution polymerization was a suitable technique for this step. The yield and the molecular weight of the product were related to the ratio of the prepolymer to BA, the reaction time, and temperature. GPC showed that the molecular weight increased with a higher ratio of BA to pre-PEO. The intrinsic viscosity of the copolymers was only slightly dependent on reaction time, but decreased at higher reaction temperatures, as did the amount of PEA homopolymer.