The use of preformed poly(ethylene oxide) (PEO) and carboxyl-terminated polybutadiene (CTPB) for the preparation of block polymers is reported. Block polymerization was carried out by esterification and by coupling of equimolar amounts of these polymers with 2,4-toluene diisocyanate (TDI). When esterification was carried out, conversion of the two preformed polymers and block polymer composition varied with reaction temperature, catalyst used, and molecular weight of the PEO. Full conversions were not obtained. Better results were achieved when the preformed polymers were coupled with TDI. Tensile properties and water absorption capability of these block polymers were determined. Hydrogels with high water content up to 82% were obtained.