Block polymers of AB, BAB, and ABA type, derived from preformed poly(ethylene oxide) (PEO) of different molecular weight and hydroxy-terminated polybutadiene (HTPB) were prepared. Poly(ethylene oxide-b-butadiene) and poly(butadiene-b-ethylene oxide-b-butadiene) were prepared by reaction of PEO, which was previously endcapped with TDI, with HTPB at a 1:1 or 1:2 reactants molar ratio. Poly(ethylene-oxide-b-butadiene-b-ethylene oxide) were prepared by reaction of isocyanate-endcapped HTPB with PEO at a molar ratio of reactants of 2:1. High reaction yields were obtained. Correlation between tensile properties and water absorption with block polymer composition was found.