We describe the preparation of a new set of amphiphilic block copolymers with well-defined molecular weights and block volume fractions. The synthesis of a variety of polyalkane-poly(ethylene oxide) block copolymers was accomplished by a new polymerization - hydrogenation sequence. Initially, anionic polymerization of either butadiene or isoprene was performed followed by end capping with ethylene oxide. The resulting hydroxyl-terminated polydienes were catalytically hydrogenated to give the corresponding hydroxyl-terminated polyalkanes. These polymeric alcohols were then titrated with potassium naphthalenide to yield the analogous potassium alkoxides. This type of macroinitiator was employed in the polymerization of ethylene oxide. Seventeen polyalkane - poly(ethylene oxide) block copolymers were prepared in near quantitative yields with molecular weights ranging from (1.4 to 8.7) × 10 3 and poly(ethylene oxide) volume fractions ranging from 0.29 to 0.73. These polymers are model materials for block copolymer phase behavior studies.