The use of the polyiminophosphazene base t-Bu-P-4 (1) for the anionic polymerization of ethylene oxide is described. Polymerization initiated by a monoalkoxide of the protonated base leads to well-defined poly(ethylene oxide)s with low polydispersity (<(M)over bar (w)>/<(M)over bar (n)> approximate to 1.1). Furthermore, graft copolymers of poly[ethylene-co-(vinyl alcohol)] (PEVA) with poly(ethylene oxide) and a star macromolecule were synthesized from multifunctional polyalkoxides in high yields.