An ideal system for stimuli-responsive and amphiphilic (block) polymers would be the copolymerization of aziridines with epoxides. However, to date, no copolymerization of these two highly strained three-membered heterocycles had been achieved. Herein, we report the combination of the living oxy- and azaanionic ring-opening polymerization of ethylene oxide (EO) and sulfonamide-activated aziridines. In a single step, well-defined amphiphilic block copolymers are obtained by a one-pot copolymerization. Real-time 1H NMR spectroscopy revealed the highest difference in reactivity ratios ever reported for an anionic copolymerization (with r1 = 265 and r2 = 0.004 for 2-methyl-N-tosylaziridine/EO and r1 = 151 and r2 = 0.013 for 2-methyl-N-mesylaziridine/EO), leading to the formation of block copolymers with monomodal and moderate molecular weight distributions (Mw/Mn mostly ≤1.3). The amphiphilic diblock copolymers were used to stabilize emulsions and to prepare polymeric nanoparticles by miniemulsion polymerization, representing a novel class of nonionic and responsive surfactants. In addition, this unique comonomer reactivity of activated-Az/EO allows fast access to multiblock copolymers, and we prepared the first amphiphilic penta- or tetrablock copolymers containing aziridines in only one or two steps, respectively. These examples render the combination of epoxide and aziridine copolymerizations via a powerful strategy for producing sophisticated macromolecular architectures and nanostructures.