“…4,9 We have developed new monomers and initiator-systems during the last few years, expanding this still rather unexplored approach to polysulfonamides and amines. [5][6][7][8]15,16 With a similar ring-strain of 111 kJ mol −1 for ethylene imine as for ethylene oxide (114 kJ mol −1 ), the anionic ringopening polymerization should be feasible. 17,18 In contrast to unsubstituted ethylene imine, which can only be polymerized via a cationic mechanism, leading to branched PEI ( poly(ethylene imine)), 19 N-protected aziridines can also be polymerized anionically, due to their activating group.…”