Janus Effect of Lewis Acid Enables One‐Step Block Copolymerization of Ethylene Oxide and N‐Sulfonyl Aziridine

Abstract One‐step sequence‐selective block copolymerization requires stringent catalytic control of monomers relative activity and enchainment order. It has been especially rare for A n B m ‐type block copolymers from simple binary monomer mixtures. Here, ethylene oxide (EO) and N‐ sulfonyl aziridine (Az) compose a valid pair provided with a bicomponent metal‐free catalyst. Optimal Lewis acid/base ratio allows the two monomers to strictly block‐copolymerize in a reverse order (EO‐first) as compared with the conventional anionic route (Az‐first). Livingness of the copolymerization facilitates one‐pot synthesis of multiblock copolymers by addition of mixed monomers in batches. Calculation results reveal that a Janus effect of Lewis acid on the two monomers is key to enlarge the activity difference and reverse the enchainment order.