N-Triflylation Enables δ-Valerolactam-Epoxide Alternating Copolymerization

δ-Valerolactam (VL), a six-membered cyclic amide, is easily accessible but hardly polymerizable, unlike other-membered homologues. We have discovered that simple N-triflylation effectively activates VL for undergoing copolymerization with epoxides. The strong electron-withdrawing triflyl group allows mild organobases, in cooperation with triethyl borane and an alcohol initiator, to trigger the reaction at room temperature, affording strictly alternating poly(ester-sulfonamide) with controlled molar mass and low dispersity. The method is proven applicable to a variety of epoxides, regardless of polarity and bulkiness of the substituents, and the products exhibit good chemical degradability, thermal/enzymatic stability, and a wide range of glass transition temperatures. The study indicates that N-sulfonylation and ring-opening (alternating) copolymerization together may build up a versatile platform to support the design and construction of heteroatom-rich polymers using conventionally nonpolymerizable compounds.