Janus Effect of Lewis Acid Enables One‐Step Block Copolymerization of Ethylene Oxide andN‐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.

Alternating Copolymerization of Epoxides and Isothiocyanates to Diverse Functional Polythioimidocarbonates and Related Block Polymers†

“…Notably, the negative effect of boron catalysts was also reported by Zhao and co‐workers in the ring‐opening polymerization of N ‐sulfonyl aziridine. [ 67 ]…”

Organoboron-mediated polymerizations

“…In addition, Zhao's group disclosed that TEB catalyzed the ROP of N-sulfonyl aziridine. 284 N-sulfonyl aziridine is highly reactive and undergoes ROP in the presence of common anion initiators. However, Zhao and coworkers noticed that, once TEB was added, polymerization slowed down.…”

“…Fig.86Adverse effect of boron in catalyzing the copolymerization of ROP of N-sulfonyl aziridine catalyzed by TEB reported by Zhao and coworkers 284. …”

Switchable copolymerization of mixed monomers catalyzed by imidazolium ionic liquids

“…In virtue of increasing environmental concerns and rapidly growing demands for polymeric materials free of metal residuals to meet the requirement of applications in biomedicine, microelectronics and food packaging, organocatalysts can be specially developed for the switchable polymerization to cultivate a metal-free route for block copolymers. [35][36][37][38][39][40][41][42][43] For example, Zhao et al 35 and the Li group, 36 respectively, demonstrated that the phosphazene (t-BuP 1 ) catalyst with the benzyl alcohol initiator can bridge and switch two different catalytic cycles involving the ring-opening alternating copolymerization (ROAC) of epoxides with anhydrides and the ROP of LA, producing sequence-controlled block copolyesters from mixed feedstocks via a metal-free route. Moreover, organic Lewis pairs of the phosphazene base and triethylborane have been employed for the synthesis of polyester-polyether block copolymers in a one-pot strategy, by the selective copolymerization of epoxides with cyclic esters, carbonates and cyclic anhydrides, respectively.…”