Phosphazene Bases as Organocatalysts for Ring‐Opening Polymerization of Cyclic Esters.

Over the past several years, organocatalyzed polymerization reactions have attracted considerable attention, and these efforts have led to major advances. A large number of organic compounds have been proven active for the polymerization of a large variety of monomers. In particular, phosphazene bases (PBs) are a family of extremely strong, non‐nucleophilic, and uncharged auxiliary bases, and have shown their remarkable potential as organocatalysts for the ring‐opening polymerization (ROP) of cyclic monomers. By deprotonation of weak acids or in combination with lithium cation, PBs significantly enhance the nucleophilicity of the initiator/chain‐end, thus allowing fast and usually controlled anionic polymerization. In this feature article, the recent advances in phosphazene‐catalyzed ROP of cyclic esters are summarized. This review is divided into three sections, including general features, design and synthesis, and catalytic applications. It aims to provide a critical analysis of PB‐mediated ROP systems and a useful guide for the further design of organocatalysts applied to polymer synthesis. An outlook is given at the end. Phosphazene bases (PBs) are a family of extremely strong and non‐nucleophilic bases having remarkable potential as organocatalysts for different types of polymerization reactions. This feature article emphasizes the general features and synthetic methods of PBs and focuses on their applications in the ring‐opening polymerization of cyclic ester monomers. [ABSTRACT FROM AUTHOR]