Acid‐Promoted Polarity Switch Enables Efficient Radical Polymerization of Vinyl Ethyl Sulfide

Herein, we report a new concept for the polymerization of electron-rich vinyl sulfides based on an acid-induced polarity switch, termed monomer-Umpolung, resulting in the transient formation of electron-deficient olefins. The polarity switch activates the monomer and facilitates radical formation, thereby enabling both initiation and propagation and resulting in rapid and efficient free radical polymerization with a monomodal molecular weight distribution. We show that the reactivity can be tailored by utilizing a range of readily available acids, including sulfuric acid, acetic acid, and trifluoroacetic acid. We believe that this work will open new possibilities for the polymerization of otherwise less reactive monomers and will have a significant impact on advanced (co)polymerization strategies.