Bulk Stereoselective Cationic Polymerization of Vinyl Ethers by the Coordination of ZrCl₄ with Tunable Spirocyclic Phosphoric Acids

Abstract

Control over stereochemistry in poly(vinyl ether)s leads to a notable change in their physical properties, yet remains a grand challenge. Here, we demonstrate the bulk stereoselective cationic polymerization of vinyl ethers using ZrCl4 coordinated with a spirocyclic phosphoric acid (SPA). The widely variable substituents in SPAs exert a profound impact on the stereochemical and activity outcome of the polymerization: the % m of poly(vinyl ether)s linearly increases with the Hammett substituent constant (σ) of SPAs; the catalytic activity increases with the σ; the large steric hindrance groups lead to decreased polymerization activity. Mechanism studies suggest that the coordination of ZrCl4 with three equivalents of SPAs generates the chiral complex. The complex can abstract chlorine from the initiator/chain end to form the chiral ion pair allowing the selective facial addition of incoming monomers. The catalyst system features characteristics of no solvent, low loads, high tacticity control, high monomer scope, and recyclability.