Design of Benign Initiator for Living Cationic Polymerization of Vinyl Ethers: Facile in Situ Generation of Vinyl Ether-Hydrogen Halide Adducts and Subsequent Controlled Polymerization without a Lewis Acid Catalyst

A Lewis acid-free initiating system for cationic polymerization of alkyl vinyl ethers (VEs) was developed using CF3SO3H and tetraalkylammonium halides (nBu(4)NX; X = I, Br, or Cl). The reaction of CF3SO3H, nBu(4)NX, and an alkyl YE generated a VE-hydrogen halide adduct. The labile carbon-halogen bond, such as a carbon-iodine bond, cleaved without a Lewis acid catalyst to induce the living cationic polymerization of VEs. Combining halide anions with suitable nucleophilicities according to monomer reactivity was indispensable for controlled polymerization. Another prerequisite was that the polymerization be conducted at a suitable temperature. After the initiation step, the polymerization probably proceeded via the mechanisms similar to those for the previously reported systems using hydrogen halide and an ammonium salt with a noncoordinating anion. The present system was also useful as a facile method for the synthesis of VE-hydrogen halide adducts without the use of harmful gaseous hydrogen halides. The adducts formed were shown to function as cationogens for living cationic polymerization using Lewis acid metal catalysts.