Cationic photopolymerization of vinyl ethers by the sensitized photolysis of onium tetrakis(pentafluorophenyl)borate initiators has been investigated in this study. The onium berates were sensitized by anthracene and initiated the photopolymerization of the vinyl ethers. The rate of polymerization increased with the decrease in the free-energy change from the excited singlet state of anthracene to the onium cation of the onium berates. The acid generated by the decomposition of the onium berates formed nonacidic products by heating.