Photoinduced Superacceleration of Metal-Free Living Cationic Polymerization Using Diaryliodonium Salts as Organic Lewis Acid Catalysts

Living cationic polymerization of vinyl ethers (VEs) using diaryliodonium (DAI) salts as organic Lewis acid catalysts was accelerated without loss of livingness via UV light irradiation during polymerization. Before UV irradiation, the polymerization proceeded via carbocation generation from the carbon-iodine bonds at the propagating ends through the abstraction of the iodide anion by the DAI salts. Our initial expectation regarding the effect of UV irradiation during the polymerization was the stop of polymerization or the loss of polymerization control due to the decomposition of the DAI salts; however, accelerated living polymerization occurred. Based on our thorough investigation, the acceleration associated with livingness likely occurred by the change in the polymerization mechanism from atom transfer mechanisms to degenerative chain transfer mechanisms. In particular, iodide anions were consumed in the DAI salt decomposition, which led to a gradual generation of carbocations that did not contain iodide counteranions and resulted in an iodine transfer-type degenerative chain transfer polymerization. Acceleration was also observed in cationic polymerizations of functional group-containing VEs and styrenes.