Initiation of Cationic Polymerization of Cyclic Ethers by Redox Radical-Chain Reactions of Onium Salts

Article abstract of DOI:10.1021/jo00085a030

Redox radical-chain reactions of diaryliodonium halides (Ar2I(+)X(-)) with tetrahydrofuran (THF) and 1,3-dioxolane to give arenes (ArH) and iodoarenes (ArI) are reported.When the reactions are initiated by irradiation at 313 nm, the quantum yield for the formation of iodoarene is substantially greater than 1 (Φ ca. 2-20).Nonphotochemical radical initiators give the same reaction, showing that the photochemical step is simply an initiation step.The key propagation step in these reactions is a single-electron reduction of the onium salts by ether-derived radicals.The photoinitiated reaction with THF follows zero-order kinetics, showing that termination does not compete with electron transfer.In addition, the same nonphotochemical conditions that give radical-chain reduction of the diaryliodonium halides give rapid cationic polymerization of the ethers when the iodonium hexafluorophosphates are used.These observations establish the connection between the redox chemistry of the iodonium salt and the cationic polymerization of the eters.The polymerization of THF by iodonium salt in the presence of free radicals is accelerated by the addition of trimethyl phosphite (TMP).Furthermore, triarylsulfonium salts will initiate polymerization of THF in the presence of TMP and radical sources.Therefore, redox-chain reduction of these onium salts by TMP can also initiate cationic polymerization of the cyclic ethers.