Diversifying Cationic RAFT Polymerization with Various Counteranions: Generation of Cationic Species from Organic...

A combination of hydrogen chloride adduct of isobutyl vinyl ether (IBVE-HCl) and various metal salts (AgOTf, AgPF₆, AgSbF₆, NaBArF (BArF: [3,5-(CF₃)₂Ph]₄B)) efficiently generated initiating cationic species with different low, weakly, or non-nucleophilic counteranions (OTf^-, PF₆^-, SbF₆^-, BArF^-) and induced a cationic reversible-addition-fragmentation chain-transfer (RAFT) or degenerative chain-transfer (DT) polymerization of IBVE, ethyl vinyl ether, p-methoxystyrene, and α-methylstyrene (αMS) in the presence of appropriate thiocarbonylthio compounds or thioethers as reversible chain-transfer agents. The polymerization behaviors in terms of polymerization rate, polymer molecular weight, terminal structure, and stereochemistry were affected by the counteranions, whereas the molecular weight control was achieved by appropriate RAFT or DT agents for all of these counteranions. With a weakly or noncoordinating BArF anion and a trithiocarbonate, a nearly atactic poly(IBVE) with a narrow molecular weight distribution (M_w/M_n < 1.1) was obtained. When using nonoxoanions, such as SbF₆^-, PF₆^-, and BArF^-, in the presence of thioethers, controlled cationic polymerization of αMS was achieved while frequent irreversible β-proton elimination occurred using TfO^-. Thus, this method widens the scope of living or controlled cationic polymerizations with various counteranions.