Metal Triflates and Tetrafluoroborates as Water-Tolerant Lewis Acids for Cationic Polymerization in Aqueous Media

Metal triflates or tetrafluoroborates, such as Zn(OTf) 2, Cu(OTf) 2, Sn(OTf) 2, and Zn(BF 4 ) 2 (OTf = −OSO 2 CF 3 ), were employed as water-tolerant Lewis acids for the emulsion cationic polymerization of p -methoxystyrene (pMOS) in heterogeneous aqueous media. All these metal compounds, in addition to rare earth metal triflates such as Yb(OTf) 3 already reported by us, induced the polymerization of pMOS in conjunction with the pMOS−HCl adduct ( 1 ) (initiator) and dodecyltrimethylammonium chloride (surfactant) at 30 °C in water. The pMOS polymerization was controlled, where the molecular weights of the polymer increased with monomer conversion and the molecular weight distributions were relatively narrow ( M w / M n ∼ 1.4). 1 H NMR analysis of the obtained polymers showed that the chlorine atom originating from 1 was attached to the growing polymer terminal. In addition, the water tolerance of these catalysts was confirmed by 19 F NMR analysis. Thus, the emulsion cationic polymerization proceeds via reversible activation of the C−Cl terminal mediated by the water-tolerant Lewis acid, which enters from the aqueous phase into the organic phase.