Stereospecific Living Cationic Polymerization of N-Vinylcarbazole through the Design of ZnCl2-Derived Counteranions.

Highly stereospecific living polymerization of N-vinylcarbazole (NVC) successfully proceeded via a cationic mechanism as a result of the elaborate design of counteranions using an initiating system consisting of CF3SO3H, nBu4NX (X = Cl, Br, I), and a Lewis acid catalyst. The use of ZnCl2 and an appropriate amount of nBu4NCl quantitatively generated highly isotactic polymers (mm = 94%) with narrow molecular weight distributions (Mw/Mn ∼ 1.3) and molecular weights proportional to monomer conversion. In this system, a ZnCl42- species, which was formed as a counteranion of the propagating carbocation, most likely contributed to the stereoregulation of the polymers because the mm value drastically varied depending on the polymerization conditions, such as the Lewis acid catalyst and amount of added salt. Isotactic poly(N-vinylcarbazole) (PVK) showed different properties than atactic PVK based on fluorescence and differential scanning calorimetry (DSC) analysis.