Abstract: | This paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) poly(IBVE)]. At −78 °C, living polymerization was induced with the HCl-IBVE adduct (1)/ZnCl2 system in a EtNO2/CH2Cl2 mixture, whereas similar systems with EtAlCl2 led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl2 and 1/EtAlCl2 were directly analyzed by 1H NMR spectroscopy. |