Highly isotactic poly(vinyl alcohol). III: Heterogeneous cationic polymerization of tert-butyl vinyl ether

We studied the polymerization of tert-butyl vinyl ether (tBVE) and benzyl vinyl ether with heterogeneous catalysts, that is, modified Ziegler type (Vandenberg type) catalysts and metal sulfate–sulfuric acid complexes. berg type catalysts gave high molecular weight and highly isotactic poly(tBVE)s with relatively narrow molecular weight distribution at high temperature, and then the resultant poly(tBVE)s were converted into the stereoregular poly(vinyl alcohol)s (PVAs). With titanium based Vandenberg type catalyst, a relative high isotactic PVA, which has 52% triad isotacticity, was obtained from the poly(tBVE) polymerized at 30 °C. It was found from NMR study that the content of the triad tacticity of PVAs derived from poly(tBVE) catalyzed by titanium based catalysts agreed with the value calculated from the chain-end control model (Boveyʹs model). This fact suggests that the steric structure of the adding monomer in this system is determined by same mechanism to homogeneous BF3 complexes catalysts system. On contrast to that, the metal sulfate–sulfuric acid complexes show significantly low activity to tBVE polymerization.