Syndiospecific Living Polymerization of Propene with [<i>t</i>-BuNSiMe₂Flu]TiMe₂ Using MAO as Cocatalyst

Abstract

Propene polymerization was conducted at 0 °C by [t-BuNSiMe2Flu]TiMe2 combined with B(C6F5)3, MAO, or the MAO which had been dried in a vacuum and washed with hexane before use. The effect of cocatalyst was investigated under atmospheric pressure of propene in a semibatch system where polymerization rate was followed by the amount of propene consumed. The B(C6F5)3 system was deactivated within 30 min, while the MAO system showed steady polymerization rate. On the other hand, the activity of the dried MAO system was so high that the kinetic profile could not be evaluated precisely. The MAO system gave the low molecular weight polymer, and the number of polymer chains was more than 10 times higher than the amount of titanium complex employed. In the dried MAO system, however, the produced polymer showed the highest molecular weight and narrowest molecular weight distributions of about 1.2. The batchwise polymerization with the dried MAO system indicated that propene polymerization proceeded quantitatively regardless of the monomer charged, and the number-average molecular weight of the polymer obtained increased linearly against the polymer yield with keeping the molecular weight distribution narrow and the number of polymer chains constant. The results of postpolymerization testified that living polymerization proceeded under these conditions. The 13C NMR measurement indicated that syndiotactic-rich polypropenes were produced in a highly regiospecific manner by this catalyst system.