In this study, the stopped-flow (SF) technique was extended for Ziegler-Natta polymerization over a quasi-living period in order to obtain deeper insights into chain transfer (CT) reactions. Propylene polymerization with a TiCl4/MgCl2 catalyst containing 2-isopentyl-2-isopropyl-1,3-dimethoxypropane as an internal donor exhibited a linear growth of Mn for the polymerization time below 0.3 s, indicating quasi-living polymerization. Over 0.4 s, Mn deviates from the linearity in a convergent manner due to the increasing contribution of CT reactions. On the other hand, the polymerization yield evolved completely proportionally to the polymerization time even up to 1.6 s, which enabled us to presume a constant active site concentration ([C*]). In spite of the expected heterogeneity of active sites, the time-Mn curve was accurately fit by a theoretical equation. Thus, we have revealed that the SF technique can be applied for the simultaneous determination of propagation and CT rate constants in heterogeneous ZN polymerization.
View Full Article