Kinetics of olefin copolymerization with heterogeneous Ziegler-Natta catalysts
1995
Kissin, Yury V.
The kinetics of the ethylene/1-hexene copolymerization reaction with a Ti-based Ziegler-Natta catalyst has been studied. Kinetic analysis established the existence of several populations of active centers in the catalyst. The centers differ in two aspects: their ability to incorporate α-olefin units into copolymer chains (i.e., their reactivity ratios) and the average molecular weights of the polymer chains they produce. The centers of different populations are formed at different rates and have different kinetic stabilities. As a consequence, both the molecular weight distributions of the copolymers and their compositional distributions are relatively broad and change with in time. Two kinds of catalyst poisons were found. The poisons of the first type, arylalkoxysilanes, preferentially deactivate the centers which have the highest ability to copolymerize α-olefins with ethylene. These poisons decrease the average α-olefin content in the copolymers and the fraction of their olefin-rich components. The poisons of the second type, conjugated dienes, preferentially deactivate the centers which have the lowest ability to copolymerize α-olefins with ethylene. These poisons significantly increase the content of the olefin-rich components in the copolymers.
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