EFFECTS OF REMOVING THF FROM THE TICL3(AA)/3MGCL2/THF CATALYST SYSTEM ON THE ETHYLENE PROPYLENE COPOLYMERIZATION MECHANISM

Abstract

TiCl3(AA)/MgCl2/THF (T3ME) catalyst was prepared by reacting TiCl3(AA) and MgCl2 in a solution of tetrahydrofuran (THF), and THF was removed from T3ME by diethylaluminum chloride to make four different catalysts with different THF contents (T3MED2, T3MED4, T3MED8, T3MED12). The investigation through XRD and ESR indicated that the removal of THF resulted in a change of the state of the Ti3+ species, isolated Ti3+ species for T3ME, T3MED2, and T3MED4 catalysts, and multinuclear Ti3+ species for T3MED12 and TiCl3(AA) catalysts. The C-13 NMR study showed that the microstructure of ethylene-propylene copolymers strongly depended upon the nature of Ti3+. The activity and stereospecificity for homopolymerization depended on the THF content of the catalyst, and the molecular weight distribution of copolymer became broader with THF removal. Multinuclear Ti3+ species increased the relative reactivity of propylene in the copolymerization, and isolated Ti3+ species with vacancies favored the random insertion of propylene in the ethylene main chain.