Species on the Activated TiCl4/MgCl2 Pre-catalyst for Diene Polymerizations

Understanding the nature of the active species of the TiCl4/MgCl2 Ziegler–Natta catalyst is special important and challenge. In this work, the pre-treated TiCl4/MgCl2 pre-catalyst by heptane washing (H-Cat) and AlR3 activation (Al-Cat) were prepared and analyzed and then used to conduct butadiene (Bd)-isoprene (Ip) copolymerizations. It was proved that the adsorbed Al compounds on the Al-Cat surfaces after suffering heptane washing increased with the increase in the concentration of alkylaluminium in the pre-catalyst activation process, indicating the stable absorption of Al compounds on the active species and then influencing the catalytic behavior of the active species. Correlated the titanium oxidation state and the catalytic activity, Ti3+ species were more likely the active species for Bd-Ip copolymerization. Ti3+with adsorption of AlR2Cl on Mg adjacent to the Ti species showed reduced activity and produced polymers with high trans-1,4-configuration and relatively high molecular weight (Mw). This study is anxious to provide further understanding on the mechanism of conjugated diene polymerization catalyzed by heterogeneous Ziegler–Natta catalysts. The increase in alkylaluminium concentration during the pre-catalyst activation process changed the chemical surroundings and oxidant state of Ti and then resulted in an obvious increase in adsorbed Al and Ti2+ amount on the catalyst surface, which influenced the activity and stereoregularity for diene polymerization.