Effect of internal and external electron donors on stereospecific polymerization of isoprene with TiCl4/MgCl2 type Ziegler-Natta catalysts

Two TiCl4/MgCl2 type Ziegler-Natta catalysts containing ethyl benzoate (EB) and dibutyl phthalate (DBP) as internal electron donors (ID) were prepared for isoprene polymerizations using five kinds of external electron donors (ED) (phenyltrimethoxysilane (ED-1), dicyclopentyl(dimethoxy)silane (ED-2), 2-butyl-2-ethyl-1,3-dimethoxypropane (ED-3), 1,3-dimethoxypropane (ED-4) and di(2-ethylhexyl)phthalate (ED-5)). The structure features of TiCl4/ID/MgCl2 catalysts were characterized and the effect of ID and ED on polymerization behaviors was studied. EB had higher adsorption content on catalyst surface, higher catalytic activity and lower trans-1,4 stereoselectivity than DBP. Appropriate introduction of ED-1 and ED-2, expect ED-3, ED-4 and ED-5, caused the enhancement in polymerization activity and trans-1,4 content, while excess addition led to the deactivation. The effect of ED on equilibrium between selective activation and deactivation of active species significantly relied on the electron donor type and concentration.