Effects of Ti/Mg molar ratio on bi-supported SiO2/MgCl2 (ethoxide type)/TiCl4 catalysts in ethylenehomopolymerization and ethylene/1-hexenecopolymerization

SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide(Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg molar ratios, which showedsignificant effects on the active centers and pore structures of the catalysts. The formation amount of β-MgCl2carrier increased to a maximum with increasing the Ti/Mg molar ratio from 1.50 to 2.25, and then decreased withthe further increasing of Ti/Mg molar to 2.50. When the Ti/Mg molar ratio reached 2.25, the catalyst showed thebest performance of polymerization, which could be attributed to the most active centers, high surface area andloose surface structure, mainly owing to the high conversion of Mg(OEt)2 to β-MgCl2. The polymers obtainedshowed medium and high molecular weight (Mw) with medium molecular weight distribution (MWD). In contrastto the conventional Mg(OEt)2-based ZN catalysts, the sphericity of particles was easy to control in this bi-supportedcatalyst. Furthermore, the prepared catalysts exhibited rather high activity, good copolymerization ability andhydrogen response. Polyolefins J (2018) 5: 1-13

Keywords:

Polyethylene , magnesium ethoxide , Ti/Mg molar ratio , Ziegler-Natta catalyst , pore structure