Ethylene polymerization using new modified methylaluminoxane-metallocene catalysts

Abstract

The slurry polymerization of ethylene with bis(cyclopentadienyl)zirconium dichloride [Cp₂ ZrCl₂] in combination with methylaluminoxane [MAO] was investigated to study the effect of different [Al]/[Zr] ratio, polymerization temperatures, ethylene partial pressures, catalyst concentrations, and hydrated salts in preparing methylaluminoxane. The experimental results suggested that the catalytic activity and polymerization rate of this catalyst system were the highest at [Al]/[Zr] of 6000, polymerization temperature of 348 Kelvin, ethylene partial pressure of 70 ps. Measurements of the water releasing rate from hydrated salt for reaction with trimethylaluminum to methylaluminoxane by Thermal Gravimetry Analysis (TGA) showed that the suitability of hydrated salt for preparing methylaluminoxane was in the following order : Al₂(SO₄)₃•18H₂O ˃ Al₂(SO₄)₃•16H₂O ˃ CuSO₄•5H₂O ˃ Na₂S₂O₃•5H₂O ˃ AlCl₃S₂•6H₂O. DSC, FT-IR and SEM techniques were used to measure the properties of polyethylene products. The result showed that the higher melting temperature of polyethylene was obtained at lower catalytic activity.