Linear low‐density polyethylene synthesis promoted by homogeneous and supported catalysts

Linear low‐density polyethylenes (LLDPEs) were obtained through the copolymerization of ethylene with 1‐hexene using (nBuCp)2ZrCl2 co‐catalyzed by methylaluminoxane (MAO). For comparative reasons, the same metallocene was supported on silica (0.85 wt%Zr/SiO2) by grafting. The copolymerizations were performed in toluene, at 1.6 bar of ethylene, 60 °C and in an Al/Zr molar ratio of 2500. The 1‐hexene concentration varied from 0 to 0.50 mol L−1. The resulting copolymers were characterized by GPC, DSC and 13C NMR. The catalytic activities remained close to 2 × 107 and 7 × 106 (g pol) mol Zr−1 bar−1 h−1 for the homogeneous and supported systems, respectively. For the homogeneous system, the catalytic activity and the comonomer incorporation increased with the 1‐hexene concentration up to 0.30 mol l−1. Higher comonomer concentrations led to a decrease in catalytic activity in the case of the homogeneous system. The highest comonomer incorporation (6.3 mol%) was achieved with 0.50 mol l−1 of 1‐hexene in the reaction medium. The supported system afforded lower comonomer incorporations (maximum 4.0 mol%). The effect of the 1‐hexene incorporation can also be evaluated through the polymer properties, namely, crystallinity, melting temperature, molecular weight and polydispersity. © 1999 Society of Chemical Industry