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