Long Chain Branching in Ethylene Polymerization Using Binary Homogeneous Metallocene Catalyst System

Abstract

ABSTRACTThe solution polymerization of ethylene using a binary metallocene system (BMS), [C5Me4(SiMe2NtBu)]TiMe2 (CGC-Ti) / zirconocene dichloride (Cp2ZrCl2) / tris(pentafluorophenyl)boron (TPFPB) / modified methylaluminoxane (MMAO), has been carried out in a high-temperature, high-pressure continuous stirred-tank reactor (CSTR) at 140 °C, 500 psig and with a mean residence time of 4 minutes. A series of BMS with different catalyst and cocatalyst incorporation were used. The utilization of Cp2ZrCl2 and MMAO in the BMS reduced the activity greatly, and the effect of MMAO was more severe. Formation of long chain branches decreased even though more macromonomer was produced. Polyethylenes with higher molecular weight and broader molecular weight distribution were synthesized using the binary systems than those produced using the CGC-Ti catalyst alone. The overall rate constants of ethylene propagation, long chain branching, ethylene macromonomer formation via chain transfer to monomer and β-hydride eliminati...