Single and binary catalyst systems based on nickel and palladium in polymerization of ethylene

Abstract

The catalyst -N,N-bis-2,6-dibenzhydryl-4-ethoxyphenyl-butane-2,3-diimine- nickel dibromide, a late transition metal catalyst, was prepared and used in ethylene polymerization. The effects of reaction parameters such as polymerization temperature, co-catalyst to catalyst molar ratio and monomer pressure on the polymerization were investigated. The a-diimine nickel-based catalyst was demonstrated to be thermally robust at a temperature as high as 90 °C. The highest activity of the catalyst -494 kg polyethylene -mol cat--1 h-1 was obtained at [Al]/[Ni] = 600:1, temperature of 90 °C and pressure of 5 bar. In addition, the performance of a binary catalyst using nickel- and palladium- based complexes was compared with that of the corresponding individual catalytic systems in ethylene polymerization. In a study of the catalyst systems, the average molecular weight and molecular weight distribution for the binary polymerization were between those for the individual catalytic polymerizations; however, the binary catalyst activity was lower than that of the two individual ones. The obtained polyethylenes had high molecular weights in the region of 105 g mol-1. Gel permeation chromatography analysis showed a narrow molecular weight distribution of 1.44 for the nickel-based catalyst and 1.61 for the binary catalyst system. The branching density of the polyethylenes generated using the binary catalytic system -30 branches/1000 C- was lower than that generated using the nickel-based catalyst -51/1000 C-. X-ray diffrac- tion study of the polymer chains showed higher crystallinity with lower branching of the polymer obtained. Also Fourier transform infrared spectra confirmed that all obtained polymers were low-density polyethylene.