Low Density Polyethylene by Tandem Catalysis with Single Site Ti(IV)/Co(II) Catalysts

A variety of branched polyethylenes (PE), ranging from semicrystalline linear low density polyethylene to completely amorphous low density polyethylene and rubbery PE, can be produced from ethylene alone by tandem catalysis using as oligomerization catalysts the (imino)pyridyl Co(II) complexes NBTCoCl2 (1) ({6-(benzo[b]thiophen-2-yl)-2-(imine)pyridyl)}CoCl2), NETCoCl2 (2) ({6-(4-ethylthiophen-2-yl)-2-(imine)pyridyl)}CoCl2), or NPhCoCl2 (3) ({6-(phenyl)-2-(imine)pyridyl)}CoCl2) and as a copolymerization catalyst [η5-C5Me4)SiMe2(t-BuN)]TiCl2 (4). The catalytic activity of the systems 1/4/MAO, 2/4/MAO, and 3/4/MAO has been evaluated under comparable experimental conditions (T = 30°C, [ethylene] = 0.35 mol/l), varying the molar fraction of the cobalt precursors. A positive comonomer effect was observed for all the systems investigated. The maximum productivity (4570 kg PE (mol Ti)−1 h−1) was obtained for the benzothiophenyl-substituted cobalt complex. An effective control of the branching in the polymer backbone was achieved by varying either the oligomerization catalyst or its molar fraction. Completely amorphous materials with T g as low as-60°C could be obtained.