Synthesis of Branched Polyethylene from Ethylene by Tandem Action of Iron and Zirconium Single Site Catalysts

Abstract

The synthesis of low-density polyethylene from ethylene as the only monomer feed has been investigated as an alternative route to branched polyethylene and to obtain new materials with different properties, avoiding the need to feed 1-alkenes into the polymerization process. The details of the evaluation of two combination catalyst systems based on single site catalysts are discussed. The {[(2-ArNC(Me))2C5H3N]FeCl2} (Ar = 2-C6H4(Et)) compound, designated as catalyst 1, oligomerizes ethylene to produce linear α-olefins with high selectivity, and Me2SiInd2ZrCl2 (2) or EtInd2ZrCl2 (3) are used as catalysts that incorporate the α-olefins in the polymer. For catalyst 1 in the presence of methylaluminoxane (MAO) and ethylene, a wide range of α-olefin products were found, both soluble and insoluble. Also, tandem catalyst combinations 1 and 2 or 1 and 3 in the presence of ethylene alone can readily produce branched polyethylene with levels of 1−4 branches per 100 units of ethylene. A change in activity was found for variations in the Fe/Zr ratio for both systems, with lower activity but higher frequency of branching in the polymer backbone for catalyst 2. The final product obtained by the 1/3/MAO systems, however, shows a more homogeneous structure as determined by DSC and GPC.