Preparation of linear low-density polyethylene by in situ copolymerization of ethylene with Zr supported on montmorillonite/Fe/methylaluminoxane catalyst system

Linear low-density polyethylene (LLDPE) was prepared by in situ copolymerization of ethylene with dual-functional catalysts that were composed of rac-Et(Ind)₂ZrCl₂ supported on montmorillonite (MMT) and {[(2-ArN=C(Me))₂C₅H₃N]FeCl₂} [Ar = 2,4-C₆H₄(Me)₂] oligomerization catalyst. A series of polyethylenes with different degrees of branching were obtained by adjusting the ratio of Fe and Zr (Fe/Zr). DSC, NMR, GPC, SEM, and density-gradient method were used to characterize the polymers. With increasing Fe/Zr ratio, the densities and melting points of polymers decreased, whereas the branching degrees and molecular weights increased. When the Fe/Zr ratio was increased, the activities of the catalysts decreased at atmospheric pressure and increased at 0.7 MPa ethylene pressure. SEM micrographs revealed that the morphology of branched polyethylene, produced with the catalyst supported on MMT, is better than that produced by the catalyst in a homogeneous system.