Simple and Strong Dative Attachment of α-Diimine Nickel (II) Catalysts on Supports for Ethylene Polymerization with Controlled Morphology

Abstract

In this article, preparation of novel spherical MgCl₂ supported α-diimine nickel (II) catalysts for ethylene polymerization in slurry phase is reported. α-Diimine ligands were synthesized by condensation reaction of 2, 6-disubstituted alkyls or aryls anilines and Ace naphthoquinone Which have hydroxyl functionality in their para-position. Hydroxyl functionalized α-diimine attached strongly on to the spherical MgCl₂ support surface by dative bonding. No linker was needed to attach the complexes onto the support surface and the amount of loaded Nickel was controllable to improve morphology and especially bulk density of polymer powder. A significant reduction in catalysts activity has happened when homogeneous catalysts were supported onto silica but this reduction was decreased when they were supported onto thermally treated spherical MgCl₂. As homogeneous bis(N,N′-(4-(3-hydroxyl-propyl)-2,6-di[(4-tert-butyl-phenyl)-phenyl) amino] Ace naphthoquinone Nickel dibromide(d) showed the highest activity among other evaluated homogeneous catalysts, its MgCl₂ supported catalyst (d/S-MgCl₂) has shown the highest activity among MgCl₂ supported catalysts too. These MgCl₂ supported catalysts were pre-polymerized in presence of ethylene monomer in the mild polymerization condition to yield a pre-polymerized catalyst with polymer/catalyst weight ratio equal to six. Ethylene polymerization was carried out to make spherical particles of polyethylene without reactor fouling by these pre-polymerized catalysts. Clearly, it is shown in SEM images that the spherical morphology of MgCl₂ support is replicated in the produced polymer. The molecular weight and molecular weight distribution of produced polymer with MgCl₂ supported catalysts were higher than those produced by homogeneous catalysts.

Graphic Abstract

α–Diimine nickel (II) complexes have hydroxy functionality where produce strong dative bonding onto spherical MgCl₂. This bonding is strong enough that these catalysts are suitable for slurry polymerization of ethylene without reactor fouling due to catalyst leaching from support. The chemical structure of MgCl₂ leads to high active supported catalysts. The molecular weight and polydispersity index of produced polymrers using these supported catalysts are higher than those produced by equivalent homogeneous catalysts and are controllable by selection of appropriate ligand for used α–diimine nickel (II) complex or hydrogen concentration in ethylene polymerization.