Various MgCl2-supported Ziegler-Natta (ZN) catalysts are synthesized with the intention to influence polymerization performance and 1-butene incorporation in an ethylene copolymer. Modifications are introduced during different steps in the synthesis process, namely support preparation, titanation, and catalyst workup. While multiple different effects are observed upon modification, heat treatment during titanation shows the greatest impact. Increasing the heat-treatment temperature increases polymerization activity. More importantly, the 1-butene distribution can be shifted toward a more homogeneous profile. The amount of 1-butene incorporated is similar to both for short- and for very long-chain molecules. This behavior has so far been known only from metallocene-based polyethylene and suggests that active sites are distributed more homogeneously in the ZN catalyst.

A MgCl 2 -based Ziegler–Natta catalyst was characterized using X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and IR spectra. We focused on the XRD reflection at 2θ = 50° to determine the thickness of MgCl 2 crystals, and validated these results with TEM pictures. SEM pictures were taken in order to measure the size of the nanoparticles formed by the MgCl 2 crystals. Several compounds were synthesized for comparison and to aid interpretation of the infrared (IR) spectra. The catalysts were prepared by precipitating MgCl 2 , which was used as support material and subsequently treated with TiCl 4 . The thickness of the catalyst crystals was calculated from the XRD reflection at 2θ = 50°. Changing the precipitation temperature within a range from 40 to 90 °C altered the thickness of the MgCl 2 crystal plates. The maximum thickness of 7 nm was achieved at a precipitation temperature of 60 °C. The SEM pictures showed that the nanoparticles had a diameter of ~200 nm. A crystal base unit had a volume that corresponded to that of a sphere of 3.5 nm radius. Thus, we estimated that a typical catalyst particle with a diameter of 20 μm contained about one million nanoparticles, each of which consisted of about 25,000 MgCl 2 crystal units.

The characteristic features of LLDPE polymerization with ZN catalyst are the time drift effect during polymerization and the bending effect when trying to decrease density of the copolymer by adding more comonomer to the polymerization. The time drift in LLDPE polymerization is revealed by a constant decrease of comonomer incorporation during polymerization time. The bending is revealed by difficulties in lowering the density of LLDPE material below the density of 920 kg/m(3). With increasing comonomer content during polymerization, the density does not decrease, but the soluble fraction increases. To try to observe if these phenomena are connected, two types of catalysts, SiO2 supported and precipitated MgCl2 ZN catalysts, were studied. A short time (10 min) and an extended time (60 min) copolymerization test series where the polymerizations were performed in the presence of a gradually increasing comonomer amount. Both catalysts show a strong bending when density is presented as a function of 1-hexene both in 10- and 60-min polymerization, indicating no connection between time drift and bending. The density, melting point, and crystallinity results all indicate that both catalysts are making similar copolymer material with identical chemical composition distribution. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 826-836, 2010

L'invention porte sur un procede perfectionne pour adapter la distribution de la masse moleculaire et l'incorporation de comonomere d'un polymere de l'ethylene multimodal ayant un composant de masse moleculaire inferieure et un composant de masse moleculaire superieure. Ce procede comprend la polymerisation de l'ethylene et facultativement d'au moins une autre alpha-olefine en au moins deux etapes, au moins une etape etant effectuee dans une phase de bouillie en presence d'un systeme perfectionne de catalyseur Ziegler-Natta solide, ledit systeme catalyseur comprenant 1) un pro-catalyseur solide forme par mise en contact d'au moins : a) un complexe d'alcoolate de Mg represente par la formule (I) : Mg(OR1)2-n(R1)n, dans laquelle les R1 representent chacun independamment un groupe hydrocarbyle en C1-C20 ; et 0 ≤ n < 2 et peut etre ou peut ne pas etre un entier ; b) un compose de l'aluminium represente par la formule (II) Al(R2)mX3-m, dans laquelle les R2 representent chacun independamment un alkyle ayant jusqu'a 6 atomes de carbone ; les X representent chacun independamment un halogene ; 0 ≤ m < 3 et m peut etre ou peut ne pas etre un entier, c) un compose du vanadium et un compose du titane dans des proportions telles qu'elles fournissent un rapport molaire de V:Ti de 99:1 a 1:99 et d) facultativement un ou plusieurs composes ligands organiques qui sont choisis parmi des composes organiques comprenant un squelette d'anion cyclopentadienyle, de facon a fournir le pro-catalyseur solide et 2) un ou plusieurs co-catalyseurs organometalliques representes par la formule (III), dans laquelle les R representent chacun independamment un groupe alkyle en C1-C20, 0 ≤ x ≤ 2 ; 1 ≤ y ≤ 3 ; 0 ≤ z ≤ 2 et x + y + z = 3, x, y et z peuvent etre ou peuvent ne pas etre des entiers. L'invention porte egalement sur un polymere pouvant etre obtenu par ce procede et sur l'utili