PE Mol Zr Research Articles

Octadecyl‐modified silica supports for metallocene catalyst applied in ethylene polymerization

AbstractChemical modification of silica‐based supports is an alternative route for modulating the active sites of metallocene catalysts, presenting the potential to obtain polyethylenes with improved properties. Therefore, this work investigates the effect of octadecylsilane content in silica support on the behavior of resulting supported metallocene catalysts on ethylene polymerization. For this propose, a series of octadecyl‐modified silicas whit different amounts of octadecyl (ODS) groups were synthesized by a modified Stöber sol–gel method and then applied as supports for a metallocene catalyst. The supported metallocene catalysts were evaluated in ethylene polymerization and ethylene/1‐hexene copolymerization reactions. Besides, studies of the growth kinetics of polyethylene particles in a gas phase reactor were performed using videomicroscopy. The octadecylsilane content in the supports was in the range of 0.2 to 1.4 mmol g−1. DRIFTS and 13C CP/MAS NMR results showed a predominance of an all‐trans octadecyl chain conformation. SEM images showed spherical particle morphology for silicas having octadecylsilane content up to 0.6 mmol g−1. The supported catalysts presented activity in ethylene polymerization in the range of 1100–1900 kg PE molZr−1 h−1 bar−1. The surface polarity of the catalyst influenced the molar mass of the resulting polyethylene. The increase of the ODS content on the silica surface led to a supported catalyst with slower kinetic behavior in the gas phase, which might be attributed to the diffusive effects of the octadecyl layer on the catalyst surface.

Reactivity of a new family of diamido-diamine cyclam-based zirconium complexes in ethylene polymerization

Abstract Compounds of general formula [(∗Bn2Cyclam)ZrCl2] (∗Bn = 4-tBuC6H4CH2, (4) and 4-CF3C6H4CH2, (5)) were synthesised using Zr(CH2SiMe3)2Cl2(Et2O)2 and the corresponding ligand precursors 1,8-(4-tbutylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H2(4-tBuBn)2Cyclam), (4a), and 1,8-(4-trifluoromethylbenzyl)-1,4,8,11-tetraazacyclotetradecane (H2(4-CF3Bn)2Cyclam), (5a). Complexes 4 and 5, in addition to other [(∗Bn2Cyclam)ZrCl2] compounds previously described by some of us (∗Bn = PhCH2, (1), 3,5-Me2C6H3CH2, (2) and 3,5-tBu2C6H3CH2, (3)) were tested in the polymerization of ethylene in the presence of MAO. System 4/MAO presents the highest activity (2790 g PE molZr−1 h−1 atm−1). The polymers formed are slight to moderately branched polyethylenes with a percentage of branching ranging between 1.2% and 3.3%. The melting points obtained by differential scanning calorimetry (DSC) ranging from 128 to 140 °C, are consistent with rather high average molecular weight polymers with crystallinity close to 50%.

Supported metallocene on mesoporous materials

A series of hybrid supported catalysts was prepared by sequentially grafting Cp 2 ZrCl 2 and ( n BuCp) 2 ZrCl 2 (1:3 ratio) onto alumino-silicates (MCM-41, SBA-15, MCM-22, ITQ-2), alumina and chrysotiles (native and leached). Supports and catalysts were characterized by Rutherford backscattering spectrometry, atomic force microscopy and nitrogen adsorption. Grafted metal content laid between 0.2 and 0.8 wt.% Zr/SiO 2 and 0.9 wt.% Zr/Al 2 O 3 . All the systems were shown to be active in ethylene polymerization with methylaluminoxane as the cocatalyst. Catalyst activity and molecular weight were shown to depend on the textural characteristic of the silicas, namely grain size and pore diameter. The highest activity in ethylene polymerization (ca. 3200 kg PE mol Zr −1 h −1 ) was obtained with the supported catalyst using SBA-15 with average particle size around 0.21 μm. Resulting polymers were characterized by gel permeation chromatography and differential scanning calorimetry. A series of hybrid supported catalysts was prepared by sequentially grafting Cp 2 ZrCl 2 and ( n BuCp) 2 ZrCl 2 (1:3 ratio) onto alumino-silicates, alumina and chrysotile. The supported catalysts were characterized by Rutherford backscattering spectrometry, atomic force microscopy and nitrogen adsorption grafted metal content. Catalyst activity and polyethylene molecular weight were shown to be dependent on textural properties of the supports.

Effect of the silica texture on grafting metallocene catalysts

A series of hybrid supported catalysts was prepared by sequentially grafting Cp 2ZrCl 2 and ( nBuCp) 2ZrCl 2 (1:3 ratio) onto synthesized xerogel, aerogel and commercial silicas. Supports and catalysts were characterized by Rutherford backscattering spectrometry, energy-dispersive X-ray scanning electron microscopy, atomic force microscopy and nitrogen adsorption. Grafted metal content laid between 0.15 and 0.5 wt.% Zr/SiO 2. All the systems were shown to be active in ethylene polymerization with methylaluminoxane as the co-catalyst. Catalyst activity and molecular weight were shown to depend on the textural characteristic of the silicas, namely grain size and pore diameter. The highest activity in ethylene polymerization (ca. 5310 kg PE mol Zr −1 h −1) was obtained with the supported catalyst using commercial silicas with average particle size around 50 μm. Particles with sizes of 80–90 μm obtained less activity. Resulting polymers were characterized by gel permeation chromatography and differential scanning calorimetry.