Supported hybrid catalysts based on zirconocene and tris(pyrazolyl)borate titanium derivatives

Abstract

A series of hybrid supported catalysts were prepared by combining (iBuCp) 2 ZrCl 2 and {Tp Ms* }TiCl 3 complex (Tp Ms* ϭ HB(3-mesityl-pyrazolyl) 2 (5-mesityl-pyrazolyl) Ϫ ) sequentially grafted onto MAO (methylaluminoxane)-modified silica according to a Plackett Burmann 2 3 design. Supported catalysts were prepared taking into account the immobilization order, silica pretreatment temperature, and grafting temperature. Grafted metal content was comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectronic spectroscopy (XPS), and inductively coupled plasma-optical emission spectroscopy (ICP-OES). The resulting catalysts were evaluated in terms of catalyst activity and polymer properties. According to RBS measurements, grafted metal content remained comprised between 0.1 and 0.5 wt % Zr/SiO 2 and 0.1 and 0.3 wt % Ti/SiO 2 depending on the immobilization order and on silica pretreatment temperature. All the systems were shown to be active in ethylene polymerization having external MAO as cocatalyst. Catalyst activity seemed to be governed by the zirconocene species, influenced slightly by Ti ones. Resulting polymers were characterized by DSC and GPC. The polyethylenes mostly presented higher molecular weight than those produced by homogeneous catalysts or by zirconocene grafted on bare or on MAO-modified silica.

Bimodal/Broad Polyethylene Prepared in a Disentangled State

“…Usually, the β-H chain transfer rate is gradually decreased with decreasing polymerization temperature, resulting in polyethylene with a high M w value. 37,38 In our systems, the M w value of polyethylene was dominated by the high-molecular-weight composition because of the higher activity of VCl 3 . Polyethylene with a higher M w value obtained by VCl 3 can be achieved at low polymerization temperature.…”

Alargamento da distribuição de massa molar de polímeros sintetizados com catalisadores metalocênicos dual-site

“…65 Resultados semelhantes encontram-se descritos na literatura envolvendo a combinação de um metaloceno ((iBuCp) 2 ZrCl 2 ) e um não-metaloceno (derivado de tripirazolilborato de titânio) sobre sílica funcionalizada com MAO. 66 A influência do suporte sobre o desempenho dos complexos metalocênicos vai além do controle morfológico da partícula de polímero. A interação da superfície do suporte com a do complexo metalocênico influencia o mecanismo cinético do complexo devido a fatores eletrônicos e de impedimento esteroquímicos.…”

Atomic spectrometry update. Industrial analysis: metals, chemicals and advanced materials

“…342 Rutherford backscattering spectrometry (RBS), XPS and ICP-OES have been used for the determination of grafted metal content on a series of supported hybrid catalysts based on zirconocene and tri(pyrazolyl)borate titanium derivatives. 343 All the catalysts were shown to be active in ethylene polymerization and catalyst activity was governed by the zirconocene species. The polymers produced were characterized by DSC and GPC.…”