Dual catalyst system composed by nickel and vanadium complexes containing nitrogen ligands for ethylene polymerization

Abstract

Blendas de polietileno ramificado/polietileno de alta densidade (BPE/HDPE) foram preparadas usando uma combinação de catalisadores [NiCl 2 (diimina-α)] (1) (diimina-α = 1,4-bis(2,6-diisopropilfenila)-acenafeteno) e [Tp Ms* VCl 2 (N t Bu)] (2) (Tp Ms* = hidridobis(3-mesitilapirazol-1-il)(5-mesitilapirazol-1-il)). As reações de polimerização foram realizadas em hexano ou tolueno em três diferentes temperaturas (0, 30 e 50 °C), utilizando várias razões molares de níquel (x Ni ), na presença de metilaluminoxano (MAO) como cocatalisador. Em todas as temperaturas, as atividades mostraram uma correlação aproximadamente linear com x Ni , indicando o não aparecimento de um efeito sinérgico entre as espécies de níquel e vanádio. Altas atividades foram obtidas a 0 °C. As temperaturas de fusão (T m ) das blendas de polietileno produzidas a 0 °C diminuem conforme a x Ni aumenta no meio reacional, indicando uma boa miscibilidade entre as fases de polietileno produzidas por ambos catalisadores. A morfologia da superfície das blendas de BPE/HDPE estudadas por microscopia eletrônica de varredura (MEV) revelou uma baixa miscibilidade entre as fases de PE, principalmente no caso das blendas poliméricas produzidas a alta temperatura (50 ºC).Branched polyethylene/high-density polyethylene blends (BPE/HDPE) were prepared using the combined [NiCl 2 (α-diimine)] (1) (α-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and [Tp Ms* VCl 2 (N t Bu)] (2) (Tp Ms* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) catalysts. The polymerization reactions were performed in hexane or toluene at three different polymerization temperatures (0, 30 and 50 °C) and several nickel molar fractions (x Ni ), using MAO as cocatalyst. At all temperatures, the activities show an approximate linear correlation with x Ni , indicating a non-synergistic effect between the nickel and the vanadium species. Higher activities were found in toluene at 0 °C. The melting temperatures for the polyethylene blends produced at 0 °C decrease as x Ni increases in the medium indicating good miscibility between the polyethylene phases made by both catalysts. The surface morphology of the BPE/HDPE blends studied by scanning electron microscopy (SEM) revealed low miscibility between the PE phases mainly in the case of the polymer blends produced at high temperature (50 ºC).

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