A New Post-Metallocene-Ti Catalyst with Maltolate Bidentade Ligand: an Investigation in Heterogeneous Polymerization Reactions in Different Mesoporous Supports

Abstract

A new titanium catalyst easily synthesized from ethylmaltol bidentate chelator ligand was studied in homogeneous and heterogeneous ethylene polymerization. The dichlorobis(3-hydroxy-2-ethyl-4-pyrone)titanium(IV) complex was characterized by 1 H and 13 C NMR (nuclear magnetic resonance), UV-Vis and elemental analysis. Theoretical study by density functional theory (DFT) showed that the complex chlorines exhibit cis configuration, which is important for the activity in olefin polymerization. The complex was supported by two methods, direct impregnation or methylaluminoxane (MAO) pre-treatment, in five mesoporous supports: MCM-41 (micro and nano), SBA-15 and also the corresponding modified Al species. All the catalytic systems were active in ethylene polymerization and the catalytic activity was strongly influenced by the method of immobilization of the catalyst and the type of support. Keywords: catalysis, synthesis, mesoporous support, immobilization, polyethylene IntroductionPolyethylene (PE) has a broad application in different segments of the everyday life, from food packaging to resistant pieces for engineering. Due to the polymer industrial demands, continuous development of new technologies and synthetic methods for obtaining this material are necessary. Existing processes, involving polyethylene synthesis in industrial and/or research scale, use Ziegler-Natta, metallocene, and more recently, postmetallocene catalysts. Our research group has studied the synthesis of different post-metallocene catalysts and tested these complexes in ethylene polymerization. Organometallic complexes of Ti and Zr were obtained from bidentate chelator ligands as naphthoquinone, methylpyrone, ethylpyrone and 3-hydroxyflavone. [1][2][3][4][5] All the synthesized complexes were active in homogeneous ethylene polymerization at different reaction conditions. 3-Hydroxy-2-methyl-4-pyrone (methylpyrone or maltol) is a non-toxic compound of natural occurrence in many plants, 6 while 3-hydroxy-2-ethyl-4-pyrone (ethylmaltol) is a synthetic commercial product. These organic compounds are commonly used in food industries as flavor ingredients. Both hydroxypyrones are characterized by their synthetic versatility and they easily coordinate with transition metals of group IV to give L 2 MCl 2 complexes.7 Bis(maltolate) metal(IV) complexes are extensively used in medical studies to assess their therapeutic value as active agents against diabetes, as agents for controlling metal levels in the body and as contrast agents in imaging applications. [8][9][10][11][12] Maltolate complexes appear attractive to catalyze olefin polymerization reaction as well. In 2001, Sobota et al. 13 synthesized and characterized titanium complexes of methylmaltol and verified their catalytic activity in ethylene and propylene polymerization. Subsequently, our research group has synthesized several Ti and Zr complexes Gheno et al. 2083 Vol. 27, No. 11, 2016 analogous based in maltolate ligands. The synthesized complexes were shown to be active in the ethylene...