TiCl4/MgCl2/MCM-41 Bi-Supported Ziegler–Natta Catalyst: Effects of Catalyst Composition on Ethylene/1-Hexene Copolymerization

Abstract

TiCl4/MgCl2/MCM-41 type bi-supported Ziegler-Natta catalysts with different MgCl2/MCM-41 ratios were synthesized by adsorbing TiCl4 onto MgCl2 crystallites anchored in mesopores of MCM-41 (mesoporous silica with 3.4 nm pore size). Ethylene/1-hexene copolymerization with the catalysts was conducted at different 1-hexene concentrations and ethylene pressures. MgCl2/MCM-41 composite supports and the catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption analysis (BET), and elemental analysis. The copolymers were fractionated by extraction with boiling n-heptane, and comonomer contents of the fractions were determined. Under 4 bar ethylene pressure, the bi-supported catalysts showed higher activity and a stronger comonomer activation effect than the TiCl4/MgCl2 catalyst. In comparison with the TiCl4/MgCl2 catalyst, the bi-supported catalysts produced much less copolymer fraction of low molecular weight and high 1-hexene content, meaning that the active center distribution of the catalyst was significantly changed by introducing MCM-41 in the support. The copolymer produced by the bi-supported catalysts showed similar melting temperature to that produced by TiCl4/MgCl2 under the same polymerization conditions. The space confinement effect of the mesopores of MCM-41 on the size and structure of MgCl2 crystallites is proposed as the main reason for the special active center distribution of the bi-supported catalysts.

Polymerization of α-olefins and their copolymerization with ethylene by half-sandwich scandium catalysts with an N-heterocyclic carbene ligand

“…A concentrated toluene solution at −30 °C gave 2 as yellow crystals (0.965 g, 79% yield). 1 14 mL of n-butyllithium (2.5 M, 35.0 mmol) was added dropwise to the 30 mL THF solution of fluorene (5.818 g, 35.0 mmol) at −78 °C, and the mixture was warmed to room temperature slowly and kept stirring for 1 h. The obtained fluorenyllithium solution was added dropwise to 50 mL THF solution of 1,4-dibromobutane (15.114 g, 70.0 mmol) at −78 °C within 1 h. the reaction was warmed to room temperature slowly and stirred for 12 h. All the volatiles were removed under vacuum and the residues were passed through an alumina column with hexane as an eluent to afford pure fluorenyl-H-(CH 2 ) 4 -Br (6.853 g, 65% yield). The reaction of fluorenyl-H-(CH 2 ) 4 -Br (6.853 g, 22.8 mmol) with 1-isopropylimidazole (2.512 g, 22.8 mmol) in 1,4-dioxane (20 mL) at 100 °C under reflux for 5 days gave sticky oils after the removal of volatiles.…”

“…Drying of methanol gave the anticipated compound {fluorenyl-H-(CH 2 ) 4 -NHC-H}Br (8.066 g, 86% yield). 1 In a glovebox, 5 mL toluene solution of LiCH 2 SiMe 3 (0.188 g, 2.0 mmol) was added slowly to the 10 mL toluene suspension of {fluorenyl-H-(CH 2 ) 4 -NHC-H}Br (0.823 g, 2.0 mmol) at room temperature and stirred for 2 h. Then, the mixture was added slowly to Sc(CH 2 SiMe 3 ) 3 (THF) 2 (0.902 g, 2.0 mmol) in 10 mL toluene at room temperature and stirred for 12 h. All the volatiles were removed under vacuum and the residues were re-dissolved in toluene and filtered. A concentrated toluene solution at −30 °C gave 3a as yellow crystals (0.735 g, 67% yield).…”

“…The yellow crystals 3b (0.642 g, 60% yield) were obtained by recrystallization from the toluene solution at −30 °C. 1 In a glovebox, 1-hexene (0.84 g, 10 mmol) was added under vigorous stirring to a reaction mixture of 3b (5.3 mg, 10 μmol) and [Ph 3 C][B(C 6 F 5 ) 4 ] (9.2 mg, 10 μmol) in toluene (12 mL). After 5 min, polymerization was terminated by the addition of 1 mL methanol.…”

“…The development of efficient catalysts for the polymerization of α-olefins and their copolymerization with ethylene to synthesize high-performance polyolefins has been the subject of intense scrutiny in both academic and industrial research. [1][2][3][4][5] The fine-tuning of the stereo-electronic properties of the ancillary ligands in homogeneous catalysts proved to be a key tool for controlling the reactivity and catalytic performances. [6][7][8][9][10] The most extensively investigated catalysts for the polymerization of α-olefins and their copolymerization with ethylene are group 4 metallocene catalysts, 2,4,10-17 constrained geometry catalysts (CGC), 3,6,7,18 and post-metallocene catalysts.…”

Interaction of Polyphenylsilsesquioxane with Various β-Diketonate Complexes of Titanium by Mechanochemical Activation

“…Titansiloxanes are of considerable scientific and practical interest. They have been widely used as Ziegler-Natta catalysts [17][18][19][20], oxidation and polymerization catalysts [21][22][23], and for epoxidation [24,25]. In addition, they are precursors of materials for medicine and microbiology [26,27].…”