Abstract
Supported olefin polymerization catalysts can prevent reactor-fouling problems and produce uniform polymer particles. Constrained geometry complexes (CGCs) have less sterically hindered active sites than bis-cyclopentadienyl metallocene catalysts. In the literature, micrometer-sized silica particles were used for supporting CGC catalysts, which might have strong mass transfer limitations. This study aims to improve the activity of supported CGC catalysts by using nanometer-sized silica. Ti[(C5Me4)SiMe2(NtBu)]Cl2, a “constrained-geometry” titanium catalyst, was supported on MAO-treated silicas (nano-sized and micro-sized) by an impregnation method. Ethylene homo-polymerization and co-polymerization with 1-octene were carried out in a temperature range of 80–120 °C using toluene as the solvent. Catalysts prepared and polymers produced were characterized. For both catalysts and for both reactions, the maximum activities occurred at 100 °C, which is significantly higher than that (60 °C) reported before for supported bis-cyclopentadienyl metallocene catalysts containing zirconium, and is lower than that (≥140 °C) used for unsupported Ti[(C5Me4)SiMe2(NtBu)]Me2 catalyst. Activities of nano-sized catalyst were 2.6 and 1.6 times those of micro-sized catalyst for homopolymerization and copolymerization, respectively. The former produced polymers with higher crystallinity and melting point than the latter. In addition, copolymer produced with nanosized catalyst contained more 1-octene than that produced with microsized catalyst.
Highlights
Ethylene homo-polymers and copolymers are the most common polymers, accounting for about 38% of all the global plastics made today [1]
About three quarters of the PE is produced via reactions catalyzed by transition metal catalysts, including Ziegler-Natta catalysts, metallocene catalysts, constrained geometry catalysts and supported metal oxides (Philips process) [1,3]
The optimum polymerization temperature for achieving the maximum activity occurred at 100 ◦ C for both silica sizes and for both reactions, which was higher than that reported before for zirconcenes, but was lower than that (≥140 ◦ C) used for unsupported Dow catalyst (Ti[(C5 Me4 )SiMe2 (Nt Bu)]Me2 )
Summary
Ethylene homo-polymers and copolymers (abbreviated as PE) are the most common polymers, accounting for about 38% of all the global plastics made today [1]. Their applications include bags, films, housewares, bottles, containers, pipe, tubing, wire and cable insulation, conduits and coatings [2]. About three quarters of the PE is produced via reactions catalyzed by transition metal catalysts, including Ziegler-Natta catalysts, metallocene catalysts, constrained geometry catalysts and supported metal oxides (Philips process) [1,3]. Compared to bis-cyclopentadienyl metallocenes, CGCs have less sterically hindered active sites and have better ability for incorporating α-olefins, higher stability toward MAO, and are stable up to 160 ◦ C [5]
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