This study focuses on gas-phase polymerization of ethylene using the titanium-based Ziegler–Natta catalysts prepared from different magnesium sources including MgCl2 (Cat A), magnesium powder (Cat B), and Mg(OEt)2 (Cat C). During polymerization, different cocatalysts were also used. It was found that Cat C with triethylaluminum as a cocatalyst exhibited the highest activity. This was likely attributed to optimal distribution of active sites on the catalyst surface. It can be observed by increased temperature in the reactor due to highly exothermic reaction during polymerization. By the way, the morphologies of the polymer obtained from this catalyst were spherical, which is more preferable. Besides the catalytic activity, crystallinity and morphology were also affected by the different magnesium sources used to prepare the catalysts. 相似文献
Novel heterogeneous catalysts were prepared using immobilization of bis(2‐decylsulfanylethyl)amine–CrCl3 (Cr‐SNS‐D) on various supports, namely commercial TiO2, Al2O3 and magnetic Fe3O4@SiO2 nanoparticles, to yield solid catalysts denoted as support@Cr‐SNS‐D. The structure of the catalysts was confirmed on the basis of spectroscopic analyses, N2 adsorption–desorption and inductively coupled plasma (ICP) analysis. The surface areas of Al2O3@Cr‐SNS‐D, Fe3O4@SiO2@Cr‐SNS‐D and TiO2@Cr‐SNS‐D catalysts were determined to be 70, 23 and 41 m2 g?1, respectively. A decrease in surface area from that of the supports clearly establishes accurate immobilization of Cr‐SNS‐D catalyst on the surface of the parent carriers. The loading of Cr was determined to be 0.02, 0.16 and 0.11 mmol g?1 for Cr‐SNS‐D supported on TiO2, Al2O3 and Fe3O4@SiO2, respectively, using ICP analysis. After preparation and full characterization of the catalysts, ethylene trimerization reaction was accomplished in 40 ml of dry toluene, at 80°C and 25 bar ethylene pressure and in the presence of methylaluminoxane (Al/Cr = 700) within 30 min. The supported chromium catalysts were found to be efficient and selective for the ethylene trimerization reaction. The highest activity (74 650 g1‐hexene gCr?1 h?1), as well as no polyethylene formation during reaction processes, was observed when TiO2 was used as the catalyst support. 相似文献
A new generation of MgCl2‐supported catalysts for the polymerization of propene without any external donors was prepared. Two diethers, 9,9‐bis(methoxymethyl)fluorene (for Cat‐A) and 2,2‐dipropyl‐1,3‐dimethoxypropane (for Cat‐B) differing in the bulkiness of alkyl substituents in position 2, have been used as internal donors in MgCl2/TiCl4/diether‐AlR3 catalysts. The weight‐average molecular weights produced with both catalysts were over 3.5×105 at low temperature in slurry polymerization (< 40°C). Cat‐A showed higher activity and produced higher isotactic polypropene than Cat‐B. The activity of both catalysts proved to be dependent on the temperature. 相似文献
In this work, different types of polyethylene (linear, spiral nanofibers and microspheres) were obtained via confined polymerization by a PPM-supported Ziegler-Natta catalyst. Firstly, the Ziegler-Natta catalyst was chemical bonded inside the porous polymer microspheres (PPMs) supports with different pore diameter and supports size through chemical reaction. Then slightly and highly confined polymerization occurred in the PPM-supported Ziegler-Natta catalysts. SEM results illustrated that the slightly confined polymerization was easy to obtain linear and spiral nanofibers, and the nanofibers were observed in polyethylene catalyzed by PPMs-1#/cat and PPMs-2#/cat with low pore diameter (about 23 nm). Furthermore, the highly confined polymerization produced polyethylene microspheres, which obtained through other PPM-supported Ziegler-Natta catalysts with high pore diameter. In addition, high second melting point (Tm2: up to 143.3 °C) is a unique property of the polyethylene obtained by the PPM-supported Ziegler-Natta catalyst after removing the residue through physical treatment. The high Tm2 was ascribed to low surface free energy (σe), which was owing to the entanglement of polyethylene polymerized in the PPMs supports with interconnected multi-modal pore structure. 相似文献
The possibility of using RnP(O)(CH2OR′)3—n (R = alkyl, R′ = methyl or acyl, n = 0–2) polydentate phosphine oxides as external electron donors for the titanium-magnesium catalysts for isotactic polypropylene synthesis is demonstrated for the first time. The kinetics of propylene polymerization in liquid monomer at 70°C and the isotacticity and molecular-weight characteristics of the resulting polypropylene are studied as functions of the nature of the substituents at the phosphorus atoms in the external donor and the molar ratio of the cocatalyst AlEt3 to the external electron donor. Among the compounds examined, isoamyldi(methoxymethyl)phosphine oxide (R = iso-Am, R′ = Me, n = 1) is the most efficient. The isotacticity index of the polypropylene (PP) synthesized on the titanium-magnesium catalyst with this external donor is as high as 94–95%, and the activity of the catalyst (Cat) in the absence of hydrogen is 5.0–6.5 (kg PP) (g Cat)?1 h?1. With the optimum combination, the activity of this catalyst is ≈5 (kg PP) (g Cat)?1 h?1 and the isotacticity index is 94%. These parameters are close to those obtained for propylene polymerization in the absence of hydrogen on the same titanium-magnesium catalyst with phenyltriethoxysilane (external donor used in the industrial synthesis of PP): the activity is 5.6 (kg PP) (g Cat)?1 h?1, and the isotacticity index is 95%. The introduction of hydrogen into the reaction zone makes it possible to efficiently control the molecular weight of PP, increases the catalyst activity by a factor of 1.5–2.5, and somewhat decreases the isotacticity index (from 94 to 91–92%). 相似文献
This study is aimed at atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) using a novel catalyst. The bis-(2-dodecylsulfanyl-ethyl)-amine (SNS) tridentate ligand with mixed donor atoms was synthesized in high purity using inexpensive reagents and was reacted with copper(I) bromide to produce the CuBr/SNS catalyst. The catalyst mediated living polymerization of MMA yielding polymers with controlled molecular masses and narrow molecular mass distributions (PDI < 1.25). Also, the kinetic plot exhibited a linear increase of ln([M]0/[M]) versus time, indicating constant concentration of propagating radicals during the polymerization. The products were characterized by 1H NMR, 13C NMR, FT-IR, UV-VIS, GC and elemental analyses (CHNS) and by GPC. 相似文献
The substituted β-ketoiminato palladium(II) complexes, Pd[CH3C(O)CHC(NAr)CH3](Pph3)(Me) (1 Ar = α-napthyl, 2 Ar = fluorenyl), can be prepared from the reaction of (COD)PdMeCl and Pph3 with the appropriate ligand. After activation of 1 and 2 with methylaluminoxane (MAO), the resulting palladium(II) complexes are used as catalysts for ethylene polymerization, yielding linear polyethylene. The effects of temperature, co-catalyst to catalyst molar ratio and polymerization time on catalyst activities are reported. The catalyst activity decreases above −20 °C due to catalyst deactivation and optimum co-catalyst to catalyst ratio is 300:1. 相似文献
Two (SiO2/MgR2/MgCl2)·TiClx model catalysts are made by refluxing TiCl4 with 0.35 wt% Cr modified silica gel/alkyl Mg adducts or silica gel/alkyl Mg adducts, which are named as Cr/Ti‐based bimetallic Cat‐1 and Ti‐based monometallic Cat‐2, respectively. The kinetics, active center counting, morphology, and polymer characterizations are studied to disclose the effect of low loading Cr active sites on the Cr/Ti‐based bimetallic Cat‐1 polymerization under mild conditions. The activity of Cat‐1 is 120.4% higher than that of Cat‐2, with a 114.1% higher [C*]/[M] value. Morphology results show the Cat‐1 fragmentation in the first 3 min is highly accelerated, which helps to release buried clustered Ti sites. Differential scanning calorimetry results show that low‐temperature heat absorbing shoulder of polyethylene (PE) from Cat‐2 demonstrates the signal of low crystallinity polymer made by Cat‐2 during the first 60 s, verifying the fluffy polymer in morphology results. GPC results show PE from Cat‐1 has a higher Mw in the first 3 min while a lower Mw in the end. The Cat‐1, which release active sites faster, has a high Mw in the early time. Lower Mw in the 900 s attributes to the effect of relative lower Mw polymer made by Cr sites, compared with Cat‐2. 相似文献
Summary: The effective immobilization and activation of a single‐site chromium catalyst for ethylene polymerization has been achieved using MgCl2/AlRn(OEt)3 − n supports, without the use of methylaluminoxane (MAO) or a borate activator. High catalyst activity and a spherical polyethylene‐particle morphology is obtained. Furthermore, the single‐site characteristics of the catalyst are retained, the narrow molecular weight distribution of the polymers obtained are apparent from gel permeation chromatography (GPC) and confirmed by rheological characterization.
Shear frequency dependence of the storage modulus of (♦ and ▴) polyethylene ( = 1.8–1.9) prepared using an immobilized Cr catalyst, compared to (▪) a reference polymer having = 4.1. 相似文献
A supported magnesium-vanadium-aluminium catalyst was prepared by depositing –with the use of a milling technique–VOCl3 on the MgCl2(THF)2 support and subsequent activation with diethylaluminium chloride. Catalytic activity of the obtained system for ethylene polymerization was evaluated as a function of Mg/V and Al/V ratios as well as catalyst ageing time and polymerization temperature. High concentrations of THF in the catalytic system and considerable excess of an organoaluminium co-catalyst were found to have no deactivating action on vanadium active sites. The catalyst obtained is stable and its activity for ethylene polymerization is high. It yields polyethylene with higher molecular weight and higher melting point than offered by the materials produced with the use of a corresponding unsupported vanadium catalyst or a titanium-based system on the same magnesium support. Kinetic investigations confirmed stability of this catalyst irrespective of its concentration in the polymerization medium or of monomer concentration. Moreover, analysis of the kinetic findings revealed that over 80% of vanadium employed forms active polymerization sites. 相似文献
Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE. 相似文献