非邻苯二甲酸酯内给电子体聚丙烯催化剂的研究进展

本文综述了非邻苯二甲酸酯类内给电子体催化剂的研究进展,对目前已处于工业化应用的3种非邻苯二甲酸酯类化合物催化剂的性能特点进行了详细对比.针对日趋严格的清洁型聚丙烯要求,展望了非邻苯二甲酸酯类给电子体化合物以及相关催化剂的发展前景.     

New evidence of the presence of internal electron donors in active sites of heterogeneous Ziegler-Natta catalysts

Poly(propylene) samples produced by heterogeneous Ziegler-Natta catalysts containing different internal electron donors were fractionated by using temperature rising elution fractionation; some key fractions were analyzed with ¹³C NMR. It was found that internal electron donors with different structures can convert aspecific active sites into different isospectrific ones. The employment of bis(2-ethylhexyl) phthalate as internal electron donor leads to chemically inverted structures in the atactic fraction. This suggests that an internal electron donor may also exist in the environment of aspecific active sites.     

Effect of multi-ethers and conventional alkoxysilanes as external donors on the 4th generation Ziegler-Natta catalysts for propylene polymerization

The multi-ether compounds with different numbers of methoxy groups containing 1,3-dimethoxy-2,2-bis(methoxymethyl)propane and 1-methoxy-2,2-bis(methoxymethyl)butane were synthesized using the Williamson reaction from pentaerythritol and 1,1,1-tris(hydroxymethyl)propane, respectively, in the presence of sodium hydride and methyl iodide in tetrahydrofuran and they were characterized by ¹H NMR, ¹³C NMR, and FTIR spectroscopy. These compounds were employed as external donors in the polymerization of propylene using the industrial Ziegler-Natta catalyst. A commercial spherical MgCl₂-supported Ziegler-Natta catalyst containing diisobutyl phthalate as the internal donor was used for the polymerization of propylene. The role of ether compounds and industrial alkoxysilanes on the properties of polypropylene were studied using the xylene solubility method, melt flow index, gel permeation chromatography, scanning electron microscopy, and differential scanning calorimetry. The addition of the electron donors has led to improvements in the activity and selectivity of the Ziegler-Natta catalyst system.     

Stereo- and enantioselective polymerization of hexa-1,5-diene on heterogeneous Ziegler-Natta catalysts obtained with the use of optically active internal donors

Pure racemates and individual enantiomers of diethyl 2,3-diisopropylsuccinate ((+,−)-DIPS and (−)-DIPS) and 2,3-diisopropyl-1,4-dimethoxybutane ((+,−)-DPDMB and (+)-DPDMB) were prepared. The synthesized compounds and diethyl phthalate were used as internal donors for the preparation of heterogeneous Ziegler-Natta catalysts. Polymerization of hexa-1,5-diene was carried out on these catalysts. The obtained samples of poly(methylene-1,3-cyclopentane) were studied by ¹³C NMR spectroscopy and polarimetry. The induction of optical activity to polymer is observed with (−)-DIPS as the internal donor. The induction value makes up 15–20% from the value recorded in the case of optically active metallocene catalysts. The emergence of induction may be associated with the presence of close contact between the titanium atom and the donor molecule within the active site of catalyst, as well as with the fact that the donor molecule either deactivates a part of the stereospecific titanium centers or influences the structure of the titanium centers during their formation and development.     

Comparison of the role of new ethers and conventional alkoxysilanes as external donors in the polymerization of propylene using the industrial Ziegler-Natta catalyst

Two new ethers were synthesized using the Williamson reaction from related alcohols and were used as external donors in propylene polymerization in the presence of the industrial diisobutyl phthalate-based MgCl₂-supported Ziegler-Natta catalyst. For comparison the propylene polymerization was carried out in the presence of silane and in the absence of external donors. The produced polymers were characterized by differential scanning calorimetry, xylene extraction, melt flow index, scanning electron microscopy and gel permeation chromatography. The isotacticity, molecular weight and molecular weight distribution, melt flow index, crystallinity degree and thermal properties of polypropylenes were influenced by the type of external donors.     

New penta-ether as the internal donor in the MgCl2-supported Ziegler-Natta catalysts for propylene polymerization

The penta-ether compound was synthesized by the reaction of di(trimethylolpropane) with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl₂-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional Ziegler- Natta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl₂-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a penta-ether/Mg molar ratio equal to 0.21.     

Steric equivalence between internal and external donors as polymerization stereoregulators: A molecular mechanics study

New models for steric environment of Ti isospecific polymerization sites on MgCl₂ microcrystals are presented. They directly involve the presence of a donor molecule in order to obtain chiral activable Ti atoms otherwise belonging to isolated adsorbed TiCl₄ molecules or Ti₂Cl₈ dimers which are lacking the required symmetry. The most important steric features of donor molecules have been obtained through structure-activity relationships and molecular comparisons, while their adsorption on MgCl₂ faces lateral to (001) has been studied through a conformational analysis approach.     

Density functional study on the role of electron donors in propylene polymerization using Ziegler-Natta catalyst

The role of electron donors in propylene polymerization using Ziegler-Natta model catalyst [TiCl₂CH₃]⁺ has been investigated using density functional calculations at B3LYP/6-31G* level. Methyl benzoate (MBz) and para-methoxy methyl benzoate (p-OMe-MBz) are the electron donors considered in this study. We have found two major roles of these electron donors that match well with the corresponding experimental results. First, for both the catalysts having different electron donors, the propylene insertion in Ti-CH₃ bond in syn-fashion rather than anti-fashion has lower activation barriers (E_act). This indicates that the regioselectivity of propylene insertion is maintained in the presence of the electron donors. Secondly, co-ordination of electron donors is found to increase the activation barriers of propylene insertion, which explains the experimentally observed drop in catalytic activity of [TiCl₂Me]⁺ on adding electron donors.     

Ethylene polymerization with homogeneous Ziegler-Natta catalysts: theoretical study on the role of ion pairs in the polymerization mechanism

The thermodynamics of the reaction of an ethylene molecule with the Cp₂TiCH₃Cl/Al(CH₃)₂Cl system (Cp = η₅-C₅H₅), as a model for olefin polymerization with homogeneous Ziegler-Natta catalysts, was investigated via quantum mechanical DFT calculations. The comparison of the calculated energies for three possible titanium-olefin coordinated intermediates, the ionic complex Cp₂TiCH₃(C₂H₄)⁺/Al(CH₃)₂Cl, the bimetallic complex Cp₂TiCH₃(C₂H₄)^δ+ · Al(CH₃)₂Cl and the olefin-separated ion pair Cp₂TiCH/C₂H₄/Al(CH₃)₂Cl, shows that the most feasible polymerization mechanism occurs via olefin-separated ion pair.     

A new test for the detection of aralkyl and dialkyl ketones containing the -CO-CH2-group

Summary Dialkyl and aralkyl ketones containing the group R-CO-CH₂-give with 2,2-dinitrobiphenyl a blue or violet coloration with an absorption maximum between 560 and 590 nm. The sensitivity of the test is given for about 50 ketones.

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Zusammenfassung Dialkyl- und Arylalkylketone mit der Gruppe R-CO-CH₂- geben mit 2,2-Dinitrodiphenyl eine blaue oder violette Färbung mit einem Absorptionsmaximum zwischen 560 and 590 nm. Die Empfindlichkeit der Probe wird für etwa 50 Ketone angegeben.

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Résumé Les dialcoyles et aryl-alcoyles cétones contenant le groupement R-CO-CH₂-donnent avec le dinitro-2,2 biphényle une coloration bleue ou violette présentant un maximum d'absorption entre 560 et 590 nm. L'auteur donne la sensibilité de l'essai pour une cinquantaine de cétones.

     

Minor products and initiation rate in the chain pyrolysis of propane

With a continuous jet-stirred tank reactor operating at small space time (0.05–1.2 s) the kinetics of the formation of six minor products (ethane, isobutane, butene-1, 2,3-dimethyl-butane, 4-methylpentene-1, and 1,5-hexadiene) are studied during the pyrolysis of propane, at small extents of reaction and over the temperature range of 600–780°C. The experimental results are in agreement with the free radical mechanism proposed by Jezequel, Baronnet, and Niclause for this reaction. They show that the two most important termination processes are The measured rates of formation of the minor products are consistent with the quasi-identical values estimated by Jezequel and co-workers (between 475 and 505°C) and by Allara and Edelson (between 510 and 560°C) for kinetic parameters (A₁ ? 10^16.65 s^?1 and E₁ ? 84.7 kcal/mole) of the chain initiation process      

Spectroscopic investigation of heterogeneous Ziegler-Natta catalysts: Ti and Mg chloride tetrahydrofuranates, their interaction compound, and the role of the activator

X-ray powder diffraction (XRPD), Infrared, Raman, and UV/Vis spectroscopy have been used to investigate the structural, vibrational, and optical properties of Ti and Mg chloride tetrahydrofuranates as precursors of heterogeneous Ziegler-Natta catalysts for polyethylene production; as well as their interaction compound (pro-catalyst) and the final catalyst obtained after interaction with the AlR(3) activator. Although the structure of the precursors and of the pro-catalyst were well known, that of the catalyst (obtained by reaction of the pro-catalyst with AlR(3)) was not easily obtainable from XRPD data. IR and Raman spectroscopy provided important information on tetrahydrofuran (thf) coordination and on the ν(M-Cl) region; whereas UV/Vis spectroscopy gave the direct proof on both the formal oxidation state and the coordination environment of the active Ti sites. Those presented herein are among the first direct experimental data on the structure of the active Ti sites in Ziegler-Natta catalysts, and can be used to validate the many computational studies that have been increasing exponentially in the last few decades.     

Characterization of the changes in the initial morphology for MgCl2-supported Ziegler-Natta polymerization catalysts

Recently considerable detail has become available on the initial morphology and the morphological changes that occur for silica based Cr catalysts for ethylene polymerization. These catalysts are produced as a dry powder and may be employed either in gas phase or in slurry processes. MgCl₂-supported Ziegler-Natta polymerization catalysts are often prepared and employed as slurries. They usually are never dried and thus few studies have employed the spectra of physical techniques common to the characterization of pore structure. In the current study, we have carefully removed the solvent for both ball-milled and precipitated MgCl₂-supported catalysts. These catalysts are characterized by physical sorption, mercury porosimetry, and electron microscopy both as prepared and during the initial stages of polymerization (to ～ 100 g of polymer/g of catalyst). We find that the initial catalyst may be represented by a complex agglomerate of small crystallites as contrasted with the branched pore network found in Cr/silica catalysts. As a result, it is concluded that the initial fragmentation of the MgCl₂ based systems is more uniform as contrasted with the progressive fragmentation of the silica-based system. This fragmentation mechanism facilitates the retention of greater polymer/catalyst surface during the initial stages of the polymerization. © 1992 John Wiley & Sons, Inc.     

A study of the surface region of the Mo-V-Te-O catalysts for propane oxidation to acrylic acid

The bulk mixed Mo-V-Te oxides possess high activity and selectivity in propane oxidation to acrylic acid and represent well-defined model catalysts for studies of the surface molecular structure-activity/selectivity relationships in this selective oxidation reaction. The elemental compositions, metal oxidation states, and catalytic functions of V, Mo, and Te in the surface region of the model Mo-V-Te-O system were examined employing low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). This study indicated that the surfaces of these catalysts are terminated with a monolayer, which possesses a different elemental composition from that of the bulk. The rates of propane consumption and formation of propylene and acrylic acid depended on the topmost surface V concentration, whereas no dependence of these reaction rates on either the surface Mo or Te concentrations was observed. These findings suggested that the bulk Mo-V-Te-O structure may function as a support for the unique active and selective surface monolayer in propane oxidation to acrylic acid. The results of this study have important practical consequences for the development of improved selective oxidation catalysts by introducing surface metal oxide components to form new surface active V-O-M sites for propane oxidation to acrylic acid.     

An NMR study of the species produced by the reactions of dialkyl magnesium and HCl with calcined silica and the polymerisation performance of Ziegler-Natta catalysts produced from this support material

The effect of calcinations on the silica surface groups and thereby on the activity of Ziegler-Natta catalysts in ethylene homopolymerisation has been studied. Silica was calcined at different temperatures and treated with MgR₂ and HCl. Silica surface groups were identified by using ¹H MAS NMR and ¹³C and ²⁹Si CP MAS NMR techniques. Magnesium, titanium and chlorine were measured by elemental analysis. Ziegler-Natta catalysts were prepared from these supports and subsequently used in ethylene homopolymerisation. Maximum activity was obtained with the catalyst based on 590 °C calcined silica. The results indicate that MgR₂ reacts with siloxane-groups (Si-O-Si) in the 300 °C calcined silica, leaving the hydrogen-bonded hydroxyl-groups unreacted. Low activity Si-O-Ti(Cl)₂-O-Si species are formed after reacting with TiCl₄. The higher activity in the catalyst based on 590 °C calcined silica can be explained by the formation of -Si(R)-O-Si-O-TiCl₃ groups, originating from the siloxane bridges which cannot form in 300 °C calcined silica. Other explanations for the higher activity are a higher Mg/Ti ratio or small amounts of crystal water formed in the 590 °C calcined silica.     

A crystallographic study of disorder in titanium trichloride,a component of Ziegler-Natta catalysts for stereospecific polymerization

The profiles of X-ray diffraction patterns have been examined for several powder samples of δ-TiCl₃, obtained by mechanical activation of γ-TiCl₃ and presenting different catalytic activities in the Ziegler-Natta stereospecific polymerization of propylene to isotactic polypropylene. Particular attention has been paid to the δ-TiCl₃ samples showing the best catalytic properties.On the basis of a previous investigation by Allegra, a mathematical treatment has been developed and a disorder function has been elaborated taking into account, in calculating the profiles of the X-ray diffraction intensities, not only the disorder effects but also the sizes of the δ-TiCl₃ crystallites. The selected experimental pattern (δ-TiCl₃, highly activated) has been well reproduced in this way and fitted by overlapping the calculated spectra of two disordered forms, labelled ?₁ and ?₂, which differ in the relative amounts cubic and hexagonal sequences of the Cl-Ti-Cl layers constituting the violet forms of TiCl₃. The best fit was achieved by introducing into the calculations crystallite sizes of about 70 Å.The results of the structural investigation are also discussed in terms of activity of the δ-TiCl₃ based catalyst for the stereospecific polymerization of propylene.     

Single step fluorination of dialkylphosphites: trichloroacetonitrile-KF as an efficient reagent for the synthesis of dialkyl fluorophosphates

The use of trichloroacetonitrile and KF mixture is described as an efficient reagent for the direct conversion of dialkylphosphites to their corresponding dialkyl fluorophosphates via in situ formation of dialkyl chlorophosphates in one-pot.