The examination of the reaction between [MgCl2(THF)2], TiCl4(3), AlCl3, AlEt3, AlEt2Cl and the synthesis and isolation of compounds as crystals and resolution of their structure by the X-ray method were the subject of our study. It was expected that these investigations would help to understand the behaviour of MgCl2 towards the transition metal and furnish useful relationships to the structure of catalyst active center and to the polymerization mechanism in TiCl4(3)/MgCl2/AlEt3 system. Our studies have revealed that the main difference between the first and higher generations of Ziegler-Natta catalysts is only the number of active centers. 相似文献
The vibrational Infrared and Raman Spectra of a MgCl2-TiCl4 Ziegler-Natta catalyst precursor with a 50/1 MgCl2/TiCl4 ratio have been recorded. The Raman spectrum of this catalyst precursor, in the range 50-500 cm−1, shows clear scattering lines which can be assigned to the complex MgCl2-TiCl4, well separated from those of the initial species. Analogous, but less clear signals can be found in the infrared spectrum. Vibrational symmetry analysis and quantum chemical calculations of suitable models of MgCl2-TiCl4 complex have been made for the interpretation of the experimentally recorded spectra. The observed spectroscopic signals can be explained in terms of the existence of only one type of MgCl2-TiCl4 complex where the TiCl4 molecules are complexed on the MgCl2 along the (110) lateral cuts in a local C2v symmetry with the Ti atoms in an octahedral coordination. 相似文献
The determination of the number of sites active in the polymerization of ethylene on the surface of α-TiCl3–Al(CH3)3 dry catalysts leads to the conclusion that this number is small in comparison to the total surface of the catalyst. Qualitatively this conclusion is also reached by two other independent methods. Infrared spectra of the catalyst before and after polymerization do not show a change in the type of bonds present in the surface. Electron microscopy proves that no active sites are formed on the basal plane of the α-TiCl3 which constitutes 95% of the total surface. The results strongly favor the lateral faces of α-TiCl3 as the preferred location of active centers. The lateral faces contain chlorine vacancies and incompletely coordinated titanium atoms. This must then be the essential conditions for the formation of active centers. The propagation of the polymer chain has been repeatedly shown to follow an insertion mechanism. The active site, therefore, necessarily contains a metal–carbon bond. The study of catalysts derived from TiCl3CH3 leads to the conclusion that a Ti? C bond on titanium of incomplete coordination is the active species in these cases. The alkylation of surface titanium atoms was proven to be an intermediate step in the catalyst formation from TiCl3 and AlR3. Survival of titanium–alkyl bonds on the lateral faces, where titanium atoms are incompletely coordinated explains best, in the light of our data, the activity of Ziegler-Natta catalysts. Coordination of aluminum alkyl compounds in or around the active center probably complicates the structure of the active centers. 相似文献
Copolymerization of ethylene and 1-butene were performed using the catalyst system TiCl3 · 1/3 AlCl3/MgCl2/THF with or without partial activation by AlEt2Cl. The catalyst and the copolymers were characterized by IR spectroscopy. The experimental results reveal that partial activation strongly affects the catalytic sensitivity toward 1-butene and obviously leads to a two-step polymerization rate profile. 相似文献
The density functional theory on the level of B3LYP/6-31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl3/AlEt2Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetryrestrictions for reactants, products, the possible transition states, and intermediates wascalculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes:(i) Coordination compounds were formed on the optimum configuration of TiCl3/AlEt2Cl.(ii) The transition states were formed. The energy di?erence between transition states and the coordination compounds was 40.687 kJ/mol. (iii) Double bond opened and Ti-C(4) bond fractured, and the polymerization was completed. The calculation results also showedthat the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6-10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization. 相似文献
Electron paramagnetic resonance (EPR) was used to study a MgCl2-supported, high-mileage olefin polymerization catalyst. Anhydrous Toho MgCl2 was the starting material. Treatment with HCl at an elevated temperature, ethyl benzoate by ball-milling, p-cresol, AlEt3, and TiCl4produced a catalyst that contained a single EPR observable Ti+3 species A, which was strongly attached to the catalyst surface, had a D3h symmetry, and no other Ti+3 ion in an immediately adjacent site. Species A constitutes only 20% of all the trivalent titaniums; the remainder is EPR-silent and may be attributed to those Ti+3 ions that have adjacent sites occupied by one or more Ti+3 ions. Activation with preformed AlEt3/methyl-p-toluate complexes produced a single Ti+3 species (C) with rhombic symmetry and displaying 27Al superhyperfin splitting which has attributes for a stereospecific active site. This species is unstable under polymerization conditions and is transformed to another species with axial symmetry and solubilization. Both processes could lead to catalyst deactivation and loss of stereospecificity. Catalysts activated by AlEt3 and methyl-p-toluate separately in various sequential orders produced a multitude of EPR-observable Ti+3 species with varying degrees of motional freedom deemed detrimental to stereospecific polymerization of α-olefins. 相似文献
Vaporization of MgCl2 and other metal halides results in monomeric gas-phase species. Cocondensation of these species with organic diluents such as heptane yields highly activated solids which are precursors to MgCl2 supported “high-mileage” catalysts for olefin polymerization. These catalysts, prepared by treatment with TiCl4 followed by standard activation with aluminum alkyls display high activity for ethylene and propylene polymerization. MgCl2 can also be evaporated into neat TiCl4 to give a related catalyst. The concentration of MgCl2 in the diluent affects catalyst properties as does the nature of the diluent. TiCl3, 3TiCl3 · AlCl3, VCl3 and other metal halides are subject to similar activation. 相似文献
The following reactions, carried out in the absence of solvents, has been studied: α-TiCl3 + Al(CH3)3 at 20°C., β-TiCl3 + Al(CH3)3 at 65°C., α-TiCl3 + Al(CH3)2Cl at 20 and 65°C., and α-TiCl3 + Al(C2H5)3 between 30 and 65°C. It appears that a general reaction mechanism, such as discussed in the preceding paper of this series, applies to all these reactions between TiCl3 and aluminum alkyls. The differences in overall stoichiometry between some of these systems may be linked to differences in stability of the intermediate Ti? C bonds. In the case of α-TiCl3 + Al(CH3)2Cl, alkylation is probably accompanied by fixation of the AlCH3Cl2 on the nonvolatile product. 相似文献
Experimental results on Ziegler-Natta catalysts, based on observations made with the electron microscope, and a qualitative comparison of the stereospecificity of various catalyst combinations are given. The polymerization of olefin in these experiments is performed in the gas phase on dry catalysts in the absence of solvent or excess aluminium alkyl. The crystallographic structure of the lateral faces of α-TiCl3 is established by electron microscopy and electron diffraction. The electron micrographs of α-TiCl3–AlMe3 catalysts show that the active centers, which are revealed by the dotwise formation of polymer, are located along the growth spirals, on lateral faces, and on surface defects. These regions of the surface are the only regions in which the surface titanium atoms are incompletely coordinated. The presence of chlorine vacancies and exposed titanium atoms is therefore an essential condition for the formation of active centers. However, the number of active centers is small in comparison to the number of incompletely coordinated titanium atoms, and hence it is concluded that the normally occurring α-TiCl3 sites with one vacancy do not yield active centers on reaction with aluminum alkyl. It is proposed that the reaction with aluminum alkyl on such sites leads ultimately to a bimetallic complex which fills the original vacancy on the titanium atom. That the complexation is reversible and that the deblocked alkylated site, which is of the type proposed by Cossee, is an active center is not excluded. Such a center would, however, give atactic polymer. Similar complex formation on a TiCl3 site having originally two vacancies would leave one vacancy on the titanium atom. This is believed to be the center of stereospecific polymerization. A model of this active center and a mechanism of polymer growth on it are proposed. 相似文献
Polymerization of vinylcyclohexane (VCHA) with TiCl3–aluminum alkyl catalysts was investigated. The polymerization rate of VCHA was low due to the branch at the position adjacent to the reacting double bond. The effects of aluminum alkyl on the polymerization and monomer-isomerization were observed; the polymer yield decreased in the following order: (CH3)3Al > (i–C4H9)3Al > (C2H5)3Al. Isomerization of VCHA was observed with the TiCl3–(i–C4H9)3Al and the TiCl3–(C2H5)3Al catalysts during the polymerization, while with the TiCl3–(CH3)3Al catalyst such isomerization was not observed. Monomer-isomerization copolymerization of VCHA and trans-2-butene took place to give copolymers consisting of VCHA and 1-butene units. 相似文献
Summary: A tandem catalytic system, composed of (η5‐C5H4CMe2C6H5)TiCl3 ( 1 )/MMAO (modified methyl aluminoxane) and [(η5‐C5Me4)SiMe2(tBuN)]TiCl2 ( 2 )/MMAO, was applied for the synthesis of ethylene–hex‐1‐ene copolymers with ethylene as the only monomer stock. During the reaction, 1 /MMAO trimerized ethylene to hex‐1‐ene, while 2 /MMAO copolymerized ethylene with the in situ produced hex‐1‐ene to poly(ethylene–hex‐1‐ene). By changing the catalyst ratio and reaction conditions, a series of copolymer grades with different hex‐1‐ene fractions at high purity were effectively produced.
The overall strategy of the tandem 1 / 2 /MMAO catalytic system. 相似文献