JAIST Repository: Ziegler-Natta触媒に用いられるチタン及びマグネシウム塩化物の振動分光
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(2) Vibrational spectra of titanium chlorides and magnesium chlorides used for the Ziegler-Natta catalyst Hideharu Miyaoka Ziegler-Natta catalyst (ZNc) composed of titanium chlorides and magnesium chlorides has been used for the production of highly stereospecific polyolefins. Although a large number of studies have been made on this catalyst, its catalytic mechanism has not yet been clear.. In order to clarify its catalytic mechanism, it is important to perform. the in situ observation of the catalytic reaction on a model thin film ZNc by vibrational spectroscopy.. For this. observation, vibrational spectra of crystalline TiCln (n=2, 3, and 4) and MgCl2 thin film are necessary as the basic data. The aims of this work are (1) to obtain vibrational data of TiCln (n=2,3,and 4) by Raman scattering, and (2) to establish the production method of crystalline MgCl2 thin film available for the vibrational spectroscopic observation. The observed Raman spectra of TiCln are shown in Fig. 1. The Raman spectrum of crystalline TiCl2 shown in Fig. 1 is the first data, so far as we know.. In the spectrum of crystalline α-TiCl3, five clear Raman bands are seen.. The frequencies of these five bands are different from those reported in Ref. 1.. Four clear Raman bands are seen in the. spectrum of TiCl4. The frequencies of these observed bands agree well with those reported in Ref. 2 and 3.. In order. to make assignments of these observed bands in Fig. 1, normal modes were calculated by the GF method. Through the calculation, we find that the Ti-Cl stretching force constant increases as the oxidation number of the Ti increases. This result provides important information for the investigation of the catalytic reaction , because the Ti-Cl stretching force constant can be a good indicator of the catalytic activity. Next, the Raman observation of ball-milled α-TiCl3 was performed to investigate the milling effect leading to an increase in the activity of ZNc. A new band appears at 224 cm-1 for ball-milled α-TiCl3. This band probably results from the breakdown of the crystal symmetry. In order to prepare the MgCl2 film, MgCl2 was sublimed from a glass crucible heated at about 420℃ and deposited on a Ag film in UHV. The observed Raman spectrum of the MgCl2 thin film is shown in Fig. 2. Two Raman modes A1g and Eg are clearly seen in the spectrum.. Due to the SERS (surface enhanced Raman scattering). effect of Ag film substrate the observation Raman scattering from the very thin MgCl2 film has become possible. Since observed band frequencies agree with those of MgCl2 crystal and the observed band widthes are not so broad, we 6. 5. Raman intensity (cps). Raman intensity (arb. units). conclude that the crystallinity of the deposited film is good.. Si(substrate). A1g. 4. 4. crystalline α—TiCl3. Eg. 3. 2. 2. crystalline TiCl2. 1. MgCl2: 35Å Ag: 301Å. liquid TiCl4 0 0. 200. 400. 600. 800. —1. Stokes shift (cm ). Fig. 1: Raman spectra of TiCln (n=2, 3, 4). 0 0. 200. 400. 600. 800. —1. Stokes shift (cm ). Fig. 2: Raman spectrum of MgCl2 thin film. [1] I. Kanesaka, K. Kawai, T. Miyatake, and M. Kakugo, Spectrochim. Acta. 42A, 705 (1984). [2] R. J. H. Clark and P. D. Mitchell, J. Chem. Soc. Faraday Trans. II 71, 515 (1975). [3] I. I. Kondilenko, V. E. Pogorelov, V. L. Strizhevskii, and E. E. Shinkareva, Optika I. Spektrosk. 26, 203 (1969). [4] E. G. M. Tornqvist, Annals of N. Y. Acad. Sci. 155, 447 (1969)..
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