The main kinetic behavior of the slurry polymerization of propene with a MgC1,-supported TiC14/C,H,COOC,H, catalyst, activated by Al(C,H,), , was studied. Examination of the dependence of the polymerization rate on temperature and concentrations of A1(C2H5), and of propene resulted in a Langmuir-Hinshelwood rate law with the number of polymerization centers dependent on time. The polymerization rate as function of the polymerization temperature shows a maximum, which is compatible with the rate law. The analysis of the phenomenon of an optimum temperature gave 15 kJ . mol-' and 36 kJ . mol-' for the activation energy of the rate determining step and the adsorption energy of Al(C,H,), , respectively. Examination of the rapid decay of the polymerization rate showed that the main part of the decay is represented by a second order decay independent of the amount of polymer produced, which can be understood by a second order decay of surface sites by A1 (C,H5),. The number of active centers of the catalyst in gas phase polymerization was estimated applying the inhibition method with carbon monoxide. The results show a constant value for the propagation rate constant, kp, during the second order rate decay. The observed polymerization kinetics strongly suggest the existence of two kinds of polymerization centers (isotactic and atactic).
N u m z u 41 0, Japan Synopsis Thermal analysis in combination with infrared spectroscopy was applied to investigate the states of ethylbenzoate (EB) and TiC1, in the simple type of the MgC1,-supported high-yield catalysts. A further attempt was made to evaluate kinetic parameters in the initial stage of propylene polymerization (i Is) by a stopped flow method. The catalysts employed in the present study were prepared by co-grinding MgC1, and TiCl, . EB complex. Thermal analysis and infrared spectroscopy showed that TiC1, . EB complex decomposes during co-grinding process. It was also indicated that EB, thus produced, has strong interaction with MgCl,. This was consistent with observations made by infrared spectroscopy. It was deduced that EB and TiCl, are supported at separate sites of MgCl, in the co-ground catalyst. Kinetic parameters including rate constants of propagation ( h,) and transfer (k,,), and concentration of polymerization centers ([C*]) were determined. The values of k , and k,, remained almost constant throughout the range of co-grinding time, but [C*] increased with time of co-grinding. No significant changes in the value of k , were observed. Accordingly, the improvement of catalyst activity was attributed to an increase in [C*] rather than k,. These results lead to the conclusion that the complex decomposes during the co-grinding to yield EB and TiC1, which interact only with MgCl,.
Several new peaks observed in the 13C NMR spectra of polypropylene prepared with a VC14/A1(C2H5)2Cl catalyst were assigned to the chemical inversion in the chain such as an isolated head-to-head or tail-to-tail unit.
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