Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The determination of active centres concentration in ethylene polymerization using various TiCl4/MgH2-Al(C2H5)3 catalytic systems, by the 14CO radio-tagging method, is reported. It is found that with increasing the absolute titanium amount the concentration of active centres, [C*], increases, whereas the propagation rate constant, kp, decreases. In addition, using various TiCl4/MgH2 catalysts in ethylene polymerization, it is found that the lower the Ti content, the higher is the surface area of the catalyst and the higher is the polymerization activity. Determination of [C*] shows consclusively that the decrease in the polymerization activity observed to occur with increasing the Ti content, and thus decreasing the surface area, is unequivocally due to a reduction in the concentration of active centres but not to any fundamental change in the value of the propagation rate constant.
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