Number of Active Centers and Propagation Rate Constants in the Ethylene Polymerization with Catalysts Based on 2,6-bis(imino)pyridyl Complexe of Iron(II)
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By using 14CO quenching method the number of active centers (CP) and propagation rate constants (KP) at ethylene polymerization with homogeneous catalyst LFeCl2 and supported catalysts LFeCl2/MgCl2, LFeCl2/SiO2 and LFeCl2/Al2O3 (L: 2,6-(2,6-(Me)2C6H3N=CMe)2C5H3N) have been determined. Al(i-Bu)3 as a cocatalyst was used in these experiments.
For homogeneous complex the sharp decay of polymerization rate is observed: activity decreases in 5 – 10 times for 10 min at 350C. It is found Cp value consists 40% of total Fe content in the initial stage of polymerization and decreases to 16% for 10 min. The propagation rate constant decreases from 2.6.104 to 0.82.104 L/(mol.s) at polymerization for 10 min.
For all supported catalysts the polymerization rate is stable with polymerization time (70oC). We have found the number of active centers consists the small portion (2 – 3.5 %) from the total Fe content in catalysts. The KP values (700C) are equal to 2.2.104, 1.104 and 1.7.104 L/(mol.s) in the case of supports MgCl2, SiO2 and Al2O3, respectively.
Addition of hydrogen at ethylene polymerization with all supported catalysts proceeds to increase of activity. Data on the Cp and Kp values have been obtained at polymerization with hydrogen. The introduction of hydrogen slightly influences the Cp values, but increases the Kp values in 1.3-3 times.
Data on the effect of polymerization temperature on the activity, Cp and Kp values at ethylene polymerization with supported catalysts are obtained and discussed.