Kinetic Study of Ethylene Polymerization Over Supported Bis(imino)pyridine Iron (II) Catalysts

Abstract

Abstract Summary: The number of active centers ( C P ) and propagation rate constants ( k P ) for polymerization of ethylene with supported catalysts LFeCl 2 /SiO 2 , LFeCl 2 /Al 2 O 3 and LFeCl 2 /MgCl 2 (L = 2,6‐(2,6‐(Me) 2 C 6 H 3 NCMe) 2 C 5 H 3 N), activated by an Al( i ‐Bu) 3 co‐catalyst, were determined by a method of polymerization inhibition with radioactive 14 CO. In contrast to homogeneous systems based on LFeCl 2 , the supported catalysts are highly active and stable in ethylene polymerization at 70–80 °C. In the presence of hydrogen, the activity of the supported catalysts substantially increases (2–4 fold). The data obtained on the effect of hydrogen on the calculated C P and k P values suggests that for ethylene polymerization without hydrogen, the “dormant” active centers are formed in the catalytic systems. A scheme for the formation of these “dormant” centers and their reactivation in presence of hydrogen is suggested. For the investigated supported catalysts the C P values were found to be only 2 to 4% of the total iron complex content in the catalysts. The k P value for the catalysts prepared using different supports (SiO 2 , Al 2 O 3 and MgCl 2 ) were close (3.2 × 10 4 to 4.5 × 10 4 L · (mol · s) −1 at 70 °C). The support composition affects neither the molecular mass (MM) nor the molecular mass distribution (MMD) of the polymers produced. The obtained C P and k P values and data on the polymer MM and MMD lead to conclusion that the nature of the support has almost no effect on the structure of the active centers and the distribution of their reactivity. Effect of support on the MMD of PE produced over supported LFeCl 2 catalysts. magnified image Effect of support on the MMD of PE produced over supported LFeCl 2 catalysts.