Summary: Method of polymerization inhibition by radioactive carbon monoxide (14CO) has been used to determine the number of active centers (CP) and propagation rate constant (kP) for ethylene polymerization with homogeneous complex 2,6‐(2,6‐(Me)2C6H3NCMe)2C5H3NFeCl2 (LFeCl2), activated with methylalumoxane (MAO) or Al(i‐Bu)3. With both activators the rate profile of polymerization was unstable: high activity [0.8 × 103–1.5 × 103 kg PE per (molFe · h · atm) at 35 °C] of the initial period sharply decreases (sevenfold in 10 min). In the beginning of polymerization with the catalysts LFeCl2/MAO and LFeCl2/Al(i‐Bu)3, the CP values were found to be 8 and 41% of total Fe‐complex content in catalysts, respectively, and decreased 1.5–2‐fold in 9 min. As polymerization proceeds, the kP value for LFeCl2/MAO system decreases from 5 × 104 to 1.5 × 104 L · (mol · s)−1 LFeCl2/MAO, and for LFeCl2/Al(i‐Bu)3 system from 2.6 × 104 to 0.82 × 104 L · (mol · s)−1. Data on the effect of polymerization time on polyethylene molar mass distribution are presented. Basing on the obtained results it was suggested that highly reactive, but unstable centers, dominating at short polymerization times, produce low‐molar‐mass polyethylene, while polyethylene with higher molar mass is produced by less active (low kP) and more stable centers.Data showing change in molar mass distribution of polyethylene with polymerization time.magnified imageData showing change in molar mass distribution of polyethylene with polymerization time.

Data on the number of active centers (Cp) and propagation rate constants (Kp) have been obtained by means of polymerization quenching with 14CO of propylene and ethylene polymerization with supported titanium‐magnesium catalysts (TMC) with different composition. In the case of propylene polymerization the Cp and Kp values have been measured separately for isospecific, aspecific and low stereospecific centers. Effects of MgCl2 support, internal and external donors are discussed on the basis of data obtained.Data on the strong effect of diffusion limitation at ethylene polymerization with number of TMC have been obtained and a set of methods have been used to exclude this effect. Data on Cp and Kp values at ethylene polymerization with low stereospecific and highly stereospecific catalysts are presented.

Summary: The number of active centers (CP) and propagation rate constants (kP) for polymerization of ethylene with supported catalysts LFeCl2/SiO2, LFeCl2/Al2O3 and LFeCl2/MgCl2 (L = 2,6‐(2,6‐(Me)2C6H3NCMe)2C5H3N), activated by an Al(i‐Bu)3 co‐catalyst, were determined by a method of polymerization inhibition with radioactive 14CO. In contrast to homogeneous systems based on LFeCl2, 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 CP and kP 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 CP values were found to be only 2 to 4% of the total iron complex content in the catalysts. The kP value for the catalysts prepared using different supports (SiO2, Al2O3 and MgCl2) were close (3.2 × 104 to 4.5 × 104 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 CP and kP 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 LFeCl2 catalysts.magnified imageEffect of support on the MMD of PE produced over supported LFeCl2 catalysts.

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The electron paramagnetic resonance (EPR) method was used to investigate the formation of alkylated Ti­(III) species in superactive titanium–magnesium catalysts with a low titanium content during their interaction with an organoaluminum activator (AlMe3), as well as the interaction of alkylated Ti­(III) surface species with carbon monoxide. EPR data on the content of alkylated Ti­(III) species in these catalysts agree well with the number of Ti–R bonds that are determined after the interaction of radioactive carbon monoxide (14CO) with catalyst activated by triethylaluminum in the absence of monomer. Parameters of EPR spectra of the Ti­(III) species having different structure and composition on the surface of titanium–magnesium catalysts were calculated by quantum-chemical simulations. The calculated g-values are consistent with the g-values observed in EPR spectra of the catalysts. Analysis of the literature data and results of our study made it possible to propose the parameters of EPR spectra characterizing the alkylated Ti­(III) species that can serve as precursors of the active sites in supported Ziegler–Natta catalysts.