Determination of the Number of Active Centers in Ziegler-Natta Polymerizations of Olefins

Abstract

Four intrinsically different methods for the determination of the number of active centers were employed in propylene polymerization catalyzed by the typical heterogeneous system TICI, /AlEt,Cl: (i) determination of M, (GPC method) and calculation of number of macromolecules therefrom; (ii) quenching with BuOT and determination of tritium in the polymer; (iii) quenching with CO or CO, and determination of carbonyl groups in the polymer (IR spectroscopy); (iv) quenching with SO, and determination of sulfur in the polymer. The first two methods exhibited a reasonable agreement for the number of active centers. Method (iii) gave much lower values, whereas method (iv) was found to be virtually unsuitable due to a high extent of side reactions of SO, with the polymer. A similar comparison of the methods was made in ethylene polymerization catalyzed by the typical homogeneous systems Cp,TiEtCl/AIEtCl, and Cp,TiEtCl/alumoxane. Method (ii) gave a much lower number of active centers than method (i), due perhaps to a low extent of alcoholysis of the Ti-C bond or to a high kinetic isotope effect. CO, appeared to be entirely inert as a quenching agent and CO had been reported to show side reactions. It follows that none of the above quenching methods have universal application and thus literature data should be considered with caution.

Active center determinations on MgCl2‐supported fourth‐ and fifth‐generation Ziegler–Natta catalysts for propylene polymerization

“…Throughout the years, various methods have been developed for the determination of the number of active centers in Ziegler–Natta catalysts, each method having its own specific advantages and limitations 8. Stopped‐flow polymerization, first developed by Keii et al,9 makes use of the fact that at extremely short polymerization times (<1 s), propylene polymerization with MgCl 2 ‐supported catalysts can be quasi‐living, so that the polymer molecular weight increases with polymerization time.…”

Stereochemistry of Polymerization

“…[C*] is usually determined from experiments in which the active sites are quenched (made inactive) with CH 3 O 3 H, 14 CO, or 14 CO 2 [Jaber and Fink, 1989;Mejzlik et al, 1986Mejzlik et al, , 1988Tait and Watkins, 1989;Vozka and Mejzlik, 1990]. Other methods include the use of number-average molecular weight (combined with polymer yield) and 14 C-labeled group I-III metal component.…”

A new method of active center determination for olefin polymerization with supported Ziegler-Natta catalysts

“…The methods based on quenching the propagating chains with 14 CO or CS 2 are complicated by possible reversibility of the quenching reactions and presence of side reactions. 10,13,17,19,22,25 We have previously used acetyl chloride as a quenching agent to react with the active centers in heterogeneous Ziegler-Natta catalysts. 9,26,27 The reaction of acetyl chloride with TiCl 3 -AlR 3 catalyzed 1-octene polymerization system was found to be very fast and irreversible.…”

“…In the past decades, several methods have been developed for the determination of active center concentration. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The method using CH 3 OT as a quenching agent to tag the active centers has been proved to be a reliable one for both homogeneous and heterogeneous catalyst systems. 10,11 However, this method suffers from the limitation that only an average value of C p can be estimated.…”