Kinetics of Ziegler-Natta polymerization

The kinetics of Ziegler-Natta polymerization, like the mechanism of the reaction, are complex. The relatively few polymerizations that are homogeneous behave in a manner generally similar to noncoordination ionic polymerizations (Chapter 8). However, as has been pointed out earlier, the heterogeneity of the reaction system is more of a rule in Ziegler-Natta polymerization than an exception. The heterogeneous systems usually exhibit complicated behavior [2,5,7], as can be seen from some typical kinetic rate-time profiles, types (a)-(f) in Fig. 9.6. Such profiles are significant in 

Ziegler-Natta polymerizations in that their particular shape may be characteristic of a particular catalyst or catalyst-monomer system. In general, such profiles can be considered to consist of three periods, viz., an acceleration period, a stationary period, and a decay period. Some catalyst systems show all three types. 

Type (a) behavior is shown by many first generation catalyst systems, e.g., a-TiCla, VCI3, etc., when used with dialkylaluminum halides as co- 

The nature of this acceleration period was a subject of debate for a long time. Early research by Natta and Pasquon [12] using a-TiCls catalysts established that breakdown of the a-TiCls matrix took place due to the mechanical pressure of the growing polymer chains in the early stages of the polymerization, thus exposing fresh Ti atoms and leading to the formation of new active centers with consequent increase in the polymerization rate. After breakdown of the a-TiCls matrix to primary crystallites has taken place, a steady rate is observed for a significant period of time. Such attainment of a steady-rate behavior permits accurate measurement of polymerization kinetics. 

Type (b) behavior, in which the rate of polymerization increases in the acceleration period to reach a maximum and then decreases, is often observed when trialkylaluminum compound usually produces a more active but less stable catalyst. 

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Keii, T., Kinetics of Ziegler-Natta Polymerization. Kodansha Scientific Books, Tokyo, 1972. 

Keii T (1982) Kinetics of Ziegler-Natta polymerization. Chapman Hall, London... 

The summations extend from n = 2 to n. = oo.) Keii [Kinetics of Ziegler-Natta Polymerization, Kodansha, Tokyo, 1972] has noted that under steady-state reaction conditions, the number of polymer molecules with degree of polymerization n desorbing per unit catalyst surface area in unit time may be written as... 

Several articles have been published that give detailed information on the subject of this review, covering the literature up to 1975-1979. These include books by Pracejus (6) and Boor (6a) and a chapter by Caunt (7), together with an account of the kinetics of Ziegler-Natta polymerization by Keii (8). In addition, a memorial volume (9) to Ziegler, edited by Chien, summarizes contributions to most fields of study on coordination polymerization. The following areas are reviewed in reference (9) (i)... 

Ziegler-Natta Catalysts Kinetics of Ziegler-Natta Polymerizations Practical Features of Ziegler-Natta Polymerizations Comparisons of Cis-1,4-Polydienes Metallocene Catalysts... 

T. Keii, Kinetics of Ziegler Natta Polymerizations, Halsted Press, New York (1973). 

Using the above type of experimental set-up for propylene polymerization with TiCl3-AlEt3 in n-heptane, the rate of polymerization was measured P . Keii, Kinetics of Ziegler-Natta Polymerizations , Halsted Press, New York, 1973] at different... 

Kinetics of Ziegler-Natta Polymerization 9.4.1 Typical Shapes of Kinetic Curves... 

Using the above type of experimental set-up for propylene polymerization with TiQs-AlEts in n-heptane, the rate of polymerization was measured [T. Keii, Kinetics of Ziegler-Natta Polymerizations , Halsted Press, New York, 1973] at different speeds of stirring and constant propylene pressure. The results obtained indicated that there were two different steady-state rate curves for the stirring speeds of 400 and 600 rpm. In each case, a steady bulk monomer concentration was reached in about 3-4 hours. Show how the overall process at steady state can be modeled to show dependence of the polymerization rate on stirring speed and to enable determination of both the mass transfer rate constant and polymerization rate constant from rate measurements at different stirring speeds. 

T. Keii, Kinetic of Ziegler —Natta Polymerizations, Chapman Hall (1972). 

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