Ziegler-Natta polymerization kinetics

Ziegler—Natta polymerization kinetics are, as indicated in the introduction, difficult to study experimentally, particularly those based on insoluble transition metal compounds. They are also complicated by the interaction of concurrent chemical reactions and by physical processes which may have either accelerating or retarding influences on the polymerization. 

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... 

Homogeneous kinetics are applicable to some Ziegler-Natta polymerizations, when adsorption of initiator components or monomer is not important. The polymerization rate is expressed as... 

Adsorption phenomena are important in most Ziegler-Natta polymerizations, and this requires treatment by heterogeneous kinetics [Bohm, 1978 Boor, 1979 Chien and Ang, 1987 Chien and Hu, 1987 Cooper, 1976 Keii, 1972 Tait and Watkins, 1989]. The exact form of the resulting kinetic expressions differs depending on the specific adsorption... 

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)... 

T. Keii, A Kinetic Approach to Elucidate the Mechanism of Ziegler-Natta Polymerization, in Ref. 9, p. 263. 

By far the most important industrial coordination polymerization processes are Ziegler-Natta polymerizations of 1-olefins [107-110], most notably the production of high-density polyethene [111] and stereo-specific olefin polymers and copolymers [108], However, these processes employ solid catalysts, and the complex kinetics on their surfaces have no place in a book on homogeneous reactions. 

Kinetic Features of Ziegler-Natta Polymerization of Olefins. 84... 

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

Control of Distribution in Polyolefins with Catalytic Systems Table 2. Kinetic scheme for Ziegler-Natta polymerization (ethylene)... 

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... 

Problem 9.9 The kinetic rate behavior of Ziegler-Natta polymerization of ethylene and propylene is given by the empirical equation... 

The monometallic mechanism of Cossee and Arlman [10] for Ziegler-Natta polymerization has found favor in the literature because it is based upon quantum mechanical considerations rather than on agreement with the kinetic data [5]. According to this mechanism, as described earlier and shown in Figs. 9.3 and 9.4, the initiation process involves interaction of aluminum alkyl with an octahedral ligand vacancy around Ti which results... 

The kinetics are much simpler in homogeneous metallocene-based catalyst systems, especially in base-free cationic catalyzed polymerization systems, than those in heterogeneous systems. The polymerizations with homogeneous metallocene catalysts are no doubt the best systems for kinetic study of Ziegler-Natta polymerization. The a-olefin polymerization with these catalysts also offers a good opportunity to study the durability and deactivation of the catalysts, since the polymerization systems remain homogeneous over a considerable long reaction period [50]. 

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

Certain Ziegler-Natta polymerization systems showing stable kinetic ratetime profiles of the type (a) in Fig. 9.6 agree well with Eq. (9.39) in rate behavior. Describe how kinetic experiments would be planned and the results analyzed in order to derive the kinetic parameters of this equation. 

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