Ziegler polymerizations 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. 

There is vast experimental and theoretical evidence supporting the existence of multiple site types on heterogeneous Ziegler-Natta catalysts. From a mathematical modelling point of view, each site type has distinct polymerization kinetic constants and consequently produces polymer chains with different average properties. 

Keywords polymerization kinetics, polymerization reactors, mathematical modelling, molecular weight distribution (MWD), chemical composition distribution (CCD), Ziegler-Natta catalysts, metallocenes, microstructure, isotacticity distribution, mass transfer resistances, heat transfer resistances, effects of multiple site types. 

McLaughlin, K. W. Ziegler-Natta catalyzed polymerization kinetics Origin of the molecnlar weight distribution. Ph. D. Thesis, Texas A M University, College Station, TX, May 1986. Chem. Abstr. 1986,1986, 609462. 

The resulting complex (complex II), octahedral and with a vacant coordination position, is considered to be a potentially active site. The kinetic behavior has been shown to be consistent with a simple Ziegler-Natta kinetic scheme involving a rapid bimolecular decomposition of the active centers [481]. In general, all these reactions were found to have polymerization rates that are first order with regard to the monomer and 0.5 order with regard to the catalyst or initiator and oxygen [458]. 

The use of water as a co-catalyst in Ziegler-type polymerizations was first introduced in 1962 (47). The reaction kinetics and crystallinity of the resulting polymers measured by x-ray scattering has been studied (48—51). 

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

Evaluation and Analysis of a Multisite Kinetic Model for Polymerization Initiated with Supported Ziegler—Natta Catalysts... 

Heterogeneous Ziegler-Natta catalysts used to polymerize olefins exhibit phenomena characteristic of active site heterogeneity (1- 5). Complex kinetic models which account for this likelihood have been developed and used only in simulation studies (6-7). 

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... 

Cooper, W., Kinetics of Polymerization Initiated by Ziegler-Natta and Related Catalysts, Chap. 3 in Comprehensive Chemical Kinetics, Vol. 15, C. H. Bamford and C. F. H. Tipper, eds., Elsevier, New York, 1976. 

Figure 5.11 Qualitative illustration of the kinetic control in chemical reactions. Ziegler-Natta stereospecifle polymerizations are examples of kinetic control. Most enzymatic reactions are kinetically controlled - those for instance which lead to...

The first example of Iiving polyolefin with a uniform chain length was found in the low-temperature polymerization of propylene with the soluble catalyst composed of V(acac)3 and Al(C1Hi)2Cl. The mechanism of the living coordination polymerization is discussed on the basis of the kinetic and stereochemical data. Subsequently, some applications of living polypropylene are introduced to prepare tailor-made polymers such as terminally functionalized polymers and block copolymers which exhibit new characteristic properties. Finally, new types of soluble Ziegler-Natta catalysts are briefly surveyed in connection with the synthesis of living polyolefins. 

The first example of a living polyolefin with a uniform chain length was disclosed in 1979 by Doi, Ueki and Keii 47,48) who used the soluble Ziegler-Natta catalyst composed of V(acac)3 (acac = acetylacetonate anion) and A1(C2H5)2C1 for the polymerization of propylene. In this review, we deal with the kinetics and mechanism of living coordination polymerization of a-olefins with soluble Ziegler-Natta catalysts and the synthesis of well-defined block copolymers by the use of living polyolefins. 

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