Kinetics of Anionic Polymerization

A general description of anionic polymerization kinetics is complicated by the associations that may occur, particularly in nonpolar (hydrocarbon) solvents. The rate of propagation is proportional to the product of the monomer concentration and the concentration of active living chains [Pj]  

With negligible association (e.g., in THF solvent or hydrocarbons at -BuLi concentrations less than 10 mol), each initiator molecule starts a growing chain, and in the absence of terminating impurities, the number of active living chains equals the number of initiator molecules added. 

Unlike the case for free-radical addition, this can be readily integrated for abatchreactor 

Because anionic polymerizations are generally carried out in rather dilute solutions in inert solvents, volume changes with conversion tend to be much smaller than when undiluted monomer is polymerized. This often justifies the neglect of volume change (s = 0) for which Equation 10.9 becomes 

Example 10.3 For an isothermal reaction (constant kp) subject to the assumptions in Example 10.2, obtain an expression that relates x to time. Neglect volume change. 

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Slomkowski, S., and Penczek, S., Influence of dibenzo-18-crown-6 ether on the kinetics of anionic polymerization of p-propiolactone, Macromolecules, 9, 367-369, 1976. 

Remarkably few systematic studies have been made of the kinetics of anionic polymerization in non-polar solvents containing small amounts of ethers in contrast, studies of bulk ether systems abound. Several studies have appeared 156 158) in which the propagation reactions involving styryllithium were measured in mixtures of benzene or toluene with ethers. The kinetic orders, in some cases, of the reactions were identical to those observed in the absence of the ether. Thus, in part, the conclusion was reached 157,1581 that the ethers did not disrupt the dimeric degree of aggregation of poly(styryl)lithium. The ethers used were tetrahydrofuran 156), anisole 157), diphenyl ether 158), and the ortho and para isomers of ethylanisole157). 

Bar-Ilan and Zilkha [24] have attempted to study the kinetics of anionic polymerization of EO initiated by anhydrous KOH. Initiation was slow and inefficient and no direct measurement of the number of active sites was made. As we shall see in later sections, such complications need to be overcome before really meaningful kinetic parameters can be obtained. 

Due to the relatively fast side reactions consuming both initiator and growth centres, the evaluation of the kinetics of anionic polymerization becomes very difficult. We are dealing with a system of varying concentration of both active species which, according to schemes (45), (51) and (52), can be not only consumed but also regenerated in the complicated set of side reactions. Hence, the key problem of the anionic lactam polymerization consists in the determination of the instantaneous concentrations of lactam anions and growth centres. 

The lack of termination greatly simplifies studies of the kinetics of anionic polymerization. The living polymer may be prepared at the desired concentration, then mixed with monomer. A reaction then ensues and its progress can be followed by any suitable technique. Since termination is eliminated, the polymerization is first order with respect to monomer, and hence its concentration is given by the usual equation ... 

The simple kinetics of anionic polymerization described earlier exists because the initiator is converted completely from the inactive form, CA, to the active form, C "A" (or C -bA ) before any propagation reactions take place. However, some initiators (e.g, lithium alkyls and aryls) maintain an equilibrium between the active form and the inactive form. Moreover, this equilibrium may extend to the growing anionic chains also. In such a situation we must write the initiation steps as... 

In a series of papers43 4S), the kinetics of anionic polymerization of ethylene oxide in conjunction with different catalysts were studied. These studies expand our understanding of the mechanism of living polymerization systems and provide new information on the processes of active center association. Herein, primarily, lies the specific nature of the heteroatomic systems, as compared with the vinyl monomers studied earlier 9 ... 

This paper describes the elimination of a systematic error in the Baker-Williams (BW) method, a combination of the BW and the gel permeation chromatography (GPC) methods for elimination of the effects of side reactions on the molecular weight distributions, and, finally, the application of these methods to some problems in the kinetics of anionic polymerization of styrene and methyl methacrylate. 

Remarkably few systematic studies have been made of the kinetics of anionic polymerization in non-polar solvents containing small amounts of ethers in contrast, studies of bulk ether systems abound. Several studies have appeared Yvhich... 

The kinetics of anionic polymerization of MMA is complicated by chain-end association effects and the... 

Axel H. E. Muller obtained his PhD in 1977 from Johannes Gutenberg University in Mainz, Germany, for the work on the kinetics of anionic polymerization with G. V. Schulz. Since 1999, he has been professor and chair of macromolecular chemistry at the University of Bayreuth. In 2004, he received the lUPAC MACRO Distinguished Polymer Scientist Award and since 2011, he has been a Fellow of the Polymer Chemistry Division of the American Chemical Society. He is senior editor of the journal Polymer. His research interests focus on the design of well-defined polymer stmctures by controlled/living polymerization techniques and on self-organized nanostructures and hybrids obtained from them. He has coedited five books and published over 400 research papers. 

Higashi et al. [262] investigated the anionic polymerization of / -MeSt with -amylsodium in -hexane at 0°C. The polymer obtained could be fractionated in benzene-soluble, acetone-soluble, and insoluble fractions. The IR spectra of these fractions showed distinct differences, but no further explanation was given. Hirohara et al. [263,264] reported on the kinetics of anionic polymerization of o-, m-, and /7-methylstyrene in methyltetrahydro-furan at 25°C using several organometallic initiators. 

Rodriguez-Guadairama LA. Application of online near infrared spectroscopy to study the kinetics of anionic polymerization of butadiene. Eur Polym J 2007 43 928-937. 

The most striking aspect of anionic polymerization is that termination sometimes may not occur unless impurities are present. This can lead to species known as living polymers. The detailed mechanisms and kinetics of anionic polymerization are best considered for individual systems since each reaction is controlled by the nature of the initiator, monomer and solvent and the presence of impurities. 

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