Copolymerization multicomponent

When chains grow from more than two monomers, we speak of multicomponent copolymerization. In a simple case, the number of active centre types in the medium equals the number of copropagating monomers. Many systems are also known where the number of participating centres exceeds the number of monomers. In other cases, the monomers undergo complex formation so that their complexes take part as individual components in copropagation. Let us first pay attention to some cases generated by complications in nominally two-component systems. 

The majority of the above mentioned kinetic schemes were used for the description of the multicomponent copolymerization of three or more types m of monomers. The generalization of the scheme (2.1) for m = 3 was carried out by Alfred and Goldfinger [45] and for arbitrary m — by Walling and Briggs [46]. In this case the terminal model 

This important peculiarity, which allows one to determine the kinetic parameters of m-component copolymerization on the basis of the analysis of the experimental data obtained under the copolymerization of m(m — l)/2 monomer pairs vanishes if one uses other kinetic models instead of the terminal one. There are a number of models describing multicomponent systems which account for the influence of the penultimate unit [47], the formation of the binary [48] and triple [49] complexes and also for the depolymerization reactions [50], However, up to now, all such models have a limited range of application since the current experimental techniques do not allow one to determine correctly a great number of their kinetic parameters. 

Terpolymerization, the simultaneous polymerization of three monomers, has become increasingly important from the commercial viewpoint. The improvements that are obtained by copolymerizing styrene with acrylonitrile or butadiene have been mentioned previously. The radical terpolymerization of styrene with acrylonitrile and butadiene increases even further the degree of variation in properties that can be built into the final product. Many other commercial uses of terpolymerization exist. In most of these the terpolymer has two of the monomers present in major amounts to obtain the gross properties desired, with the third monomer in a minor amount for modification of a special property. Thus the ethylene-propylene elastomers are terpolymerized with minor amounts of a diene in order to allow the product to be subsquently crosslinked. 

The quantitative treatment of terpolymerization is quite complex, since nine propagation reactions 

The assumption of steady-state concentrations for Mp, M2. and M3 radicals can be expressed as 

Combination of Eqs. 6-43 with 6-44, and the use of the appropriate rate expressions from Eq. 6-41 for each R term, yield the terpolymer composition as 

A simpler expression for the terpolymer composition has been obtained by expressing the steady state with the relationships 

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Valvassori, A. and Sartori, G. Present Status of the Multicomponent Copolymerization Theory. VoL 5, pp. 28-58. 

These latter have been tabulated for a great many pairs (M M ) of particular monomers [35]. This circumstance offers in many cases an opportunity to carry out the calculation of statistical characteristics of the products of multicomponent copolymerization without the need for additional experiments to determine the kinetic parameters of the model. 

Free-radical multicomponent copolymerization of dialkylstannyl maleates or dialkylstannyl dimethacrylates with methallyl alcohol (or (J-hydroxyalkyl acrylates) and vinyl monomers (sryrene, methacrylic acid or methacrylamide) yields polymeric powders. Due to their storage and thermal stability and impact strength they are used as protective coatings 79). 

Multichannel analyzer (MCA), 26 434 Multichannel detection, in concentric hemispherical analyzers, 24 106 Multiclient studies, 15 635-636 Multicollector-I CP-MS (MC-ICP-MS), archaeological materials, 5 743 Multicolor displays, LEDs in, 22 175 Multicompartment drum filters, 11 357 Multicomponent copolymerization, 7 619-620... 

The two monomers enter into the copolymer in overall amounts determined by their relative concentrations and reactivities. The simultaneous chain polymerization of different monomers can also be carried out with mixtures of three or more monomers. Such polymerizations are generally referred to as multicomponent copolymerizations the term terpolymerization is specifically used for systems of three monomers. 

The mostly well-known discussion concerning multicomponent copolymerization theory is probably connected with so-called simplified equations put forward in papers [143-147] for the description of S(x) dependence. These equations can be obtained from the general Walling-Briggs equations (3.8), (4.10) via substituting in them expression a /a for Bs. The derivation of these simplified equations is based on the assumption that the rate of the monomer Mj addition to the radical R, is equal to the rate of the monomer addition to the radical Rj ... 

Examples of calculations of such characteristics for the concrete terpolymer are presented, for instance, in the monograph listed as Ref. [6]. Similar computer calculations of the trajectories i(p) and X(p) which determine the values of the statistical characteristics (5.3) and (5.7) can be in principle carried out for other processes of multicomponent copolymerization. However, the original approach [6, 201, 13-15, 18, 202, 203] allows one to use traditional methods of dynamic systems theory [204] to reveal the main qualitative peculiarities of the behavior of the trajectories X(p) and X(p) only via the elementary arithmetical operations by means of a pocket microcalculator. 

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