Multicomponent mixtures polymerization

It is the intent of this doeument to define the terms most commonly encountered in the field of polymer blends and eomposites. The scope has been limited to mixtures in which the eomponents differ in ehemical composition or molar mass or both and in which the continuous phase is polymeric. Many of the materials described by the term multiphase are two-phase systems that may show a multitude of finely dispersed phase domains. Hence, incidental thermodynamic descriptions are mainly limited to binary mixtures, although they can be and, in the scientific literature, have been generalized to multicomponent mixtures. Crystalline polymers and liquid-crystal polymers have been considered in other documents [1,2] and are not discussed here. 

Alberty, R. A., Kinetics and equilibrium of the polymerization of benzene series aromatic hydrocarbons in a flame. In Kinetic and Thermodynamic Lumping of Multicomponent Mixtures. (As-tarita, G., and Sandler, R. I., eds.), Elsevier, Amsterdam, 1991, p. 277. 

The most important solvents to be treated are the light alcohols, ethanol, the propanols, and butanols. Other solvents are esters like ethyl and butyl acetate, ketones like acetone, butanone (MEK) or methyl isobutyl ketone, ethers like tet-rahydrofuran (THF) or methyl tertiary butyl ether, or acetonitrile, or mixtures of these solvents. The selectivity of the polymeric membranes for all components in such mixtures is high and fairly similar, multicomponent mixtures can thus... 

Information about the monomeric composition and structure can be obtained with pyrolysis MS but sequence information is lost [46]. The method was used in several applications, such as structural identification of homopolymers, differentiation of isomeric structures, copolymer composition and sequential analysis, identification of oligomers formed in the polymerization reactions, and identification of volatile additives contained in polymer samples [47]. One of the main challenges of the technique is the identification of the products in the spectrum of the multicomponent mixture produced by thermal degradation. 

In this work, examples are shown of the use of the computerized analytical approach in multicomponent polymer systems. The approach works well for both fractionated and whole polymers. The methodology can (1) permit differentiation to be made as to Whether the given sample conprises one conponent or a mixture of several components (2) allow the NMR spectrum of a polymer mixture to be analyzed in an unbiased fashion (3) give information on mole fractions and reaction probabilities that can be significant variables in understanding catalyst structures or polymerization mechanisms. 

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. 

For convenience, multicomponent polymeric materials based on cellu-losics may be grouped into three classes, namely (a) combinations of wood with plastics (WPC), (b) mechanical mixtures in the form of fibers, such as cotton/polyester staple-mixed fibers and cellulosic fiber-filled polymer sheets, and (c) incorporations of cellulosics at a hyperfine structural level. The latter can be further ramified, for instance as follows ... 

Numerous models of gels are based on the widespread polymeric model considering gels as mixtures of multicomponent branched polymers of different weight. Then, the main problem consists in the evaluation of the weight distribution of polymers. 

In recent years, much attention has been paid to multicomponent polymer mixtures in which one or both components are crosslinked and in which the potential exists for mutual entanglement or interpenetration of the chains of the components. A few miscible pairs have been reported, but immiscibility is by far the most common case. Combinations of polyurethanes and acrylics or methacrylics have long been attractive because the components can, in principle, be formed by independent and non-interfering polymerization reactions. 

There are at least four general types of combinations of crosslinked (x) and linear (1) polymers in a two-component system both components crosslinked (xx), one or the other component crosslinked (lx or xl), and both components linear (11). Where at least one of the components has been polymerized in the presence of the other, the xx forms have often been called interpenetrating polymer networks (IPN), the lx and the xl forms termed "semi-IPNs", and the last, linear or in situ blends. There are also a number of ways in which the components can be formed and assembled into a multicomponent system. Sequential IPNs are prepared by swelling one network polymer with the precursors of the second and polymerizing. Simultaneous IPNs are formed from a mixture of the precursors of both components polymerization to form each component by independent reactions is carried out in the presence of the other precursors or products. Usually, the simultaneous IPNs that have been reported are extremes in the component formation sequence the first component is formed before the second polymerization is begun. Sequential IPNs and simultaneous IPNs of the same composition do not necessarily have the same morphology and properties. 

The kinetics of emulsion polymerization reactions are complex because of the numerous chemical and physical phenomena that can occur in the multicomponent, multiphase mixture. A large amount of literature exists on kinetics problems. The general references listed at the end of this chapter contain many important papers. The review paper by Ugelstad and Hansen (11) is a comprehensive treatment of batch kinetics. The purpose of the remainder of this chapter is to present the general kinetics problems and some of the published results. The reader should use the references cited earlier for a more detailed study. 

We have considered so far free-radical polymerizations where only one monomer is used and the product is a homopdlymer. The same type of polymerization can also be carried out with a mixture of two or more monomers to produce a polymer product that contains two or more different mer units in the same polymer chain. The polymerization is then termed a copolymerization and the product is termed a copolymer. Monomers taking part in copolymerization are referred to as comonomers. The simultaneous polymerization of two monomers is known as binary copolymerization and that of three monomers as ternary copolymerization, and so on. The term multicomponent copolymerization embraces all such cases. The relative proportions of the different mer units in the copolymer chain depend on the relative concentrations of the comonomers in the feed mixture and on their relative reactivities. This will be the main subject of our discussion in this chapter. 

An alternative to physical blending is the polymerization of two or more monomers referred to as copolymerization. When more than two monomers are used, the product is referred to as a multicomponent copolymer, and in the special case of three monomers, the term terpolymer is used. Of course, adding more than one monomer type to the reaction mixture results in added complexity in the kinetic reaction mechanisms. This complexity arises... 

To explain the behavior of a polymeric multicomponent system, the polymer is considered as a mixture of two polymer species, PI and P2. By doing this, the polymer-solvent system can be illustrated using a ternary Gibbs triangular diagram. It is assumed that one species of the polymer, PI, has a lower molecular mass than P2 and is completely miscible with the solvent, whereas P2 exhibits an immiscibility region (Figure 15.5). 

Block-like and segmented polymers represent chemically bound "multicomponent" systems that, in our opinion, are able to mimic some of the non-bonded interactions occurring in blends of either compatible or not compatible pol3nners, and to describe phenomena connected with phase segregation and the onset of peculiar micromorpho-logical properties. Additionally, liquid crystal polymers, even though "monocomponent" from a macrochemical point of view in that constituted of only one polymeric material, in reality do behave, under certain selected thermodynamic conditions, as mechanical mixtures of at least two components. 

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