Subject polymer mixture

Figure 8.3b shows that phase separation in polymer mixtures results in two solution phases which are both dilute with respect to solute. Even the relatively more concentrated phase is only 10-20% by volume in polymer, while the more dilute phase is nearly pure solvent. The important thing to remember from both the theoretical and experimental curves of Fig. 8.3 is that both of the phases which separate contain some polymer. If it is the polymer-rich or precipitated phase that is subjected to further work-up, the method is called fractional precipitation. If the polymer-poor phase is the focus of attention, the method... 

The mechanical synthesis of block and graft copolymer is a method of sizable versatility. It can be performed (as already stated) during polymer processing and in standard equipment. The reaction, also, can be carried out by subjecting a mixture of two or more polymers to mechanical degradation in either the solid, elastic-melt, or solution states. It is, also, possible to induce reaction mechanically between polymers and monomers. 

Polymer miscibihty has been the subject of numerous studies. Pressure is a thermodynamic parameter that can affect the phase behavior of polymer mixture and that can be used to enhance the miscibility of polymers. This properly may have an important apphcation in controlhng microstructure. The phase behavior of blends and block copolymers under pressure has recently received significant attention 1-3). 

The metallocene is added to the supported MAO as a solution in toluene or aliphatic hydrocarbon. Subsequently subjecting the mixture to microwaves has been claimed to fix the metal component on the support and reduce reactor fouling (adhesion of polymer to reactor surfaces). The metallocene can also be dry-blended with the support, avoiding solubilization of the finished catalyst. ... 

Component substances (e.g., additives) in a polymer mixture are subject to registration. 

If we study the composition of the surface of a pol)mier solution or a polymer mixture we should expect to find that the composition of the region near the surface is not the same as that of the bulk. The same applies to an interface between such a system and a solid for example a colloidal particle suspended in a polymer solution will often be coated with a layer of polymer, that may well be able to stabilise the colloid, preventing its aggregation. In polymer solutions this phenomena is known as adsorption, if the polymer accumulates at the surface, or depletion, if it is the solvent that is favoured there in polymer blends one often refers to the surface segregation or surface enrichment of one component of the mixture. However, these different names describe what is essentially the same phenomenon, the subject of this chapter. 

Of course the limiting case of one polymer in a mixture being much shorter than the other is a polymer solution. However, segregation and depletion of polymers at the surface of pol5mier solutions is both more complex than segregation from polymer mixtures and arguably more important, so it forms the subject of the next section. 

In a mixture of hard spheres and depletants a phase transition occurs upon exceeding a certain concentration of colloidal spheres and/or depletants. This is the subject of Chaps. 3-6 in this book. A key parameter in describing the phase stability of colloid-polymer mixtures is the size ratio q,... 

The above complex situation suggests that without a good plan, UV stability problems will never be resolved for polymer mixtures, which is already confirmed by very little understanding of principles governing UV stability of pol3mier blends today. Literature on this subject is very limited and was already... 

Polymer Mixtures and Their Solutions.—Polymer mixtures have been widely reviewed " - - -1 . with the main emphasis directed at their phase behaviour (compatibility, see Chapter 4). Nagarajan remarks that the subject is widely discussed but vaguely understood having undergone technical rather than scientific development , a comment perhaps illustrated by the theoretical... 

Polymer blends and compatibilizing agents historically have been the subject of a wide variety of studies and an extensive body of literature on these materials exists. Without specific chenucal interactions between dissimilar polymers, most polymer mixtures tend to phase separate due to the unfavorable entropy of mixing between the polymer chains. Efforts to control or retard the phase separation process have led to the research and development of compatibilizing agents for polymer blends. For a variety of systems the dispersed phase particle size has been found to decrease with increasing copolymer concentration. Above a critical concentration of copolymer, the size of the dispersed phase remains constant. 

Before reviewing thermodynamic models of particle/polymer mixtures, we consider a slightly different liynamic problem how can the addition of particles influence the phase separation of two polymers. Such a problem statement assumes that (i) particle addition does not impact the incompatibility of the polymers in the blend and (ii) particles can impact the mobility of nearby polymer molecules. Numerous papers and reviews deal with this subject, and our discussion here certainly will not be exhaustive, but will provide a brief overview of the major results. 

Coating solutions often exhibit a mixture of viscous and elastic behavior, with the response of a particular system depending on the stmcture of the material and the extent of deformation. Eor example, polymer melts can be highly elastic if a polymer chain can stretch when subjected to deformation. 

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