Miscible polymer blends components

Finally, similar effects can be seen in miscible polymer blends where the surface tension correlates with the enrichment of the lower-energy component at the surface as monitored by x-ray photoelectron spectroscopy [104],... 

Fig. la —c. Schematic drawing of some specific examples of polymer molecules at an interface (a) the free surface of a homopolymer, (b) the surface enrichment of one component in a miscible polymer blend, and (c) the interface between polymers of different molecular weight and/or chemical composition... 

Simulation Study of Relaxation Processes in the Dynamical Fast Component of Miscible Polymer Blends. 

In the future we will witness a drive towards more complexity. In this review, we have discussed a number of preliminary experiments pointing in this direction. In polymer blends, the question of dynamic mixing on a local scale was addressed and the Rouse dynamics in miscible polymer blends was studied. How the tube confinement evolves in blends where the two components have different tube diameters is a completely open question. Also, the question of how... 

Comparisons of the theory with experiment can not be presently made due to the lack of data on well characterized molecular IPN. Indications about its validity can, however, be deduced by examining its consistency at extreme cases of material behavior. The agreement at the one-component limit, for example, provided that the rubber is not very weak (iji not very small), has been successfully demonstrated by Ferry and coworkers [ ]. A useful result is obtained at the version of the theory applicable to the fluid state (i.e., at the limit of zero crosslinking). From the last two terms of Equation 13, the following relationship can be derived for the plateau [ ] and time dependent relaxation modulus of miscible polymer blends ... 

J. A. Zawada, Component contributions to the dynamics of miscible polymer blends, Ph J). Thesis, Stanford University (1993). 

J. Zawada, C. Ylitalo, G. Fuller, R. Colby, and T. Long, Component relaxation dynamics in a miscible polymer blend Polyethylene oxide)/poly(methyl methacrylate), Macromolecules, 25,2896 (1992). 

Miscible Blends. Both Components Amorphous. Certainly one of the most commercially important and publicized examples of a miscible polymer blend system is that based on polystyrene and poly(phenylene oxide), which is sold under the trade name Noryl by General Electric. Many fundamental studies of this system have been published, many of which were devoted to proving that these two components are miscible in a thermodynamic sense (see chapter 5 of Ref. 10 by MacKnight, Karasz, and Fried). Commercial interest in this system involves both... 

Improvement in cost, processability, and performance of polymers can also be achieved through blending two or more polymers. The blends may be homogeneous, heterogeneous, or a bit of both. Properties of miscible polymer blends may be intermediate between those of the individual components (i.e., additive behavior), as is typically the case for Tg. In other cases, blend properties may exhibit either positive or negative deviation from additivity. 

A group of new, fully miscible, polymer blends consisting of various styrene-maleic anhydride terpolymers blended with styrene-acrylonitrile copolymer and rubber-modified versions of these materials have been prepared and investigated. In particular the effects of chemical composition of the components on heat resistance and the miscibility behavior of the blends have been elucidated. Toughness and response to elevated temperature air aging are also examined. Appropriate combinations of the components may be melt blended to provide an enhanced balance of heat resistance, chemical resistance, and toughness. 

The soluble blend system is a single phase material in which two components (such as two polymeric species or a polymer and a solvent) are dissolved molecularly as a homogeneous solution in the thermodynamic sense. A miscible polymer blend, a block copolymer in a disordered state, and a polymer solution are examples. Whether a homogeneous solution of this kind is regarded as a soluble blend system or as a dilute particulate system discussed above is often simply a matter of viewpoint. When there is a dilute solution of polymer molecules in a solvent and the focus of interest is the size and shape of the polymer molecules, the theoretical tools developed for the dilute particulate systems are more useful. If, on the other hand, the investigator is interested in the thermodynamic properties of the solution, the equations developed for the blend system are more appropriate. 

Miscible polymer blends behave similar to what is expected of a single phase system. Their properties are a combination of the properties of the pure components and in many cases they are intermediate between those of the components. The characteristics of the components affecting the properties of miscible blends are their chemical structure and molecular weight, their concentra-... 

Figure 3.1. Possible crystallization temperature ranges for a crystallizable miscible polymer blend (1 - crystallizable component, 2 = amorphous component) [Runt and Martynowicz, 1986].

Figure 3.3. Schematic representation of the different types of segregation of the amorphous component in crystaUizable miscible polymer blends (fuU hnes crystaUizable component, dotted hnes amorphous component).

A simultaneous (or concurrent) crystallization can only occur when the crystallization temperature ranges overlap and if the crystallizability of both blend components is similar. Cocrystallization is only possible when the components are isomorphic or miscible in the amorphous as well as in the crystalline phase. In both cases mixed crystals can result, but in the case of concurrent crystallization no changes in crystal strucmre may be induced. Cocrystallization requires chemical compatibihty, close matching of the chain conformations, lattice symmetry and comparable lattice dimensions [Olabisi et al., 1979]. Some examples of miscible polymer blends with two crystalline components are given in Table 3.3 together with the type of crystalhzation. 

Table 3.3. Crystallization types of miscible polymer blends consisting of two crystallizable components...

When dealing with crystallizable miscible polymer blends containing a non-crystallizable component, some refinements had to be made. Some modifications were proposed by Alfonso and Russell... 

During crystallization of a miscible polymer blend, the composition of the amorphous phase changes, i.e., becomes poorer on the crystallizable component. In some cases, a liquid-liquid phase separation can take place as a result of the crystallization. This phenomenon will be discussed more in detail in the next section. 

By definition, miscible polymer blends are singlephase mixtures. Miscibility depends on the molecular weight, concentration, temperature, pressure, deformation rate, etc. Flow of these systems can be compared to that of solutions of low molecular weight, miscible components, or to flow of mixtures of polymeric fractions. Both models are far from perfect, but they serve to illustrate the basic behavior of miscible systems. 

Miscible polymer blends are less common that immiscible ones. The miscibility is usually confined to a specific range of independent variables, such as chain configuration, molecular weight, composition (viz. for alternate copolymers), temperature, pressure, etc. Nevertheless, Krause repotted that 1680 two-, three-, or four-component polymeric mixtures were identified as miscible in 780 publications [Krause, 1980]. More detailed listing is provided in Appendix 2 of this Handbook. Unfortunately, the rheological smdies of miscible systems are relatively rare. 

Thus, for miscible polymer blends, the relaxation spectrum is a linear function of the relaxation spectra of the components and their weight fractions, Wj, hence one may use rheological functions to detect miscibility/immiscibility of polymer blends. An example is presented in Figure 7.14 [Utracki and Schlund, 1987]. 

The best commercial advantages of a polymer blend can be summarized by the word versatility [Olabisi et ah, 1979]. Unfortunately, miscible polymer-polymer blends usually show additivity of the component polymers properties, thus their versatility is limited. Furthermore, tike any other single-phase resin, for most apphcations miscible blends need to be toughened and/or reinforced. Thus, with the exception of PMMA/PVDF blends (primarily used for coatings) there are no miscible blends on the market The interest in miscible polymer blends is for the purpose of compatibUization and judicious selection of the processing conditions that may lead to the spinodal decomposition-type morphology (see Chapter 8 Morphology in this Handbook). 

Owing to low values of the combinatorial entropy mixing, miscibility in polymer-polymer systems requires the existence of strong specific interactions between the components, such as hydrogen bonding [Olabisi et al., 1979 Sole, 1982 Walsh and Rostami, 1985 Utracki, 1989]. The thermodynamic characterization of the interactions in miscible polymer blends has been the subject of extensive studies [Deshpande et al., 1974 Olabisi, 1975 Mandal et al., 1989 Lezeano et al., 1992, 1995, 1996 Farooque and Deshpande, 1992 Juana et al., 1994]. 

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