Incompatibility of the components

See Starch and Sucrose for information concerning the incompatibilities of the component materials of sugar spheres. 

The properties of incompatible polymer blends depend to a large extent on the mutual dispersion of the components, on the super-molecular structure within the phase of a single component, and on the structure of the interface. These structural parameters, in turn, depend on the processing or mixing conditions and on the strength of the thermodynamic incompatibility of the components as well. These boundary conditions together with the cooling rate control also the solidification process of a melt. 

The properties of polymer mixtures depend on the method by which they are obtained and are determined by many factors by sizes of particles of the dispersed phase, by their shape and number in bulk, and by the thermodynamic affinity of the components for one another [19]. Linear polymers blend either in the course of their mutual dissolution or, in two-phase systems, under conditions of thermodynamic incompatibility of the components, when the dispersion is forced. The mixtures formed can be compatible (forming true solutions of one polymer in another), incompatible (representing a typical colloid system), quasicompatible (characterized by microscopic homogeneity at a level above heterogeneity on the molecular level), or pseudocompatible (with a strong adhesion interaction on the boundary) [106]. 

Blends. Blends of iPP with poly(styrene)-6Zoc -poly(ethylene-co-l-butene) were prepared imder various conditions and imaged by afm, where macrophase separation because of incompatibility of the components was observed (Fig. 17). The degree of phase segregation was shown to be dependent on the thermal history of the sample (118). Blends of iPP and different poly(ethylene-butene) (PEB) copolymers were imaged. The authors foimd that iPP and PEB containing 88% butene were miscible, and PEB containing <88% butene were partially to totally immiscible, and polybutene (100% butene) was partially miscible. So, there is a narrow window of miscibility for these blends (119). 

The addition of a comonomer to a semicrystalline polymer typically causes a loss in crystallinity, unless the second monomer crystallizes with the first. The decrease in crystallinity is very significant as small quantities of the comonomer are added, and it is accompanied by reductions in stiffness, hardness and melting point. Because vinyl polymers are thermoplastic and completely miscible with most organic solvents, copolymerization with vinyl monomers is a logical route to conventional processability and environmental stability. This route was pursued by polymer chemists who desired these properties in an electrically conductive material. But with the low percolation threshold observed in simple blends of vinyl polymers and conducting polymers, work on copolymerization has been abandoned in favor of composites. The two principal drawbacks of composites are incompatibility of the components and lack of genuine solution processability. What follows is a brief review of efforts to obtain electrically conducting and processable random vinyl copolymers of 3-methylthiophene. 

The microscopic morphology of polymer blends results basically from the incompatibility of the components, while other factors that influence blend morphology include the processing conditions (e.g., application of shear forces, use of compatibilizer, cooling rate from the melt). Two types of morphology may be observed, namely cocontinuous and dispersed the latter type is usually observed when one of the components is in a minority. 

Heterogeneous polymeric sterns on the basis of two polymers can be also realized in the form of interpenetrating polymeric networks 155,156). Such systems are interesting in that they consist of two continuous, not chemically inter-connecting polymeric networks which cannot be separated because of mutual penetration of segments of one network into the cells of the other. The appearance in IPN of a transitional region caused by the incompatibility of the components increases the heterr neity of such systems and can be noted on their viscoelastic properties (157). 

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