Polyblends homogeneity

Evidently, the homogeneous complex phase is an equilibrium property for copolymers. Any effects resulting from the history of specimen preparation (cf., photomicrographs and dashed lines in Figures 9 and 10) are eliminated by annealing. In contrast, for polyblends the compatible phase is a metastable state. 

Of course, Flory has not defined the criteria for compatibility. If compatibility is to mean single homogeneous phase and is associated with nearly complete mixing of the molecules at the molecular level, as it does for simple liquids, no polyblends are known to be truly compatible. So what does compatibility mean when applied to polyblends A search of the literature revealed that various methods have been used to determine compatibility of polyblends and each method has its own standard and sensitivity. 

Here n is the average refractive index, k is Boltzman s constant, and T is absolute temperature (13). If a polyblend were to form a homogeneous network, the stress would be distributed equally between network chains of different composition. Assuming that the size of the statistical segments of the component polymers remains unaffected by the mixing process, the stress-optical coefficient would simply be additive by composition. Since the stress-optical coefficient of butadiene-styrene copolymers, at constant vinyl content, is a linear function of composition (Figure 9), a homogeneous blend of such polymers would be expected to exhibit the same stress-optical coefficient as a copolymer of the same styrene content. Actually, all blends examined show an elevation of Ka which increases with the breadth of the composition distribution (Table III). Such an elevation can be justified if the blends have a two- or multiphase domain structure in which the phases differ in modulus. If we consider the domains to be coupled either in series or in parallel (the true situation will be intermediate), then it is easily shown that... 

Where the two phases are completely compatible, a homogeneous polyblend results which behaves like a plasticized resin (one phase). If two polymers are compatible, the mixture is transparent rather than opaque. If the two phases are incompatible, the product is usually opaque and rather friable. When the two phases are partially compatibilized at their interfaces, the polyblend system may then assume a hard, impact-resistant character. However, incompatible or partially compatible mixtures may be transparent if the individual components are transparent and if both components have nearly the same refractive indices. Furthermore, if the particle size of the dispersed phase is much less than the wavelength of visible light (requiring a particle size of 0.1/a or less), the blends may be transparent. 

By combining the concepts of copolymer homogeneity, matching refractive indices, and partial compatibilization via grafting, impact resistant polyblend systems can be produced from numerous monomer combinations that approach optical clarity. 

Homogeneous single-phase polyblends are very rare. Liquid-liquid phase separation of optically homogeneous polyblends of a styrene/acrylonitrile copolymer with poly (methyl methacrylate) has been studied by L. P. McMaster. A quantitative test method of the dynamic mechanical properties of multiphase polymer systems was developed by L. Bohn. He was able to demonstrate the correlation between shear modulus and gel volume of brittle polymers... 

Elastomers with similar polarities and solubility characteristics can be easily combined to produce miscible polyblend (18). Miscible polymer blend is a polymer blend, which is homogeneous down to the molecular level and associated with the negative value of the free energy of mixing and the domain size is comparable to the dimensions of the macromolecular statistical segment. Complete miscibility in a mixture of two polymers requires that the following condition be fulfilled (19) ... 

Isomorphous Systems (Homogeneous Copolymers or Compatible Polyblends)... 

In isomorphous systems, the eomponent monomers oceupy similar volumes and are capable of replacing each other in the erystal system The resulting eopolymer, irrespective of its geometry, is necessarily homogeneous, and polyblends of the individual homopolymers or copolymers have similar transition properties. Copolymerization merely shifts the Tg to the position intermediate between those of the two homopolymers it does not alter the temperature range or the modulus within the transition r on (Figure 4.4). This shift is illustrated in Figure 4.4, which shows the modulus temperature eurves for polybuladiene (100/0) and polystyrene (0/100) and for various compositions of butadiene-styrene eopolymer. 

Interpenetrating polymer networks (IPN s) are a novel type of polyblend composed of crossllnked polymers. They are more or less intimate mixtures of two or more distinct crosslinked polymers with no covalent bonds between the polymers. True IPN s may be described as combinations of chemically dissimilar polymers in which the chains of one polymer are completely entangled with those of the other, i.e., a homogeneous morphology results. 

These were both sulfonated and neutralized to zinc ionomers. Tensile strength of blends was homogeneously dependent on polyblend ratio [80]. 

This and butyl rubber were both sulfonated and converted to zinc ionomers. Polyblends gave homogeneous tensile strengths [80]. 

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