Results for polymer blends

In the previous section, the methodic aspects of computer simulations of phase transitions in polymer blends were emphasized. In the present section, we briefly review some of the most important results that have been obtained so far. 

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Flexural tests may be carried out in tensile or compression test machines. In standard tests, three-point bending test is preferred, although it develops maximum stress localized opposite the center point (support). If the material in this region is not representative of the whole, this may lead to some errors. Four-point test, offers equal stress distribution over the whole of the span between the inner two supports (points) and gives more realistic results for polymer blends (Figure 12.3). Expressions for the calculation of flexural strength and modulus for differently shaped specimens are given in Table 12.4. 

Using this technique, hard filler particles in a matrix become more clearly detectable without superposition by brittle fracture edges of the matrix polymer, as illustrated in Fig. 1.36. in this unconventional approach, the fracture surface must be obtained at a temperature at which the matrix is soft (the temperature must be sufficiently high above the glass transition temperature of the matrix) and the inclusions are hard (below the glass transition temperatures of the particles) at the same time. Besides the study of polymer composites, this procedure can also yield successful results for polymer blends, where the rubber particles were hardened by osmium tetroxide treatment. For instance, taking a fracture of an ABS polymer at 130°C, the temperature is well above the glass transition temperature of the SAN matrix, but the stained particles remain hard [12]. 

Many commercially important polymers are actually mixtures of two or more polymer components that differ from one another in composition (for copolymers) or in microstructure (for homopolymers). Such mixtures may be the deliberate result of polymer blending, polymer synthesis, or the presence of different types of initiators or catalytic sites that produce different polymer chains. The ung spectral data of the whole polymer in such systems would include contributions from all its components, and as such should be treated with care. 

The role of the miscibility of semi-IPN components on the mechanical properties has been discussed. The linear bisnadimide was a benzhydrol bisnadimide (Fig. 33). Three polyimides prepared from the same diamine and three different dianhydrides (Fig. 37) were used as linear components. The blends were cured up to 300 °C in a similar fashion to the bisnadimide alone. The results for the blend containing 20% by weight of linear polymers are summarized in Table 9. The non-miscible character of the components gives a phase segregation leading to the best toughness [121]. 

The mixing entropy calculated above includes only the translational entropy that results from the many possible locations for the centre of mass of each component. The calculation assumes that the conformational entropy of a polymer is identical in the mixed and pure states. This assumption is very good for polymer blends, where each chain is nearly... 

As mentioned in Part 7.1, for polymer blends the relation between the steady-state shear viscosity and concentration can be quite complex. In the following discussion, the constant stress (not the constant rate) viscosity, corrected for the yield and time effects, will be considered. To illustrate flexibility of Equation 7.125 to describe (and thus to facilitate interpretation of the rheological results) r vs. < > dependence examples of computations are shown in Figures 7.24-7.31. 

A particularly attractive application of hydrotropy in organic synthesis arises when the product is bulkier than the reactant, with the result that it has lower solubility than the reactant in the hydrotrope solution. Consequently, it selectively precipitates out of the reaction mixture and can be easily filtered out. Then the hydrotropic solution can be recycled, thus minimizing the environmental hazards associated with waste disposal. An important example is the synthesis of Diels-Alder adducts that act as flame retardants for polymer blends and formulations. One of these is also used in the manufacture of the pesticide Endosulfan. The reaction involves a diene such as hexachloro-pentadiene or anthracene and a dienophile such as p-benzoquinone or maleic anhydride. The following typical reaction carried out by Sadvilkar (1995) gave excellent results ... 

For the analytically tractable thread polymer model, and the R-MMSA or R-MPY/HTA closure approximations, k = 0 values of the direct correlation functions are precisely the same in the long chain limit as found for polymer blends in Sect. 8. In particular, for the symmetric block coprdymer, the R-MMSA closure yields [67,86] the mean field result Xinc = 3Co- Thus, within the symmetric thread idealization and the incompres fe approximation ctf Eq. (9.5), PRISM/R-MMSA theory reduces to Leibler theory for all compositions and block architectures [67,86]. 

Sf methacrylate copolymers as compatibilizers for polymer blends with PMMA. Both, the calculation of interaction parameters and experimental results showed... 

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