Polymer positively deviating

These equations suggest that a plot of M vs conversion should be linear. A positive deviation from the line predicted by eq. 16 indicates incomplete usage of transfer agent (T) while a negative deviation indicates that other sources of polymer chains are significant (e.g. the initiator). 

The heat of fusion AHf (obtained from the area under the DSC melting curve) and percentage crystallinity calculated from AHf is found to be linearly dependent on butadiene content, and independent of the polymer architecture. This is shown in Figure 3. Also, the density of the block copolymers was found to be linearly dependent on butadiene content (see Figure 4). The linear additivity of density (specific volume) has been observed by other workers for incompatible block copolymers of styrene and butadiene indicating that very little change in density from that of pure components has occurred on forming the block copolymers.(32) While the above statement is somewhat plausible, these workers have utilized the small positive deviation from the linear additivity law to estimate the thickness of the boundary in SB block copolymers.(32)... 

As the concentration of polyvinyl chloride and glycerol palmitostearate was increased between 15% and 20%, a non-significant decrease in released amount was obtained, while a slight difference in the amount released was observed beween 10% and 15% of polymer concentration (Table 4). Deviations from the Higuchi equation were observed (Table 3). These positive deviations might be due to the air entrapped in the matrix. Similar results were also obtained with polyvinyl chloride by Desai et al. [14] and Korsmeyer etal. [15]. 

The assumption that the polymer spectra and structure correspond to those of the model compounds rests essentially on the approximate correspondence of peak positions. It is important that the spectra be compared at approximately the same temperature, as there is a marked dependence of the peak positions upon temperature. For the polymer at 150°, the peak positions, in -values with respect to the solvent as + 63.8 , are 104.2, 106.0, 125.6, and 127.8. At 25°, the solvent peak position was found to be +63.2 if>, and the model compound peak positions were 106.3, 108.8, 126.6, and 128.9, deviating substantially from the polymer positions. When the model compound spectra are observed at 150°, there is a marked down-field" shift, which brings the - values into much closer correspondence with those of the polymer 104.1, 106.2, 126.2, and 127.7. There appear to be some small relative changes as well, particularly for the meso compound, for the appearance of its AB-type CFa resonance is distinctly temperature dependent. The most likely explanation for this behavior is that it arises from changes in the relative populations of the internal-rotation energy levels, which correspond to changes in the time-averaged conformational structures of the molecules. 

Liquid Sorption. Liquid sorption measurements were performed gravlraetrlcally on polymer A In methanol-water and methanol-Isooctane solutions. The results are plotted In Figs. 11 and 12. In Fig. 11, a linear tle-llne was drawn through the solvent uptake data points for the pure liquids. It appears that the amount of methanol (or water) absorbed by the polymer Is linearly proportional to the mole fraction of methanol In the solution. However, proof of this assertion requires the Independent measurement of the species dissolved In the polymer. In other words, the partitioning of the solvents within the polyurethane Is not known. In contrast to the aforementioned behavior, positive deviations were observed from the linear tle-llne In Isooctane-methanol solutions. This Indicates that an excess of one liquid, and of possibly both, was sorbed by the polymer (Fig. 12). These results also demonstrate that methanol Is much more compatible with the polyurethanes than water (I.e., methanol Is absorbed to a much greater degree In the polymer than water). 

It can be seen from the data points for poly (1,4-butadiene) and polyisoprene in Figure 12.9 that the CM of polymers with all-c/.v double bonds in their backbones deviates only slightly (-10%) from Equation 12.27, while the of polymers with ail-trans double bonds shows a very large systematic positive deviation. These results are also consequences of Equation 12.3. The correlation between o2 and CM for silicone-type polymers (see Figure 12.9) is given by... 

This relationship is shown in Figure 13 where Polymer 1 has a permeability 1000 times higher than that of Polymer 2. Published data have small negative deviations from this theoretical relationship. Part of the deviation can be explained by densification of the blend relative to the starting components. Random copolymers, which are forced (by covalent bonds) to imitate combinations of two materials, have permeabilities that are similar to miscible blends. However, the deviations from equation 18 tend to be positive. A series of styrene—methacrylonitrile copolymers were studied (11) and slight positive deviations were found. Figure 14 shows the oxygen permeabilities of a series of vinylidene chloride— -butyl acrylate copolymers [9011-09-0]. 

There is a mounting evidence that PDB is not a rule for miscible polymer blends. Depending on the system and method of preparation, polymer blends can show either a positive deviation, negative deviation, or additivity. Note that miscibility in polymeric systems requires strong specific interactions, which in turn affect the free volume, thus the rheological behavior. It has been demonstrated that Newtonian viscosity can be described by the relation [Utracki, 1983 1985 1986] ... 

It should be noted that the Doi and Ohta theory predicts oifly an enhancement of viscosity, the so called emulsion-hke behavior that results in positive deviation from the log-additivity rule, PDB. However, the theory does not have a mechanism that may generate an opposite behavior that may result in a negative deviation from the log-additivity rule, NDB. The latter deviation has been reported for the viscosity vs. concentration dependencies of PET/PA-66 blends [Utracki et ah, 1982]. The NDB deviation was introduced into the viscosity-concentration dependence of immiscible polymer blends in the form of interlayer slip caused by steady-state shearing at large strains that modify the morphology [Utracki, 1991]. 

In the case of both the mechanical properties studied (tensile strength and elongation), on comparison of the properties of the component polymers and the blends, the non-irradiated blends showed negative deviation from the linear additivity of the properties. However, on irradiation, this negative deviation was changed into positive deviation. Some of the mechanical... 

There are four types of the polymer blends (i) Additive blends whose melt viscosity follows Equation 18.3, (ii) Blends with a positive deviation of from Equation 18.3. These include blends with strong interphase interactions, (iii) Blends with a negative deviation from the logarithmic additivity, which is typical of incompatible components with weak interphase interactions, (iv) Blends that show both positive and negative deviations of py from the additive values (such a relationship is typical of materials in which structural changes take place during flowing). 

By way of contrast, the segments are mutually repulsive in a good solvent since, by definition, contacts with solvent molecules are enthalpically favoured. This tends to cause the polymer chains to swell, a process that is counteracted by the loss in configurational entropy as the chains expand. Nonetheless, the polymer molecules are mutually repulsive so that the volume available in the polymer solution is effectively reduced below the nominal volume. This causes the effective polymer concentration to be greater than that expected for an ideal system and results in positive deviations from ideality. 

This remarkably simple result has been checked experimentally by preparing rubbers in which each crosslinking molecule produces exactly two network chains. The positive deviation (Eig. 3.13) from the prediction of Eq. (3.19) is attributed to physical entanglements, which exist in the polymer before crosslinking. Therefore, rubbers are one of the few solids for... 

MSE/MST and MSEE/MST blends were miscible by DSC measurements. Their density vs. composition curves showed positive deviations from the linear additivity rule volume contraction upon mixing two miscible polymer pairs was confirmed. Permeability vs. composition plot also showed large negative deviations from the semilogarithmic mixing rule. The permeability coefficient of the 50/50 MSE/MST blend was the lowest of all the materials tested it is comparable to EVAL-F and much lower than any other commercial barrier polymers. The volume shrinkage in the compatible blends show that the free volume is reduced, thus reducing the permeability. 

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