Low ion contents

As an indication of the changes in deformation modes that can be produced in ionomers by increase of ion content, consider poly(styrene-co-sodium methacrylate). In ionomers of low ion content, the only observed deformation mode in strained thin films cast from tetra hydrofuran (THF), a nonpolar solvent, is localized crazing. But for ion contents near to or above the critical value of about 6 mol%, both crazing and shear deformation bands have been observed. This is demonstrated in the transmission electron microscope (TEM) scan of Fig. 3 for an ionomer of 8.2 mol% ion content. Somewhat similar deformation patterns have also been observed in a Na-SPS ionomer having an ion content of 7.5 mol%. Clearly, in both of these ionomers, the presence of a... 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

For ionomer samples with low ion. content (less than 5 mol %), only crazes are formed. Figure 24 shows a typical TEM picture of a craze in a deformed thin film of an ionomer with low ion content. This can be compared with the craze structure of starting PS (Fig. 12b). Also, in Fig. 25 two views of the craze microstructure in PS (Fig. 25a and b) are compared with corresponding views (Fig. 25c and d) of the craze structure of the ionomer containing 4.8 mol % ion content. These micrographs show typical structural features of crazes of glassy polymers a) a midrib of lower fibril... 

Here, possible micromechanisms of ionomers are discussed. At low ion content (less than 5 mol %), only crazes are noted and these appear to become unstable with increasing ion content. These ionomer samples tend to be more brittle compared with the PS precursor. This is probably due to the aosslinking effect produced by the ionic multiplets that are present. As mentioned before, it is known that small ionic aggregates (multiplets) are produced due to ionic dipole attractions and that... 

These ionic crosslinks decrease chain mobility, less energy is dissipated and less plastic deformation takes place. Also, as we will describe, the ionomers with low ion content show poorer fatigue performance with increasing ion content. Evidently, the loss of chain mobility causes embrittlement of glassy polymers, and this is probably responsible for the observed effects seen here in ionomer samples with low ion content. 

In sulphonated PS ionomers of low ion content, crazing appears to be the dominant deformation mode in tension and the resulting craze structure is similar to that observed in PS. For higher ion contents (above 5 mol %) fewer crazes appear and some degree of localized shear deformation is present. 

The semicrystalline, supermolecular structure of the organic carboxylate and the amorphous structure of the sulfonate resins have been studied with x-ray scattering and mechanical relaxation. This work shows no trace of crystallinity in the sulfonates, but the stress-relaxation data suggests the presence of a common structural feature, ion-clustered structure. with regions of high and low ion content. In "Figure 2 is shown the x-ray diffraction patterns depicting the supermolecular structure of perfluorocarboxylate and the sulfonate. Here is shown the amorphous halos in both... 

In the 3-arm star PIB lonomers, most of the ionic aggregates should be multiplets due to the low ion content (2.4 mole %) (3-4). Figure 2 shows only the shoulder for secondary transition in the tan 6 curve (around 30°C) thus, only very small amounts of ions exist as clusters (35), if they are present at all. Most of the ions are thus expected to exist as small multiplets, i.e. quartets. Moreover, it is difficult for the molecules to flow due to network crosslinks resulting from the presence of the trifunctional linkages. As is seen in the G curve in Figure 2, the well-defined rubbery plateau... 

Cooper et al. reported that solid-state 23Na NMR is useful for observing the sodium cation in sulfonated polystyrene ionomers (NaSPS).44 Three NMR peaks were detected, corresponding to isolated ion pairs, aggregated ions and hydrated ions (Fig. 14). The distributions of these three types of sodium cations are systematically influenced by hydration treatment, sulfonation level and neutralization level. Fully dried NaSPS at low ion content shows that the isolated and aggregated sodium ions in NaSPS are available for hydration. As the sulfonation level increases, the fraction of sodium ions held in isolated ion pairs decreases while the fraction of ionic species in the ionic aggregates increases. This coincides with a shift in the peak position of the aggregated sodium ions to low frequency, indicative of increased quadrupolar interactions. 

The microphase structure and mechanical properties of the blends containing neat acrylonitrile-butadiene-styrene copolymer (ABS), styrene-acrylonitrile copolymer (SAN) and sodium sulfonated SAN ionomer have been investigated as a function of ion content of the ionomer in the blend by Park et a/.51 The interfacial adhesion was quantified by H NMR solid echo experiments. The amount of interphase for the blend containing the SAN ionomer with low ion content (3.1 mol%) was nearly the same as that of ABS, but it decreases with the ion content of the ionomer for the blend with an ion content greater than 3.1 mol%. Changing the ionomer content in the blends shows a positive deviation from the rule of mixtures in tensile properties of the blends containing the SAN ionomer with low ion content. This seems to result from the enhanced tensile properties of the SAN ionomer, interfacial adhesion between the rubber and matrix, and the stress concentration effect of the secondary particles. 

The mobility of geothite in water was measured as a function of HS concentration and the presence of calcium. The mobility is highly concentration dependent up to a calcium concentration of 2 rngL k The effect of bivalent ions is not great for high HS concentrations and low ion content (Tipping and Heaton (1983)). 

Attainment of equilibrium downstream of flame fronts makes it possible to use flames as media for studying high-temperature thermodynamics. Equilibrium may be approached via collisional ionization or chemi-ionization. When small concentrations of alkali metals are added to flames of low ion content, e.g., hydrogen or carbon monoxide flames, ions are produced by collisional reactions ... 

PEI resins are made from high-purity intermediates and have very low ion content. With proper handling and isolation, total extractable inorganic ions are below 100 ppb. Sulfate and chloride ion content can be below 20 ppb. This high purity is useful for preparation of film and handling equipment to make semiconductor wafers and chips for microprocessors, as well as bum-in test sockets. 

Fig. 39 TEM pictures of SPI ultrathin membranes. Left SPI with very long ionic sequences and low ion content inducing a macroscopic phase separation in ion-rich (black) and ion-poor (white) domains. Right homogeneous SPI (short ionic sequences) revealing the foliated structure on a nanometric scale...

So far most studies of aggregation behavior have been conducted with low polarity solvents such as THF [4,9,15]. Recently there have been a few reports with nonpolar solvents such as xylene [16-18]. While these systems require low ion contents to form a solution, the ionomer electrical environment is more similar to that found in the solid state (i.e. low dielectric constant). In this work we use static and dynamic light scattering techniques to examine the aggregation behavior of sulfonated polystyrene ionomers in a nonpolar solvent, toluene. 

Features High solids, low vise, sol n. very low VOC good heat resist. freeze-thaw stable low ion content no amine odor... 

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