Ionomer dissolving

It has been suggested, for these reasons, that ionomers dissolved in nonaqueous solutions can be used to improve the quality of light scattering data [23]. The results obtained so far have indicated that this is indeed the case the scattered intensity of light from an ionomer nonaqueous solution is much stronger than that from a polyelectrolyte aqueous solution, since the number... 

These results confirm the observation that polyelectrolyte aqueous solutions show two separate decay modes in the autocorrelation function and support our contention that ionic polymer systems generally behave similarly in polar solvents [23], To support this, it may be added that similar dynamic scattering behavior was recently reported for another type of ionomer, polyurethane ionomer, dissolved in a polar solvent, dimethylacetamide (e = 38) [92], Finally, it should be stressed that the explanation given above for light scattering (both static and dynamic) behavior of salt-free polyelectrolytes is based on the major role of intermolecular electrostatic interactions in causing characteristic behavior. No intramolecular interactions are explicitly included to explain the behavior. This is in accord with our contention that much of the polyelectrolyte behavior, especially structure-related aspects, is determined by intermolecular interactions [23]. 

The general procedure to prepare solution-cast PFSA membrane is as follows. First, since the PFSF cannot dissolve in common solvents, it should be converted to Na+ form ionomer by hydrolysis with aqueous NaOH. Afterward, the Na+ form ionomer is immersed into FI2SO4 or HNO3 solution to convert to H+ form ionomer. Then, the H+ form ionomer dissolves in solvent. The reported solvents include dimethylfor-mamide (DMF), dimethyl sulfoxide (DMSO), ethylene glycol (EG), and mixture of water with alcohols. Finally, the membranes were fabricated by solution cast of the obtained H+ form ionomer solution. 

For small-scale preparation of samples for scientific studies, the precursor polymer may be dissolved in xylene at 80°C, followed by addition of the cation source. A gelled fluid is normally obtained immediately, and the ionomer is recovered as a powder by chopping the gel in a large excess of acetone using a laboratory blender. 

The presence of these ionic groups gives the polymer greater mechanical strength and chemical resistance than it might otherwise have. Indeed the ionomer is resistant to dissolution in many solvents because of its unconventional chemical character, often being too ionic to dissolve in non-polar solvents and too organic to dissolve in polar solvents. 

AB cements are not only formulated from relatively small ions with well defined hydration numbers. They may also be prepared from macromolecules which dissolve in water to give multiply charged species known as polyelectrolytes. Cements which fall into this category are the zinc polycarboxylates and the glass-ionomers, the polyelectrolytes being poly(acrylic acid) or acrylic add copolymers. The interaction of such polymers is a complicated topic, and one which is of wide importance to a number of scientific disciplines. Molyneux (1975) has highlighted the fact that these substances form the focal point of three complex and contentious territories of sdence , namely aqueous systems, ionic systems and polymeric systems. 

Impregnating these layers with PFSA ionomer for enhanced proton conduction or hydrophobizing agents like Teflon for sufficient gas porosity is optional. However, ionomer impregnation is indispensable in CLs with thicknesses of > 1 ftm. Ultrathin CLs with - 100-200 nm, on the other hand, can operate well without these additional components, based on sufficiently high rates of transport of dissolved reactant molecules and protons in liquid water, which could ensure uniform reaction rate distributions over the entire thickness of the layer. 

In artificial saliva, release of fluoride has been shown to be reduced [234,235], a finding that may be the case for all ions released by glass-ionomer cements. There are two possible explanations for this (i) that the higher ionic strength of the external medium reduces the rate at which ions can be dissolved into it, and (ii) that the artificial saliva contained calcium ions [236], which may precipitate CaF2 on the surface, and thus impede ion transfer from that surface [237]. 

The ionic clusters act as sites of cross-linking at low temperatures. The interchain forces resulting from this ionic bond produces properties normally associated with a cross-linked thermoset polymer. The association in ionomers can be partially overcome through application of heat and pressure allowing processability while truly" cross-linked network polymers cannot be remelted, dissolved or reshaped. Thus, ionomers are often referred to as processable thermosets. 

Solubility of Ionomers. Ionic bonding with metal ions decreases solubility in organic solvents (6,11). Commercial ionomers can generally be swollen by certain solvents such as aromatic hydrocarbons at elevated temperatures, but do not dissolve completely to give viscous solutions. Resistance to surface etching by oiganic solvents is high in most cases. 

Polymer 2 dissolves slowly in 98% sulfuric acid without degradation of molecular weight, and is sulfonated regiospecifically and quantitatively to give ionomer 9. This material, unlike the parent polymer 7, is strongly hydrophilic and dissolves readily in... 

Typical solution viscosities for SPS lonomers dissolved In THF are shown In Figure 1. As mentioned above, the reduced viscosity of the Ionomer solution at low concentrations Is less than that of unmodified polystyrene. It Is of Interest to focus on this low concentration limit and to determine the molecular basis for the lowered viscosity. 

The work described in the present paper concerns the Influence of water and organic solvents on the ionic interactions in lightly sulfonated polystyrene (SFS) ionomers. The focus will be specifically directed towards the Influence of the solvent environment on the cation-anion and cation-cation interactions. Fourier transform Infrared spectroscopy (FTIR) was used to probe the former while electron spin resonance spectroscopy (ESR) was used to study the latter. Experiments were carried out with dissolved, swollen, and bulk ionomers. 

In a previous paper (2), the author described a method to dissolve the sulfonyl fluoride precursor form of a perfluorinated sulfonate ionomer. Commercially available forms of Nafion are supplied as activated membranes (i.e., saponified from the precursor to the ionic form), and near-quantitative reconstitution of the precursor functionality (such as RSOjF) must first be performed using a chemical reagent such as SF. f4) before dissolution in perhalogenated solvents is possible. Besides adding to the cost of membrane manufacture, SF. is extremely toxic and corrosive and must be handled in nickel alloy pressure equipment. Therefore, a method for dissolving perfluorinated ionomers directly would be more desirable. 

Table I. Solvents capable of dissolving perfluorinated ionomers and ionomer precursors at atmospheric pressure and elevated temperature.

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