Effect of Water on Internal Aggregate Structure in Zinc-Neutralized Ionomers

Abstract

The effect of water on zinc-neutralized ethylene-methacrylic acid (E-MAA) ionomers and sulfonated polystyrene (SPS) ionomers was studied. The change in weight after soaking in water was quantified as a function of zinc content and correlated to changes in spectra from zinc-edge extended X-ray absorption fine structure spectroscopy (EXAFS). EXAFS patterns for the fully dried ionomers were characteristic of zinc surrounded by four oxygen atoms. E-MAA ionomers absorbed much less water per zinc atom than SPS ionomers. Addition of water changed the EXAFS pattern in E-MAA ionomers, but the pattern was still characteristic of zinc coordinated to four oxygen atoms. This change was consistent with water replacing chelating carboxylate anions coordinated to zinc at the edges of aggregates or coordinated to isolated zinc ions. A new interpretation of the v a(COO -) infrared vibration was developed from this work. In SPS, addition of water caused zinc to become 6-fold coordinated to oxygen, which is suggestive of zinc totally solvated by water.

Review and critical analysis of the morphology of random ionomers across many length scales

“…The only counter examples are two XAS studies, where there is a clear disruption of ionic aggregate environment for zinc-neutralized sulfonated polystyrene [95,96]. Except for the one example of zinc-neutralized sulfonated polystyrene, it is not known how atoms are arranged in aggregates swollen by plasticizer.…”

“…In a paper on water adsorption using XAS, [96] water molecules were postulated to adsorb only at the edges of Zn-EMAA aggregates (the case where water molecules adsorbed in the interior was also shown). The number of water molecules per zinc atom decreased with increasing neutralization level, which represents what is shown in Figure 4A (i.e., zinc atoms are dots and all other atoms are not shown).…”

“…The second piece of evidence that argues for a sphere as a corner-folded plane is that STEM measurements of the same material used in XAS studies indicated no change in aggregate size with neutralization level, while water absorption [96] experiments and indirect measurements from XAS studies [48] suggest that aggregates become larger with neutralization level. Most SAXS experiments are also consistent with an increase in aggregate size with neutralization level, although again it must be pointed out that these conclusions are model-dependent.…”

Structure of ionic aggregates of ionomers. II. Effect of humidity and temperature on ethylene and styrene ionomers

“…It is important to clarify the structure of ionic aggregates to understand their effect on physical properties. Recently, there has been much attention addressing the structure of ionic aggregates of ionomers 2–8. There are many reports on small‐angle X‐ray scattering (SAXS) studies of ionomers 2–5.…”

Effect of sol-gel polymerization of tetraethylorthosilicate on internal aggregate structure in zinc-neutralized ethylene-methacrylic acid ionomers

“…This tech-nique has been used extensively to study these same zinc-neutralized materials with no TEOS polymerization, and the aggregate structure in the absence of this polymerization is well characterized. 3,4,5 EXPERIMENTAL Ethylene-methacrylic acid (E-MAA) copolymers partially neutralized with zinc were supplied by E.I. DuPont Co. as pellets.…”