EXAFS Studies of Various Sulfonated and Carboxylated Cadmium Ionomers

Abstract

Four sulfonate ionomers and one carboxylate ionomer, all neutralized with cadmium, were studied using the technique of extended X-ray absorption fine structure (EXAFS) spectroscopy. The cadmium in all four sulfonate ionomers had essentially identical EXAFS oscillations, which suggests that the influence of the identity of the polymer matrix on the local aggregate structure is minimal. In contrast, the cadmium in the carboxylate ionomer had a substantially different local environment, showing that, as expected, the local environment of the cadmium cation depends on anion type. For the sulfonate ionomers, simulations of the EXAFS oscillations with reasonable fitting parameters using the crystal structure of cadmium methanesulfonate dihydrate fit the experimental patterns very well. This agreement between theory and experiment strongly suggests that the atomic arrangement around the cadmium atom in the ionomer is the same as the arrangement around the cadmium atom in the small-molecule analogue. In the carboxylate ionomer, small but significant differences existed between the experimental pattern and the pattern generated theoretically using atomic positions derived from the small-molecule analogue cadmium acetate dihydrate. The reason for the difference is unclear; however, if the atomic positions in the ionomer were only slightly different from those in the crystal structure, this could have led to the disagreement between the experimental data and the fit.

Increased ion conduction in dual cation [sodium][tetraalkylammonium] poly[4-styrenesulfonyl(trifluoromethylsulfonyl)imide-co-ethylacrylate] ionomers

“…[N 1444 + ] vs. [N 1222 + ], that will decrease the association between ion pairs (which lead to ionic cross-links between polymer segments) and by the additional plasticiser effect of these larger cations. 23,32,33 It is also noted that the ionomer with higher EA content, e.g. N 1222 (a), shows a lower T g , which is because the exible acrylate domain will lower the T g , as observed in Na[PSTFSI-co-EA] in our previous study.…”

Decoupled ion conduction in poly(2-acrylamido-2-methyl-1-propane-sulfonic acid) homopolymers

“…[30][31][32] Tudyryn et al reported that, 31 with constant ion content, their polyester-sulfonate ionomers showed T g decreasing as counterion size increases. They suggest that this is caused by two factors 32,33 (i) larger counterions associate less with the backbone anions, forming fewer and weaker physical cross-links that then leads to a decrease in T g for ionomers (ii) larger counterions act as plasticizers, further lowering T g . However, N 14,111 + possesses the highest T g , among the ionomers prepared in this work, despite having the longest aliphatic chain.…”

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

“…Polystyrene was sulfonated using the method of Lundberg et al 14 Details of the sulfonation method are given in a previous publication. 15 The 3.4 and 5.7 mol % sulfonate substitution levels were synthesized. The acid form was dissolved in a 90/10 v/v mixture of toluene/methanol and neutralized with a stoichiometric amount of zinc acetate dihydrate to produce fully neutralized zinc sulfonated polystyrene.…”