Characterization of Highly Sulfonated SIBS Polymer Partially Neutralized With Mg+2 Cations

Report No. ARL-TR-4528
Authors: Eugene Napadensky; James M. Sloan
Date/Pages: August 2008; 30 pages
Abstract: In the search for selective membranes capable of separating protons from methanol for direct methanol fuel cells or chemical and biological toxins from water in chemical protective clothing, block copolymer ionomer membranes emerge. They are highly ordered sequence of both ionic and nonionic blocks, in which the ionic groups are randomly arranged along the polymer chain. This investigation studied one of these block copolymer ionomers, sulfonated poly(styrene-b-isobutylene-b-styrene). In this study, the characterization of transport properties and chemical structure of sulfonated poly(styrene-b-isobutylene-b styrene) block co-polymers that are partially crosslinked to a various levels with magnesium ions are reported. The vapor transport and solubility properties of both water and dimethyl-methyl phosphonate (DMMP) were studied as a function of concentration of magnesium ion exchanged into the sulfonated domains of the SIBS ionomer. The results indicate that vapor transport of both water and DMMP are significantly decreased when Mg+2 is incorporated into the ionic polymer. Fourier-transform infrared spectroscopy results revealed that a significant amount of ordering occurred as a result on the incorporation of Mg+2 ions. All the Mg+2 ions were localized into the sulfonated domains, resulting in a tighter molecular packing arrangement and thus a more ordered structure. It is this ordered structure that causes the improvement in the transport properties.
Distribution: Approved for public release
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Last Update / Reviewed: August 1, 2008