Polymer Engineering Faculty Research


Chemical crosslinking of highly sulfonated polystyrene electrospun fibers

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Electrospun nanofibers of highly sulfonated polystyrene (IEC 4.8 mequiv/g) might be good candidates for use in ion exchange applications because of their ability to form continuous, highly conducting pathways for cation transport. However, such fibers suffer in terms of dimensional stability due to high water uptake at elevated humidity. To improve the stability of the electrospun nanofiber mats in water, the polyelectrolyte was coelectrospun in the presence of a high molecular weight poly(ethylene oxide) (PEO). Addition of PEO to the spinning dope helped improve the spinnability of the polyelectrolyte and subsequent heat treatment improved the stability of the fiber mats in water. Increasing PEO concentration in the fiber mats reduced the solubility of the heat-treated fiber mats in water; suggesting that the fibers were cross-linked by or in the presence of the PEO. To understand the chemistry of this apparent cross-linking reaction, the electrospun fiber mats were heated in a solid state 1H NMR rotor and changes in the spectrum were monitored as the reaction progressed. The hypothesis is that at higher temperatures, the two polymers react with each other to form sulfonic acid esters that form water-resistant cross-links. An alternative hypothesis of a free-radical cross-linking reaction was not supported by the observations.

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