Cross-linked, polyurethane-based, ammonium poly(ionic liquid)/ionic liquid composite films for organic vapor suppression and ion conduction

Publication date: Available online 31 January 2017
Source:Polymer
Author(s): Dylan I. Mori, Rhia M. Martin, Richard D. Noble, Douglas L. Gin
A series of ammonium-diol and -triol ionic liquid (IL) monomers were synthesized and used in step-growth polymerization with the commercial di-isocyanate monomer, toluene-di-isocyanate (TDI), in the presence of free ammonium IL to form new curable ammonium-based polymerized ionic liquid/ionic liquid (PIL/IL) composite film coatings. The use of polyurethane chemistry allows for the near-complete curing of the alcohol and isocyanate monomers to yield solid, homogeneous, cross-linked polyurethane-based PIL/IL composite materials with no volatile side product formation. The physical properties and curing rates of these PIL/IL films were altered by tailoring the structures of the ammonium-alcohol IL monomers, the ratio of the linear vs. cross-linking IL monomers employed, and the amount of free IL in the curing reactions. Although ammonium-based PILs have been reported to be less thermally and electrochemically stable than their imidazolium counterparts in the literature, TGA results indicated a Tonset of up to 300 °C under air for the ammonium PIL/IL composites prepared in this study. These new PIL/IL materials were also tested as curable coatings in a toxic industrial chemical (TIC) vapor suppression and liquid uptake assay using o-dichlorobenzene (o-DCB) as a simulant for polychlorinated biphenyls. The curable PIL/IL coatings were found to suppress 88% of the o-DCB vapor on o-DCB-contaminated painted steel substrates and 79% of the o-DCB vapor on o-DCB-contaminated rubber substrates, relative to uncoated control samples. However, although effective for TIC vapor suppression, these ammonium PIL/IL coatings only sorbed less than 50% of the applied liquid o-DCB from the same test substrates, making them slightly less effective for this latter application than previously reported imidazolium-based curable PIL/IL coatings. These materials exhibited comparable ionic conductivity values to other types of PIL/IL systems previously reported in the literature. However, it was found that the more heavily cross-linked ammonium-based PIL/IL films were more prone to free IL leach-out at higher temperatures, leading to their unexpectedly higher ionic conductivity at elevated temperatures.

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