(25e) Membrane Catalysts for Optical Sensing of Anhydrides in the Gas Phase

The diffusion of low molecular weight dyes from dilute solutions with alcohol into transparent ionomeric membranes is being investigated to create unique supramolecular structures which respond optically to their environment. The membranes act as both durable dye supports and catalysts to sensitize the dyes to the presence of organic chemical hazards in the gas phase. In this paper, alteration of fluorescence dye concentration within the hydrophilic/hydrophobic domains of ionomeric membranes is shown to control sensitivity and selectivity toward gas phase exposure of various anhydrides which are considered to be occupational hazards in the polymers industry. Trimellitic, phthalic, and maleic anhydride are investigated at temperatures above the melting point of the solids. UV/VIS and FTIR are employed to identify Friedel-Crafts acylation as the sensing mechanism as well as to quantify the diffusion and solubility of the dyes and the anhydrides within the membranes. Appropriate choices of solvent for dye impregnation as well as the carrier gas for the anhydrides are shown to be critical in achieving parts per billion sensitivity and selectivity toward simultaneous exposure of the three anhydrides.