Enhanced gas selectivity in thin film composite membranes of poly(3-(2-acetoxyethyl)thiophene)

The gas transport properties of surface-treated poly(3-(2-acetoxyethyl)thiophene) (P3AcET) membranes are reported. Base or acid catalyzed hydrolysis of the ester group of P3AcET yields poly(3-(2-hydroxyethyl)thiophene) (P3HET), a highly permselective conducting polymer. Permeability coefficients were determined for as-cast P3AcET membranes (PCO2=1.42, PO2=0.24, PN2=0.05, PCH4=0.08 Barrers) and selectivity values were calculated (O2/N2=5.1, CO2/CH4=18.5). Formation of a thin selective P3HET surface layer resulted in an overall decrease in permeance (P/l) accompanied by a dramatic increase in selectivity for both the base-treated (O2/N2=12.9, CO2/CH4=20.0) and acid-treated (O2/N2=11.7, CO2/CH4=45.0) composites. Microscopic (AFM, SEM) and spectroscopic (ATR-FTIR) characterization of the thin film composites confirmed the surface specificity of the hydrolysis reaction.