Thin‐Film Composite Cyclomatrix Poly(Phenoxy)Phosphazenes Membranes for Hot Hydrogen Separation

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An interfacial polymerization process is introduced for the fabrication of thermally stable cyclomatrix poly(phenoxy)phosphazenes thin‐film composite membranes that can sieve hydrogen from hot gas mixtures. By replacing the conventionally used aqueous phase with dimethyl sulfoxide/potassium hydroxide, a variety of biphenol molecules are deprotonated to aryloxide anions that react with hexachlorocyclotriphosphazene dissolved in cyclohexane to form a thin film of a highly cross‐linked polymer film. The film membranes have persistent permselectivities for hydrogen over nitrogen (16–27) and methane (14–30) while maintaining hydrogen permeances in the order of (10 −8 –10 −7 mol m −2 s −1 Pa −1 ) at temperatures as high as 260 °C and do not lose their performance after exposure to 450 °C. The unprecedented thermal stability of these polymer membranes opens the potential for industrial membrane gas separations at elevated temperatures.