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

Abstract

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−2s−1Pa−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.

Nonaqueous Interfacial Polymerization-Derived Polyphosphazene Films for Sieving or Blocking Hydrogen Gas

“…This is evidenced by the release of H 2 O, CH 3 S, and Cl (Figure S4). The decrease in weight at temperatures exceeding 300 °C is distinct from the behavior of the diphenol-based materials of our previous study . For those materials, it was shown that the almost complete substitution of the Cl groups on the HCCP by Ar–O groups prevents the HCCP ring from opening at elevated temperatures, and no appreciable weight loss of these materials is observed for temperatures below 400 °C.…”

“…The decrease in weight at temperatures exceeding 300 °C is distinct from the behavior of the diphenol-based materials of our previous study. 14 For those materials, it was shown that the almost complete substitution of the Cl groups on the HCCP by Ar−O groups prevents the HCCP ring from opening at elevated temperatures, and no appreciable weight loss of these materials is observed for temperatures below 400 °C. Because the extent of substitution of Cl groups for the AHC-HCCP materials is much lower, the thermally induced opening of HCCP rings is more probable, causing the distinct thermal evolution of the mass.…”

“…This indicates that the AHC-HCCP networks have a low degree of cross-linking compared to our previous study. 13,14 The fact that the materials do not readily dissolve in a variety of solvents is evidence of some degree of crosslinking. The cross-link density of the networks will be affected by the extent of deprotonation of the aryl alcohols.…”

“…Most of the preparation methods involving HCCP are based on solution polymerization, and only a few studies have been dedicated to synthesizing polyphosphazene films with IP. − , Maaskant et al reported that the interfacial polycondensation of HCCP with diphenols in conventional IP is too slow to allow for ultrathin (∼10 8 m) film formation. In our previous work, we replaced the water phase with a solution of KOH in DMSO . DMSO is a polar aprotic solvent that is immiscible with organic solvents such as cyclohexane and, in addition, facilitates nucleophilic reactions between monomers.…”

“…In our previous work, we replaced the water phase with a solution of KOH in DMSO. 14 DMSO is a polar aprotic solvent that is immiscible with organic solvents such as cyclohexane and, in addition, facilitates nucleophilic reactions between monomers. In the solution of KOH in DMSO, the diphenols are (partly) deprotonated and become very soluble and reactive nucleophilic aryloxide anions, enabling the formation of ultrathin polymer films that have a molecular sieving ability at very high temperatures.…”