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Three novel polyhedral oligosilsesquioxane (POSS) nanofillers functionalized with proton-conducting sulfonic acid groups, mixed sulfonic acid and alkyl groups, and phosphonic acid groups were synthesized, characterized by IR, 1 H and 13 C NMR, and MALDI-TOF MS, and formulated into sulfonated polyphenylsulfone (S-PPSU) carrier polymers. High quality films were cast from 1-methyl-2-pyrrolidinone (NMP), and through-plane and in-plane proton conductivity, mechanical properties, water uptake, dimensional stability, and leaching behavior were measured to assess their suitability for use as hydrogen fuel cell proton exchange membranes. Various nanofiller loadings and S-PPSU sulfonation levels were studied. The morphologies of the composite membranes were determined by TEM and SEM X-ray mapping. When compared with Nafion 1 , the POSS-S-PPSU composite membranes exhibited comparable proton conductivity in combination with superior dimensional stability, heat resistance, and mechanical strength. When compared with control S-PPSU membranes, the composite POSS-S-PPSU membranes exhibited superior conductivity, comparable dimensional stability, and slightly decreased mechanical strength.

Single-layer proton exchange membranes (PEMs) have been under development for several decades. The current use of conductive polymers in PEM fuel cells has been limited primarily to single layered sulfonated fluoro polymers, e.g. Nafion. Although this architecture has certain positive characteristics, it lacks the robust properties required for use in high-temperature, low=humidity conditions. In this work, a multilayer composite PEM consisting of outer layers of sulfonated polyphenylsulfone (S-PPSU) and an inner layer blend of octa-sulfonated octaphenyl-POSS (S-POSS) and S-PPSU has been developed and shown to exhibit good conductivity, physical and chemical durability, and high strength. The multilayer composite PEM showed improved conductivity at 90 °C and 25% RH relative to analogous single-layer S-POSS-S-PPSU PEMs and to the typical sulfonated fluoro polymers currently in use.

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Hyperbranched polycarbosiloxanes and polysiloxanes with octafunctional polyhedral oligomeric silsesquioxane (POSS) branchpoints and curable alkoxysilane or silanol end-groups were formulated with linear polysiloxanes to fabricate transparent and robust nanostructured POSS-containing materials for use in a range of high performance space and solar applications. The effect of methyl vs. phenyl content, architecture and linear polysiloxane mass on transmission, thermal, physical, and proton, electron and UV radiation resistance properties was determined, and the physical properties of the nanomaterials were tailored to produce adhesives, or rigid or flexible coatings as desired. The methyl formulations showed superior electron resistance relative to a commercial space control material and to a POSS-free HB polymer control material, even when directly exposed to radiation in coating form, whereas the phenyl formulations were shown to have inferior electron and UV resistance.