Crosslinked Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes
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Crosslinked Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes. Maria Luisa Di Vona1, Debora Marani1, Cadia D’Ottavi1, Marcella Trombetta2, Enrico Traversa1, Isabelle Beurroies3, Philippe Knauth3 and Silvia Licoccia1. 1 Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy. 2 C.I.R.-Centro Interdisciplinare di Ricerca, Università Campus Bio-Medico, via Longoni 83, 00155 Roma, Italy. 3 MADIREL (UMR 6121 CNRS), Université de Provence, Centre St Jérôme, 13397 Marseille Cedex 20, France. ABSTRACT A general, efficient and experimentally simple method for the synthesis of covalently crosslinked class II hybrid polymers based on PolyEtherEtherKetone (PEEK) with a high degree of sulfonation (DS = 0.8) was performed. The synthetic strategy foreseen two steps: the first one, direct sulfonation, led to the introduction of sulfonic acid groups and to the formation of sulfone bridges among repeat units. The second step, lithiation and silylation, led to the formation of covalent bonds between the organic backbone and Si(OH)3 moieties. The materials were characterized by 1H NMR Spectroscopy, ATR/FTIR Spectroscopy, Thermogravimetric Analysis (TGA) and Mass Spectrometry. Preliminary proton conduction measurements in dry conditions were performed. The introduction of silicon groups in the system improved thermal stability. INTRODUCTION Proton-containing polymeric materials are interesting for their use in a wide variety of applications, where a flexible, yet mechanically stable, polymer matrix is essential. Intensive research is currently going on worldwide for their application as electrolytes in polymer fuel cells (PEMFCs)[1]. The currently well-developed PEMFCs technology is based on perfluorosulfonic acid membranes (PFSA) and among them the most studied is Nafion. However, these polymers suffer from severe disadvantages, such as limited operation temperature due to the humidification requirements, water and methanol cross-over and very high cost, so many studies have already been carried out to develop alternative proton conducting polymers. Aromatic hydrocarbon polymers are considered to be promising as an alternative to Nafion and, in general, to PFSA (PerFluoroSulfonic Acid) membranes. They are high performance thermoplastic polymers which exhibit high-temperature resistance, mechanical strength and oxidation stability.[2-4] The introduction of acidic units achieves proton conductivity. However, the high degree of sulfonation (DS ≥ 0.8), required for proper conductivity value (σ ≈ 10-2 Scm1 ), leads to high swelling or even water soluble products, hence lowering mechanical and morphological properties.[8] Among the several approaches that can be used to improve ionomeric membranes two seem to be worth taking into consideration: the preparation of crosslinked polymers and the formation of covalent organic-inorganic hybrid membranes. The transport properties of polymeric membranes are strongly dependent on the type and extent of
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