Microstructural characterization of PEMs based on sulfonated syndiotactic polystyrene in the δ co-crystalline phase

Syndiotactic polystyrene (s-PS) is able to form different kinds of co-crystalline phases with guest molecules of various size, shape and property. Several advanced materials have been produced starting from s-PS co-crystalline films [1-2]. In particular, sulfonated s-PS (s-SPS) can be used as proton-conductive membrane for fuel cells, as it presents high proton conductivity (comparable with Nafion). Besides, it shows a high chemical and thermo-mechanical stability and a low cost [3]. The morphology of different s-PS clathrates and the structural behavior of s-SPS upon hydration can be more thoroughly understood by combining X-rays scattering and FT-IR with SANS [4]. In fact, exploiting the neutron contrast variation between various hydrogenated and deuterated components of s-PS and s-SPS clathrates, additional and unique information about the distribution of guest molecules in the crystalline and amorphous regions and about the hydrated domains of the polymer were obtained. Moreover, the stretching of films leads to occurrence and distribution of scattering features from typical morphologies on specific directions and sectors of detection plan, which enables an accurate structural study of such complex polymeric systems. A complete SANS investigation on s-PS samples, starting from their crystallization with guest molecules to the subsequent sulfonation and hydration, was performed at SANS diffractometer KWS2 of MLZ. This experimental analysis has highlighted that the morphology of these polymeric films is characterized by hydrated channels in the amorphous phase alternated to staples of crystalline lamellae, along the stretching direction.[1]. J. Schellenberg in “Syndiotactic Polystyrene’’, John Wiley & Sons, Inc. 2010.[2]. G. Guerra et al., J. of Pol. Sci. B, Polymer Physics 2012, 50, 305.[3]. G. Fasano et al., Int. Journal. of Hydrogen Energy 2013, 36, 8038.[4]. F. Kaneko et al., Polymer 2013, 54, 3145 and Chemistry Letters, 2015, Accepted