Dielectric analysis of photocrosslinked and post-sulfonated styrene-ethylene-butylene-styrene block copolymer based membranes

A series of UV photocrosslinked and post-sulfonated membranes based on blends of styrene-ethylene-butylene-styrene triblock copolymer (SEBS) and divinylbenzene (DVB) were considered for the preparation of electrolytes for proton exchange membrane fuel cell (PEMFC) applications. Macromolecular dynamics of SEBS and SEBS-DVB membranes below and above the Tg, were analysed using dielectric thermal analysis (DETA). A sub-Tg intramolecular non-cooperative dielectric relaxation and two main relaxations, corresponding to the glass transitions of ethylene-butylene (EB) and styrene (S) blocks, were identified in the dielectric relaxation spectrum. The photocrosslinking and post-sulfonation processes affect to the entire dielectric relaxation spectrum, the apparent activation energy and the fragilities of both styrene (S) and ethylene-butylene (EB) blocks. Understanding the restrictions on the segmental mobility at low and high scale caused by both photocrosslinking and subsequent sulfonation is basic to provide an approach to ionic diffusivities. A correlation between relaxations processes and the performance of these membranes in H2/O2 – PEM single cells allows to estimate the behaviour of these membranes and to reengineer them, depending on the modification of the desired cell performance.