Micro‐Raman investigations of PVDF‐based proton‐conducting membranes

Abstract

Proton-conducting membranes of poly(vinylidene fluoride), PVDF, grafted with styrene and thereafter sulfonated, were investigated by Raman spectroscopy. The depth and surface distribution of polystyrene grafts and crosslinker, as well as the sulfonation efficiency, were determined by using confocal micro-Raman spectroscopy. Highly grafted samples show homogeneous distribution of grafted material and homogeneous sulfonation. Depth profiles reveal uneven graft distribution for samples with low and intermediate degrees of grafting. In crosslinked samples, the crosslinker concentration in the interior of the film is found to be roughly 50% of the surface concentration. In contrast to what has previously been reported, the sulfonation efficiency is poor at low graft levels and is further inhibited by the presence of divinyl benzene, DVB, as crosslinker. At degrees of grafting above ∼ 60%, the crosslinker does not affect the sulfonation efficiency and a level of 70–90% sulfonation is reached. The matrix polymer structure is found to be largely retained after irradiation, grafting, and sulfonation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3317–3327, 1999