Thermal stability of styrene grafted and sulfonated proton conducting membranes based on poly(vinylidene fluoride)

The thermal stability of styrene grafted and sulfonated poly(vinylidene fluoride), PVDF-g-PSSA, proton conducting membranes has been studied using thermal gravimetric analysis in combination with mass spectrometry and thermochromatography. The matrix polymer, PVDF, and the non-sulfonated counterpart, PVDF-g-PS, were studied as reference materials. It was found that the degradation of the PVDF-g-PS membrane proceeds in two steps starting at ca. 340 degrees C with the evolution of degradation products typical of polystyrene. The PVDF-g-PSSA membranes are stable to around 270 degrees C even in a strongly oxidising atmosphere. The degradation starts with the simultaneous evolution of water and sulfur dioxide. The polystyrene grafts start decomposing at 340 degrees C in the PVDF-g-PSSA membranes. Thus the Inetnbranes are suitable for tests in electrochemical applications at elevated temperatures.