Thermal stability and structural investigations of sulfonated polystyrene pore-filled poly(vinylidene fluoride) membranes

Sulfonated polystyrene pore-filled electrolyte membranes have been prepared by simultaneous radiation grafting of styrene into porous poly(vinylidene fluoride) (PVDF) films and subsequent sulfonation process. The effects of two-step membrane preparation procedures and grafting yield on the thermal stability and structural properties of membranes were investigated by thermal gravimetric analysis and differential scanning calorimetry, respectively. A three-step degradation pattern was observed from TGA thermograms of all the membranes, which attributed to the dehydration, desulfonation, and degradation of the PVDF backbone. The weight losses in the membranes were found to be reliant on the grafting yield. Meanwhile, the intrinsic crystallinity of the PVDF matrix was found to show a decreasing trend with increasing in grafting yield. A further decrease in crystallinity was also observed in the sulfonation reaction. The residual crystallinity of the PVDF matrix approximately 5% was still remained in the membranes even it had been subjected to severe reaction conditions. The decreased in crystallinity of the resulting membranes can be explained by the combination of the dilution effect and the crystal disruption that occurred within the membrane´s matrix.