The thermal stability of the polymer electrolyte membranes was studied by thermal
gravimetric analysis (TGA). Thermogravimetric analysis for sulfonated polysulfone
membrane with different degree of sulfonation were performed in order to investigate how
much the synthesized polysulfones are thermally stable and to explore which functional
groups are vulnerable by heat. Data obtained form TGA also give evidence on the occurrence
of sulfonation reaction of the polymer at which the degradation temperature of sulfonic group
was observed. The membrane samples were heated from 50ºC to 500ºC to study the thermal
history of the sulfonated membrane. As shown in Figure 2, polysulfone sample shows a
weight loss of 2.77% starting at about 153ºC indicating the loss of residual solvent that was
strongly bound to the polymer during the reaction. The residual solvent could only be removed
well above its boiling point when the polymer is in rubbery state. However, this was not
observed in the SPSU sample as the residual solvent cannot be removed completely from
SPSU films by heat treatment due to decomposition of sulfonic acid group below Tg value