The glass transition temperature (T

The glass transition temperature (Tg) of the sulfonated membranes was measured by DSC.
Theoretically the Tg value would increase as the degree of sulfonation increased. The glass
transition temperature of SPSU membrane was detected in the range of 192ºC and 325 ºC and
the precise determination of this value is hindered by desulfonation process occurring in the
close region of temperature12. The introduction of sulfonate groups has two effects on glass
transition temperature: firstly, increase in molecular interaction by pendant ions, i.e. ionomer
effect; and secondly, increase in molecular bulkiness. Both effects hindering the internal
rotation of polymer molecule and lead to the increased glass transition temperatures for
sulfonated polymers. It is believed that this Tg behavior for sulfonated polymer may reflect a
significant change in microstructure of the polymer 13.