Structure-property Relationships in Radiation Grafted Poly(tetrafluoroethylene)-<Emphasis Type="Italic">graft</Emphasis>-polystyrene Sulfonic Acid Membranes

Structure-property relationships in poly(tetrafluoroethylene)-graft-polystyrene sulfonic acid (PTFE-g-PSSA) membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films using simultaneous radiation-induced grafting followed by sulfonation reaction were established. The physico-chemical properties of the membranes such as ion exchange capacity, swelling and ionic conductivity were correlated with the degree of grafting and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity of membranes was studied by differential scanning calorimetry (DSC). The membranes thermal stability was evaluated using thermogravimetric analysis (TGA) and the effect of the heat treatment on the ion exchange capacity and the water uptake was investigated. The membranes were found to undergo substantial structural changes in the form of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the increase in the degree of grafting. These structural changes were found to have a collective effect on the physico-chemical properties of the membranes but their relative contribution depends on the degree of grafting.