PROTON-EXCHANGE MEMBRANES BY RADIATION GRAFTING OF STYRENE ONTO FEP FILMS .3. STRUCTURAL INVESTIGATION

Structural investigation on proton-exchange membranes, obtained by the radiation grafting of styrene onto FEP films and subsequent sulfonati on, was carried out by differential scanning calorimetry. The membrane crystallinity was found to show a decreasing trend with increasing de gree of grafting. The melting temperature of all the membranes also sh owed a slight decrease as compared to the ungrafted FEP. The results h ave been explained in terms of the cumulative effect of the decrease i n the crystalline/amorphous ratio by the incorporation of amorphous po lystrene grafts and of disruption of spherulitic crystallites of the F EP component in the membranes. The glass transition temperature of the membranes with different water contents was also evaluated. A correla tion of the glass transition temperature with the residual water in dr ied membranes was established. (C) 1994 John Wiley & Sons, Inc.