CATION-EXCHANGE MEMBRANES BY PREIRRADATION CRAFTING OF STYRENE INTO FEP FILMS .2. PROPERTIES OF COPOLYMER MEMBRANES

The structure and some physico-chemical properties of radiation grafte d FEP-g-polystyrenesulfonic acid proton exchange membranes were studie d as a function of the degree of grafting. The distribution of grafted polymer across the membrane thickness was obtained from microprobe me asurements. It was found that for low levels of grafting (ca. 3%), pol ystyrene chains are located near the membrane surface only, and the in terior of the membrane remains ungrafted. With the increasing degree o f grafting, polystyrene chains were incorporated into the interior of the membrane as well. An almost homogeneous distribution of grafts in the membrane was obtained at a graft level of > 13%. The influence of the degree of grafting on membrane properties, such as ion exchange ca pacity, swelling, and specific resistivity was studied. Three differen t states of water, viz., freezing free, freezing bound, and nonfreezin g water have been identified in noncrosslinked membranes. However, the nature and the amount of crosslinker had a profound influence on the states of water in a membrane. (C) 1996 John Wiley & Sons, Inc.