Cation permeable membranes from blends of sulfonated poly(ether ether ketone) and poly(ether sulfone)

Sulfonated poly(aryl ether ether ketone), S-PEEK, is blended with non-sulfonated poly(ether sulfone) (PES) to adjust the properties of ion permeable and ion selective membranes. In this study, membranes are prepared from blends with (i) a S-PEEK content between 10 and 100 wt.% using one S-PEEK batch with a fixed degree of sulfonation and (ii) from batches of S-PEEK with a different degree of sulfonation, but with a fixed S-PEEK content in the blend. The transparent membranes are permeable for ions with selective transport of cations over anions. At contents of S-PEEK below 40%, phenomena related to a percolation threshold of the ion exchange functionalities are observed; the measured ion exchange capacity (IEC) indicates that not all functional groups are accessible in these blends. The transport properties of membranes with a S-PEEK content in the range of 50-80 wt.% are comparable to those known for commercial ion exchange membranes. In this range, a trade-off between resistance and selectivity with increasing IEC is observed. Both, the ion conductivity and the co-ion transport number increase with increasing IEC. This is mainly caused by the increased water content with increased IEC and the number of water molecules per fixed charge. (C) 2002 Elsevier Science B.V. All rights reserved.