Sulfonation and characterization of poly (styrene-isobutylene-styrene) triblock copolymers at high ion-exchange capacities

In this study, a triblock copolymer, poly(styrene-isobutylene-styrene), was sulfonated to eight different levels ranging from 0.36 to 2.04 mequiv./g (13 to 82 mol% of styrene; styrene is 19 mol% of the unsulfonated block copolymer). These sulfonated polymers were characterized with elemental analysis and infrared spectroscopy to confirm sulfonation and determine accurate sulfortation levels. Infrared analysis revealed four additional stretching vibrations as a result of sulfonation. Also, a linear relationship between absorbance at 1006 cm(-1) (stretching of the aromatic ring in styrene caused by the para-substituted sulfonic acid) and sulfortation level (measured by elemental analysis) was found. The density and water solubility of all the sulfonated polymers were measured and increased with increasing sulfortation level, as high as 1.31 a/cm(3) and 351 wt%, respectively. In addition, a sulfonated triblock copolymer at 79 mol% sulfonation was neutralized with a cesium cation and revealed an increase in density, but a reduction in water solubility. This study demonstrates the resulting unique properties of sulfonated styrene-based block copolymers at higher ion-exchange capacities than previously reported. (C) 2004 Published by Elsevier Ltd.