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Novel ion-exchange resin beads with acid–base indicator property



Copolymers of styrene and methyl acrylate were synthesized in the form of spherical beads (0.4–1.2 mm) and sulfonated with concentrated sulfuric acid. The sulfonated copolymer shows an in-built acid–base indicator property; the yellow color in the acid medium changes to an intense pink color at the equivalence point. Also, the ion-exchange capacity of the sulfonated copolymer increases with time, reaches a maximum, and decreases thereafter. The results were explained in terms of Fourier transform infrared spectroscopic analysis considering internal Friedel–Craft acylation followed by cyclic dehydration leading to a conjugated structure. The developed ion-exchange resin also demonstrated better performance in demineralization of water as compared with the conventional polystyrene-based beads. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2166–2170, 2003