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. (C) 2003 Wiley Periodicals, Inc.