Styrene (ST)/methyl acrylate (MA) copolymers, having various MA contents (0-50 wt %), were synthesized in the form of a crosslinked bead and characterized by FTIR, solid state nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. The copolymers were sulfonated using concentrated sulfuric acid. The copolymers with a higher MA content (20 wt % or above) undergo sulfonation even at room temperature, and higher temperature was required for the completion of sulfonation in case of the samples having lower MA content. This has been explained in terms of the polarity and porosity of the beads as has been analyzed by scanning electron microscope (SEM). The sulfonated copolymer beads show built-in acid-base indicator property: yellow color in an acid medium changes to intense pink color at the equivalence point. FTIR and NMR studies clearly indicate that intramolecular cyclization takes place during sulfonation. (c) 2007 Wiley Periodicals, Inc.