Partial sulfonation of gel-type styrene-co-divinylbenzene polymer is reported and the homogeneity of the sulfonation investigated by electron microprobe analysis of the sulfur content. The morphology of the polymers was characterized by inverse steric exclusion chromatography (ISEC) and the catalytic activity was determined by measuring the reaction rates of three model reactions (synthesis of bisphenol A, alkylation of phenol by I-octene and reesterification of ethyl acetate with propanol) in a glass CSTR microreactor at steady-state conditions. Distribution of the sulfonic groups within partially functionalized beads looks fairly homogeneous at the electron microprobe resolution scale, but both ISEC morphology characterization and the catalytic experiments indicate the presence of separate sulfonated and unsulfonated domains. The effect of this morphology on the kinetics of catalytic reactions depends on the size of the reacting molecules and their affinity to both the functionalized and unfunctionalized domains of the polymer support. These findings may be useful for the development of other polymer supported catalysts. (c) 2005 Elsevier B.V. All rights reserved.