Polystyrene-based crosslinked cationic ionomers containing ammonium or phosphonium chlorides (AxRCl and PxBuCl) were reacted with decyl methanesulfonate. The kinetic data were correlated with the swelling behavior of the ionomers and the solution viscosity of the corresponding linear ionomers. The reactivity of the ionomers was independent of the particle size of the ionomer beads, indicating no diffusion control of the reaction. The solvent and the ion content of the ionomers greatly affect the reactivity. In nonpolar solvents with a low acceptor number, A(N), such as toluene, the aggregation of ionic groups with an increasing ion content reduces the reactivity. A solvent with a high value of A(N), such as chloroform, led a very low reactivity independent of the ion content. Aprotic polar solvent, such as acetonitrile, promoted the dissociation of the ionic groups and furnished a relatively high reactivity independent of the ion content. Several catalytic substitution reactions were carried out under liquid-solid-solid triphase conditions. The kinetic results were accounted for in terms of slow nucleophile transport and fast chemical reaction within the ionomer particles.