The poly(propylene imine) dendrimers DAB-dendr-(NH2)(8), DAB-dendr(NH2)(32), and DAB-dendr-(NH2)(64), were fully converted with iodomethane to quaternary ammonium ions at both chain ends and branch points and, with less iodomethane, were partially converted to quaternary ammonium ions mainly at end groups. Amidation of the primary amine ends followed by treatment with iodomethane gave the first dendrimers with quaternary ammonium ions only at branch points. After an exchange of iodide counterions for chloride, all of the quaternary ammonium ion dendrimers slightly increased the rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion in an aqueous solution. Similar quaternary ammonium ion dendrimers with more hydrophobic interiors or more hydrophobic chains on the ends were much more active catalysts for the decarboxylation. (C) 2001 John Wiley & Sons, Inc.