SMART CASCADE POLYMERS - MODULAR SYNTHESES OF 4-DIRECTIONAL DENDRITIC MACROMOLECULES WITH ACIDIC, NEUTRAL, OR BASIC TERMINAL GROUPS AND THE EFFECT OF PH CHANGES ON THEIR HYDRODYNAMIC RADII

Three series of cascade polymers possessing identical internal hierarchical architectures, but with either acidic, neutral, or basic terminal functionality, have been prepared. An iterative synthetic strategy was employed that involved amidation (via peptide coupling methods) of carboxylic acids with branched amines possessing the desired protected functionalities, followed by facile deprotection to give water-soluble cascade polymers(dendrimers). Diffusion ordered spectroscpy (H-1 DOSY NMR) of these cascade polyamides revealed that some of these polymers swell or shrink in response to the stimulus of a pH change. These data are consistent with the hypothesis that the flexible internal architecture of these cascade molecules and coulombic repulsions between (charged) terminal groups account for this ''smart'' behavior. Consequently, the proposed uses of cascade (dendritic) polymers as size standards must be tempered by this pronounced pH dependence of the hydrodynamic radii.