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

Three series of cascade polymers possessing identical internal hierarc hical architectures, but with either acidic, neutral, or basic termina l functionality, have been prepared. An iterative synthetic strategy w as 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-solubl e cascade polymers(dendrimers). Diffusion ordered spectroscpy (H-1 DOS Y NMR) of these cascade polyamides revealed that some of these polymer s swell or shrink in response to the stimulus of a pH change. These da ta are consistent with the hypothesis that the flexible internal archi tecture of these cascade molecules and coulombic repulsions between (c harged) terminal groups account for this ''smart'' behavior. Consequen tly, the proposed uses of cascade (dendritic) polymers as size standar ds must be tempered by this pronounced pH dependence of the hydrodynam ic radii.