The synthesis and characterization of a new family of polyamide dendrimers

A new family of dendrimers has been constructed with 5-hydroxy-isophthalic acid and diethanolamine as the sources of the branching units. The design of a second-generation building block in the form of an orthogonally-protected aminotetraacid (a single diethylphosphoramide-protected amine and four methyl-ester-protected carboxylic acid groups) has been established by a series of logical developments involving the synthesis of various dendrimer prototypes. This building block has been utilized in both convergent and divergent methods in the synthesis of monodisperse dendrimers up to the fourth generation and subsequently polydisperse sixth-generation dendrimers at the level of a mixture. One-, two-, and three-directional dendrimers of the second and fourth generation were synthesized in order to carry out detailed comparisons by GPC and by ¹H NMR spectroscopy. The GPC results suggest that the fourth-generation dendrimers adopt globular shapes, while the variable-temperature NMR spectroscopic investigations demonstrate that the periphery of the fourth-generation dendrimer is less mobile than either of its internal regions or the analogous portions of the second-generation dendrimer. Molecular modeling suggests highly globular shapes for the larger dendrimers and gives values for molecular radii in very close agreement with those obtained from analysis of the GPC results.