Synthesis and Self-Assembly of Amphiphilic Dendrimers Based on Aliphatic Polyether-Type Dendritic Cores

We have prepared a series of amphiphilic dendrimers with hydrophilic aliphatic polyether-type dendritic core and hydrophobic docosyl peripheries. All dendrimers from first up to fourth generation 1−4 were synthesized in good yield and high purity by a stepwise convergent approach consisting of a combination of Williamson etherification and hydroboration/oxidation steps. Differential scanning calorimetry (DSC) measurements show that the docosyl peripheries melting temperatures and corresponding heats of fusion decrease only slightly with each generation, indicative of a strong segregation between hydrophilic dendritic core and hydrophobic docosyl periphery. The DSC derived docosyl periphery crystallinity shows a gradual reduction with each generation and is corroborated by wide-angle X-ray scattering (WAXS) experiments. Amphiphilic dendrimer self-assembly in the solid state is investigated by small-angle X-ray scattering. Data from 1, 2, and 3 suggest a bilayer lamellar structure with interdigitated dendritic core packing. In contrast, data from 4 are consistent with a 2-dimensional oblique columnar assembly with hydrophilic core structure. The observed thermal and morphological behaviors are rationalized in terms of high incompatibility and intrinsic interfacial curvature between hydrophilic dendritic core and hydrophobic docosyl periphery arising from the unique dendritic molecular architecture.