Construction of Giant Dendrimers Using a Tripodal Building Block

Abstract

Giant pentane-soluble organo-silicon dendrimers have been synthesized using a triallylphenol brick according to a new divergent construction that uses a hydrosilylation−nucleophilic substitution sequence up to the ninth generation (G₉). All the reactions were monitored by ¹H, ¹³C, and ²⁹Si NMR until G₉, indicating that they were clean at the NMR accuracy until this last generation. MALDI TOF mass spectra were recorded for G₁ to G₄ and show the nature and amounts of defects that are intrinsic to the divergent construction. This technique and SEC (recorded up to G₅) confirm the monodispersity (1.00 to 1.02) from G₁ to G₅. HRTEM and AFM images recorded for the high generations disclose the expected smooth dendrimer size progression and the globular shape. At G₉, the theoretical number of termini (TNT) is 177 407 branches (abbreviation: G₉-177 047). It is estimated that more than 10⁵ terminal branches are actually present in the G₉ dendrimer, far beyond the De Gennes “dense-packing” limit (6000 branches), and it is believed that the branch termini turn inside the dendrimer toward the core. This is corroborated by lower reaction rates and yields for the highest generation numbers presumably due to intradendritic reactions. It is probable that the dendritic construction is limited by the density of branches inside the dendrimer, i.e., far beyond the dense-packing limit.