Divergent Synthesis of Polyphenylene Dendrimers:  The Role of Core and Branching Reagents upon Size and Shape

Monodisperse polyphenylene dendrimers up to the fourth generation were synthesized using a divergent growth protocol. By varying the core, dendrimers with dumbbell-, tetrahedral- and propeller-like structures were synthesized. Because of the high-density packing of benzene rings within their branches, these dendrimers are stiff and thus shape persistent. To obtain these dendrimers with a globular shape, a 4-fold (A4B) dendrimer building unit was introduced. In this case, monodisperse dendrimers are obtained only up to the second generation due to the significantly increased density of benzene rings within the structure. For structure elucidation methods, like MALDI−TOF mass spectrometry, NMR spectroscopy, GPC, VPO, TGA, and DSC were used. Dendrimers of the third and fourth generations were visualized by transmission electron microscopy.