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 synt hesized 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 branche s, these dendrimers are stiff and thus shape persistent. To obtain these de ndrimers with a globular shape, a 4-fold (A(4)B) dendrimer building unit wa s introduced. In this case, monodisperse dendrimers are obtained only up to the second generation due to the significantly increased density of benzen e 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 transmis sion electron microscopy.