Synthetic regimes due to packing constraints in dendritic molecules confirmed by labelling experiments.

Classical theory predicts that branching defects are unavoidable in large dendritic molecules when steric congestion is important. Here we report first experimental evidence of this effect via labelling measurements of an extended homologous series of generations g = 1...6 of dendronized polymers. This system exhibits a single type of defect interrogated specifically by the Sanger reagent thus permitting to identify the predicted upturn in the number of branching defects when g approaches g(max) and the polymer density approaches close packing. The average number of junctions and defects for each member of the series is recursively obtained from the measured molar concentrations of bound labels and the mass concentrations of the dendritic molecules. The number of defects increases at g=5 and becomes significant at g=6 for dendronized polymers where the g(max) was estimated to occur at 6.1 ≤ g(max) ≤ 7.1. The combination of labelling measurements with the novel theoretical analysis affords a method for characterizing high g dendritic systems.