Pushing Synthesis toward the Maximum Generation Range of Dendritic Macromolecules

The maximum generation g_max of a dendritic molecule denotes the value of the generation number g, above which such a compound cannot be synthesized without defects anymore due to steric constraints. For dendronized polymers (DPs), such a densely packed regime is entered far earlier (g_max ≈ 6) than it is for comparable dendrimers (g_max ≥ 10) because dendritic side chains are confined to a cylindrical rather than a spherical volume. We here report a long sought-after improvement to a key step in the divergent synthesis of high-g DPs which enabled obtaining the polymers of g = 6, 7, and 8. These DPs are of unprecedented dendritic perfection, and the representatives with g > 6 are to our knowledge the first molecules for which g_max has been surpassed. We suggest a straightforward parameter α which allows to assess whether any dendritic molecule is above g_max, given sufficiently efficient chemistry and the possibility of accurately determining the number of defects. Finally, we correlate gel permeation chromatography results and atomic force microscopic images with defect rates.