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) approximate to 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 a 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.