Double Exponential Dendrimer Growth

An exponentially accelerated convergent growth scheme for the synthesis of dendritic macromolecules is described and demonstrated. By this process, the number of repeat units per dendrimer accumulates according to a double exponential function in terms of generation, n. The process employs a single trifunctional monomer of the type A_p(B_p)₂ having orthogonally protected functional groups. The repetitive process involves selective removal of the protecting groups on A_p in one portion, selective removal of the protecting groups on B_p in a second portion, and subsequent coupling of the two monoprotected intermediates in a proper stoichiometric ratio. The new monodendron maintains a single A_p group at its focal point but contains x₂ B_p peripheral groups where x is the number of peripheral groups in the preceding generation. The double exponential growth scheme is demonstrated by the synthesis of a third-generation (255-mer) phenylacetylene monodendron that is characterized by ultraviolet matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (calculated molecular weight 39.972 kDa, observed mlz 39.969 kDa).