Journal of the American Chemical Society, Vol.117, No.8, 2159-2165, 1995
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 x(2)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 m/z 39.969 kDa).