Modulating Two Copper(I)-Catalyzed Orthogonal "Click" Reactions for the One-Pot Synthesis of Highly Branched Polymer Architectures at 25 °C

Controlling the rates of orthogonal "click" reactions in one-pot provides a method for designing highly branched macromolecular architectures. In this work, we constructed third generation (G3) dendrimers consisting of a wide range of chemically different polymer building blocks in one pot at 25 degrees C. This approach reduced the number of purification and chemical protection steps. Using the model polystyrene (PSTY) building block system, third generation dendrimers could be formed divergently, convergently or in parallel through modulating the Cu(I) activity for the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and nitroxide radical coupling (NRC) reactions. The parallel approach was the fastest, generating a G3 dendrimer in under 30 min, and the next fastest was the divergent pathway, followed by the very slow (24 h) convergent pathway. The resulting G3 dendrimer could be cleaved at the alkoxyamine sites back to linear polymers by heating the reaction mixture at 120 degrees C in the presence of an excess hydroxyl nitroxide. The synthetic utility of this method was further extended to coupling linear telechelic polymer building blocks, consisting of PSTY, P(t)BA, PEG, and PNIPAM, to form a range of dendrimers in high yields. Preparative SEC was used to fractionate excess starting reactants and intermediate polymer species from the product dendrimer.