Thiol-Ene Click Inspired Late-Stage Modification of Long-Chain Polyurethane Dendrimers

Compared to the synthesis of polyurethane polymers, construction of well-defined polyurethane dendrimers is challenging due to the high reactivity of externally added or in-situ formed isocyanates leading to the formation of side products. For this reason, the synthesis of dendritic polyurethanes is limited to very few reports. With primary focus of dendrimer research on the interaction of the periphery and the core, we report the synthesis of a common polyurethane dendron, which allows for late-stage variation of both the periphery and the core. The periphery can be varied simply by installing a clickable unit in the dendron and then attaching to the core and vice-versa. Thus, a common dendron allows for varying periphery and core in just two steps. To accomplish this, protecting group free one-pot multicomponent Curtius reaction was utilized to afford a robust and versatile AB2 type polyurethane dendron employing commercially available simple molecules 5-hydroxyisophthalic acid, 11-bromoundecanol, and 4- penten-1-ol. Subsequent late-stage modification of either dendrons or dendrimers via thiol-ene click reaction gave surface?functionalized alternating aromatic-aliphatic polyurethane homodendrimers to generation-three (G3). The dendrons and the dendrimers were characterized by NMR, mass spectrometry, and FT-IR analysis. A bifunctional AB2 type dendritic monomer demonstrated this approach's versatility that can either undergo a thiol-one click or attachment to the core. This approach enables the incorporation of functionalities at the periphery and the core that may not withstand the dendrimer growth for the synthesis of polyurethane dendrimers and other dendritic macromolecules