A Model for Late-Stage Modification of Polyurethane Dendrimers Using Thiol-Ene Click Chemistry

Dendritic materials possessing urethane linkage are surprisingly more stable than similar structures having functional groups such as ether, ester, amide, or carbosilane. This generates profound interest in dendritic polyurethanes. Construction of a well-defined polyurethane dendrimer is, however, challenging because of isocyanates' high reactivity. As a model of our ongoing dendrimer-research, herein, we report a protecting group-free one-pot multicomponent Curtius reaction to furnish a robust and versatile AB₂-type dendron, which ensures late-stage modification of both the dendron and dendritic macromolecule yielding a surface functionalized polyurethane dendrimer. While 5-hydroxyisophthalic acid, 11-bromoundecanol, and 4-penten-1-ol were utilized in the construction of the dendron, thiol-ene click chemistry was employed for the late-stage modification. Novel dendrons and dendrimers synthesized were characterized by NMR (1D and 2D) and high-resolution MALDI-TOF analysis. This strategy allows an easy late-stage modification of dendritic macromolecules and is highly useful in the synthesis of both symmetrical and unsymmetrical dendrimers (Janus dendrimers).