Molecular Bottlebrushes Featuring Brush-on-Brush Architecture.

Molecular bottlebrushes featuring brush-on-brush (BoB) architecture were prepared by combining azide-alkyne click chemistry, ring-opening polymerization (ROP), and atom transfer radical polymerization (ATRP). Primary side chains of diblock copolymers with a poly(ε-caprolactone) (PCL) block and a poly(α-bromo-ε-caprolactone) (P(CL-Br)) block were synthesized by ROP and then grafted onto PCL backbone by the click reaction. Then the secondary side chains of poly(oligo(ethylene glycol) acrylate) (POEGA) were grafted from the P(CL-Br) block by ATRP, yielding an amphiphilic core/shell structure. Imaging of individual macromolecules by atomic force microscopy (AFM) demonstrated dramatically thickened wormlike formation with distinct hairy side chains. Interestingly, for the BoB molecular bottlebrushes with enough long primary and secondary side chains, sufficient tension can be generated along the backbone and thus lead to its cleavage.