Molecular Bottlebrushes with Programmable Grafting Densities

Molecular bottlebrushes (MBBs) refer to a type of synthetic macromolecule with cylindrical structures that have found wide applications in biomedicine and materials science. To achieve precise control over the molecular architecture of MBBs is essential for investigating their structure–property relationship and creating optimal materials. Herein, we utilize copper-catalyzed azide–alkyne cycloaddition (CuAAC) chemistry to precisely tailor the molecular architecture of MBBs and synthesize a series of MBBs with programmable grafting density by rational combination with ring-opening metathesis polymerization (ROMP). Briefly, the multiblock copolymers (MBCPs) with varied sequences of azido, 1,3-diazido, and 1,3-triazido monomer units were synthesized by sequential ROMP and then used as the multifunctional backbones for grafting alkynyl-terminal side chains by CuAAC chemistry, producing well-defined MBBs with programmable grafting density of 1, 2, or 3 chains per unit. Atomic force microscopy (AFM) indicated that these MBBs with programmable grafting density exhibited unimolecular worm-like morphologies with gradient widths and heights along the backbone. Overall, this work proposes a robust and efficient synthesis approach for precisely tailoring the nanostructures of MBBs by a combination of CuAAC chemistry and ROMP.