Fabrication of Cyclic Brush Copolymers with Heterogeneous Amphiphilic Polymer Brushes for Controlled Drug Release

Cyclic brush (cb) copolymers that are composed of a cyclic core densely grafted with radiating polymer brushes have emerged recently as innovative materials for both fundamental and practical investigations due to their capability to form unimolecular micelles with greater stability relative to the analogues self-assembled by the bottlebrush (bb) copolymers with an identical molecular weight (MW). However, compared to the extensive and intensive studies on cb copolymers with homogeneous polymer brushes, the preparation and application of cb copolymers with heterogeneous polymer grafts remains unexplored likely due to the synthetic challenge. For this purpose, we reported in this study the first preparation of cb copolymers with heterogeneous polymer brushes using a diblock copolymer-based cyclic core template. An amphiphilic cb copolymer with both hydrophilic oligo (ethylene glycol) (OEG) and hydrophobic oligo (ε-caprolactone) (OCL) brushes grafting from a cyclic core was designed and synthesized by a combination of atom transfer radical polymerization (ATRP), intrachain click cyclization, and ring-opening polymerization (ROP) techniques. Interestingly, the resulting amphiphilic cb copolymers showed greater in vitro cytotoxicity relative to the bb analogues for anticancer drug delivery. The amphiphilic cb copolymers with heteropolymer grafts developed herein thus represent a novel platform for controlled drug release.