Facilely Control Grafting Density and Side Chain Composition of Bottlebrush Polymer

Control over polymer architecture and composition is essential for disclosing structure-property relationships and developing high-performance materials. Herein, a new method is successfully developed to synthesize bottlebrush polymer (BP) with controllable graft density and side chain composition by "grafting-from" strategy using in situ halogen exchange and reversible chain transfer catalyzed polymerization (RTCP). The main chain of the BP is first synthesized by the polymerization of methacrylates containing alkyl bromide as a side group. Then, the alkyl bromine is quantitatively converted to alkyl iodide with sodium iodide (NaI) via in situ halogen exchange to efficiently initiate the RTCP of methacrylates. By adjusting the input amount of NaI and monomers in sequence, BP named PBPEMA-g-PMMA/PBzMA/PPEGMEMA which contains three different kinds of polymer side chains including hydrophilic PPEGMEMA, hydrophobic PMMA, and PBzMA is synthesized with narrow molecular weight distribution (M_w /M_n  ≤ 1.36). The grafting density and the chain length of each polymer side chain are well controlled by the addition of NaI in batches and following RTCP. Moreover, the obtained BP self-assembled into spherical vesicles in aqueous with hydrophilic coronal structure, core region, and the hydrophobic wall between the former two, which enables to wrap hydrophobic pyrene and hydrophilic Rhodamine 6G separately or simultaneously.