Molecular bottlebrushes (MBBs), composed of polymeric side chains densely grafted on a relatively long polymer backbone, hold great potential in a variety of applications, including photonic crystals, lubrication, supersoft elastomers, and drug delivery. These complex macromolecules have been shown to exhibit intriguing conformational transitions between extended worm-like and collapsed globular states in response to external stimuli. However, such unimolecular shape transitions were restricted to rather dilute solutions due to the aggregation of unstable collapsed brush molecules, which has greatly limited the potential applications of such shape-changing MBBs. We recently developed linear homografted MBBs composed of diblock copolymer side chains that allowed for worm-to-collapsed yet stable globule shape transitions in aqueous solution, where the outer block of the diblock copolymer side chains served as a stabilizer when the inner responsive block collapsed. The brushes were prepared by grafting alkyne end-functionalized diblock copolymers onto an azide-bearing backbone via click reaction. The inner block of the brushes was a pH-responsive polymer, while the outer block was a thermoresponsive polymer. Dynamic light scattering and atomic force microscopy were employed to demonstrate the shape transition of the MBBs in aqueous solution with increasing pH at a concentration of 1.0 mg/g at ambient temperature; the collapsed state was stabilized against aggregation by the soluble outer block. Additionally, the thermoresponsive outer block provided another level of control over the solution state of the brushes, allowing for further collapse at low concentrations and aggregation of individually collapsed molecules at higher concentrations upon heating. The ability to switch molecular shapes, stabilize collapsed nano-objects against aggregation, and control the solution state may lead to potential applications of stimuli-responsive shape-changing molecular bottlebrushes.

Shape-changing linear homografted molecular bottlebrushes with doubly responsive diblock copolymer side chains

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.