Molecular bottlebrushes have been shown to exhibit intriguing worm-to-globule shape transitions in response to external stimuli. However, such shape transitions have been restricted to dilute solutions (&lt; 1.0 mg/g) or at interfaces, which has greatly limited the potential application of these shape-changing molecular bottlebrushes. Here we present a method to achieve worm-to-globule transitions in moderately concentrated aqueous solutions by using binary heterografted molecular bottlebrushes. These brushes are composed of a poly(ethylene oxide) (PEO) and a thermosensitive polymer as side chains, where PEO is much longer so as to shield the thermosensitive side chains to avoid intermolecular association during the lower critical solution temperature transition. A small amount of UV-crosslinkable groups was incorporated into the thermosensitive polymer, allowing the fixation of the brush shape at higher temperatures for atomic force microscopy characterization at ambient conditions. Three brush samples, BMB-5k, -2k, and -750, were synthesized by grafting a thermosensitive polymer with a degree of polymerization (DP) of 43 and a PEO with a DP of 114, 45, or 17, respectively, onto a backbone polymer via click chemistry. While BMB-2k and -750 underwent intermolecular aggregation at a concentration of 10 mg/g upon heating, BMB-5k collapsed intramolecularly from a wormlike to a spherical shape at concentrations of 10 and 25 mg/g. Even at 100 mg/g, at least 95% of brushes underwent a worm-to-globule transition.

Worm-to-globule shape transition of thermosensitive binary heterografted molecular bottlebrushes in water

2019 Spring National Meeting

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