Temperature-Induced Shape Changing of Thermosensitive Binary Heterografted Linear Molecular Brushes between Extended Wormlike and Stable Globular Conformations

Inspired by stimuli-triggered unraveling of the von Willebrand factor from a nonsticky globular to a stretched linear shape with exposure of functional groups in blood clotting, this article reports on the synthesis of thermosensitive binary heterografted linear molecular brushes that exhibit temperature-induced shape changing between extended wormlike and collapsed yet stable globular conformations in water. The molecular brushes are composed of two distinct side chain polymers: thermosensitive poly(ethoxydi(ethylene glycol) acrylate) (PDEGEA), which undergoes a lower critical solution temperature (LCST) transition at 9 °C in water, and poly(ethylene oxide) (PEO), which serves as a stabilizer for the collapsed state. A “grafting to” method was developed to construct molecular brushes by clicking alkyne end-functionalized side chain polymers onto an azide-bearing backbone polymer. While a 1.0 mg/g aqueous solution of PDEGEA homografted molecular brushes turned cloudy upon heating from 0 to 22 °C, at the same concentration the aqueous solution of PEO/PDEGEA binary molecular brushes remained clear, indicating the stabilization of the collapsed state against aggregation by PEO side chains. Atomic force microscopy study revealed a stretched, wormlike morphology of brushes at 0 °C and compact, globular nano-objects at 40 °C. The thermally induced shape changing was exploited to regulate the binding of biotin, which was incorporated into the thermosensitive side chains along with a fluorescent resonance energy transfer (FRET) donor, and Rhodamine B (FRET acceptor)-labeled avidin. FRET study showed that when the molecular brushes changed from the globular to the wormlike state, the binding of biotin and avidin occurred and increased significantly with time.