Dynamic Bottlebrush Random Copolymers as Triggered Macromolecular Surfactants

We synthesized acid-responsive bottlebrush random copolymers (BRCPs) comprising solketal-substituted and unsubstituted polystyrene side chains through a graft-through ring-opening metathesis polymerization strategy. Upon interfacial contact with aqueous acid, the hydrophobic solketal groups undergo in situ hydrolysis to 1,2-diols, transforming the BRCPs into amphiphilic macromolecular surfactants that dynamically reduce water/oil interfacial tension. Time-resolved pendant-drop tensiometry revealed two characteristic relaxation regimes corresponding to interfacial adsorption and post-hydrolysis reorganization. Hydrolysis followed first-order kinetics (k ≈ 0.06–0.14 h⁻¹) and accelerated with increasing backbone length, while higher grafting densities introduced steric hindrance that slowed reorganization. The interfacial tension decreased from ~25 mN m⁻¹ to ~10 mN m⁻¹ after acid exposure, and spontaneous emulsification was observed for short-backbone, densely packed architectures. These results establish design rules that link bottlebrush architecture, packing density, and dynamic interfacial responsiveness, providing a versatile platform for stimuli-triggered emulsification and adaptive soft materials.