CO2-induced reversible morphology transition from giant worms to polymersomes assembled from a block-random segmented copolymer

Abstract

Well-defined block copolymers represent “stars” among amphiphilic compounds for self-assembly. However, few studies have been directed to their block-random “hybrid” counterparts. In this work, a segmented diblock copolymer containing one random block, PEO₁₁₃-b-P(4VP₉₀-r-DEAEMA₃₀), was prepared via the RAFT technique from the hydrophilic poly(ethylene oxide) block and a random hydrophobic block copolymerized from 2-(diethylamino)ethyl methacrylate (DEAEMA) and 4-vinyl pyridine (4VP). It was found that first the copolymer in aqueous media could self-assemble into vesicles, which then fuse hierarchically into giant worm-like micelles similar to shish kebab, with length and diameter of ca. 15 μm and 215 nm, respectively. After bubbling CO₂ into the copolymer solution up to saturation (pH 5.43), the giant worms transform into polymersomes with a diameter about 75 nm, which is considerably larger than that of the spherical micelles assembled from the same polymer treated with HCl (pH 3.32). The vesicles obtained could revert to worm-like aggregates after depleting CO₂ by bubbling N₂. Protonation–deprotonation of the PDEAEMA unit, the intensive steric hindrance effect from the adjacent 4VP groups and hydrogen bonding between different 4VP units and free H₂O in the interior of polymersomes accounted for such a CO₂-driven reversible morphology transition.