Synthesis and Characterization of pH Sensitive Core-Shell-Corona Micelles of Poly(styrene-block-2-vinylpyridine-block-ethylene oxide) ABC Triblock Copolymer in Aqueous Solutions

The core-shell-corona forming ABC triblock copolymer poly(styrene-block-2-vinylpyridine-block-ethylene oxide), PS-P2VP-PEO, was synthesized using reversible addition fragmentation chain transfer (RAFT) radical polymerization and characterized by NMR and GPC as PS13-P2VP(62)-PEO47. The aggregation behavior in aqueous solution as a function of pH and temperature was studied. Turbidity measurements were used to monitor the effects associated with change in pH. The pH-sensitive P2VP block (insoluble above pH >5) and resultant protonation/deprotonation phenomenon plays decisive role in the aggregation. We found that spherical micelles of considerably low aggregation number form at pH <5. SANS and DLS characterization indicate the micelles' size and spherical shape remained virtually constant in the pH range 1 to 5. The size and shape were further confirmed by cryo-TEM.