Phase behavior and self-assembly of PSn(P2VP-b-PAA)n multiarmed multisegmented star terpolymers with ampholytic arms

We report on the phase behavior and self-assembly phenomena of (polystyrene)(n)(poly(2-vinylpyridine)-b-poly(acrylic acid))(n), PSn(P2VP-b-PAA)(n), heteroarm star block terpolymers, in DMF/water solvent mixture. The stars were prepared using a one-pot, four-step anionic polymerization method following the "in-out" approach. These multiarmed, multisegmented star terpolymers self-assemble in selective media exhibiting pH responsiveness owing to the ampholytic nature of their diblock copolymer arms. Two soluble and two insoluble states were observed depending upon the pH of the medium. At low pH (pH 1.0), core-shell unimolecular micelles, with a hydrophobic PS core and P2VP, PAA segments in the shell, were formed. At pH 3.0, H-bonding and electrostatic interactions between the P2VP and PAA segments led to compact spheres. Finally, at pH 8.0 the stars were transformed from a bis-hydrophilic state to bis-hydrophobic state, leading to a network-like intermicellar assembly.