Stimuli responsive associative polyampholytes based on ABCBA pentablock terpolymer architecture

A poly(methyl methacrylate)–poly(acrylic acid)–poly(2-vinyl pyridine)–poly(acrylic acid)–poly(methyl methacrylate) (PMMA–PAA–P2VP–PAA–PMMA), ABCBA pentablock terpolymer was synthesized by “living” anionic polymerization and was studied in aqueous media at different pH conditions in the presence of MeOH. By tuning the pH and/or the solvent selectivity and dielectric constant of the medium, reversible hydrogels of different nature were formed. At low pH the hydrogel is based on a three dimensional network comprising PMMA hydrophobic cores (physical crosslinks) interconnected by complex bridging (elastically active) chains constituted of positively charged P2VP and non-ionic PAA segments. At high pH the hydrogel is transformed reversibly to a negatively charged network the bridging chains of which comprise ionized PAA segments interrupted by hydrophobic P2VP blocks, swellable on MeOH addition. Furthermore, we found conditions for the formation of flower-like micelles of different topologies and nature like core–shell–corona micelles with positively charged corona (pH < 2), multicompartment micelles comprising P2VP and PMMA hydrophobic domains (pH 8.3, low MeOH content), micelles constituted of a centrosymmetric compartmentalized core and PAA negatively charged corona (pH 8.3, 30%, 40% MeOH), and core–shell micelles of PMMA cores (pH 8.3, 50% MeOH).