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).