Tuning of Thermo-Triggered Gel-to-Sol Transition of Aqueous Solution of Multi-Responsive Diblock Copolymer Poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate)

This article reports on the synthesis of a hydrophilic diblock copolymer composed of two distinct thermosensitive polymers with one block containing a small amount of carboxylic acid groups, poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate) (P(TEGMA-co-AA)-b-PDEGEA), and the study of thermo-induced sol−gel−sol transitions of its moderately concentrated aqueous solutions at various pH values. The diblock copolymer was obtained by the removal of tert-butyl groups of P(TEGMA-co-tert-butyl acrylate)-b-PDEGEA, which was synthesized by reversible addition−fragmentation chain transfer polymerization. PTEGMA and PDEGEA are thermosensitive polymers with lower critical solution temperatures (LCSTs) of 58 and 9 °C, respectively, in water. The incorporation of a small amount of carboxylic acid groups into PTEGMA allowed the LCST of the P(TEGMA-co-AA) block to be tuned by changing the solution pH. We found that a 20 wt % aqueous solution of P(TEGMA-co-AA)-b-PDEGEA with pH of 3.11 (measured at 0 °C) underwent multiple phase transitions upon heating, from a clear, free-flowing liquid (