Shifting Sol–Gel Phase Diagram of a Doubly Thermosensitive Hydrophilic Diblock Copolymer Poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid) in Aqueous Solution

This article reports that the C-shaped sol–gel phase diagram of a doubly thermosensitive hydrophilic diblock copolymer with each block containing a small amount of weak acid groups in aqueous solution in the moderate concentration range can be readily and reversibly shifted by changing the solution pH. The diblock copolymer, poly(methoxytri(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid) (P(TEGMA-co-AA)-b-P(DEGEA-co-AA)), was synthesized by reversible addition–fragmentation chain transfer polymerization and postpolymerization modification. A 20 wt % aqueous solution of P(TEGMA-co-AA)-b-P(DEGEA-co-AA) with pH of 3.29 underwent sol-to-gel, gel-to-sol, and clear sol-to-cloudy sol transitions at 17 °C (Tsol–gel), 38 °C (Tgel–sol), and 55 °C (Tclouding), respectively, upon heating. With the increase of pH, all transition temperatures shifted to high values; for instance, the Tsol–gel, Tgel–sol, and Tclouding were 20, 45, and 63 °C, respectively, at pH = 5.1...