Reversibly switchable pH- and thermoresponsive core-shell nanogels based on poly(NiPAAm)-graft-poly(2-carboxyethyl-2-oxazoline)s

Amphiphilic graft copolymers with a thermosensitive PNiPAAm backbone and pH-sensitive hydrophilic poly(2-carboxyethyl-2-oxazoline) graft chains are synthesized. In aqueous solution, stable micelle-like aggregates are formed by increasing the temperature in the pH range 4.5-5.5. The micelles are crosslinked by electron-beam irradiation, yielding stable core-shell nanogels of about 100 nm diameter with reversible thermo- and pH-dependent swelling behavior. The temperature sensitivity is provided by a conformational change in the PNiPAAm core, whereas the thickness of the poly(2-carboxyethyl-2- oxazoline) corona depends on pH. The reversible bisensitivity of core-crosslinked nanogels is verified by DLS, while AFM measurements demonstrate the predicted core-shell structures of the aggregates. Stable micelles formed from graft copolymers with a thermosensitive poly(N-isopropylacrylamide) backbone and pH-sensitive hydrophilic poly(2- carboxyethyl-2-oxazoline) graft chains are successfully crosslinked by electron-beam irradiation, yielding bisensitive core-shell-type nanogels with reversible thermo- and pH-dependent swelling behavior addressed independently within the core and shell structure.