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 4.55.5. The micelles are crosslinked by electron-beam irradiation, yielding stable coreshell 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 coreshell structures of the aggregates.