Study of pH/temperature dual stimuli-responsive nanogels with interpenetrating polymer network structure

Nanogels with interpenetrating polymer network (IPN) structure based on poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) were synthesized by in situ polymerization of acrylic acid and N, N'-methylenebisacrylamide within the PNIPAM nanogels. Their IPN structure was confirmed using transmission electron microscopy after staining by uranyl acetate. The temperature- or pH-dependent hydrodynamic diameters measured using dynamic laser light scattering show that the IPN nanogels have pH and temperature dual stimuli-responsive properties. As compared to previously reported pH/temperature dual stimuli-responsive nanogels, these IPN nanogels have the advantage of less mutual interference between the temperature-responsive and pH-responsive components, which is beneficial for their applications in controlled drug release and sensors. The temperature- and pH-triggered volume phase transition mechanisms of the IPN nanogels were tested by probing the microenvironment change of their PNIPAM and PAA chains upon phase transition using infrared (IR) absorption spectra measured at different pH values and IR difference spectra obtained by subtracting the IR spectrum obtained before temperature-induced phase transition from that obtained after phase transition. Copyright (c) 2012 Society of Chemical Industry