We present the synthesis and characterization of a series of pH-responsive hydrogel nanoparticles based on crosslinked 2-(diethylaminoethyl) methacrylate and poly(ethylene glycol) methyl ether methacrylate (P(DEAEMA-g-PEGMA)). Variants of this polymer were created using t-butyl methacrylate (P(DEAEMA-co-TBMA-g-PEGMA)) or t-butylaminoethyl methacrylate (P(DEAEMA-co-TBAEMA-g-PEGMA)). The synthesis of these materials was accomplished using a facile photoemulsion polymerization. Polymer composition was verified using H-1 NMR spectroscopy and closely approximates the copolymer composition estimated from reactivity ratios. Particle formulations possess a dry diameter of 50-65 nm as determined by transmission electron microscopy and collapsed hydrodynamic diameter of 70-100 nm as determined by dynamic light scattering. Dynamic light scattering and pyrene fluorescence spectroscopy were used to probe the pH-dependent phase transition in the hydrogel nanoparticles from collapsed hydrophobe to swollen hydrophile. The inclusion of t-butyl methacrylate served to depress the nanogel pKa and critical pH for phase transition to <6.9 while the inclusion of t-butylamino methacrylate had the opposite effect. We show that these hydrogel nanoparticles possess tunable physicochemical properties that can be adjusted by changing copolymer composition. (C) 2013 Elsevier Ltd. All rights reserved.