Reduction and pH-responsive performance of nitroxide radical-containing copolymers probed by EPR spectroscopy

Although stimuli-responsive polymers have appeared as promising materials for drug administration, the effectiveness of these materials on various bioinspired stimuli is still open for dispute. In this work, the stimuli-responsive behaviors of radical-containing nonamphiphilic copolymers were investigated using electron paramagnetic resonance (EPR) spectroscopy while altering the pH and reductant concentration. The concentration of radicals in the aqueous solution had a considerable impact on self-assembly. The nitroxide radicals (hydrophobic) were converted to hydroxylamine (hydrophilic) when ascorbic acid (Asc) was added as a reductant, and the assemblies were switched to dissolution with a rate control behavior. The behavior of morphological change was observed in the acidic pH due to the disproportionation reaction of nitroxide radicals forming cationic species. The acquired results give new insights into the colloidal nanoparticles of nonamphiphilic copolymers and encourage the development of comparable responsive nanoparticles with intriguing drug delivery applications.