Thermoresponsive nanoparticles are synthesized from ionic random terpolymer precursors. A distinct temperature-dependent aggregation-redissolution behavior is observed within a subtle balance between polymer ionic charge and hydrophobic content, which is used for colloidal synthesis of nanoparticles in aqueous medium and without surfactants. The solution thermal history provides a robust mean to customize the size of nanoparticles that can be disentangled on command.