CO₂-Switchable Multi-Stimuli-Responsive Polymer Nanoparticle Dispersion

CO2-switchable multi-stimuli-responsive polymer nanoparticles (MSPNs), a combination of protonated poly(2-dimethylamino-ethyl methacrylate) (PDMAEMA) and hydrophobic poly(methyl methacrylate) (PMMA), were prepared by carbon-dioxide-assisted (CO2-assisted) emulsion polymerization. These MSPNs exhibited excellent thermal properties and unique temperature-/pH-responsive and CO2-/nitrogen-switchable (CO2-/N2-switchable) abilities, making them highly attractive multifunctional polymer nanoparticles with potential for many applications. Importantly, dispersion experiments and morphological studies clearly confirmed that these newly developed nanoparticles not only possess efficient, reversible CO2-/N2-switchable aggregation/redispersion ability, but also can remain in stable colloidal dispersion at low pH and promote rapid precipitation of nanoparticles at high pH. With simple preparation and high reproducibility, this approach provides a potentially novel pathway for the development of next-generation multifunctional MSPNs.