Synthesis and Investigation of Stimuli-Responsive Amphiphilic Latex Nanoparticles by Seeded Emulsion Polymerization

Stimuli-responsive amphiphilic core-shell polymer nanoparticles are an important category of smart materials which have been studied due to their advantages of changing of physical or chemical properties in response of stimuli. In this study, poly[2(dimethylamino)ethyl methacrylate] (PDMAEMA) as hydrophilic core with hydrophobic layer polystyrene (PS) as shell were synthesized by seeded emulsion polymerization to achieve dual-sensitive core-shell nanoparticle (CSNP). Temperature- and CO2- responsive CSNPs were investigated as two important smart behaviors. The CSNPs were characterized by dynamic light scattering (DLS) and scanning electron microscopy (SEM). In addition, two essential parameters including the polymerization conversion and stability of polymer latexes were investigated. Obtained results showed that hydrophilicity-hydrophobicity balance of the latex nanoparticles could be changed by variation of temperature and induction of CO2 gas flow, as a result of temperature- and CO2-responsivities of the PDMAEMA core. The particle size of CSNP was increased when the temperature rised above the lower critical solution temperature (LCST) of the PDMAEMA. It is due to the formation of hydrogen bonds between water molecules and tertiary amine group which lead to swell in PDMAEMA below LCST, and deswelling from water above LCST of the PDMAEMA. Furthermore, the size of the latex nanoparticles was increased from 696 nm to 853 nm after CO2-bubbling which led to increase hydrophilicity or water swelling of PDMAEMA in latex nanoparticles.