Polar Gradient Latex Particles with Hydrophilic Core and Hydrophobic Shell Prepared via Multistep Emulsion Polymerization

Monodisperse polar gradient particles were synthesized via a three-step emulsion polymerization using poly(butyl acrylate-methyl methacrylate-methacrylic acid-ethylene glycol dimethacrylate) (P(BA-MMA-MAA-EGDMA)) as core, poly(methyl methacrylate-methacrylic acid-styrene) (P(St-MMA-MAA)) as interlayer and polystyrene (PSt) as shell. The particle growth and encapsulation in each emulsion polymerization step were followed by transmission electron microscopy (TEM), dynamic light scattering (DLS) and conductometric titration. Results indicated that the feeding mode and the interlayer were essential to prepare the polar gradient latex particles with hydrophilic core and hydrophobic shell. The morphologies of the two-layer core/interlayer and three-layer core/interlayer/shell particles were observed in TEM micrographs, and the sequential encapsulations of the carboxyl-containing core and the core/interlayer particles were confirmed by an increase in the particle size as well as an increase in the buried carboxyl percentage.