Monodisperse polystyrene latex particles functionalized by the macromonomer technique

Abstract

Monodisperse core-shell latex particles functionalized with surface groups that were introduced by the macromonomer technique were obtained by means of a two-step emulsion polymerization process in a batch reactor at 70 °C. In the first step the cores were synthesized by means of a batch emulsion polymerization of styrene (St), and in the second step, the shells were formed by batch emulsion copolymerizations of St and different macromonomers using the seeds obtained previously. Macromonomers were synthesized by anionic "living" polymerization. They are constituted of a poly(ethylene oxide) hydrophilic block and a hydrophobic block or sequence end-fitted with an unsaturation. The latexes were characterized by gravimetry, transmission electron microscopy (TEM), and conductometric titrations to obtain the conversion, the particle size distribution (PSD), and the surface charge density (σ), respectively. The colloidal stability of the cores and final latexes were determined by measuring the critical coagulation concentration (CCC) at two pHs (7 and 2) using KBr as electrolyte. The surface charges of the latexes were moderately low, with corresponding moderately low CCCs. The presence of spacers, confirmed with a disk centrifuge photosedimentometer (DCP) and photon correlation spectrophotometer (PCS), did not increase the CCC. During the CCC measurements, at high electrolyte concentrations, the reduced solubility of the spacer PEO moiety in the solution resulted in its collapse on the particle surface.