Synthesis of cationic poly(methyl methacrylate)-poly(N-isopropyl acrylamide) core-shell latexes via two-stage emulsion copolymerization

Thermally sensitive poly(methyl methacrylate (MMA))-poly(N-isopropylacrylamide (NIPAM)) core-shell particles were prepared via a two-stage emulsion copolymerization process. Methylene bisacrylamide (MBA), 2,2′-azobis (2-amidinopropane) dihydrochloride (V50) and dodecylethyl dimethyl ammonium bromide (DEDAB) were used as crosslinker, cationic initiator and surfactant, respectively. Functional core-shell particles were prepared using aminoethyl methacrylate hydrochloride (AEMH) as cationic co-monomer to increase the surface charge density. The influences of the crosslinker and co-monomer concentrations on the thickness and swelling capacity of the PNIPAM-based shell layer were studied. The latex particle size and particle size distribution were determined both by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Monodisperse particles were produced with diameters between 150-250 nm (at 25 °C) and 140-190 nm (at 50 °C). The surface charge density was determined by chemical titration and higher values (∼10 μmol/g) were obtained for the functional core-shell particles. The electrokinetic properties of the dispersions at several pH and temperature values confirm the presence of the shell layer and cationic surface charges.