Ethylene-modified latexes: Preparation, miscibility enhancement, and barrier properties

Ethylene-modified latexes were prepared by the emulsion polymerization of styrene using poly(ethylene-co-acrylic acid) (EAA), [M_n: 18,800 g mol^-1, acid number:140], as a polymeric emulsifier. EAA containing 20% portion of acrylic acid could form aggregates like micelles. The rate of polymerization of styrene using EAA is found to increase with increasing EAA concentration. This result is similar to that obtained in emulsion polymerization using conventional surfactant. The polystyrene (PS) latexes prepared using EAA exhibited small particle size and monodisperse particle size distribution in the presence of excess neutralizing agent which reduces the repulsion between charges along the EAA chain. The EAA-grafted-PS formed in situ during emulsion polymerization led to the improvement of miscibility between EAA and PS. The dynamic mechanical properties of the ethylene-modified PS films exhibit single glass transition temperature values, thus conforming to the law of miscibility. The grafted or anchoring of EAA into the particles improved the barrier properties, such as chemical resistance, of ethylene-modified PS films.