Synthesis and characterization of multiphase latexes prepared by two-step emulsion polymerization

Abstract

In this work core/shell (polystyrene(PS)/polymethylmethacrylate (PMMA)) latexes and inverse latex systems (PMMA/PS) were prepared by two-step emulsion polymerization. In order to avoid complications when characterizing the structured latexes, monodisperse PS and PMMA latexes of various diameters were prepared by seeded emulsion polymerization and used as core systems. In the second-step polymerization the formation of a new crop of latexes is avoided by the controlled level level of surfactant and initiator. For the characterization of the core, core/shell, and inverse system various experimental methods were used, e.g., electronmicroscopy (TEM, thin-sectioning, shadowcasting, SEM) [1], small-angle x-ray scattering (SAXS) [2,3], ultracentrifugation (UC), soap titration [1] and measurement of densities and refractive indexes. From the shadow-casting a very characteristic behavior of PMMA phase could be observed, and this was used for the determination of surface polymer phase of structured latex particles [1]. All these experimental results showed that the given system PS/PMMA exhibits the assumed core/shell structure. [1, 2] However, in the inverse system PMMA/PS more complicated, heterogeneous structures were observed [1], e.g., depending upon the addition method of the second monomer and particle size of the core.