ELECTRON-MICROSCOPY STUDIES OF POLYSTYRENE POLY(METHYL METHACRYLATE) CORE-SHELL LATEX-PARTICLES

Poly(methyl methacrylate)-polystyrene (PS-PMMA) core-shell latex particles were prepared by two-stage emulsion polymerization under monomer-starved conditions. These particles were examined by three different transmission electron microscopy techniques: cryosectioning, beam damage in ice, and freeze-fracture (FFTEM). This is the first reported application of FFTEM to the study of composite latex morphology. From these experiments we learn that the second stage polymer forms a shell surrounding the seed. In addition, we infer that some second stage monomer polymerizes within the latex seed. A very interesting observation is that when MMA is polymerized in the presence of PS seed latex, some polystyrene migrates to the surface of the PMMA shell. These results are explained in terms of a combination of thermodynamic and kinetic factors affecting the polymerization and morphology evolution process.