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

Poly(methyl methacrylate)-polystyrene (PS-PMMA) core-shell latex parti cles were prepared by two-stage emulsion polymerization under monomer- starved conditions. These particles were examined by three different t ransmission electron microscopy techniques: cryosectioning, beam damag e in ice, and freeze-fracture (FFTEM). This is the first reported appl ication of FFTEM to the study of composite latex morphology. From thes e experiments we learn that the second stage polymer forms a shell sur rounding the seed. In addition, we infer that some second stage monome r polymerizes within the latex seed. A very interesting observation is that when MMA is polymerized in the presence of PS seed latex, some p olystyrene migrates to the surface of the PMMA shell. These results ar e explained in terms of a combination of thermodynamic and kinetic fac tors affecting the polymerization and morphology evolution process.