Electron microscopy studies of polystyrene-poly(methyl methacrylate) core-shell latex particles

Abstract

Poly(methyl methacrylate)-polystyrene (PS-PMMA) core-shell latex particles were prepared by twostage 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.Latex materials in which a core of one polymer is surrounded by a shell of a second polymer1-6 are important in many different industrial applications. Core-shell materials are employed as impact modifiers for plastics, in adhesives, and for a variety of coatings applications. It is widely believed that the properties that the latex contribute to these systems are intimately related to the detailed morphology of the latex particles themselves. One of the current challenges in the field of polymeric microspheres is to learn how to characterize these structures more completely so that one can develop better synthetic methods to prepare particles with controlled morphology.

Non-equilibrium particle morphology in dispersion-polymerized polystyrene particles

“…It seems clear that the large particles are formed in an equilibrium nodular morphology, so the morphology cannot be used to infer anything about mechanism. Thus, there is less mechanistic information available from FFTEM than may have seemed the case to previous investigators (10,11). On the other hand, the small dispersionpolymerized particles were formed in a radial non-equilibrium morphology that could be converted into the nodular morphology by either heating or precipitation.…”

“…The prior authors applied freeze fracture TEM (FFTEM) to several colloidal particles and concluded that the observed structures implied something about the mechanisms of particle nucleation and growth (10,11). Since our mechanistic study suggested small and large particles grew by different mechanisms, we were anxious to have a look at the freeze fracture morphologies of the polystyrene particles.…”

Preparation by suspension polymerization and characterization of polystyrene (PS)-poly(methyl methacrylate) (PMMA) core-shell nanocomposites

“…They showed that the seed particles having higher glass transition temperature than the polymerization temperature had an advantage in producing core-shell polymer particles. Shivers et al 40 showed that in the preparation of PS-PMMA core-shell latex particles by two-stage emulsion polymerization, some PS migrates to the surface of the PMMA shell when MMA was polymerized in the presence of PS seed latex. They explained this finding in terms of a combination of thermodynamic and kinetic factors affecting the polymerization and morphology evolution process.…”

Preparation of core–shell latex particles by emulsion co-polymerization of styrene and butyl acrylate, and evaluation of their pigment properties in emulsion paints

“…Two-stage emulsion polymerization is a common route for the preparation of core-shell polymer particles. [11][12][13] Using this method, Okubo and Mori 14 prepared different kinds of core-shell polymer particles. Moreover, they developed a dynamic swelling method for the preparation of many multiform core-shell particles.…”