PRACTICAL METHODS TO CONTROL MORPHOLOGY OF HETEROGENEOUS POLYMER PARTICLES

This review focusses on processes in which emulsion polymerizations are carried out in stages so that previously formed particles are either overcoated in subsequent polymerization stages or engulf the second and later stage polymers. These products are often called ''core-shell'' particles. Basically, the most stable state of the final system is the one with the lowest net interfacial energy. In the case of a two-stage emulsion polymerization there can be three interfacial tensions to consider. Several mutually consistent, effective thermodynamic treatments have been published. At present, they serve primarily to predict when the morphology of multi-stage polymerization products may not be a simple reflection of the synthesis sequences. It is possible, and frequently desirable, however to produce particle structures that appear at first glance to be thermodynamically forbidden. This is achieved either by changing the surface characteristics of a polymer from those of the bulk material or by employing kinetic factors to anchor energetically unprofitable morphologies. This paper summarizes methods of both types that have been reported to control the texture of structured latex particles in order to produce designed morphologies.