PRACTICAL METHODS TO CONTROL MORPHOLOGY OF HETEROGENEOUS POLYMER PARTICLES

This review focusses on processes in which emulsion polymerizations ar e carried out in stages so that previously formed particles are either overcoated in subsequent polymerization stages or engulf the second a nd later stage polymers. These products are often called ''core-shell' ' particles. Basically, the most stable state of the final system is t he one with the lowest net interfacial energy. In the case of a two-st age emulsion polymerization there can be three interfacial tensions to consider. Several mutually consistent, effective thermodynamic treatm ents 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 fr equently desirable, however to produce particle structures that appear at first glance to be thermodynamically forbidden. This is achieved e ither by changing the surface characteristics of a polymer from those of the bulk material or by employing kinetic factors to anchor energet ically unprofitable morphologies. This paper summarizes methods of bot h types that have been reported to control the texture of structured l atex particles in order to produce designed morphologies.