Revisiting the Mechanism of Radical Entry in Emulsion Polymerization

Understanding the mechanism of radical entry has been a major challenge in the development of process-by-design in emulsion polymerization systems. Although many theories have been put forward across decades of experimental work, conclusive evidence of the determining factors in radical entry across the range of systems that are of industrial importance has not been forthcoming. In this work, a new technique for elucidating the root causes of radical entry is described. The technique involves the initial synthesis of a miniemulsion system in which the monomer droplets contain a hydrophobic, UV-active radical trap. This method allows the rate of entry to be followed by UV-vis spectroscopy and, furthermore, by MALDI-ToF-MS analysis of the oligomeric products present in the aqueous and organic phases; it is shown that it is possible to gain additional insights into the nature of radical entry.