The dynamics of morphology development in multiphase latex particles

The use of multistage emulsion polymerization to produce particles containing multiple polymer phases is widespread throughout the coatings, impact plastics and adhesives industries. Such composite particles often improve various application properties compared to related single-phase latices or latex blends. The properties obtained depend in large part on the morphology of the multiphase particles, creating an incentive to understand the underlying mechanisms that drive morphology development in these particles as they are formed in the polymerization reactor. Much attention has been devoted to understanding the thermodynamic factors that influence morphology control, but in fact the majority of systems are produced under kinetic control, resulting in non-equilibrium structures. There are three main kinetic factors involved as the morphology develops during the second stage polymerization. These are (1) penetration of polymer radical chains into the particle interior after entry from the water phase, (2) phase separation of immiscible polymer chains produced in the different polymerization stages and (3) spatial rearrangement of phase separated domains. We have summarized our knowledge and understanding of morphology development in a concise decision tree flow chart which can be used for morphology prediction. The validity and use of this decision tree is illustrated through a series of experimental examples.