Theoretical aspects of particle swelling in living free radical miniemulsion polymerization

Living free radical reactions originally were carried out in bulk or solution. Recently, this chemistry has been carried out in water-based systems (emulsion and miniemulsion living free radical polymerization). Significant colloidal instability early in the polymerization has been found in several of these systems. With the hypothesis that something unique to living free radical polymerization was causing colloidal instability beyond that found in conventional free radical emulsion polymerization, the swelling of polymer particles during the early stages of living free radical miniemulsion polymerization was investigated. A new superswelling state caused by the presence of a large number of oligomers was found. This superswelling could be used to explain the instability issues reported. The effect of various factors on the superswelling state was studied. It was found that superswelling state is rather sensitive to recipe variations. Simply increasing the costabilizer level and/or using a nonionic polymeric surfactant would probably eliminate superswelling and hence the instability.