The Study Of High-Rate Polymerization Based On A Concentrated Emulsion

A concentrated emulsion is an emulsion whose volume fraction of the dispersed phase is higher than 74%, which is corresponds to the close packing of spheres of the same size. At high volume fractions, the concentrated emulsions are composed of polyhedral cells, separated by thin films of continuous phase. This kind of structure of the concentrated emulsion provides, because of a high interfacial area, high rates of initiation and interfacial reaction.In the high rate polymerization, the initiation occurred at the interface between the droplets and the continuous phase using redox initiators, with the reducing and oxidation constituents soluble in separated phases, and the polymerization was carried out under adiabatic conditions. Since the concentration of droplets is high, the heat generated in the reaction can be efficiently used to accelerate the polymerization. In 30min a high conversion, about 80%, was reached.This procedure was employed to polymerize acrylonitrile (AN) and a comonomer, the high reaction rate of the former being responsible for the high rate of polymerization. The comonomers studied included vinylacetate (VAC) and butyl acrylate (BA). The effect of various reaction conditions on the high rate concentrated emulsion polymerization of ANA/AC and AN/BA systems were investigated, and a comparison was made between the adiabatic and the combined adiabatic followed by heating procedure. It was found that the high rate polymerization was caused by a severe gel effect.Because of the gel effect in the concentrated emulsion system, the molecular weight of the product increased with time, and the reaction was no longer controlled by the reactivity, but became controlled by diffusion. The effect of the polymerization rate on the conversion, molecular weight and composition of the product was discussed. This suggests the particular mechanism of the concentrated emulsion polymerization.