Concentrated emulsions pathways to polymer blending

Abstract

A new method of preparation of polymer composites involving the concentrated emulsion polymerization is described. In this kind of emulsion, the volume fraction of the dispersed phase is very large (as large as 0.99), while the volume fraction of the continuous phase is very small. In the present case, a monomer containing an appropriate initiator constitutes the dispersed phase and a dilute solution of surfactant in water constitutes the continuous phase. In a first step, two such concentrated emulsions containing different monomers were prepared and each of them was subjected to heating at 40°C for partial polymerization. Subsequently, the two partially polymerized systems were mechanically mixed, and the mixture was subjected to additional polymerization, drying, and sintering by heating at various temperatures for various time intervals. Partially polymerized concentrated emulsions of polystyrene, poly(buthyl methacrylate), poly(buthyl acrylate), and cross linked polystyrene, whose conversions were less than 5%, were employed. Conversions higher than 5% led to large increases in the viscosity of the concentrated emulsions, making their mixing difficult. N.m.r. spectroscopy was used to obtain information about the extent of copolymerization between the two monomers. Electron microscopy examination of the surfaces obtained by the fracture of the composites revealed that the latex particles aggregated with relatively slight changes in size and shape.