The inverse mini-emulsion polymerization of acrylamide

Polymerizable mini-emulsions were formulated in cyclohexane as a continuous medium. The kinetics of free-radical polymerization of acrylamide (AAm) in inverse mini-emulsion (water/ cyclohexane/ Tween 85) was investigated. Sterically-stabilized inverse mini-emulsion polymerizations are very fast and reach the final conversion within several minutes. The dependence of the mini-emulsion polymerization rate of acrylamide vs. conversion is described by a curve with two non-stationary rate intervals. This behavior is discussed in terms of the gel effect and the mixed micellar/droplet nucleation mode. The maximum polymerization rate and the number of polymer particles increase with increasing the concentration of the non-ionic emulsifier Tween 85. The dependence of the surface tension vs. emulsifier concentration in the presence or absence of polymer particles is described by the curve with a minimum. The increase in the surface tension is prescribed to the preferential adsorption of emulsifier by the non-micellar aggregates. The slight electrical conductivity indicates the formation of the non-percolating monomer and polymer dispersions.