Stable free-radical emulsion polymerization

Polymerizations of styrene under emulsion stable free-radical polymerization conditions are reported. Precipitation of an acetone solution of a low molecular weight TEMPO-terminated polystyrene into an aqueous solution of poly(vinyl alcohol) enables the formation of emulsion particles that can be swollen with monomer and subsequently polymerized. The polymerizations proceed in a living manner, yielding polymers that show an incremental increase in molecular weight with time and have narrow molecular weight distributions. Plots of number-average molecular weight versus conversion are linear, indicating a controlled polymerization. The resulting latexes are colloidally stable, and particle size distributions are Gaussian with an average particle diameter of 450 nm. These results constitute the first successful example of an SFRP emulsion process in which the product is not contaminated with a conventionally produced broad molecular weight distribution polymer.