Ultrasonically initiated emulsion polymerization of styrene in the presence of Fe2+

Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of Fe2+. The addition of a small amount of Fe2+ markedly enhanced the polymerization rate of styrene. In the presence of 50 μM Fe2+, the conversion of monomer in the reaction time of 60 min was 2.4 times as high as that in the absence of Fe2+. The increase in the polymerization rate was due to higher concentration of hydroxyl (OH) radicals generated via Fenton reaction of Fe2+ with hydrogen peroxide (H2O2), which was proved by a lower amount of H2O2 in Fe2+ aqueous solution compared with that in pure water during ultrasonic irradiation. However, the addition of excessive Fe2+ had no further accelerating effect on the polymerization rate due to the reduction of OH radicals by Fe2+. So it is an effective way to add an appropriate amount of Fe2+ to accelerate ultrasonically initiated emulsion polymerization of styrene.