Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of the volatile hydrogen radical scavenger CCl4. With addition of CCl4 the polymerization rates first increased and then decreased.The increase of H2O2' yield and the decrease of pH and the produced polystyrene's molecular weight in the presence of CCl4

and the effect of non-volatile hydrogen radical scavenger on ultrasonically initiated emulsion polymerization of styrene indicates that the observed enhancement can be explained as follows.CCl4 may enter cavitation bubbles and further react with hydrogen radicals (·H) from the sonolysis of water to produce new radicals ·CCl3

so as to reduce the recombination of ·H and ·OH.Therefore more radicals would be present in the systems for initiating polymerization.In addition

the effect of CCl4 on ultrasonically initiated emulsion polymerization of methyl methacrylate(MMA) was studied.The results showed that CCl4 did not significantly enhance the ultrasonically initiated emulsion polymerization rate of MMA due to high vapor pressure and solubility of MMA

which would reduce the efficiency of CCl4 scavenging ·H.