A latex of anionic polyacrylamide dispersed in an aqueous solution was prepared through aqueous two-phase copolymerization of acrylamide(AM)/acrylic acid(AA)/methyl methacrylate(MMA)with the stabilizer poly(acrylic acid sodium)in ammonium sulfate solution and 2

2′-azobis［2-(2-imidazolin-2-yl)propane］-dihydrochloride as initiator.By using spectrophotometer

the phase separation point was determined online where the transparence of reaction solution declined suddenly.The effect of various parameters on the critical conversion and critical molecular weight at phase separation was measured by the bromating method and gel permeation chromatography respectively.The experimental results showed that the addition of MMA could introduce hydrophobicity to the polymer chain and increase the interfacial tension of the two phases

as a result it was easier for the polymer chain to precipitate

which in accordance made the critical conversion and critical molecular weight at phase separation decrease.The total concentration of AM and AA was also related to the relative amount of MMA segment in the polymer chain. As the total concentration of AM and AA increased

the relative amount of MMA chain segment decreased. Thus the critical conversion at phase separation decreased while the critical molecular weight at phase separation increased.AA introduced electrostatic repulsion to the polymer chain and as the mass feed ratio of AA to AM decreased

the polymer chain was easier to coalesce because of the decrease of electrostatic repulsion.Salt concentration and stabilizer concentration had similar effects on the critical conversion at phase separation

but different effects on the critical molecular weight at phase separation.In addition

the increase of temperature was unfavorable for phase separation.It enhanced the solubility of the polymer chain and accelerated the growth of the polymer chain.