Precipitation polymerization of acrylic acid in supercritical CO2 is studied. The effect of the temperature

the pressure of CO2

the concentration of the monomer and the initiator ae explored. It shows that the decrease of the concentration of the monomer

the increase of the pressure of CO2

the decrease of the temperature of the increase of the concentration of the initiator will all decrease the molecular weight of the product. The scanning electron micrographs indicate that the water-soluble polyacrylic acid powder obtained from this experiment is formed by primary particles of about 1～2 μ m size.In addition

the pressure increases with the increasing of the yield

it is speculaed to be due to the separation of phases during polymerization.