Precipitation polymerizations of acrylic acid (AA) in compressed carbon dioxide (65 bar) with different cosolvents, acetic acid, ethanol, and tetrahydrofuran, were studied. Analyses by viscosity measurement and differential scanning calorimetry indicate that the cosolvents have a pronounced effect on the properties of the product. Scanning electron microscopy shows that the products progress from microparticles to bicontinuous networks to fibers with the change of cosolvents and reaction conditions. Measurement of the volume expansion (DeltaV%) of the liquid phase containing different cosolvents indicates that the miscibility of compressed CO2 with the liquid phase is dependent on the cosolvent. (C) 2003 Wiley Periodicals, Inc.