Polymerization of methyl methacrylate (MMA) in chloroform (CF), ethyl acetate (EA), and iso-amyl acetate (iAA) with compressed CO2 as antisolvent has been carried out at 333.2 K and different monomer concentrations. The results show that at the low monomer concentration (1 mol l(-1)) the addition of the antisolvent CO2 reduces the yield and the molecular weight of the poly(methyl methacrylate) (PMMA). At the higher monomer concentration (4 mol l(-1)) the yield decreases initially, and then increases With the increase of CO2 pressure or the volume expansion ratio (VER) of the solution. The molecular weight and the molecular weight distribution of the products also vary with VER. (C) 2002 Elsevier Science B.V. All rights reserved.