Polystyrene microparticles were synthesized by emulsion polymerization in supercritical carbon dioxide (sc-CO2) using (polydimethylsiloxane) (PDMS) as a surfactant/stabilizer and azobisisobutyronitrile (AIBN) as initiator. The emulsion polymerization was carried out by varying pressures within the range 13.79–17.93 MPa. At the end of polymerization, powdered polymeric micoparticles were collected by depressurizing CO2. The powdered polymeric microparticles were characterized by SEM, GPC, DSC and TGA. The influence of pressure on conversion, molecular weight, particle size and polydispersity index was studied. The molecular weight (Mn) of the polymer is in the range of 35,542 to 45,078 g/mol. Polydispersity index is in the range of 1.45–1.86 and particle size in the range of 3.25 µm–6.3 µm.