Reported herein is a green route for the synthesis of macroporous polystyrene particles by suspension polymerization in water in sc-CO2 medium using polyvinyl alcohol (PVA) as stabilizer, divinylbenzene (DVB) as cross-linker, and azobisisobutyronitrile (AIBN) as initiator. The solvent properties of sc-CO2 are adjusted in such a way that it acts as a pressure-adjustable porogen. All the reactions were carried out at pressures of 70320 bar and a temperature of 75 degrees C with an agitation speed of 700 rpm. With an increase in pressure (>70 bar), the diameter of the particles increases (822 mu m), and the surface area of the particles also increases. Similarly, the pore diameter of the particle was observed to be increasing with an increase in pressure and to reach a maximum value (209 nm) at pressure 200 bar. The diameters of the microspheres and the pore size were controlled by varying the pressure of CO2 inside the reactor during the polymerization process. The porous polymer particles were characterized by SEM, TEM, GPC, BET absorption isotherm, and TGA. (c) 2011 Wiley Periodicals, Inc. Adv Polym Techn 32: 154162, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20246