The present study focuses on synthesizing styrene-methylmethacrylate (St-MMA) copolymer particles in a batch reactor using suspension polymerization process at different copolymer compositions. Also for further comparisons, the neat polystyrene (PS) and polymethyl methacrylate (PMMA) were synthesized by the same method. The solubility and diffusivity of supercritical carbon dioxide (scCO(2)) into the synthesized copolymers at two temperatures (393 and 423) K and pressures in the range from (5 to 12) MPa were measured by a magnetic suspension balance. The Sanchez-Lacombe (SL) equation of state was used to estimate the swelling effect of CO2 on copolymers. The results showed that the solubility and diffusivity of CO2 increased with increasing of CO2 pressure and slightly improved with methyl methacrylate (MMA) content in copolymer. As well as the solubility of CO2 in samples decreased with temperature increment and contrary behavior was observed for diffusivity. Fujita, Maeda and Paul's diffusion models were combined to estimate the diffusion coefficients for the copolymers and neat polymers. (C) 2012 Elsevier Ltd. All rights reserved.