Phase equilibria in systems with monodisperse and polydisperse polystyrene, cyclohexane and carbon dioxide have been investigated. Calculations of cloud-point curves as well as molecular weight distributions of the polymer in the coexisting phases have been carried out for CO2 concentrations of up to 22.4 wt.%, temperatures up to 250 degrees C and pressures up to 150 bar. The SAFT equation of state was used within a multicomponent flash algorithm which incorporates the concept of pseudocomponents. A direct comparison of experiment and calculation shows the performance of SAFT for calculations of molecular-weight fractionation in complex systems.