This paper studied, through modeling and computer simulation, the thermal-induced phase separation phenomenon in a symmetric polymer blend via spinodal decomposition. The one-dimensional model consisted of the Cahn-Hilliard theory for spinodal decomposition, and incorporated the Flory-Huggins-deGennes free energy equation, the slow mode mobility theory and reptation model for polymer diffusion. The numerical results replicated frequently reported experimental observations published in the literature for the early and intermediate stages of spinodal decomposition for symmetric polymer blends. Furthermore, the numerical results indicate that a dimensionless diffusion coefficient may be used as a parameter to control the formation and evolution of the phase-separated regions during spinodal decomposition as a means to customize functional polymeric materials with predefined material properties. (c) 2005 Elsevier Ltd. All rights reserved.