With the many possible composition combinations possible for copolymers there is a critical need to develop methods of predicting the properties of these materials. This paper examines the applicability of popular, current vapor-liquid equilibria prediction models in characterizing the solubility of solvents in copolymers. In some cases anomalous behavior is observed where the solubility of the solvent in the copolymer is greater than or less than in either of the composite homopolymers. Two popular UNIFAC models and the group-contribution, lattice-fluid equation of state (GCLF-EoS) have been evaluated for this application. In general the UNIFAC models showed a better capability than the GCLF-EoS. There is a need for more sophisticated methods for predicting the complex interactions that can be present in copolymer systems. (C) 2009 Elsevier B.V. All rights reserved.