Perturbed hard-sphere-chain (PHSC) theory equation of state (EOS), which is based on the square-well model of Alder et al. is applied to calculate and predict the solubilities of solvents and gases in polymers and copolymer. The calculations with one temperature-independent binary parameter K-12, and the predictions with K-12 = 0 are performed for 29 polymer solutions and 9 copolymer mixtures. The obtained results show that this EOS can describe vapor-liquid equilibria(VLE) of high concentration polymer and copolymer solutions very well. The purely predicted results show that the equation has very good predicting potential.