Using our simple lattice-based equation of state, we capture the effect of deuterium substitution in polystyrene (PS), predicting both the pure component melt properties and the remarkable shift in the coexistence curve when hPS is replaced by dPS M forming a blend with poly(vinyl methyl ether) (PVME). Taking advantage of a rare opportunity to compare with experimental pure component data, we demonstrate that by characterizing the deuterated component through analysis or neutron scattering data, we are able to make predictions for the pure dPS PVT properties which are in superb agreement with experiment. Calculations and measurement show that the dPS volume (per repeat unit) is slightly larger than that for hPS at low pressure, an effect which can he correlated with a difference in the model energetic parameter (epsilon). In addition, we find that the dPS coefficient of thermal expansion (alpha) is larger than that for hPS and thus closer to the value for PVME. We propose that the increased similarity of the alpha's for dPS and PVME is connected to the increased miscibility of the dPS/PVME blend, a linkage which may be helpful to experimentalists in anticipating the potential effect on phase stability of polymer blends when deuterium substitution is employed.