A perturbed Lennard–Jones chain equation of state for polymer liquids

The perturbed Lennard–Jones chain (PLJC) equation of state is formulated based on the first-order variational perturbation theory. The model consists of three parameters, namely, number of segments per chain molecule, m, segment size, σ, and segment energy, ε/k. Given the molecular weight, the PLJC equation was used to quantify the pressure–specific volume–temperature properties of a large number of polymer liquids. Very good agreement was found between the predicted and experimentally measured specific volumes. The accuracy of the PLJC equation of state compares favorably with other polymer equations of state. We further proposed a modification to the PLJC equation to include the molecular weight as a parameter in the equation of state and hence, rendering the modified equation of state, itself molecular weight-independent. This modified perturbed Lennard–Jones chain (mPLJC) model was found to represent experimentally measured data very well.