On accuracy of predicting densities and solubility parameters of polymers using atomistic simulations

Molecular dynamics simulation is performed to compute densities and solubility parameters of polymers. TEAM force field is validated on monomers and then employed for predictions for polymers built with different chain lengths. The calculated densities converge when the polymer chain lengths are >10 repeat units. With the consideration of polymer crystallinity, the predictions agree well with experimental data. The solubility parameters calculated from the cohesive energy densities exhibit systematical and progressive underestimates as the chain lengths increase, indicating the energy contribution from polymer chain conformation changes from bulk state to solution must be included in order to calculate the solubility parameters correctly. A model using the radiuses of gyration to represent the conformation changes is proposed to correct the systematical error.