Polymer equations of state derived from molecular simulation

Abstract

This work characterizes fluid equations of state for many common polymers from small oligomers to the infinite chain limit. The methodology applies the formalism of discontinuous molecular dynamics (DMD) and thermodynamic perturbation theory (TPT) previously developed for polyethylene [1,2]. Oligomers with each structure are simulated for a series of molecular weights varying from the monomer to roughly 1100g/mol. Each oligomer is simulated at 21 densities to interpolate the reference and perturbation contributions to the equation of state. Plotting the perturbation term vs. density for a polymer series leads to an asymptotic inference in the long chain limit. Interpolation functions are then developed to characterize the polymer at any molecular weight. The polymers characterized include polyethyleneoxide, polylacticacid, polypropylene, polyisoprene, and polystyrene.The characterizations are compared to the result of Wertheim's theory of polymerization to show how individual monomer structure lead distinctive behavior. Given these characterizations, it is straightforward to predict phase behavior of polymer blends and solutions that can be tested by experiment and targeted molecular simulations at specific compositions.