Molecular Modeling of Polyetherimides*

Molecular modeling plays an increasingly important role in quantifying properties of polymeric materials and clarifying molecular mechanisms underlying material behavior. We use both atomistic and coarse-grained molecular dynamics (MD) and Monte Carlo (MC) simulations to investigate polyetherimides (PEIs), which are widely used for automotive industry, aircrafts, medical instruments, and chemical devices. We have developed a transferrable coarse-grained MD model of PEIs that is able to capture their thermal expansion properties and mechanical moduli, and demonstrated the importance of including entropic correction terms in the calculation of potentials of mean force when the coarse-grained force field is trained with atomistic MD simulations. To understand the dispersity of branched PEIs, we have developed a MC simulation tool based on the Gillespie algorithm for their polymerization reaction including branching. The comparison between MC simulations, the Stockmayer theory, and experiments on the molecular weight distributions of branched PEIs will be discussed. We use simulations to clarify the application range of the Stockmayer theory and to investigate the branching behavior of PEIs when the theory is not applicable.