Coarse-Grained Molecular Dynamics Modeling of A Branched Polyetherimide

A coarse-grained model is developed to allow large-scale molecular dynamics simulations of a branched polyetherimide derived from two backbone monomers [4,4'-bisphenol A dianhydride (BPADA) and m-phenylenediamine (MPD)], a chain terminator [phthalic anhydride (PA)], and a branching agent [tris[4-(4-aminophenoxy)phenyl] ethane (TAPE)]. An atomistic model is first built for the branched polyetherimide. A systematic protocol based on chemistry-informed grouping of atoms, derivation of bond and angle interaction by fitting bond and angle distributions to Gaussian functions, and parameterization of nonbonded interactions by potential of mean force (PMF) calculations, is used to construct the coarse-grained model. A six-pair geometry, with one atomic group fixed at center and six replicates of another atomic group placed surrounding the central group in a NaCl structure, has been demonstrated to significantly speed up the PMF calculations. Furthermore, we propose a universal entropic correction term to the PMFs that can make the resulting coarse-grained model transferable temperature-wise, by enabling the model to capture the thermal expansion property of the polymer. The coarse-grained model has been applied to explore the mechanical, structural, and rheological properties of the branched polyetherimide.