Coarse-Grained Molecular Dynamics Modeling of a Branched Polyetherimide

A coarse-grained
model is developed to allow large-scale molecular
dynamics (MD) 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 interactions by direct
Boltzmann inversion, and parameterization of nonbonded interactions
by potential of mean force (PMF) calculations via gas-phase MD simulations
of atomic group pairs is used to construct the coarse-grained model.
A six-pair geometry, with one atomic group at the center and six replicates
of the other atomic group placed surrounding the central group in
a NaCl structure, has been demonstrated to significantly speed up
the PMF calculations and partially capture the many-body aspect of
the PMFs. Furthermore, we propose a 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.