Coarse‐grained A‐graft‐B model of poly(lactic acid) for molecular dynamics simulations

Abstract

A mesoscopic model of poly(lactic acid) is developed where the polymer is represented as an A-graft-B chain with monomer units consisting of two covalently connected beads. A coarse-graining algorithm is proposed to convert an atomistic model of PLA into a coarse-grained one. The developed model is based on atomistic simulations of oligolactides to take into account terminal groups correctly. It was used for coarse-grained simulations of polylactide. Gyration radii and end to end distances of polymer chains as well as the density of the polymer melt are shown to be in a good agreement with those obtained from atomistic simulations. The thermal expansion coefficients of the OLA melts calculated using the coarse-grained model are in reasonable agreement with those obtained from all-atom molecular dynamics. The model provides a 17-fold speedup compared with atomistic calculations.

Reverse Mapping Algorithm for Multi-scale Numerical Simulation of Polylactic Acid

“…The assignment of separate side pendant for the methyl group allowed explicit treatment of the PLA stereosequence. The macroscopic and microscopic properties of the systems calculated using the coarse-grained model closely resemble those calculated using atomistic simulations for both polymer and oligomer melt in a wide range of temperatures [3].…”

“…The simulations using the coarse-grained model were performed using an unmodified version of GROMACS [1] on "Lomonosov-2" supercomputer [8]. It was shown [3] that the coarse-grained model provides a 17-fold speedup compared with atomistic calculations.…”

“…The atomistic structure was restored based on positions of coarse-grained beads with the help of monomer-scale structure fragments (templates). The templates included atomic coordinates and the positions of A and B coarse-grained beads calculated as centers of masses of the corresponding atoms according to the forward mapping procedure [3]. The templates for the start, middle, and end monomer units are shown in Fig.…”

“…The latter includes coarse-grained simulations using specially tailored models and requires efficient algorithms for switching between the coarse-grained and atomistic representations. In the previous paper [3] we proposed an A-graft-B coarse-grained model of PLA, with each monomer unit represented by an A-B dumbbell. The assignment of separate side pendant for the methyl group allowed explicit treatment of the PLA stereosequence.…”

Temperature-Transferable Coarse-Grained Models for Volumetric Properties of Poly(lactic Acid)

“…These CG models mapped each monomer as one bead, which were called 1:1 CG model. In another study, 10 the PLA was represented as an A-graft-B chain, which belonged to the 1:2 CG model, namely, each monomer was reduced to two CG beads. This CG model was also parametrized using the IBI method to match the distributions for the CG bonds, angles, and dihedrals and radial distribution functions (RDFs) for the nonbonded CG interactions at a single high temperature.…”