Effects of chain length on the structure and dynamics of polyvinyl chloride during atomistic molecular dynamics simulations

Molecular dynamics (MD) simulations have proven to be useful for predicting and interpreting the conformational and dynamic properties of various polymer-solvent systems. The number of repeat units used to represent a polymer chain in an MD study is intended to provide a balance between the computational demands and the reliability of the specific phenomena being studied. To date, this balance has not received sufficient attention. Here, we investigate how the chain length of an atomistic polymer model influences the structure and dynamics of the polymer in different solvents. Seven different polyvinyl chloride (PVC) models, ranging from 5 to 240 -(CH2CHCl)- repeat units, are studied using atomistic MD simulations in two polar organic solvents: tetrahydrofuran (THF) and dimethylformamide (DMF). After benchmarking our MD results against experimental density data, we calculate polymer end-to-end distances, radii of gyration, radial distribution functions, shape descriptors, end-to-end vector correlation functions, dihedral autocorrelation functions, surface areas, surface electrostatic potentials, glass transition temperature and melt viscosities. Our MD simulations demonstrate that most of these properties converge when approximately 100-120 repeat units are used to represent PVC, and this convergence behaviour is observed in different solvents and at different temperatures.