Detailed Molecular Structure of Glassy Poly(phenylene oxide) (PPO) Studied by Molecular Dynamics Simulations

Abstract

A modeling approach based on sequential stages of pressure compression (NPT) and constant volume (NVT) molecular dynamics (MD) simulations was used effectively for generation of models of glassy samples of poly(phenylene oxide) PPO. Starting from a large periodic simulation box the samples were brought down to the desired density using NPT simulations and also NVT simulations for energy and structural relaxation. The GROMOS 45a3 force-field, with appropriate intermolecular potentials for PPO, was used to model the interatomic interactions. The PPO glassy phase was studied by independently generating 9 samples with different numbers of chains (for the chains of repeat units 15, 25 and 40). Structural analysis included dihedral angle distribution, intra-chain and inter-chain radial distribution functions, radius-of-gyration and torsion angle distributions, free volume and the orientation distributions of intra-chain and inter-chain phenylene rings. The simulated solubility parameter was in excellent agreement with experimental data for PPO. This computational study of the glassy phase of PPO is an extension of earlier studies by others on single, unperturbed chains of PPO.