Combined Molecular Dynamics and DFT Simulation Study of the Molecular and Polymer Properties of a Catechol-Based Cyclic Oligomer of Polyether Ether Ketone.

The geometrical, energetic, noncovalent, and material properties of a catechol-based cyclic oligomer of Polyether Ether Ketone (PEEK) called o-PEEK were investigated using Molecular Dynamics (MD) and Density Functional Theory (DFT) simulations. The DFT (and MD) calculation performed with the PBEsol functional (and COMPASS II force field) gave a density of 1.39 (and 1.36) gcm-3 and a volume of 2744.5 (and 2808.5) cm3 for o-PEEK and are comparable with the corresponding experimental values of 1.328 gcm-3 and 2884.6 cm3, respectively. The absolute values of the glass transition temperature (Tg) MD simulated using the unit-cell and 2 × 2 × 2 supercell geometries of the o-PEEK system were 424.4 and 428.6 K, respectively. Although these values slightly differ from each other, both are close to the experiment (Tg = 418.2 K). The results of the (charge) density gradient analysis suggest that the supramolecular assembly between the o-PEEK oligomers in the experimentally observed infinite semi-crystal is driven by a wide range of noncovalent interactions. While the individual local interactions between the oligomers were recognized to be weak-to-medium in strength and are theoretically difficult to quantify, the B97-D3/cc-pVTZ level stabilization energy responsible for the formation of each of the five binary complex configurations extracted from the PBEsol relaxed 2 × 2 × 2 supercell geometry of the o-PEEK system was calculated to vary between -3.5 and -33.0 kcal mol-1.