Molecular dynamics simulations of polymers of unsubstituted and substituted poly(p-phenylene terephthalate)s in the bulk state

Full Paper: A molecular dynamics simulation has been carried out on polymer s of p-phenylene terephthatate (PPT) and 1,4-phenylene-2-octyloxy terephtha late (PTA8) at six different temperatures: 300 K, 375 K, 450 K, 575 K, 600 K, and 625 K. The periodic simulation boxes consisted of 18 (PPT) or 16 (PT A8) chains with 9 monomer units. The Compass force field was used in the si mulations. The crystallographic data and density obtained from the NPT simu lation at room temperature agreed well with the experimental data of PPT. O ur simulations showed that, in the case of PTA8, the crystal --> layered ne matics phase transition temperature (T-m) is close to the experimental valu e for the polymer similar to PTA8. The average initial structure was obtain ed from X-ray scattering data. The simulated X-ray data indicated the exist ence of a biaxial nematic phase, in accordance with experimental findings. [GRAPHICS] Final structures of PPT at 300 K and 625 K. Hydrogen atoms are blanked out for clarity.