CONFORMATIONS AND ORDER IN ATACTIC POLY(VINYL CHLORIDE) MELTS FROM MOLECULAR-DYNAMICS SIMULATIONS

Molecular dynamics simulations of atactic poly(vinyl chloride) (PVC) melts at 450 and 600 K were performed including individual hydrogens and utilizing an ab initio quantum chemistry based force field. Electrostatic interactions were considered by employing partial atomic charges with a distance-dependent dielectric constant. The effects of polar electrostatic interactions and packing on chain conformations and intermolecular orientational correlations were examined individually by performing additional simulations of isolated chains and melts without intermolecular Coulombic interactions. Pair distribution functions show strong temperature dependence but are relatively insensitive to electrostatic interactions. Reasonably good agreement between calculated and experimental X-ray scattering profiles is found for PVC melts at 450 K. Chain conformations in PVC melts are found to be extended relative to the conformations of isolated chains. Moreover, significant temperature-dependent orientational order is seen in PVC melts, with highly parallel chain segments being distributed in small localized clusters. These deviations from the unperturbed chain model are attributable to the presence of polar intermolecular interactions in PVC melts.