THE LOCAL ENERGY APPROXIMATION AND THE PREDICTABILITY OF CHAIN CONFIGURATIONS IN POLYMER MELTS

The configurations of a series of short polar model molecules for poly (vinyl chloride), PVC, and poly(ethylene oxide), PEG, have been determ ined from extensive molecular dynamics simulations of the correspondin g bulk melts. Their conformational and configurational properties are compared to those sampled for the same models by a pivot Monte Carlo p rocedure based on the assumption that chain configurations in the melt depend only on highly localized near-neighbor intramolecular interact ions. The comparison proves favorable for all neutral and polar chains , with the exception of the realistic model leading to the gauche effe ct in PEG. Discrepancies in the latter case are related to the failure of the single-chain local energy approximation to account for the spe cific competition between intramolecular ''1 ... 5'' C-H ... O and int ermolecular C-H ... O electrostatic interactions in the PEO bulk melts . (C) 1996 American Institute of Physics.