Simulation of orientation of uniaxially stretched poly(vinyl phenol) by molecular dynamics

Molecular dynamics were performed for the simulation of the uniaxial deformation of poly(vinyl phenol) under periodic boundary conditions with the Parrinello-Rahman scheme followed by relaxation under NVT conditions (constant number of atoms, volume, and temperature). Changes in the orientation of the main chain, benzene segments, and hydrogen bonds were analyzed with the second-order Legendre polynomial, <P-2(cos theta)>. Conformational changes were also followed. During deformation, backbone and phenyl rings both initially orient parallel to the draw direction. After relaxation, the chain is oriented parallel to the deformation direction, and side groups orient approximately perpendicular to this direction, in agreement with experimental data reported in the literature. Orientation values are higher than experimental values, as expected from the limited relaxation time range attainable in the simulations. Deformation proceeds by changes from gauche conformers to nontrans, nongauche, and trans conformers, whereas relaxation mainly allows high-energy nontrans, nongauche conformers to convert into lower energy trans conformers. Values of the alpha angle for ring and bonded O-H segments agree with those in the literature. Differences observed for free hydroxyl moieties are discussed. (C) 2002 Wiley Periodicals, Inc.