Molecular structure and orientation in processed polymers: 1. Analysis of X-ray scattering data

Abstract

We present a method for analyzing the molecular scale orientation and structure of processed polymers using wide angle X-ray scattering data (WAXS). The technique is applied to the analysis of solution-spun fibers of a liquid crystalline polyester comprised of 1,4-hydroxybenzoic acid, isophthalic acid, and hydroquinone. The orientation distribution function (ODF) of the non-crystalline component of the polyester is constructed using a Legendre polynomial series expansion. To construct a consistent molecular scale description, a Monte Carlo sampling scheme which incorporates the standard Metropolis sampling was employed, coupled with a weighting factor that favors structures which are in closer accord with the experimental WAXS data. The members of the ensemble sampled by the simulation consist of rhombic lattices on which oligomers are placed in an aligned state. The conformation of each oligomer was obtained using a rotational isomeric state description. By direct comparison of the experimental and calculated structure factor coefficients, the ODF for the structural ensemble was deduced. For the polyester fiber considered here, a two-component system consisting of oriented and unoriented non-crystalline components is required for complete characterization of the scattering properties of the sample. The sample contains a negligible amount of crystalline material, but 85% of the sample is aligned locally (i.e. with respect to nearest neighbor chains). However, as the fibers are spun from an isotropic solution, the global orientation (i.e. orientation with respect to the sample axis) remains low.