Structural phases of sodium-doped polyparaphenylene vinylene

Abstract

The structural phases of sodium-doped polyparaphenylene vinylene have been investigated by in situ x-ray-diffraction methods using oriented polymer samples. Complete doping is achieved and, at doping concentrations of approximately 55% per mole weight of sodium, a crystalline hexagonal phase is found. This phase is characterized by a quasi-one-dimensional channel structure in which sodium ions fill columns formed by three polymer chains. At room temperature the scattering from the linear arrays of these sodium ions is observed, and the intrachannel sodium ion spacing is incommensurate with that of the polymer chain repeat. At slightly higher doping levels a transformation to another less-ordered structural phase occurs. In this phase the alkali-metal columns are still identifiable, but the structural integrity of the host is diminished. Structural models for both doped phases are proposed, and structure-factor calculations of the equatorial reflections yield good agreement with the experimental data.