This research is a study of conformation disorder in polymer systems by vibrational spectroscopy. Disorder plays an important role in determining the properties of polymeric materials, and this has stimulated much activity aimed at characterizing and understanding its complex nature. The range of applicability of vibrational spectroscopy to disorder has been seriously limited by the absence of a general, but practical, theory that can be used to provide quantitative relations between the conformational statistics and the infrared or Raman spectrum of a system of disordered chain molecules. Work by the authors has led to a model that enables general relations to be established between the structure and spectra of disordered chains. The model is based on the finding that the vibrations of disordered chains have some of the long-range coherence of ordered chains. Preliminary results on a simple system show that infrared band shapes calculated with this model reproduce the main features of those observed. This model will be modified to make it more widely applicable. A second approach to this problem will also be pursued in which the spectra of ensembles of disordered chains are generated numerically by summing the spectra computed for each constituent conformer. Spectra obtained in this way will be used to develop models that relate spectra and disorder, and to test conformational models that have been proposed for various polymers. In addition, vibrational spectroscopy and other available techniques, including inelastic neutron scattering, will be used to study a variety of disordered polymer systems. Special emphasis will be devoted to systems that exist in nonequilibrium states and to chain monolayers, liquid crystals, and liquid crystal polymers.
