Publications
Short-range helical ordering of isotactic vinyl polymers in the liquid state
Wide-angle x-ray scattering measurements on various vinyl polymer melts show that the main amorphous peak (at k {approx} 1.5 A{sup -1}) in the structure factor initially broadens, and then forms a 'pre-peak' that shifts to lower k as the size of the pendant group increases. To investigate this behavior we performed self-consistent PRISM calculations on isotactic polypropylene and polystyrene liquids. Good qualitative agreement was seen for the theoretical structure factors with scattering data. Analysis of the torsional angle distribution shows a significant amount of short-range helical content in the iPP and iPS melts. At 450 K the average number of consecutive trans/gauche pairs along the chain backbone was significantly higher than for a random distribution of torsional angles. The theory indicates that the location of the pre-peak is a measure of the helix-helix correlation distance or helix 'thickness'.