LONGITUDINAL ACOUSTIC MODE IN ISOTACTIC POLYPROPYLENE.

The observation and characterization of a longitudinal acoustic mode (LAM) in n-paraffins and in PE is well established. The earliest observation of such a Raman active fundamental mode in n-paraffins, whose frequency is inversely proportional to the planar zig-zag chain length, was made by Mizushima and Shimanouchi. Following the demonstration of a LAM in PE, attempts were made to find the exact relationship between this frequency and the length of the planar zig zag carbon chain. Although an attempt has been made to observe the LAM in isotactic PP, the search was unsuccessful in isothermally crystallized or cold-drawn material. In this paper the authors report the successful observation of the LAM in isotactic polypropylene prepared under special conditions of extrusion and orientation. Raman spectra obtained in this investigation are presented and analyzed.