| Abstract: | Raman spectroscopy is used to investigate the conformation and packing of isotactic crystalline α-phase polypropylene compared with lower-order β-phase isotactic polypropylene and to study the solution behavior of atactic polypropylene. The high-frequency region of the spectrum is analyzed in light of a normal-mode calculation that takes into account the methyl-group vibrations. This region is sensitive to both chain conformation and packing, and because of the high intensity of the methyl and methylene high-frequency stretching modes, it can be used to probe small changes in intermolecular or intramolecular order. Differences in the thermal behavior between the two solid isotactic polypropylene samples are explained interms of packing defects which exist in the β-phase form. In the solution study, we demonstrate that, for molecules in which bands sensitive to intermolecular interactions exist, as is the case of the methyl and methylene vibrations of polypropylene, spectroscopic techniques can be used to estimate the minimum overlap concentration. |
