Einige polymerspezifische Anwendungen der Schwingungsspektroskopie

Abstract

Analysis of the frequencies, intensities and line shapes of bands which are sensitive to the chain conformation provides insight into the structure of polymeric solids and permits a study of the elastic properties of the lamellae. In a first example we deal with the multicomponent structure of the Raman spectrum of polyethylene. The general appearance of the spectra is indicative for the existence of a transition region in addition to the orthorhombic crystalline phase and a melt-like amorphous phase. In this transition region chains are stretched but have lost their lateral order. The mass fractions of the three coexisting phases can be determined. Two further examples discuss properties of the longitudinal acoustical modes which appear in the low frequency Raman spectrum of polyethylene and n-alkanes. Evaluation of the n-alkane data permits a determination of the crystalline elastic modulus E_e in chain direction and of the interlamellar forces. The frequencies measured for a solution crystallized sample PE speak in favour of a highly anisotropic state of order in the disordered surface layers.