Vibrational Spectra of Poly(ethylene terephthalate) Chains in the Mesomorphic Form

Vibrational (infrared and Raman) spectra of poly(ethylene terephthalate) (PET) chains included in the mesomorphic phase, as established by X-ray diffraction patterns, are compared with spectra of corresponding amorphous and crystalline (triclinic) phases. The study indicates the presence of similar amounts of amorphous phase in semicrystalline and mesomorphic films. For the mesomorphic phase, occurrence of extended linear chains with disordered conformation, which was suggested by combination of X-ray diffraction data and conformational analysis, is confirmed. In particular, a detailed analysis of conformationally sensitive spectral regions confirms the presence of sequences with trans OCCO dihedral angles and trans or gauche COCC dihedral angles. The reported analysis also allows discriminating between crystalline peaks corresponding to vibrational modes of long or short trans-planar PET stretches.