Effect of Crystallinity on the XPS Spectrum of Poly(Ethylene Terephthalate)

High resolution x-ray photoelectron spectra (XPS) are reported for poly(ethylene terephthalate) (PET) in the form of biaxially oriented crystalline film and amorphous polymer melt (i.e., molten inside the spectrometer during analysis). A small(∼0.14 eV) but unambiguous shift of the C 1s glycol component, relative to the aromatic and carboxyl components, is observed on going from crystalline film to amorphous polymer melt. It is known from x-ray diffraction data and infrared spectroscopy that the crystalline to amorphous transition is accompanied by a change from trans to gauche conformation of the glycol unit of the polymer repeat unit, and we ascribe the observed C 1s glycol shift to the same effect. Small differences between crystalline and amorphous PET are also observed in the valence band. Under the conditions of the XPS analysis the polymer melt appears to be electrically conducting.