Core Electron Absorption Spectra of Poly(ethylene terephthalate) and Poly(ethylene 2,6-naphthalate) Films

Abstract

ABSTRACT:Absorption spectra by means of the transmission method and total electron yield method were obtained for poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) films in the soft X-ray region by use of synchrotron radiation. The absorptions at 285.6 and 289.3 eV were due to Cls->n* transitions, showing stronger intensities for obliquely incident light than for normal. Broad absorptions consisting of humps at 293.5, 296.9, and 304.5 eV were originated in Cls->cr* transitions, having stronger intensities for an incident beam normal to the film plane than for oliquely incident light. The strong absorption of core electrons of oxygen appeared near 540.5 eV and was attributed to an Ols--.cr* transition; a neighboring peak at 532.3 eV was sensitive to the incident angle and was assigned as O!s--.n* transition. Oscillator strength and other optical features are briefly discussed. KEY WORDSPolarized Absorption Spectra / Synchrotron Radiation / Poly(ethylene terephthalate) / Poly(ethylene naphthalate) / Biaxially Oriented Films/ Total Electron Yield/ Transmission / Carbon K Edge/ Oxygen K Edge / Oscillator Strength / Absorption and em1ss10n spectra of the valence electrons of poly(ethylene terephthalate) (PET) have been studied for the clarification of photochemical and photophysical features. 1 -10 The polarized absorption and reflection spectra of uniaxially drawn PET films were analyzed in detail in the ultraviolet region down to 190 nm (or up to about 6.5 eV); the transition energies observed therein were compared with theoretical values from molecular orbital calculations. 8 -i O The emission spectra were measured and their origins were discussed. 4 -8 • 1° Furthermore, X-ray photoelectron spectrum of the valence band of PET in the binding energy up to about 30 e V was obtained by use of synchrotron radiation, together with simulation calculations 11 • 12 ; conformational effects were revealed in the spectra. 12 The spectroscopy related to the core electrons, whose energy corresponds to far ultraviolet or soft X-ray, has been studied for PET by means of X-ray photoelectron spectroscopy (XPS); whereby, assignments were given for three kinds of carbon ( carbonyl, aromatic, and aliphatic) and two kinds of oxygen (carbonyl and ester). 12 -15 Recently, electron energy loss spectroscopy (EELS) was applied to PET 16 ; spectral features of this polymer were discussed with the aid of core excitation spectra of small molecule analogues and extended Ruckel molecular orbital calculations of dimethylterephthalate.Absorption spectra of core electrons of polymers were first obtained by Seki et a/ 1 7 for very thin oriented syndiotactic 1,2-polybutadiene films. By use of a synchrotron radiation, they observed anisotropic absorp-127

Polarized NEXAFS Spectroscopic Studies of Poly(butylene terephthalate), Poly(ethylene terephthalate), and Their Model Compounds

“…From the θ-dependence of the spectral features of PAM, we can assign the peaks A, A‘, B, C, E, and F to π* excitations and D, G, H, I, and J to σ* excitations. This is in agreement with the well-established assignment that the peak A in the spectrum of PET is due to the π* excitation in the benzene ring. − As seen later, such estimation of molecular orientations is also supported by the polarization dependence of the O K-edge spectra.…”

“…The peaks G, H, and J cover broad σ* resonances attributed to the CC(ring), C−C, CO, and C−O bonds. − …”

“…Near edge X-ray absorption fine structure (NEXAFS) spectroscopy, also known as X-ray absorption near edge structure (XANES) spectroscopy, is a recently developed branch of X-ray spectroscopy, which is useful as a new tool of basic studies on material characterization and also as an analytical technique for chemical specification . For polymers, NEXAFS offers information about the identification of the polymeric chain and the functional groups, their orientation, and also the unoccupied electronic structures both in the bulk and at the surface. − Also the characterization of polymers using NEXAFS in the field of micro-NEXAFS and organic reaction is rapidly growing. − In these studies, it is critically important to make correct interpretation of the spectra of fundamental polymers, since they form the basis for interpreting the spectra of more complex polymers.…”

“…Recently the NEXAFS and ISEELS spectra of PET and related molecules have been extensively studied. The spectra of PET itself has been reported by several groups, − including biaxially elongated ones . The ISEELS spectra of small related molecules in the vapor phase were measured, and theoretical calculations of the state of the art have been performed for these molecules. ,, However, there are still some ambiguity about the spectral assignments.…”

Design and application of a zone plate monochromator for laboratory soft x-ray sources

“…[23][24][25][26] The use of characteristic resonance peaks due to inner shell transitions 1s -2p(*) ͓where 2p(*) denotes an unoccupied molecular state͔, which appear in a carbon or nitrogen near edge spectrum would provide a useful tool for molecular imaging. Highly monochromatized x rays are required for the measurements of XANES profiles.…”