Polymer Primary Structures Studied by ESCA and EHCO Methods

Abstract

The electronic structure (core and valence levels) of various simple polymers has been investigated by ESCA (Electron Spectroscopy for Chemical Analysis), with the aid of original EHCO (Extended Hückel Crystalline Orbitals) calculations giving corresponding density of states and band structure schemes. Simple monosubstituted homopolymers derived from polyethylene ([CH₂-CHX]_n) have been chosen in order to study the influence of X substituents (X = -F, -Cl, -OH, -CH₃, -CH₂CH₃, -C₆H₅, -C₆H₁₁ corresponding respectively to poly(vinyl fluoride), poly(vinyl chloride), poly(vinyl alcohol), poly(propylene), poly(1-butene), poly(styrene), and poly(vinyl cyclohexane)) through the chemical shifts measured for the core levels, and the alteration of the valence band structures. Assignment of the valence molecular orbitals is made with the aid of the theoretical calculations and with comparison of spectra recorded for molecules similar to the monomeric units. Emphasis is put on the very significant information provided by the valence band spectra for polymers containing only carbon and hydrogen atoms. Valence band data are used to calculate physical parameters (first ionization potential, energy gap, work function) of importance to deduce electrical properties for the polymers.