Study of the Chemical Environment inside Free Volume Holes in Halogenated Styrene Polymers Using Positron Annihilation Spectroscopy

Abstract

In this paper, a systematic study is provided of the chemical environment inside free volume holes in a series of halogenated polystyrenes ( p -position), −[CH 2 CH C 6 H 5 X] n – (X = F, Cl, Br, I), by using positron annihilation spectroscopy. In such polymers it was determined that the chemical environment is the major effect on Doppler broadening of two 511 keV γ photons from positron–electron annihilation. Doppler broadening energy spectroscopy (DBES) and positron annihilation lifetime spectroscopy (PALS) were combined in a novel approach to study the chemical environment in a polymer system. A highly linear relationship between Doppler broadenings caused by electron kinetic energies of valence electrons and the ionization potentials of halogen elements was obtained, as well as a similar correlation with the results from ab initio molecular orbital (MO) calculations for monohalogenobenzenes, C 6 H 5 X (X = F, Cl, Br, I). The results demonstrate that the combination of DBES and PALS may provide an effective way to study the chemical environment inside free volume holes in polymers.