Polymer Structure Determination Using Electron Diffraction Techniques

Abstract

The crystallographic structure of organic crystals is most commonly studied using x-ray diffraction (XRD) techniques. Unfortunately, rather large crystals, at least 106 µm3. are required for XRD analysis, and it is often quite difficult and sometimes impossible to prepare such large crystals. On the other hand, electron diffraction techniques, although not nearly as precise as XRD, do afford the capability of studying much smaller crystals. The minimum size for electron diffraction is on the order of 10-3 µm3 (0.1 µm2 area by 0.01 µm thick). Since most polymer crystals are very sensitive to radiation damage caused by the beam in the electron microscope, special precautions must be taken to minimize beam damage to the specimen. Our approach to minimizing radiation damage, while still obtaining usable diffraction data, is described in terms of using the condenser-objective lens optics of the Philips 301 S(TEM) electron microscope. Three examples of the application of electron diffraction structure analysis are given. These include the structures of halogenated polysulfur nitride (SN)x, neutral α,α'-polypyrrole, and poly(p-hydroxybenzoic acid) (PHBA).