Polymer crystallography

Abstract

The two primary crystallographic techniques used for studying polymer structure, X-ray fibre diffraction analysis and polymer electron crystallography, are described in this chapter. X-ray fibre diffraction analysis is a collection of crystallographic techniques used to determine molecular and crystal structures of molecules, or molecular assemblies, that form specimens (often fibres) in which the molecules, assemblies or crystallites are approximately parallel but not otherwise ordered. The theory and techniques of structure determination by X-ray fibre diffraction analysis are reviewed. Fibre specimens, the theory of diffraction by these specimens, intensity data collection and processing, and the variety of structure determination methods used for the various kinds of specimens studied by fibre diffraction are described. Polymer electron crystallography may be defined as the quantitative use of electron micrographs and electron diffraction intensities for the determination of polymer crystal structures. Data from thin single microcrystals are required for successful structure determination. Crystallization and data-collection techniques are described and two approaches to crystal structure analysis are discussed. Keywords: polymer crystallography; fibres; helical symmetry; random copolymers; polymer electron crystallography; X-ray fibre diffraction analysis; noncrystalline fibres; polycrystalline fibres; partially crystalline fibres; multidimensional isomorphous replacement; molecular-dynamics refinement; electron-diffraction data