Electron diffraction of synthetic polymers: the model compound approach to polymer structure.

X-ray fiber diffraction is a technique most often used to establish the structure of chemically regular crystalline polymers. However, this technique has many shortcomings. Some of them are: ambiguities regarding the choice of the space group, limited intensity data, often large diffraction spots, and overlapping intensities. Microsingle crystals of synthetic polymers, when they can be produced, happen to have dimensions that are well suited to being studied by electron diffraction. Electron diffraction data from microsingle crystals often complement the X-ray fiber data. Strictly speaking, one does not solve the crystal structure of a polymer in the conventional way but rather one chooses from among many potentially acceptable models the one which fits the X-ray and/or the electron diffraction data best. The various steps of model building, its placing within the unit cell, and structure refinement will be discussed.