Abstract
The morphology of crystallites in a low molecular weight copolymer of 1,4-oxybenzoate and 2,6-oxynaphthoate units is investigated with transmission electron microscopy (TEM), scanning electron microscopy (SEM) and small-angle X-ray scattering. Selected-area electron diffraction patterns exhibit aperiodic meridional maxima, indicating random sequencing of units along the chains, while sharp equatorial reflections suggest some level of crystallinity. Strongly diffracting crystalline entities, whose number and dimensions depend on thermal history, can be imaged in dark-field TEM. They orient with their thin axis parallel to the molecular director. Similar crystallites are also observed in SEM micrographs of chemically etched bulk samples, and give rise to a small-angle reflection on the meridian of an X-ray fibre pattern. The reflection corresponds to the mean distance between crystallite centres. Crystal thicknesses determined from mean crystallite spacings and percentage crystallinities (measured from wide-angle X-ray scattering) are compared with predictions for various models. The data clearly indicate lateral register between aperiodic sequences, which is the basis of non-periodic layer crystallites.
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