Imaging Synthetic Polymer Crystals and Defects on Atomic Length-Scales*

Determining atomic-scale structures in polymers is difficult because they degrade rapidly when studied by electron microscopy, and techniques such as x-ray scattering average over volumes much larger than the unit cells. We obtained cryo-electron microscopy images of crystals of a peptoid polymer in which we see a variety of crystalline motifs. A combination of crystallographic and single particle methods, developed for cryo-electron microscopy of biological macromolecules, was used to obtain high resolution images of the crystals. Individual specimens contain grains that are mirror images of each other with concomitant grain boundaries. Our approach is robust and may enable direct visualization of crystalline grains and grain boundaries on atomic length scales in a variety of polymers.