Atomic-level determination of polymer chain structures by electron microscopy combined with molecular simulation*

The primary structures (arrangement of monomer units) and secondary structures (torsion angles around C-C bonds and chain conformations) of single polymer chains are fundamental aspects that determine the properties and behaviors of polymers at various scales, from the molecular to macroscopic levels. Thus, the real-space observation of the primary and secondary structures provides us with a lot of information essential to understanding the nature of polymeric materials.

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) can potentially observe materials’ internal structures at atomic scales. Among these techniques, annular dark-field STEM (ADF-STEM) can image heavy atoms much brighter than light atoms.

In the present study, we visualized the atomic-level steric structures of single polymer chains labeled with heavy atoms using ADF-STEM imaging and molecular mechanics simulations. The estimated molecular structures exhibited the chain conformations adsorbed on a flat substrate. In addition, the local chain conformations were associated with the energetically favored torsion angles for the local tacticity (sequence of enantiomers) of them. At the conference, we will present the detailed process of the structural determination and then discuss what we have revealed with the analysis.