Atomic-Scale\nImaging of Polymers and Precision Molecular\nWeight Analysis

Polymer design requires\nfine control over syntheses and a thorough\nunderstanding of their macromolecular structure. Herein, near-atomic\nlevel imaging of polymers is achieved, enabling the precise determination\nof one of the most important macromolecular characteristics: molecular\nweight. By judiciously designing and synthesizing different linear\nmetal(loid)-rich homopolymers, subnanoscale polymer imaging is achieved\nthrough annular dark field-scanning transmission electron microscopy\n(ADF-STEM), owing to the incorporation of high <i>Z</i> atoms\nin the side chain of the monomeric units. The molecular weight of\nthese polymers can be precisely determined by detecting and counting\ntheir metal(loid) atoms upon ADF-STEM imaging, at sample concentrations\nas low as 10 μg·mL<sup>–1</sup>. Notably, a commonly\nused C, H, and O-containing polymer (<i>i.e.</i>, poly(methyl\nacrylate)) that was thus far inaccessible at the atomic scale is derivatized\nto allow for subnano-level imaging, thus expanding the scope of our\napproach toward the atomic-level visualization of commodity polymers.