Molecule by Molecule Characterization of a Polymer Molecular Mass Distribution via Mass Photometry

Polymer analysis tools form the backbone of modern polymer technology. However, traditional tools like size exclusion chromatography (SEC) coupled with online detectors fractionate based on hydrodynamic volume. This analysis assumes that all molecules in a fraction are identical, an assumption that is increasingly strained for chemically complex macromolecules. Most importantly, characterization of the molecular mass distribution (MMD) is typically reduced to the reporting of several moments of the MMD, like Mn and Mw, the number and weight-averaged molecular masses, which constitutes a significant loss of information. In contrast, a molecule-by-molecule elucidation of the full MMD would yield an extremely informative new perspective on macromolecule diversity, while eliminating the limitations and time commitment associated with fractionation. Here, we show that mass photometry (MP), whereby the interferometric scattering signal of individual molecules is correlated with mass, of high-molecular weight polyethylene oxide (PEO) allows elucidation of the full polymer MMD. In some cases, multiple subpopulations are directly and conveniently revealed. This effort provides the first single-molecule measurement of the MMD of a synthetic polymer, bypassing artifacts introduced by bulk-scale measurements. Determined Dispersity values agree with bulk analysis for samples with a single major population but diverge when multiple populations are present. Integration of MP with SEC conspicuously shows how multiple populations are present in and evolve over subsequent collected fractions.