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) fractionate based on hydrodynamic volume. This analysis assumes all molecules in a fraction are identical, an increasingly strained assumption for complex macromolecules. Importantly, characterization of the molecular mass distribution (MMD) is typically reduced to reporting several moments of the MMD, like number and weight-averaged molecular masses, 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 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 MMD. In some cases, multiple subpopulations are directly revealed. This effort provides the first single-molecule measurement of the MMD of a synthetic polymer, bypassing artifacts introduced by bulk-scale measurements. Further, we show that the dispersity (Đ) can be precisely determined in a manner that is largely calibration-free, allowing determination of Đ in functional polymers where monodisperse standards are unavailable. Integration of MP with SEC conspicuously shows how multiple populations are present in collected fractions.