Synthetic polymeric materials have broad size distributions that often makes analysis complex. Currently Size Exclusion Chromatography (SEC) is the gold standard for determining the full molar mass distribution of a sample. However Synthetic chemists are regularly producing new types of polymers where SEC is no longer a suitable technique. Unlike many other forms of chromatography SEC relies on there being no affinity between the analyte sample and the stationary phase and so any column retention can be fatal for analysis. Additionally advanced SEC methods (such as viscometric or light scattered coupled techniques) cannot have the mobile phase changed without extensive additional recalibration work. This makes analysis of different polymer types in close succession problematic using a single chromatography system. One alternative proposed is 1H DOSY NMR analysis, a highly versatile analytical method. DOSY NMR has been adopted by the polymer community to confirm polymer functionalisation / grafting efficiency but recent work by several groups have shown it can provide addtional information such as molar mass dispersity or sample hydrodynamic radii. A single DOSY measurement can indicate approximate polymer molar mass, dispersity and hydrodynamic radii. Under the right conditions DOSY NMR can provide quantifiably similar size distributions to size exclusion chromatography, with decreased resolution but increased flexibility regarding solvent choices. DOSY parameters need to be adjusted for polymer analysis but with an increased number of gradient steps the results can be considered comparable to SEC analysis - providing low resolution size distributions of polymer samples without physically seperating the analyte material - thus reducing the consideration of problematic analyte / mobile phase interactions.

Low resolution size chromatographs? The potential applications of diffusion ordered spectroscopy NMR in analysis of polymer size distributions

2019 Fall National Meeting

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