Polydispersity index of polymers revealed by DOSY NMR

The polydispersity of a polymer chain is usually measured by its polydispersity index (PDI). In this study we present a method which allows to estimate the PDI of linear polymers from a simple diffusion experiment. The approach is based on the differential diffusion profile observed for the main polymer chain signal versus the extremity signal. From this difference, a statistical analysis of the DOSY spectrum allows the PDI to be estimated accurately, to the condition that the Flory coefficient of the polymer chain is known. Alternatively, the mass average molar mass Mw and the number average molar mass Mn can be extracted separately from the same spectrum. Results on PEO mixes reveal that, using this new method, PDI can be estimated with a very good accuracy. This method can easily be applied to almost any kind of linear polymers.