Critical need for absolute molecular weight determination on size exclusion chromatography system

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The size, or molecular weight, of a polymer is one of the most important factors in determining physical properties. Viscosity, degree of crystallinity, stiffness, bioavailability, conductivity, and other properties are all intimately associated with molecular weight. For example, for a given identical repeat unit of ethylene, polypropylene with a low molecular weight may be used as a plastic bag but polypropylene with ultrahigh high molecular weight may be used as anti-stab vests. Size exclusion chromatography (SEC) is a ubiquitous equipment to determine the molecular weight. The molecular weight is estimated by the time it takes for the polymer to elute from the column: the smaller the polymer, the more it interacts with the stationary solid phase of the column, the longer it takes to elute. Notably, typical methods widespread in the polymer research community and also at UofT inaccurately determine the molecular weight. Most researchers use a set of standard polymer samples with known molecular weight to create a calibration curve to correlate the time it takes for a polymer to elute and its known molecular weight. However, the time it takes to elute is intimately related to the identity of the polymer. For the same molecular weight, a polymer that is tightly coiled in a select solvent will elute at a different time that a polymer that is loosely coiled. Thus, the identity of the standard polymer samples used to create the calibration curve must match the identity of the polymer to be characterized. Since there are limited standards, often poly(styrene) or poly(methyl methacrylate) is used as a standard. Thus, the molecular weights determined by SEC calibrated against a standard is only a good estimated if the unknown polymer behaves like the standards. As new polymers are being developed at UofT, we are discovering that this estimation is no longer appropriate, where there are very large discrepancies. The requested SEC system coupled with a multi-angle light scattering technique, the first of its type at UofT and surrounding institutions to our knowledge, will enable the local polymer research community to determine absolute molecular weight. Moreover, the selected solvent system of chloroform is missing from UofT, which is the only solvent which solubilizes the new conjugated polymers developed by some of the UofT researchers. Also, it uses a quick analysis procedure and 85% less solvent per run than any system that is available on the market. The five co-PIs include Tran, Khan, Seferos, Winnik, and Bender, with more than 50 highly qualified personnel as potential users at the onset.