Chemical heterogeneity, defined as the change in average chemical composition as a function of copolymer molar mass, affects processing and end-use properties of copolymers such as toughness, brittleness, and biodegradability. In one-dimensional size-based macromolecular separations (e.g., size-exclusion or hydrodynamic chromatography, or flow field-flow fractionation), chemical heterogeneity is usually determined with via multiple detection, employing a series of detectors with different sensitivities (e.g., refractometry combined with UV spectroscopy), or using chemically-sensitive detection methods such as infrared (IR) or, less commonly, nuclear magnetic resonance spectroscopy. To date, Raman spectroscopy appears to have been overlooked as a potential macromolecular separations detection method for the purposes of determining copolymer chemical heterogeneity. This, in spite of the fact that Raman presents a number of advantages over, e.g., IR, especially as regards the characterization of water-soluble copolymers. Here, we examine the feasibility of coupling size-exclusion chromatography (SEC) to Raman detection in continuous off-line fashion, akin to the way SEC is coupled to IR using a solvent elimination interface. Results of our heart-cut experiments, which involved a gradient random copolymer of styrene and methyl methacrylate, were compared to chemical heterogeneity information for the same copolymer obtained via on-line SEC/MALS/UV/DRI. Our results demonstrate that continuous off-line Raman detection for macromolecular separations is feasible and, furthermore, that this type of coupling should be possible employing the same or similar hardware to that currently used for continuous off-line IR detection in size-based macromolecular separations.

Measuring copolymer chemical heterogeneity by combining SEC with offline Raman spectroscopy

254th National Meeting (2017)

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