Stopped-Flow (SF) NMR spectroscopy is an information-rich analytical technique for the elucidation of kinetics on time scales potentially as short as a few milliseconds. Cyclic polylactic acid (PLA) is a biodegradable polymer with applications in medicine, semiconductor coatings and consumer plastics.  SF NMR spectroscopy gives new insight into the zwitterionic polymerization of lactide as catalyzed by 1,3-dimesitylimidazol-2-ylidene (IMes) to produce cyclic PLA.  The high information content of NMR allows direct observation of reaction progress and catalyst speciation.  The kinetic information gained from SF NMR permits construction of a more complete mechanistic model.                A new design of SF NMR probes enables examination of a wider variety of systems.  A modified Bruker wide-bore 360 MHz probe uses a two-jet mixer constructed of polychlorotrifluoroethylene (PCTFE) which allows solutions to mix and reach the acquisition coil with short dead times and fast flow rates.  Complete magnetization and temperature equilibration of reagents is achieved by wrapping reagent lines around the acquisition coil. These modifications allow accurate study of reactions on shorter time regimes and at variable temperatures.

Development of stopped-flow NMR spectroscopy to elucidate fast kinetics

248th National Meeting (2014)

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