Lee, Y., et al., Detection of Living Anionic Species in Polymerization Reactions Using Hyperpolarized NMR. J. Am. Chem. Soc., 2013. 135(12): p. 4636-4639.
http://dx.doi.org/10.1021/ja4001008
Intermediates during the anionic polymerization of styrene were observed using hyperpolarized NMR. Dissolution dynamic nuclear polarization (DNP) of monomers provides a sufficient signal-to-noise ratio for detection of 13C NMR signals in real time as the reaction progresses. Because of its large chemical shift dispersion, 13C is well-suited to distinguish and characterize the chemical species that arise during the reaction. At the same time, incorporation of hyperpolarized small-molecule monomers is a unique way to generate polymers that exhibit a transient signal enhancement at the active site. This strategy is applicable despite the decay of the hyperpolarization of the polymer due to rapid spin-lattice relaxation. Real-time measurements on polymerization reactions provide both mechanistic and kinetic information without the need for stable isotope labeling of the molecules of interest. These capabilities are orthogonal to currently established methods that separate synthesis and analysis into two steps, making dissolution DNP an attractive method to study polymerization reactions.