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Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR

Brownbill, Nick J., Sprick, Reiner Sebastian, Bonillo, Baltasar, Pawsey, Shane, Aussenac, Fabien, Fielding, Alistair J., Cooper, Andrew I., Blanc, Frédéric
Macromolecules 2018 v.51 no.8 pp. 3088-3096
benzene, carbon, composite polymers, magnetic fields, nuclear magnetic resonance spectroscopy, photocatalysis, solids, stable isotopes, stoichiometry, temperature
Dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (NMR) offers a recent approach to dramatically enhance NMR signals and has enabled detailed structural information to be obtained in a series of amorphous photocatalytic copolymers of alternating pyrene and benzene monomer units, the structures of which cannot be reliably established by other spectroscopic or analytical techniques. Large ¹³C cross-polarization (CP) magic angle spinning (MAS) signal enhancements were obtained at high magnetic fields (9.4–14.1 T) and low temperature (110–120 K), permitting the acquisition of a ¹³C INADEQUATE spectrum at natural abundance and facilitating complete spectral assignments, including when small amounts of specific monomers are present. The high ¹³C signal-to-noise ratios obtained are harnessed to record quantitative multiple contact CP NMR data, used to determine the polymers’ composition. This correlates well with the putative pyrene:benzene stoichiometry from the monomer feed ratio, enabling their structures to be understood.