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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.