Macromolecules, Vol.51, No.8, 3088-3096, 2018
Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR
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 C-13 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 C-13 INADEQUATE spectrum at natural abundance and facilitating complete spectral assignments, including when small amounts of specific monomers are present. The high C-13 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.