Solid-state NMR tools for the structural characterization of POSiSils: Si sensitivity improvement with MC-CP and 2D Si- Si DQ-SQ at natural abundance.

The H- Si multiple-contact cross polarization (MC-CP) MAS NMR experiment is evaluated for the class of silicate-siloxane copolymers called POSiSils, that is, polyoligosiloxysilicones. It proves a reasonably good solution to tackle the challenge of recording quantitative Si NMR data in experimental time much reduced compared with single pulse acquisition. In a second time, we report Si- Si MC-CP double-quantum single-quantum (MC-CP-DQ-SQ) NMR experiment, which provides information about the through-space proximities between all silicon species despite the high degree of heterogeneity of this material. This work furthers the NMR tools for NMR crystallography for inorganic polymers, as it covers flexible polymers with different dimensionalities and long or heterogeneous relaxation characteristics at low Si natural abundance.