Solid-state NMR tools for the structural characterization of POSiSils: 29 Si sensitivity improvement with MC-CP and 2D 29 Si- 29 Si DQ-SQ at natural abundance.

The 1 H-29 Si multiple-contact CP (MC-CP) MAS NMR experiment is evaluated for the class of silicate-siloxane copolymers called Posisils, i.e. polyoligosiloxysilicones. It proves a reasonably good solution to tackle the challenge of recording quantitative 29 Si NMR data in experimental time much reduced compared to single pulse acquisition. In a second time, we report 29 Si-29 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/heterogeneous relaxation characteristics at low 29 Si natural abundance.