Probing local environments in PDCs with solid-state NMR combined with ab-initio calculations

Reference	Presenter	Authors (Institution)	Abstract
18-004	Christel Gervais	Gervais, C.(university Pierre et Marie Curie); Salameh, C.(Institut Européen des Membranes); Viard, A.(University of Bayreuth); Schmidt, M.(Institut Européen des Membranes); Babonneau, F.(University Pierre et Marie Curie); Miele, P.(Institut Européen des Membranes); Bernard, S.(University of Limoges);	In the polymeric route to ceramics, the polymer architecture may strongly influence the structure of the final ceramic. It is therefore essential to rely on characterization tools to get a precise description of the polymer structure, and then be able to follow step-by-step the polymer-to-ceramic conversion. The samples usually do not present any long range order, which prevents the use of X-Ray diffraction. High resolution solid state magic angle spinning nuclear magnetic resonance (MAS NMR) appears therefore to be extremely useful to characterize the different intermediates. This technique is sometimes challenging because of the lack of sensitivity of the isotopes in natural abundance (15N) or a lack of resolution of the spectra due to the quadrupolar character of the isotopes (11B or 27Al). However, an appropriate combination of solid state NMR techniques such as double resonance experiments ({X}-{Y}, X = 1H, 29Si, Y = 29Si, 13C, 15N…), multiple-quantum (MQ) MAS sequence for quadrupolar nuclei, use of high magnetic fields can help to get a better description of the various environments present in the structures. Nonetheless, even using a large panel of specific sequences, interpretation of the spectra may be difficult due to small chemical shift ranges resulting in overlapping signals. Moreover, observed signals may not be in full agreement with expected structures of the PDCs that are often very complex. In this context, ab- initio calculations of NMR parameters can be extremely useful in helping to the understanding of the spectra and for the assignment of the sites present in the polymers and the ceramics.
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