In the namesake publication for this session, Lippmaa and coworkers raided the mineral cabinet to provide a wide range of structures and chemistries to probe the 29Si chemical shift in the solid state. In the years since, the 29Si MAS NMR spectrum has provided insight into the structure and function of a range of natural and engineered materials. The power of this method is highlighted when it is applied to complex and disordered systems. We will present recent advancements by our group to enhance the 29Si MAS NMR signal from disordered glass and silicone polymer systems. Two important techniques have been used extensively to increase the signal to noise from 29Si MAS NMR; CPMG acquisition and CP/MAS. While powerful for many systems, there are some disadvantages for each when applied to highly disordered and potentially mobile environments such as those present in glasses and polymers. In the case of CPMG, short T2’s present in glassy or disorder systems can prevent quantification by preferentially enhancing signal from components with long T2’s. We will show how using SCORE processing of CPMG data sets can separate out signals with disparate T2’s while also enhancing signal to noise. These methods will be illustrated on 29Si MATPASS/CPMG spectra of slag materials. The relative motions of proton functional groups in polymers quench dipole coupling and prevent the collection of 29Si{1H} CP/MAS data sets in mobile systems. We will discuss using CP sequences that introduce 29Si-1H NOE interactions to help enhance the CP interaction. Both systems demonstrate how after 40 years we are still pushing the 29Si MAS technique to new limits.

Advances in collecting, processing, and analyzing 29Si NMR of complex disordered materials

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.