Silicon NMR is a powerful analytical method used to characterize various types of materials. The NMR-active isotope is 29Si and silicon signals of different chemical groups spread over a wide chemical shift range. In this case study we utilize the high sensitivity of silicon to the surrounding atoms to confirm the composition of polysiloxanes.
The large chemical shift dispersion of 29Si is illustrated in Fig. 1, where we show the 29Si DEPT spectra of trimethoxymethylsilane (top), trimethoxyphenylsilane (middle) and dimethoxydimethylsilane (bottom) measured on a Spinsolve 80 MHz Silicon spectrometer. Each of these molecules has a unique chemical shift and can be easily differentiated from each other.
Figure 1: 29Si-DEPT spectra of trimethoxymethylsilane (top), trimethoxyphenylsilane (middle) and dimethoxydimethylsilane
Figure 2 shows the 29Si DEPT spectrum of poly(dimethylsiloxane-co-methylhydrosiloxane), trimethylsilyl terminated, measured on a Spinsolve 80 MHz Silicon spectrometer and the excellent agreement of the single building blocks to the predicted chemical shifts.
Figure 2: 29Si-DEPT spectrum of poly(dimethylsiloxane-co-methylhydrosiloxane) (CAS 68037-59-2, M = 950 g/mol) and the assignment of the NMR signals.