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29Si and 13C NMR Investigation of the Polysilane-to-Poly(carbosilane) Conversion of Poly(methylchlorosilanes) Using Cross-Polarization and Inversion Recovery Cross-Polarization Techniques

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journal contribution
posted on 11.07.1996, 00:00 by Florence Babonneau, Jocelyne Maquet, Christian Bonhomme, Robin Richter, Gerhard Roewer, Djamila Bahloul
The polysilane-to-polycarbosilane transformation of polymethylchlorosilane prepared from based-catalyzed disproportionation of 1,1,2,2-tetrachlorodimethyldisilane has been characterized in detail by 29Si and 13C magic angle spinning nuclear magnetic resonance, using cross-polarization as well as inversion recovery cross-polarization techniques. These techniques allow a clear insight in the protonated environment of a given nucleus, in particular to distinguish between strongly coupled nuclei such as 13CH2 and moderately coupled ones such as 13CH3. For the first time, the IRCP sequence was also used to probe the environment of 29Si nuclei in such systems and proved to be very effective in distinguishing the silane and carbosilane sites. The 180−450 °C temperature range was investigated:  the formation of carbosilane units was clearly demonstrated by 13C and also 29Si NMR experiments. The various 29Si and 13C sites were thus identified due to their polarization inversion behavior and quantified. Comparison of these results with a thermogravimetric analysis coupled with mass spectrometry allowed us to propose two different mechanisms for the formation of carbosilane units in such system:  at low temperature (T ≥ 180 °C), it is suggested that carbosilane units are formed via condensation reactions between Si−Cl and H−C groups, while at higher temperature (T ≥ 380 °C), the so-called “Kumada rearrangement” occurs.