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

摘要

The polysilane-to-polycarbosilane transformation of polymethylchlorosilane prepared from based-catalyzed disproportionation of 1,1,2,2-tetrachlorodimethyldisilane has been characterized in detail by ~(29)Si and ~(13)C 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 ~(13)CH_2 and moderately coupled ones such as ~(13)CH_3. For the first time, the IRCP sequence was also used to probe the environment of ~(29)Si nuclei in such systems and proved to be very effective in distinguishing the silane and carbosilane sites. The 180-450℃ temperature range was investigated: the formation of carbosilane units was clearly demonstrated by ~(13)C and also ~(29)Si NMR experiments. The various ~(29)Si and ~(13)C 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℃), it is suggested that carbosilane units are formed via condensation reactions between Si-Cl and H-C groups, while at higher temperature (T ≥ 380℃), the so-called "Kumada rearrangement" occurs.