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
13
CH2 and moderately coupled
ones
such as 13
CH3. 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.
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