Pyrolysis of poly[(silylene)diacetylenes]: Direct evidence between their morphology and thermal behavior

Ceramics and Nanostructures from Molecular Precursors

“…In the case of C1, the X-ray diffraction (XRD) pattern reveals the presence of a lattice in which the repeat distance of the diacetylene backbone is 4.6 . [29,30] The crystallinity decreases in the order Me > Ph > SiMe 3 , as observed by XRD, and the temperature of cross-linking follows the same order (Me: 200 8C, Ph: 225 ± 315 8C, SiMe 3 : 350 8C; Figure 2). This cross-linking reaction between the CCÀCC chains explains why the isolated dimethylsilyl units react with each other to form a SiC network.…”

“…However, the IR and NMR features of solid F' and solid G' (silica-containing G) permit unambiguous identification of cleavage of the SiÀCC bond and the presence of G inside the silica matrix. The complete transformation of T units into Q units is particularly illustrative and obvious in the 29 Si NMR spectrum.…”

“…[32] This transformation is likely the key step leading to a cross-linked material which aids the formation of SiC. [29] In the case of polymer C1, the formation of the carbon matrix was detected by both IR and 13 C CP-MAS NMR spectroscopy (CP-MAS Cross-polarization magic angle spinning), which shows the transformation of sp into sp 2 carbon atoms, corresponding to the transformation of CCÀCC units into enynes and butatrienes at 200 8C and then final formation of the sp 2 -carbon matrix above 400 8C. [30] In agreement with this explanation, we observed that the exothermic transformation is highly dependent on the steric hindrance of the groups attached to silicon.…”

“…Let us consider identification at the molecular level: Solid-state 13 C NMR spectroscopy is a means of identifying the molecular units present in the solid, while 29 Si NMR spectroscopy provides information about the degree of polycondensation of the silica network. For example, two different precursors D and E can be used for the elaboration of two nanostructural materials; E is obtained by treatment of D with [Cr(CO) 6 ] (Scheme 16).…”

“…This observation is in agreement with an electronic interaction induced by silicon atoms which favors charge delocalization. A possible explanation corresponding to a chain-to-chain conduction mechanism can be eliminated since, in this hypothesis, the highest values should be obtained with the dimethyl polymer C1, which exhibits the best crystallinity [29] and the shortest distance between the acetylenic chains (4.6 ). In contrast, the phenylated polymer C2 should exhibit a lower conductivity since the steric hindrance, which increases the repulsion between the polymeric chains, should prevent the chain-to-chain conduction mechanism.…”